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L_0567 | importance of seedless plants | T_3085 | But some seedless plants still have uses in society today. Peat moss is commonly used by gardeners to improve soils, since it is really good at absorbing and holding water ( Figure 1.1). Depending on the location, ferns have several different uses worldwide. Ferns are found in many gardens as ornaments, and are used as indoor plants. In tropical regions, the fern is used as a food source by many locals. The fronds can also be used to weave hats and baskets. The fiddleheads of certain species of ferns are used in gourmet food. Some species of ferns, such as the maidenhair fern, are used as medicines. In Southeast Asia, the fern is used in rice fields as a biological fertilizer. Much of the worlds fossil fuels consist of remains of ferns and their relatives. The horsetails reedy exterior and silica content made it popular as a metal polisher and abrasive cleanser. Herbalists still use horsetail to treat a variety of kidney/bladder problems, including inflammation, infection, and kidney stones, and it is used as a remedy for brittle nails. Club moss is also used to treat kidney ailments and digestive problems. Club moss spores can be dusted onto the skin and provide relief from itching and irritation, and provide the skin with protection. Extinct forests of club moss have fossilized and developed into huge beds of coal. Sphagnum, or peat moss, is commonly added to soil to help absorb water, and keep it in the soil. | text | null |
L_0573 | innate behavior of animals | T_3097 | Many animal behaviors are ways that animals act, naturally. They dont have to learn how to behave in these ways. Cats are natural-born hunters. They dont need to learn how to hunt. Spiders spin their complex webs without learning how to do it from other spiders. Birds and wasps know how to build nests without being taught. These behaviors are called innate. An innate behavior is any behavior that occurs naturally in all animals of a given species. An innate behavior is also called an instinct. The first time an animal performs an innate behavior, the animal does it well. The animal does not have to practice the behavior in order to get it right or become better at it. Innate behaviors are also predictable. All members of a species perform an innate behavior in the same way. From the examples described above, you can probably tell that innate behaviors usually involve important actions, like eating and caring for the young. There are many other examples of innate behaviors. For example, did you know that honeybees dance? The honeybee pictured below has found a source of food ( Figure 1.1). When the bee returns to its hive, it will do a dance. This dance is called the waggle dance. The way the bee moves during its dance tells other bees in the hive where to find the food. Honeybees can do the waggle dance without learning it from other bees, so it is an innate behavior. Besides building nests, birds have other innate behaviors. One example occurs in gulls, which are pictured below ( Figure 1.2); one of the chicks is pecking at a red spot on the mothers beak. This innate behavior causes the mother Left: This mother gull will feed her chick after it pecks at a red spot on her beak. Both pecking and feeding behaviors are innate. Right: When these baby birds open their mouths wide, their mother in- stinctively feeds them. This innate behav- ior is called gaping. to feed the chick. In many other species of birds, the chicks open their mouths wide whenever the mother returns to the nest ( Figure 1.2). This innate behavior, called gaping, causes the mother to feed them. Another example of innate behavior in birds is egg rolling. It happens in some species of water birds, like the graylag goose ( Figure 1.3). Graylag geese make nests on the ground. If an egg rolls out of the nest, a mother goose uses her bill to push it back into the nest. Returning the egg to the nest helps ensure that the egg will hatch. | text | null |
L_0573 | innate behavior of animals | T_3097 | Many animal behaviors are ways that animals act, naturally. They dont have to learn how to behave in these ways. Cats are natural-born hunters. They dont need to learn how to hunt. Spiders spin their complex webs without learning how to do it from other spiders. Birds and wasps know how to build nests without being taught. These behaviors are called innate. An innate behavior is any behavior that occurs naturally in all animals of a given species. An innate behavior is also called an instinct. The first time an animal performs an innate behavior, the animal does it well. The animal does not have to practice the behavior in order to get it right or become better at it. Innate behaviors are also predictable. All members of a species perform an innate behavior in the same way. From the examples described above, you can probably tell that innate behaviors usually involve important actions, like eating and caring for the young. There are many other examples of innate behaviors. For example, did you know that honeybees dance? The honeybee pictured below has found a source of food ( Figure 1.1). When the bee returns to its hive, it will do a dance. This dance is called the waggle dance. The way the bee moves during its dance tells other bees in the hive where to find the food. Honeybees can do the waggle dance without learning it from other bees, so it is an innate behavior. Besides building nests, birds have other innate behaviors. One example occurs in gulls, which are pictured below ( Figure 1.2); one of the chicks is pecking at a red spot on the mothers beak. This innate behavior causes the mother Left: This mother gull will feed her chick after it pecks at a red spot on her beak. Both pecking and feeding behaviors are innate. Right: When these baby birds open their mouths wide, their mother in- stinctively feeds them. This innate behav- ior is called gaping. to feed the chick. In many other species of birds, the chicks open their mouths wide whenever the mother returns to the nest ( Figure 1.2). This innate behavior, called gaping, causes the mother to feed them. Another example of innate behavior in birds is egg rolling. It happens in some species of water birds, like the graylag goose ( Figure 1.3). Graylag geese make nests on the ground. If an egg rolls out of the nest, a mother goose uses her bill to push it back into the nest. Returning the egg to the nest helps ensure that the egg will hatch. | text | null |
L_0573 | innate behavior of animals | T_3098 | All animals have innate behaviors, even human beings. Can you think of human behaviors that do not have to be learned? Chances are, you will have a hard time thinking of any. The only truly innate behaviors in humans are called reflex behaviors. They occur mainly in babies. Like innate behaviors in other animals, reflex behaviors in human babies may help them survive. An example of a reflex behavior in babies is the sucking reflex. Newborns instinctively suck on a nipple that is placed in their mouth. It is easy to see how this behavior evolved. It increases the chances of a baby feeding and surviving. Another example of a reflex behavior in babies is the grasp reflex ( Figure 1.4). Babies instinctively grasp an object placed in the palm of their hand. Their grip may be surprisingly strong. How do you think this behavior might increase a babys chances of surviving? This female graylag goose is a ground- nesting water bird. Before her chicks hatch, the mother protects the eggs. She will use her bill to push eggs back into the nest if they roll out. This is an example of an innate behavior. How could this behavior increase the gooses fitness? One of the few innate behaviors in human beings is the grasp reflex. It occurs only in babies. | text | null |
L_0573 | innate behavior of animals | T_3098 | All animals have innate behaviors, even human beings. Can you think of human behaviors that do not have to be learned? Chances are, you will have a hard time thinking of any. The only truly innate behaviors in humans are called reflex behaviors. They occur mainly in babies. Like innate behaviors in other animals, reflex behaviors in human babies may help them survive. An example of a reflex behavior in babies is the sucking reflex. Newborns instinctively suck on a nipple that is placed in their mouth. It is easy to see how this behavior evolved. It increases the chances of a baby feeding and surviving. Another example of a reflex behavior in babies is the grasp reflex ( Figure 1.4). Babies instinctively grasp an object placed in the palm of their hand. Their grip may be surprisingly strong. How do you think this behavior might increase a babys chances of surviving? This female graylag goose is a ground- nesting water bird. Before her chicks hatch, the mother protects the eggs. She will use her bill to push eggs back into the nest if they roll out. This is an example of an innate behavior. How could this behavior increase the gooses fitness? One of the few innate behaviors in human beings is the grasp reflex. It occurs only in babies. | text | null |
L_0574 | insect food | T_3099 | What do insets eat? Practically anything they want. There are so many different insects, that among all of them, no potential food is safe. Lots of insects eat plants, some insects eat other insects, and some even drink blood. Many insects eat nectar from plants. And some insects will eat whatever scraps of food you leave lying around. A few insects, such as mayflies and some moths, never eat. Thats because their lives are over in just a few hours or days. Once these insects become adults, they lay eggs, and then die. On the other hand, some insects are very healthy eaters. A silkworm eats enough leaves to increase its weight more than 4,000 times in just 56 days, as the silkworm increases in size about 10,000 times since birth. A locust eats its own weight in plants every day. Just imagine eating your own weight in food every day. You probably couldnt. You would most likely get very sick even if you tried. | text | null |
L_0574 | insect food | T_3100 | Insects eat in many different ways and they eat a huge range of foods. Around half are plant-eaters, feeding on leaves, roots, seeds, nectar, or wood. Aphids and leafhoppers suck up the sap from plants. Praying mantises are predators, hunting other small creatures, including insects like moths, caterpillars, flies, beetles, and spiders. Insects like mosquitoes and aphids have special mouthparts that help them pierce and suck. Others, like assassin bugs ( Figure 1.1) and certain species of female mosquitoes, eat other insects. Fleas and lice are parasites, eating the flesh or blood of larger animals without killing them. Insects have different types of appendages (arms and legs) adapted for capturing and feeding on prey. They also have special senses that help them detect prey. Furthermore, insects have a wide range of mouthparts used for feeding. An assassin bug feasts on a beetle. Examples of chewing insects include dragonflies, grasshoppers, and beetles. These insects use one pair of jaws to bite off bits of food and grind them down. Another pair of jaws helps to push the food down the throat. Some larvae also have chewing mouthparts, as in the caterpillar stages of moths and butterflies ( Figure 1.2). Caterpillar feeding on a host plant. Some insects use siphoning, as if sucking through a straw, like moths and butterflies. This long mouth-tube that they use to suck up the nectar of the flower is called a proboscis. Some moths, however, have no mouthparts at all. Some insects obtain food by sponging, like the housefly. Sponging means that the mouthpart can absorb liquid food and send it to the esophagus. The housefly is able to eat solid food by releasing saliva and dabbing it over the food. As the saliva dissolves the food, the sponging mouthpart absorbs the liquid food. Sponging Chewing Siphoning Used to suck liquids | text | null |
L_0574 | insect food | T_3100 | Insects eat in many different ways and they eat a huge range of foods. Around half are plant-eaters, feeding on leaves, roots, seeds, nectar, or wood. Aphids and leafhoppers suck up the sap from plants. Praying mantises are predators, hunting other small creatures, including insects like moths, caterpillars, flies, beetles, and spiders. Insects like mosquitoes and aphids have special mouthparts that help them pierce and suck. Others, like assassin bugs ( Figure 1.1) and certain species of female mosquitoes, eat other insects. Fleas and lice are parasites, eating the flesh or blood of larger animals without killing them. Insects have different types of appendages (arms and legs) adapted for capturing and feeding on prey. They also have special senses that help them detect prey. Furthermore, insects have a wide range of mouthparts used for feeding. An assassin bug feasts on a beetle. Examples of chewing insects include dragonflies, grasshoppers, and beetles. These insects use one pair of jaws to bite off bits of food and grind them down. Another pair of jaws helps to push the food down the throat. Some larvae also have chewing mouthparts, as in the caterpillar stages of moths and butterflies ( Figure 1.2). Caterpillar feeding on a host plant. Some insects use siphoning, as if sucking through a straw, like moths and butterflies. This long mouth-tube that they use to suck up the nectar of the flower is called a proboscis. Some moths, however, have no mouthparts at all. Some insects obtain food by sponging, like the housefly. Sponging means that the mouthpart can absorb liquid food and send it to the esophagus. The housefly is able to eat solid food by releasing saliva and dabbing it over the food. As the saliva dissolves the food, the sponging mouthpart absorbs the liquid food. Sponging Chewing Siphoning Used to suck liquids | text | null |
L_0575 | insect reproduction and life cycle | T_3101 | Most insects can reproduce very quickly within a short period of time. With a short generation time, they evolve faster and can quickly adjust to environmental changes. Most insects reproduce by sexual reproduction. The female produces eggs, which are fertilized by the male, and then the eggs are usually placed near the required food. In some insects, there is asexual reproduction during which the offspring come from a single parent. In this type of reproduction, the offspring are almost identical to the mother. This is most often seen in aphids and scale insects. With a few exceptions, all insect life begins as an egg. After leaving the egg, insects must grow and transform until reaching adulthood. Only the adult insect can mate and reproduce. The physical transformation of an insect from one stage of its life cycle to another is known as metamorphosis. | text | null |
L_0575 | insect reproduction and life cycle | T_3102 | An insect can have one of three types of metamorphosis and life cycles ( Table 1.1). Metamorphosis describes how insects transform from an immature or young insect into an adult insect in at least two stages. Insects may undergo gradual metamorphosis (incomplete), where transformation is subtle, or complete metamorphosis, where each stage of the life cycle appears quite different from the others. In some insects, there may be no true metamorphosis at all. Type of Metamorphosis None Characteristics Examples Silverfish, firebrats, springtails Only difference between adult and larvae (young or non-adult insects) is size. Occurs in the most primitive insects. Newborn insect looks like a tiny version of the adult. Incomplete Three stages: egg, nymph, and adult. Young, called nymphs, usu- ally similar to adult. Growth occurs during the nymph stage. Wings then appear as buds on nymphs or early forms. When last molt is completed, wings expand to full adult size. Dragonflies, grasshoppers, mantids, cockroaches, termites Type of Metamorphosis Complete Characteristics Most insects undergo this type. Each stage of the life cy- cleegg, larva, pupa, and adultlooks different from the others. Immature and adult stages have different forms, have different behaviors, and live in different habitats. Immature form is called lar- vae and remains similar in form but increases in size. Larvae usually have chew- ing mouthparts even if adult mouthparts are sucking ones. At last larval stage of de- velopment, insect forms into pupa ( Figure 1.1) and does not eat or move. During pupa stage, wing development begins, after which the adult emerges. Examples Butterflies, moths, flies, ants, bees, beetles The chrysalis (pupal stage) of a monarch butterfly. | text | null |
L_0576 | insects | T_3103 | Insects, with over a million described species, are the most diverse group of animals on Earth. They may be found in nearly all environments on the planet. No matter where you travel, you will see organisms from this group. Adult insects range in size from a minuscule fairy fly to a 21.9-inch-long stick insect ( Figure 1.1). | text | null |
L_0576 | insects | T_3104 | Characteristics of Insects include: Segmented bodies with an exoskeleton. The outer layer of the exoskeleton is called the cuticle. It is made up of two layers. The outer layer, or exocuticle, is thin, waxy, and water-resistant. The inner layer is much thicker. The exocuticle is extremely thin in many soft-bodied insects, such as caterpillars. The segments of the body are organized into three distinct but joined units: a head, a thorax, and an abdomen ( Figure 1.2 and Table 1.1). A diagram of a human and an insect, com- paring the three main body parts: head, thorax, and abdomen. Structure Head Thorax Abdomen Description A pair of antennae, a pair of compound eyes, and three sets of appendages that form the mouthparts. Six segmented legs and two or four wings. Contains most of the digestive, respiratory, excretory, and reproductive structures. A nervous system that is divided into a brain and a ventral nerve cord. Respiration that occurs without lungs. Insects have a system of internal tubes and sacs that oxygen travels through to reach body tissues. Air is taken in through the spiracles, openings on the sides of the abdomen. A closed digestive system, with one long enclosed coiled tube which runs lengthwise through the body, from the mouth to the anus. A circulatory system that is simple and consists of only a single tube with openings. The tube pulses and circulates blood-like fluids inside the body cavity. Various types of movement. Insect movement can include flight, walking, and swimming. Insects were the Fireflies Reproduction and predation: Some species produce flashes to attract mates; other species to attract prey. Sound Production By moving appendages Cicadas Ultrasound clicks Moths Loudest sounds among insects; have special muscles to produce sounds. Predation: Produced mostly by moths to warn bats. Chemical Wide range of insects have evolved chemical communication; chemi- cals are used to attract, repel, or provide other kinds of information; use of scents is especially well de- veloped in social insects. Dance Language Moths Honey bees Antennae of males ( Figure 1.4) can detect pheromones (chemicals released by animals that influence the behavior of others within the same species) of female moths over distances of many miles. Honey bees are the only inverte- brates to have evolved this type of communication; length of dance represents distance to be flown. | text | null |
L_0576 | insects | T_3104 | Characteristics of Insects include: Segmented bodies with an exoskeleton. The outer layer of the exoskeleton is called the cuticle. It is made up of two layers. The outer layer, or exocuticle, is thin, waxy, and water-resistant. The inner layer is much thicker. The exocuticle is extremely thin in many soft-bodied insects, such as caterpillars. The segments of the body are organized into three distinct but joined units: a head, a thorax, and an abdomen ( Figure 1.2 and Table 1.1). A diagram of a human and an insect, com- paring the three main body parts: head, thorax, and abdomen. Structure Head Thorax Abdomen Description A pair of antennae, a pair of compound eyes, and three sets of appendages that form the mouthparts. Six segmented legs and two or four wings. Contains most of the digestive, respiratory, excretory, and reproductive structures. A nervous system that is divided into a brain and a ventral nerve cord. Respiration that occurs without lungs. Insects have a system of internal tubes and sacs that oxygen travels through to reach body tissues. Air is taken in through the spiracles, openings on the sides of the abdomen. A closed digestive system, with one long enclosed coiled tube which runs lengthwise through the body, from the mouth to the anus. A circulatory system that is simple and consists of only a single tube with openings. The tube pulses and circulates blood-like fluids inside the body cavity. Various types of movement. Insect movement can include flight, walking, and swimming. Insects were the Fireflies Reproduction and predation: Some species produce flashes to attract mates; other species to attract prey. Sound Production By moving appendages Cicadas Ultrasound clicks Moths Loudest sounds among insects; have special muscles to produce sounds. Predation: Produced mostly by moths to warn bats. Chemical Wide range of insects have evolved chemical communication; chemi- cals are used to attract, repel, or provide other kinds of information; use of scents is especially well de- veloped in social insects. Dance Language Moths Honey bees Antennae of males ( Figure 1.4) can detect pheromones (chemicals released by animals that influence the behavior of others within the same species) of female moths over distances of many miles. Honey bees are the only inverte- brates to have evolved this type of communication; length of dance represents distance to be flown. | text | null |
L_0576 | insects | T_3104 | Characteristics of Insects include: Segmented bodies with an exoskeleton. The outer layer of the exoskeleton is called the cuticle. It is made up of two layers. The outer layer, or exocuticle, is thin, waxy, and water-resistant. The inner layer is much thicker. The exocuticle is extremely thin in many soft-bodied insects, such as caterpillars. The segments of the body are organized into three distinct but joined units: a head, a thorax, and an abdomen ( Figure 1.2 and Table 1.1). A diagram of a human and an insect, com- paring the three main body parts: head, thorax, and abdomen. Structure Head Thorax Abdomen Description A pair of antennae, a pair of compound eyes, and three sets of appendages that form the mouthparts. Six segmented legs and two or four wings. Contains most of the digestive, respiratory, excretory, and reproductive structures. A nervous system that is divided into a brain and a ventral nerve cord. Respiration that occurs without lungs. Insects have a system of internal tubes and sacs that oxygen travels through to reach body tissues. Air is taken in through the spiracles, openings on the sides of the abdomen. A closed digestive system, with one long enclosed coiled tube which runs lengthwise through the body, from the mouth to the anus. A circulatory system that is simple and consists of only a single tube with openings. The tube pulses and circulates blood-like fluids inside the body cavity. Various types of movement. Insect movement can include flight, walking, and swimming. Insects were the Fireflies Reproduction and predation: Some species produce flashes to attract mates; other species to attract prey. Sound Production By moving appendages Cicadas Ultrasound clicks Moths Loudest sounds among insects; have special muscles to produce sounds. Predation: Produced mostly by moths to warn bats. Chemical Wide range of insects have evolved chemical communication; chemi- cals are used to attract, repel, or provide other kinds of information; use of scents is especially well de- veloped in social insects. Dance Language Moths Honey bees Antennae of males ( Figure 1.4) can detect pheromones (chemicals released by animals that influence the behavior of others within the same species) of female moths over distances of many miles. Honey bees are the only inverte- brates to have evolved this type of communication; length of dance represents distance to be flown. | text | null |
L_0576 | insects | T_3105 | Social insects, such as termites, ants, and many bees and wasps ( Figure 1.5), are the most familiar social species. They live together in large, well-organized colonies. Only those insects which live in nests or colonies can home. Homing means that an insect can return to a single hole among many other apparently identical holes, even after a long trip or after a long time. A few insects migrate in groups. For example, the monarch butterfly flies between Mexico and North America each spring and fall ( Figure 1.5). (left) Damage to this nest brings the work- ers and soldiers of this social insect, the termite, to repair it. (center ) A wasp build- ing its nest. (right) Monarch butterflies in an overwintering cluster. | text | null |
L_0576 | insects | T_3106 | Insects are divided into two major groups: 1. Wingless: Consists of two orders, the bristle tails and the silverfish. 2. Winged insects: All other orders of insects. They are named below. Mayflies; dragonflies and damselflies; stoneflies; webspinners; angel insects; earwigs; grasshoppers, crickets, and katydids; stick insects; ice-crawlers and gladiators; cockroaches and termites; mantids; lice; thrips; true bugs, aphids, and cicadas; wasps, bees, and ants; beetles; twisted-winged parasites; snakeflies; alderflies and dobsonflies; lacewings and antlions; hangingflies (including fleas); true flies; caddisflies; and butterflies, moths, and skippers. | text | null |
L_0577 | introduction to ecology | T_3107 | Life Science can be studied at many different levels. You can study small things like cells. Or you can study big things like a group of animals. You can also study the biosphere, which is any area in which organisms live. The study of the biosphere is part of ecology, the study of how living organisms interact with each other and with their environment. | text | null |
L_0577 | introduction to ecology | T_3108 | Ecology involves many different fields, including geology, soil science, geography, meteorology, genetics, chemistry, and physics. You can also divide ecology into the study of different organisms, such as animal ecology, plant ecology, insect ecology, and so on. Ecologists also study biomes. A biome is a large community of plants and animals that live in the same place. For example, ecologists can study the biomes as diverse as the Arctic, the tropics, or the desert ( Figure 1.1). They may want to know why different species live in different biomes. They may want to know what would make a particular biome or ecosystem stable. Can you think of other aspects of a biome or ecosystem that ecologists could study? Ecologists do two types of research: An example of a biome, the Atacama Desert, in Chile. 1. Field studies. 2. Laboratory studies. Field studies involve collecting data outside in the natural world. An ecologist who completes a field study may travel to a tropical rainforest to study, count, and classify all of the insects that live in a certain area. Laboratory studies involve working inside, usually in a controlled environment. Sometimes, ecologists collect data from the field, and then they analyze that data in the lab. Also, they use computer programs to predict what will happen to organisms that live in a specific area. For example, they may make predictions about what happens to insects in the rainforest after a fire. | text | null |
L_0577 | introduction to ecology | T_3109 | All organisms have the ability to grow and reproduce. To grow and reproduce, organisms must get materials and energy from the environment. Plants obtain their energy from the sun through photosynthesis, whereas animals obtain their energy from other organisms. Either way, these plants and animals, as well as the bacteria and fungi, are constantly interacting with other species as well as the non-living parts of their ecosystem. An organisms environment includes two types of factors: 1. Abiotic factors are the parts of the environment that are not living, such as sunlight, climate, soil, water, and air. 2. Biotic factors are the parts of the environment that are alive, or were alive and then died, such as plants, animals, and their remains. Biotic factors also include bacteria, fungi and protists. Ecology studies the interactions between biotic factors, such as organisms like plants and animals, and abiotic factors. For example, all animals (biotic factors) breathe in oxygen (abiotic factor). All plants (biotic factor) absorb carbon dioxide (abiotic factor) and need water (abiotic factor) to survive. Can you think of another way that abiotic and biotic factors interact with each other? | text | null |
L_0578 | invertebrates | T_3110 | Animals are often identified as being either invertebrates or vertebrates. These are terms based on the skeletons of the animals. Vertebrates have a backbone made of bone or cartilage ( cartilage is a flexible supportive tissue. You have cartilage in your ear lobes.). Invertebrates, on the other hand, have no backbone ( Figure 1.1). Invertebrates live just about anywhere. There are so many invertebrates on this planet that it is impossible to count them all. There are probably billions of billions of invertebrates. They come in many shapes and sizes, live practically anywhere and provide many services that are vital for the survival of other organisms, including us. They have been observed in the upper reaches of the atmosphere, in the driest of the deserts and in the canopies of the wettest rainforests. They can even be found in the frozen Antarctic or on the deepest parts of the ocean floor. Snails are an example of invertebrates, animals without a backbone. All vertebrate organisms are in the phylum Chordata. Invertebrates, which make up about 95% (or more) of the animal kingdom, are divided into over 30 different phyla, some of which are listed below ( Table 1.1). Numerous invertebrate phyla have just a few species; some have only one described species, yet these are classified into separate phyla because of their unique characteristics. For example, sponges, with pores throughout their body, are from the phylum Porifera. Crabs and lobsters, with jointed appendages, are from the phylum Arthropoda. Phylum Porifera Cnidaria Platyhelminthes Nematoda Mollusca Annelida Arthropoda Echinodermata Meaning Pore bearer Stinging nettle Flat worms Thread like Soft Little ring Jointed foot Spiny skin Examples Sponges Jellyfish, corals Flatworms, tapeworms Nematodes, heartworm Snails, clams Earthworms, leeches Insects, crabs Sea stars, sea urchins | text | null |
L_0584 | learned behavior of animals | T_3128 | Just about all human behaviors are learned. Learned behavior is behavior that occurs only after experience or practice. Learned behavior has an advantage over innate behavior: it is more flexible. Learned behavior can be changed if conditions change. For example, you probably know the route from your house to your school. Assume that you moved to a new house in a different place, so you had to take a different route to school. What if following the old route was an innate behavior? You would not be able to adapt. Fortunately, it is a learned behavior. You can learn the new route just as you learned the old one. Although most animals can learn, animals with greater intelligence are better at learning and have more learned behaviors. Humans are the most intelligent animals. They depend on learned behaviors more than any other species. Other highly intelligent species include apes, our closest relatives in the animal kingdom. They include chimpanzees and gorillas. Both are also very good at learning behaviors. You may have heard of a gorilla named Koko. The psychologist, Dr. Francine Patterson, raised Koko. Dr. Patterson wanted to find out if gorillas could learn human language. Starting when Koko was just one year old, Dr. Patterson taught her to use sign language. Koko learned to use and understand more than 1,000 signs. Koko showed how much gorillas can learn. See A Conversation with Koko at . Think about some of the behaviors you have learned. They might include riding a bicycle, using a computer, and playing a musical instrument or sport. You probably did not learn all of these behaviors in the same way. Perhaps you learned some behaviors on your own, just by practicing. Other behaviors you may have learned from other people. Humans and other animals can learn behaviors in several different ways. The following methods of learning will be explored below: 1. 2. 3. 4. 5. Habituation (forming a habit) Observational learning Conditioning Play Insight learning | text | null |
L_0584 | learned behavior of animals | T_3129 | Habituation is learning to get used to something after being exposed to it for a while. Habituation usually involves getting used to something that is annoying or frightening, but not dangerous. Habituation is one of the simplest ways of learning. It occurs in just about every species of animal. You have probably learned through habituation many times. For example, maybe you were reading a book when someone turned on a television in the same room. At first, the sound of the television may have been annoying. After a while, you may no longer have noticed it. If so, you had become habituated to the sound. Another example of habituation is shown below ( Figure 1.1). Crows and most other birds are usually afraid of people. They avoid coming close to people, or they fly away when people come near them. The crows landing on this scarecrow have become used to a human in this place. They have learned that the scarecrow poses no danger. They are no longer afraid to come close. They have become habituated to the scarecrow. Can you see why habituation is useful? It lets animals ignore things that will not harm them. Without habituation, animals might waste time and energy trying to escape from things that are not really dangerous. | text | null |
L_0584 | learned behavior of animals | T_3130 | Observational learning is learning by watching and copying the behavior of someone else. Human children learn many behaviors this way. When you were a young child, you may have learned how to tie your shoes by watching your dad tie his shoes. More recently, you may have learned how to dance by watching a pop star dancing on TV. Most likely, you have learned how to do math problems by watching your teachers do problems on the board at school. Can you think of other behaviors you have learned by watching and copying other people? Other animals also learn through observational learning. For example, young wolves learn to be better hunters by watching and copying the skills of older wolves in their pack. Another example of observational learning is how some monkeys have learned to wash their food. They learned by watching and copying the behavior of other monkeys. | text | null |
L_0584 | learned behavior of animals | T_3131 | Conditioning is a way of learning that involves a reward or punishment. Did you ever train a dog to fetch a ball or stick by rewarding it with treats? If you did, you were using conditioning. Another example of conditioning is shown in the video below; the rats have been taught to play basketball by being rewarded with food pellets. What do you think would happen if the rats were no longer rewarded for this behavior? Click image to the left or use the URL below. URL: Conditioning also occurs in wild animals. For example, bees learn to find nectar in certain types of flowers because they have found nectar in those flowers before. Humans learn behaviors through conditioning, as well. A young child might learn to put away his toys by being rewarded with a bedtime story. An older child might learn to study for tests in school by being rewarded with better grades. Can you think of behaviors you have learned by being rewarded for them? Conditioning does not always involve a reward. It can involve a punishment, instead. A toddler might be punished with a time-out each time he grabs a toy from his baby brother. After several time-outs, he may learn to stop taking his brothers toys. A dog might be scolded each time she jumps up on the sofa. After repeated scolding, she may learn to stay off the sofa. A bird might become ill after eating a poisonous insect. The bird may learn from this punishment to avoid eating the same kind of insect in the future. | text | null |
L_0584 | learned behavior of animals | T_3132 | Most young mammals, including humans, like to play. Play is one ways they learn the skills that they will need as adults. Think about how kittens play. They pounce on toys and chase each other. This helps them learn how to be better predators when they are older. Big cats also play. The lion cubs pictured below are playing and practicing their hunting skills at the same time ( Figure 1.2). The dogs are playing tug-of-war with a toy ( Figure 1.2). What do you think they are learning by playing together this way? Other young animals play in different ways. For example, young deer play by running and kicking up their hooves. This helps them learn how to escape from predators. Left: These two lion cubs are playing. They are not only having fun, but they are also learning how to be better hunters. Right: These dogs are really playing. This play fighting can help them learn how to be better predators. Human children learn by playing as well. For example, playing games and sports can help them learn to follow rules and work with others. The toddlers pictured below are playing in the sand ( Figure 1.3). They are learning about the world through play. What do you think they might be learning? Playing in a sandbox is fun for young children. It can also help them learn about the world. | text | null |
L_0584 | learned behavior of animals | T_3132 | Most young mammals, including humans, like to play. Play is one ways they learn the skills that they will need as adults. Think about how kittens play. They pounce on toys and chase each other. This helps them learn how to be better predators when they are older. Big cats also play. The lion cubs pictured below are playing and practicing their hunting skills at the same time ( Figure 1.2). The dogs are playing tug-of-war with a toy ( Figure 1.2). What do you think they are learning by playing together this way? Other young animals play in different ways. For example, young deer play by running and kicking up their hooves. This helps them learn how to escape from predators. Left: These two lion cubs are playing. They are not only having fun, but they are also learning how to be better hunters. Right: These dogs are really playing. This play fighting can help them learn how to be better predators. Human children learn by playing as well. For example, playing games and sports can help them learn to follow rules and work with others. The toddlers pictured below are playing in the sand ( Figure 1.3). They are learning about the world through play. What do you think they might be learning? Playing in a sandbox is fun for young children. It can also help them learn about the world. | text | null |
L_0584 | learned behavior of animals | T_3133 | Insight learning is learning from past experiences and reasoning. It usually involves coming up with new ways to solve problems. Insight learning generally happens quickly. An animal has a sudden flash of insight. Insight learning requires relatively great intelligence. Human beings use insight learning more than any other species. They have used their intelligence to solve problems ranging from inventing the wheel to flying rockets into space. Think about problems you have solved. Maybe you figured out how to solve a new type of math problem or how to get to the next level of a video game. If you relied on your past experiences and reasoning to do it, then you were using insight learning. One type of insight learning is making tools to solve problems. Scientists used to think that humans were the only animals intelligent enough to make tools. In fact, tool-making was believed to set humans apart from all other animals. In 1960, primate expert Jane Goodall discovered that chimpanzees also make tools. She saw a chimpanzee strip leaves from a twig. Then he poked the twig into a hole in a termite mound. After termites climbed onto the twig, he pulled the twig out of the hole and ate the insects clinging to it. The chimpanzee had made a tool to fish for termites. He had used insight to solve a problem. Since then, chimpanzees have been seen making several different types of tools. For example, they sharpen sticks and use them as spears for hunting. They use stones as hammers to crack open nuts. Scientists have also observed other species of animals making tools to solve problems. A crow was seen bending a piece of wire into a hook. Then the crow used the hook to pull food out of a tube. An example of a gorilla using a walking stick is shown below ( Figure 1.4). Behaviors such as these show that other species of animals can use their experience and reasoning to solve problems. They can learn through insight. This gorilla is using a branch as a tool. She is leaning on it to keep her balance while she reaches down into swampy water to catch a fish. | text | null |
L_0585 | levels of ecological organization | T_3134 | Ecosystems can be studied at small levels or at large levels. The levels of organization are described below from the smallest to the largest: A species is a group of individuals that are genetically related and can breed to produce fertile young. Individuals are not members of the same species if their members cannot produce offspring that can also have children. The second word in the two word name given to every organism is the species name. For example, in Homo sapiens, sapiens is the species name. A population is a group of organisms belonging to the same species that live in the same area and interact with one another. A community is all of the populations of different species that live in the same area and interact with one another. A community is composed of all of the biotic factors of an area. An ecosystem includes the living organisms (all the populations) in an area and the non-living aspects of the environment ( Figure 1.1). An ecosystem is made of the biotic and abiotic factors in an area. Satellite image of Australias Great Barrier Reef, an example of a marine ecosys- tem. The biosphere is the part of the planet with living organisms ( Figure 1.2). The biosphere includes most of Earth, including part of the oceans and the atmosphere. Ecologists study ecosystems at every level, from the individual organism to the whole ecosystem and biosphere. They can ask different types of questions at each level. Examples of these questions are given in Table 1.1, using the zebra (Equus zebra) as an example. Ecosystem Level Individual Population Community Ecosystem Question How do zebras keep water in their bodies? What causes the growth of a zebra populations? How does a disturbance, like a fire or predator, affect the number of mammal species in African grasslands? How does fire affect the amount of food available in grassland ecosystems? | text | null |
L_0585 | levels of ecological organization | T_3134 | Ecosystems can be studied at small levels or at large levels. The levels of organization are described below from the smallest to the largest: A species is a group of individuals that are genetically related and can breed to produce fertile young. Individuals are not members of the same species if their members cannot produce offspring that can also have children. The second word in the two word name given to every organism is the species name. For example, in Homo sapiens, sapiens is the species name. A population is a group of organisms belonging to the same species that live in the same area and interact with one another. A community is all of the populations of different species that live in the same area and interact with one another. A community is composed of all of the biotic factors of an area. An ecosystem includes the living organisms (all the populations) in an area and the non-living aspects of the environment ( Figure 1.1). An ecosystem is made of the biotic and abiotic factors in an area. Satellite image of Australias Great Barrier Reef, an example of a marine ecosys- tem. The biosphere is the part of the planet with living organisms ( Figure 1.2). The biosphere includes most of Earth, including part of the oceans and the atmosphere. Ecologists study ecosystems at every level, from the individual organism to the whole ecosystem and biosphere. They can ask different types of questions at each level. Examples of these questions are given in Table 1.1, using the zebra (Equus zebra) as an example. Ecosystem Level Individual Population Community Ecosystem Question How do zebras keep water in their bodies? What causes the growth of a zebra populations? How does a disturbance, like a fire or predator, affect the number of mammal species in African grasslands? How does fire affect the amount of food available in grassland ecosystems? | text | null |
L_0588 | lizards and snakes | T_3145 | Lizards and snakes belong to the largest order of reptiles, Squamata. Lizards are a large group of reptiles, with nearly 5,000 species, living on every continent except Antarctica. Some places are just too cold for lizards. | text | null |
L_0588 | lizards and snakes | T_3146 | Lizards and snakes are distinguished by scales or shields and movable quadrate bones, which make it possible to open the upper jaw very wide. Quadrate bones are especially visible in snakes, because they are able to open their mouths very wide to eat large prey ( Figure 1.1). Without this ability, the snake diet would be very limited. | text | null |
L_0588 | lizards and snakes | T_3147 | Key features of lizards include: Four limbs. External ears. Movable eyelids. A short neck. A long tail, which they can shed in order to escape from predators. They eat insects. Vision, including color vision, is well-developed in lizards. You may have seen a lizard camouflaged to blend in with its surroundings. Since they have great vision, lizards communicate by changing the color of their bodies. They also communicate with chemical signals called pheromones. Adult lizards range from one inch in length, like some Caribbean geckos, to the nearly 10-foot-long Komodo dragon ( Figure 1.2). A Komodo dragon, the largest of the lizards, attaining a length of ten feet. Ko- modo dragons will eat just about anything and they often attack deer, goats, pigs, dogs and, occasionally, humans. With 40 lizard families, there is an extremely wide range of color, appearance, and size of lizards. Many lizards are capable of regenerating lost limbs or tails. Almost all lizards are carnivorous, meaning they eat animals, although most are so small that insects are their primary prey. However, some have reached sizes where they can prey on birds and mammals. On the other hand, a few species of lizards exclusively eat plants. | text | null |
L_0588 | lizards and snakes | T_3147 | Key features of lizards include: Four limbs. External ears. Movable eyelids. A short neck. A long tail, which they can shed in order to escape from predators. They eat insects. Vision, including color vision, is well-developed in lizards. You may have seen a lizard camouflaged to blend in with its surroundings. Since they have great vision, lizards communicate by changing the color of their bodies. They also communicate with chemical signals called pheromones. Adult lizards range from one inch in length, like some Caribbean geckos, to the nearly 10-foot-long Komodo dragon ( Figure 1.2). A Komodo dragon, the largest of the lizards, attaining a length of ten feet. Ko- modo dragons will eat just about anything and they often attack deer, goats, pigs, dogs and, occasionally, humans. With 40 lizard families, there is an extremely wide range of color, appearance, and size of lizards. Many lizards are capable of regenerating lost limbs or tails. Almost all lizards are carnivorous, meaning they eat animals, although most are so small that insects are their primary prey. However, some have reached sizes where they can prey on birds and mammals. On the other hand, a few species of lizards exclusively eat plants. | text | null |
L_0588 | lizards and snakes | T_3148 | Have you ever tried catching a lizard? Many lizards are good climbers or fast sprinters. Some can run on two feet, such as the collared lizard. Some, like the basilisk, can even run across the surface of water to escape danger. Many lizards can change color in response to their environments or in times of stress ( Figure 1.3). The most familiar example is the chameleon, but more subtle color changes can occur in other lizard species. A species of lizard, showing general body form and camouflage against back- ground. | text | null |
L_0588 | lizards and snakes | T_3149 | Some lizard species, including the glass lizard and flap-footed lizards, have evolved to lose their legs, or their legs are so small that they no longer work. This provides these species an evolutionary advantage in their way of life. Legless lizards almost look like snakes, though structures leftover from earlier stages of evolution remain. For example, flap-footed lizards can be distinguished from snakes by their external ears. | text | null |
L_0588 | lizards and snakes | T_3150 | Snakes are different from legless lizards because they do not have eyelids, limbs, external ears, or forelimbs. The more than 2,700 species of snake can be found on every continent except Antarctica and range in size from the tiny, 4-inch-long thread snake to pythons, to the over 17-foot-long anaconda ( Figure 1.4). In order to fit inside of snakes narrow bodies, paired organs, such as kidneys, appear one in front of the other instead of side by side. Snakes eyelids are transparent spectacle scales which remain permanently closed. Most snakes are not venomous, but some have venom capable of causing painful injury or death to humans. However, snake venom is primarily used for killing prey rather than for self-defense. Snakes that are kept as pets can have their venom removed without affecting the health of the snake. Most snakes use specialized belly scales, which grip surfaces to move ( Figure 1.5). In the shedding of scales, known as molting, the complete outer layer of skin is shed in one layer ( Figure 1.6). Molting replaces old and worn skin, allows the snake to grow, and helps it get rid of parasites such as mites and ticks. Although different snake species reproduce in different ways, all snakes use internal fertilization, where fertiliza- tion of the egg takes place inside the female. The male uses sex organs stored in its tail to transfer sperm to the female. Most species of snakes lay eggs, and most species abandon these eggs shortly after laying them. A species of anaconda, one of the largest snakes, which can be as long as 17 feet. A close-up of scales on a scarlet kingsnake, showing a tricolored pattern of red, black, and white bands. Notice the distinction between the belly scales and the rest of the snakes scales. | text | null |
L_0588 | lizards and snakes | T_3150 | Snakes are different from legless lizards because they do not have eyelids, limbs, external ears, or forelimbs. The more than 2,700 species of snake can be found on every continent except Antarctica and range in size from the tiny, 4-inch-long thread snake to pythons, to the over 17-foot-long anaconda ( Figure 1.4). In order to fit inside of snakes narrow bodies, paired organs, such as kidneys, appear one in front of the other instead of side by side. Snakes eyelids are transparent spectacle scales which remain permanently closed. Most snakes are not venomous, but some have venom capable of causing painful injury or death to humans. However, snake venom is primarily used for killing prey rather than for self-defense. Snakes that are kept as pets can have their venom removed without affecting the health of the snake. Most snakes use specialized belly scales, which grip surfaces to move ( Figure 1.5). In the shedding of scales, known as molting, the complete outer layer of skin is shed in one layer ( Figure 1.6). Molting replaces old and worn skin, allows the snake to grow, and helps it get rid of parasites such as mites and ticks. Although different snake species reproduce in different ways, all snakes use internal fertilization, where fertiliza- tion of the egg takes place inside the female. The male uses sex organs stored in its tail to transfer sperm to the female. Most species of snakes lay eggs, and most species abandon these eggs shortly after laying them. A species of anaconda, one of the largest snakes, which can be as long as 17 feet. A close-up of scales on a scarlet kingsnake, showing a tricolored pattern of red, black, and white bands. Notice the distinction between the belly scales and the rest of the snakes scales. | text | null |
L_0588 | lizards and snakes | T_3151 | All snakes are strictly carnivorous, eating small animals including lizards, other snakes, small mammals, birds, eggs, fish, snails, or insects. Because snakes cannot bite or tear their food to pieces, prey must be swallowed whole. Therefore, the body size of a snake has a major influence on its eating habits. A snake can usually estimate in advance if a prey is too large. The snakes jaw is unique in the animal kingdom. Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached. They also have many other joints in their skull, allowing them to open their mouths wide A Centralian carpet python shedding its skin. enough to swallow their prey whole. Some snakes have a venomous bite, which they use to kill their prey before eating it. Other snakes kill their prey by strangling them, and still others swallow their prey whole and alive. After eating, snakes enter a resting stage, while the process of digestion takes place. The process is highly efficient, with the snakes digestive enzymes dissolving and absorbing everything but the preys hair and claws! | text | null |
L_0592 | mammal characteristics | T_3158 | What is a mammal? These animals range from bats, cats, and rats to dogs, monkeys, elephants, and whales. They walk, run, swim, and fly. They live in the ocean, fly in the sky, walk on the prairies, and run in the savanna. There is a tremendous amount of diversity within the group in terms of reproduction, habitat, and adaptation for living in those different habitats. What allows them to live in such diverse environments? They have evolved specialized traits, unlike those of any other group of animal. Mammals (class Mammalia) are endothermic (warm-blooded) vertebrate animals with a number of unique characteristics. In most mammals, these include: The presence of hair or fur. Sweat glands. Glands specialized to produce milk, known as mammary glands. Three middle ear bones. A neocortex region in the brain, which specializes in seeing and hearing. Specialized teeth. A four-chambered heart. There are approximately 5,400 mammalian species, ranging in size from the tiny 1-2 inch bumblebee bat to the 108-foot blue whale. These are distributed in 29 orders, 153 families, and about 1,200 genera. There are three types of mammals, characterized by their method of reproduction. All mammals, except for a few, are viviparous, meaning they produce live young instead of laying eggs. The monotremes, however, have birdlike and reptilian characteristics, such as laying eggs and a cloaca. An example of a monotreme is the platypus with its birdlike beak and egg-laying characteristics. The echidnas are the only other monotreme mammals. A second type of mammal, the marsupial mammal, includes kangaroos, wallabies, koalas and possums. These mammals give birth to underdeveloped embryos, which then climb from the birth canal into a pouch on the front of the mothers body, where it feeds and continues to grow. The remainder of mammals, which is the majority of mammals, are placental mammals. These mammals develop in the mothers uterus, receiving nutrients across the placenta. Placental mammals include humans, rabbits, squirrels, whales, elephants, shrews, and armadillos. Dogs and cats, and sheep, cattle and horses are also placental mammals. Mammals are also the only animal group that evolved to live on land and then back to live in the ocean. Whales, dolphins, and porpoises have all adapted from land-dwelling creatures to a life of swimming and reproducing in the water ( Figure 1.1). Whales have evolved into the largest mammals. See Mammals- San Diego Kids at http://kids.sandiegozoo.org/animals/mammals and The Cheetah Orphans at material. Listen to They Might Be Giants - Mammal at for a description of numerous mammal traits. | text | null |
L_0593 | mammal classification | T_3159 | Traditionally, mammals were divided into groups based on their characteristics. Scientists took into consideration their anatomy (body structure), their habitats, and their feeding habits. Mammals are divided into three subclasses and about 26 orders. Some of the groups of mammals include: 1. Lagomorphs include hares and rabbits. Rabbits and hares characteristically have long ears, a short tail, and strong hind limbs that provide for a bouncing method of locomotion. They are all are small to medium-sized terrestrial herbivores. 2. Rodents include rats, mice, and other small gnawing mammals. They have a single pair of continuously growing incisors (teeth) in each of the upper and lower jaws that must be kept short by gnawing. 3. Carnivores include cats and lions and tigers, dogs and wolves, polar bears, and other meat eaters. 4. Insectivores include moles and shrews ( Figure 1.1). These mammals eat primarily insects, other arthropods, and earthworms. 5. Bats include the vampire bat. These mammals have forelimbs that form webbed wings, making bats the only mammals naturally capable of true and sustained flight. One of the subgroups of mammals is the insectivores, including this shrew. 6. Primates include monkeys, apes and humans. These mammals are characterized by detailed development of the hands and feet, a shortened snout, and a large brain. 7. Ungulates include hoofed animals, such as deer, sheep, goats, pigs, buffalo, elephants and giraffes ( Figure a thick nail rolled around the tip of the toe. The ungulates (hoofed animals), like the giraffe here, is one of the subgroups of mammals. Mammals can also be grouped according to the adaptations they form to live in a certain habitat. For example, terrestrial mammals with leaping kinds of movement, as in some marsupials and lagomorphs, typically live in open | text | null |
L_0593 | mammal classification | T_3159 | Traditionally, mammals were divided into groups based on their characteristics. Scientists took into consideration their anatomy (body structure), their habitats, and their feeding habits. Mammals are divided into three subclasses and about 26 orders. Some of the groups of mammals include: 1. Lagomorphs include hares and rabbits. Rabbits and hares characteristically have long ears, a short tail, and strong hind limbs that provide for a bouncing method of locomotion. They are all are small to medium-sized terrestrial herbivores. 2. Rodents include rats, mice, and other small gnawing mammals. They have a single pair of continuously growing incisors (teeth) in each of the upper and lower jaws that must be kept short by gnawing. 3. Carnivores include cats and lions and tigers, dogs and wolves, polar bears, and other meat eaters. 4. Insectivores include moles and shrews ( Figure 1.1). These mammals eat primarily insects, other arthropods, and earthworms. 5. Bats include the vampire bat. These mammals have forelimbs that form webbed wings, making bats the only mammals naturally capable of true and sustained flight. One of the subgroups of mammals is the insectivores, including this shrew. 6. Primates include monkeys, apes and humans. These mammals are characterized by detailed development of the hands and feet, a shortened snout, and a large brain. 7. Ungulates include hoofed animals, such as deer, sheep, goats, pigs, buffalo, elephants and giraffes ( Figure a thick nail rolled around the tip of the toe. The ungulates (hoofed animals), like the giraffe here, is one of the subgroups of mammals. Mammals can also be grouped according to the adaptations they form to live in a certain habitat. For example, terrestrial mammals with leaping kinds of movement, as in some marsupials and lagomorphs, typically live in open | text | null |
L_0593 | mammal classification | T_3159 | Traditionally, mammals were divided into groups based on their characteristics. Scientists took into consideration their anatomy (body structure), their habitats, and their feeding habits. Mammals are divided into three subclasses and about 26 orders. Some of the groups of mammals include: 1. Lagomorphs include hares and rabbits. Rabbits and hares characteristically have long ears, a short tail, and strong hind limbs that provide for a bouncing method of locomotion. They are all are small to medium-sized terrestrial herbivores. 2. Rodents include rats, mice, and other small gnawing mammals. They have a single pair of continuously growing incisors (teeth) in each of the upper and lower jaws that must be kept short by gnawing. 3. Carnivores include cats and lions and tigers, dogs and wolves, polar bears, and other meat eaters. 4. Insectivores include moles and shrews ( Figure 1.1). These mammals eat primarily insects, other arthropods, and earthworms. 5. Bats include the vampire bat. These mammals have forelimbs that form webbed wings, making bats the only mammals naturally capable of true and sustained flight. One of the subgroups of mammals is the insectivores, including this shrew. 6. Primates include monkeys, apes and humans. These mammals are characterized by detailed development of the hands and feet, a shortened snout, and a large brain. 7. Ungulates include hoofed animals, such as deer, sheep, goats, pigs, buffalo, elephants and giraffes ( Figure a thick nail rolled around the tip of the toe. The ungulates (hoofed animals), like the giraffe here, is one of the subgroups of mammals. Mammals can also be grouped according to the adaptations they form to live in a certain habitat. For example, terrestrial mammals with leaping kinds of movement, as in some marsupials and lagomorphs, typically live in open | text | null |
L_0594 | mammal reproduction | T_3160 | You probably realize that cats, dogs, people, and other mammals dont typically lay eggs. There are exceptions, however. Egg-laying is possible among the monotremes, mammals with birdlike and reptilian characteristics. Recall that mammals can be classified into three general groups, based on their reproductive strategy: the monotremes, the marsupials and the placental mammals. The egg-laying monotremes, such as echidnas ( Figure 1.1) and platypuses ( Figure 1.1), use one opening, the cloaca, to urinate, release waste, and reproduce, just like birds. They lay leathery eggs, similar to those of lizards, turtles, and crocodilians. Monotremes feed their young by sweating milk from patches on their bellies, as they lack the nipples present on other mammals. All other mammals give birth to live young and belong to one of two different categories, the marsupials and the placental mammals. A marsupial is an animal in which the embryo, which is often called a joey, is born at an immature stage. Development must be completed outside the mothers body. Most female marsupials have an abdominal pouch or skin fold where there are mammary glands. The pouch is a place for completing the development of the baby. Although blind, without fur, and with only partially formed hind legs, the tiny newborns have well developed forelimbs with claws that enable them to climb their way into their mothers pouch where they drink their mothers milk and continue their development. Marsupials include kangaroos, koalas, and opossums. Other marsupials are the wallaby and the Tasmanian Devil. Most marsupials live in Australia and nearby areas. ( Figure The echidna (right) is a member of the monotremes, the most primitive order of mammals. Another monotreme, the platy- pus (left), like other mammals in this or- der, lays eggs and has a single opening for the urinary, genital, and digestive or- gans. The majority of mammals are placental mammals. These are mammals in which the developing baby is fed through the mothers placenta. Female placental mammals develop a placenta after fertilization. A placenta is a spongy structure that passes oxygen, nutrients, and other useful substances from the mother to the fetus. It also passes carbon dioxide and other wastes from the fetus to the mother. The placenta allows the fetus to grow for a long time within the mother. A marsupial mammal, this eastern gray kangaroo has a joey (young kangaroo) in its abdominal pouch. Some mammals are alone until a female can become pregnant. Others form social groups with big differences between sexes, such as size differences, a trait called sexual dimorphism. Dominant males are those that are the largest or best-armed. These males usually have an advantage in mating. They may also keep other males from mating with females within a group. This is seen in elephant seals ( Figure 1.3), and also with elk, lions and non- human primates, including the orangutans and gorillas. Male elk grow antlers, while female elk do not have antlers. Adult male lions are not only larger than females, they have a mane of long hair on the side of the face and top of the head. | text | null |
L_0594 | mammal reproduction | T_3160 | You probably realize that cats, dogs, people, and other mammals dont typically lay eggs. There are exceptions, however. Egg-laying is possible among the monotremes, mammals with birdlike and reptilian characteristics. Recall that mammals can be classified into three general groups, based on their reproductive strategy: the monotremes, the marsupials and the placental mammals. The egg-laying monotremes, such as echidnas ( Figure 1.1) and platypuses ( Figure 1.1), use one opening, the cloaca, to urinate, release waste, and reproduce, just like birds. They lay leathery eggs, similar to those of lizards, turtles, and crocodilians. Monotremes feed their young by sweating milk from patches on their bellies, as they lack the nipples present on other mammals. All other mammals give birth to live young and belong to one of two different categories, the marsupials and the placental mammals. A marsupial is an animal in which the embryo, which is often called a joey, is born at an immature stage. Development must be completed outside the mothers body. Most female marsupials have an abdominal pouch or skin fold where there are mammary glands. The pouch is a place for completing the development of the baby. Although blind, without fur, and with only partially formed hind legs, the tiny newborns have well developed forelimbs with claws that enable them to climb their way into their mothers pouch where they drink their mothers milk and continue their development. Marsupials include kangaroos, koalas, and opossums. Other marsupials are the wallaby and the Tasmanian Devil. Most marsupials live in Australia and nearby areas. ( Figure The echidna (right) is a member of the monotremes, the most primitive order of mammals. Another monotreme, the platy- pus (left), like other mammals in this or- der, lays eggs and has a single opening for the urinary, genital, and digestive or- gans. The majority of mammals are placental mammals. These are mammals in which the developing baby is fed through the mothers placenta. Female placental mammals develop a placenta after fertilization. A placenta is a spongy structure that passes oxygen, nutrients, and other useful substances from the mother to the fetus. It also passes carbon dioxide and other wastes from the fetus to the mother. The placenta allows the fetus to grow for a long time within the mother. A marsupial mammal, this eastern gray kangaroo has a joey (young kangaroo) in its abdominal pouch. Some mammals are alone until a female can become pregnant. Others form social groups with big differences between sexes, such as size differences, a trait called sexual dimorphism. Dominant males are those that are the largest or best-armed. These males usually have an advantage in mating. They may also keep other males from mating with females within a group. This is seen in elephant seals ( Figure 1.3), and also with elk, lions and non- human primates, including the orangutans and gorillas. Male elk grow antlers, while female elk do not have antlers. Adult male lions are not only larger than females, they have a mane of long hair on the side of the face and top of the head. | text | null |
L_0595 | mass extinctions | T_3161 | An organism goes extinct when all of the members of a species die out and no more members remain. Extinctions are part of natural selection. Species often go extinct when their environment changes, and they do not have the traits they need to survive. Only those individuals with the traits needed to live in a changed environment survive (Survival of the Fittest) ( Figure 1.1). Mass extinctions, such as the extinction of dinosaurs and many marine mammals, happened after major catastrophes such as volcanic eruptions and earthquakes ( Figure 1.2). Since life began on Earth, there have been several major mass extinctions. If you look closely at the geological time scale, you will find that at least five major mass extinctions have occurred in the past 540 million years. In each mass extinction, over 50% of animal species died. Though species go extinct frequently, a mass extinction in which such a high percentage of species go extinct is rare. The total number of mass extinctions could be as high as 20. It is probable that we are currently in the midst of another mass extinction. Two of the largest extinctions are described below: The fossil of Tarbosaurus, one of the land dinosaurs that went extinct during one of the mass extinctions. At the end of the Permian Period, it is estimated that about 99.5% of individual organisms went extinct! Up to 95% of marine species perished, compared to only 70% of land species. Some scientists theorize that the extinction was caused by the formation of Pangaea, or one large continent made out of many smaller ones. One large continent has a smaller shoreline than many small ones, so reducing the shoreline space may have The supercontinent Pangaea encompassed all of todays continents in a single land mass. This configuration limited shallow coastal areas which harbor marine species. This may have contributed to the dramatic event which ended the Permianthe most massive extinction ever recorded. At the end of the Cretaceous Period, or 65 million years ago, all dinosaurs (except those which led to birds) went extinct. Some scientists believe a possible cause is a collision between the Earth and a comet or asteroid. The collision could have caused tidal waves, changed the climate, increased atmospheric dust and clouds, and reduced sunlight by 10-20%. A decrease in photosynthesis would have resulted in less plant food, leading to the extinction of the dinosaurs. Evidence for the extinction of dinosaurs by asteroid includes an iridium-rich layer in the Earth, dated at 65.5 million years ago. Iridium is rare in the Earths crust but common in comets and asteroids. Maybe the asteroid that hit the Earth left the iridium behind. After each mass extinction, new species evolve to fill the habitats where old species lived. This is well documented in the fossil record. | text | null |
L_0595 | mass extinctions | T_3161 | An organism goes extinct when all of the members of a species die out and no more members remain. Extinctions are part of natural selection. Species often go extinct when their environment changes, and they do not have the traits they need to survive. Only those individuals with the traits needed to live in a changed environment survive (Survival of the Fittest) ( Figure 1.1). Mass extinctions, such as the extinction of dinosaurs and many marine mammals, happened after major catastrophes such as volcanic eruptions and earthquakes ( Figure 1.2). Since life began on Earth, there have been several major mass extinctions. If you look closely at the geological time scale, you will find that at least five major mass extinctions have occurred in the past 540 million years. In each mass extinction, over 50% of animal species died. Though species go extinct frequently, a mass extinction in which such a high percentage of species go extinct is rare. The total number of mass extinctions could be as high as 20. It is probable that we are currently in the midst of another mass extinction. Two of the largest extinctions are described below: The fossil of Tarbosaurus, one of the land dinosaurs that went extinct during one of the mass extinctions. At the end of the Permian Period, it is estimated that about 99.5% of individual organisms went extinct! Up to 95% of marine species perished, compared to only 70% of land species. Some scientists theorize that the extinction was caused by the formation of Pangaea, or one large continent made out of many smaller ones. One large continent has a smaller shoreline than many small ones, so reducing the shoreline space may have The supercontinent Pangaea encompassed all of todays continents in a single land mass. This configuration limited shallow coastal areas which harbor marine species. This may have contributed to the dramatic event which ended the Permianthe most massive extinction ever recorded. At the end of the Cretaceous Period, or 65 million years ago, all dinosaurs (except those which led to birds) went extinct. Some scientists believe a possible cause is a collision between the Earth and a comet or asteroid. The collision could have caused tidal waves, changed the climate, increased atmospheric dust and clouds, and reduced sunlight by 10-20%. A decrease in photosynthesis would have resulted in less plant food, leading to the extinction of the dinosaurs. Evidence for the extinction of dinosaurs by asteroid includes an iridium-rich layer in the Earth, dated at 65.5 million years ago. Iridium is rare in the Earths crust but common in comets and asteroids. Maybe the asteroid that hit the Earth left the iridium behind. After each mass extinction, new species evolve to fill the habitats where old species lived. This is well documented in the fossil record. | text | null |
L_0595 | mass extinctions | T_3161 | An organism goes extinct when all of the members of a species die out and no more members remain. Extinctions are part of natural selection. Species often go extinct when their environment changes, and they do not have the traits they need to survive. Only those individuals with the traits needed to live in a changed environment survive (Survival of the Fittest) ( Figure 1.1). Mass extinctions, such as the extinction of dinosaurs and many marine mammals, happened after major catastrophes such as volcanic eruptions and earthquakes ( Figure 1.2). Since life began on Earth, there have been several major mass extinctions. If you look closely at the geological time scale, you will find that at least five major mass extinctions have occurred in the past 540 million years. In each mass extinction, over 50% of animal species died. Though species go extinct frequently, a mass extinction in which such a high percentage of species go extinct is rare. The total number of mass extinctions could be as high as 20. It is probable that we are currently in the midst of another mass extinction. Two of the largest extinctions are described below: The fossil of Tarbosaurus, one of the land dinosaurs that went extinct during one of the mass extinctions. At the end of the Permian Period, it is estimated that about 99.5% of individual organisms went extinct! Up to 95% of marine species perished, compared to only 70% of land species. Some scientists theorize that the extinction was caused by the formation of Pangaea, or one large continent made out of many smaller ones. One large continent has a smaller shoreline than many small ones, so reducing the shoreline space may have The supercontinent Pangaea encompassed all of todays continents in a single land mass. This configuration limited shallow coastal areas which harbor marine species. This may have contributed to the dramatic event which ended the Permianthe most massive extinction ever recorded. At the end of the Cretaceous Period, or 65 million years ago, all dinosaurs (except those which led to birds) went extinct. Some scientists believe a possible cause is a collision between the Earth and a comet or asteroid. The collision could have caused tidal waves, changed the climate, increased atmospheric dust and clouds, and reduced sunlight by 10-20%. A decrease in photosynthesis would have resulted in less plant food, leading to the extinction of the dinosaurs. Evidence for the extinction of dinosaurs by asteroid includes an iridium-rich layer in the Earth, dated at 65.5 million years ago. Iridium is rare in the Earths crust but common in comets and asteroids. Maybe the asteroid that hit the Earth left the iridium behind. After each mass extinction, new species evolve to fill the habitats where old species lived. This is well documented in the fossil record. | text | null |
L_0597 | mendels laws and genetics | T_3167 | Do you remember what happened when Mendel crossed purple flowered-plants and white flowered-plants? All the offspring had purple flowers. There was no blending of traits in any of Mendels experiments. Mendel had to come up with a theory of inheritance to explain his results. He developed a theory called the law of segregation. | text | null |
L_0597 | mendels laws and genetics | T_3168 | Mendel proposed that each pea plant had two hereditary factors for each trait. There were two possibilities for each hereditary factor, such as a purple factor or white factor. One factor is dominant to the other. The other trait that is masked is called the recessive factor, meaning that when both factors are present, only the effects of the dominant factor are noticeable ( Figure 1.1). Although you have two hereditary factors for each trait, each parent can only pass on one of these factors to the offspring. When the sex cells, or gametes (sperm or egg), form, the heredity factors must separate, so there is only one factor per gamete. In other words, the factors are "segregated" in each gamete. Mendels law of segregation states that the two hereditary factors separate when gametes are formed. When fertilization occurs, the offspring receive one hereditary factor from each gamete, so the resulting offspring have two factors. The law of segregation predates our understanding or meiosis. Mendel developed his theories without an under- standing of DNA, or even the knowledge that DNA existed. Quite a remarkable feat! In peas, purple flowers are dominant to white. If one of these purple flowers is crossed with a white flower, all the offspring will have purple flowers. | text | null |
L_0597 | mendels laws and genetics | T_3169 | This law explains what Mendel had seen in the F1 generation when a tall plant was crossed with a short plant. The two heredity factors in this case were the short and tall factors. Each individual in the F1 would have one of each factor, and as the tall factor is dominant to the short factor (the recessive factor), all the plants appeared tall. In describing genetic crosses, letters are used. The dominant factor is represented with a capital letter (T for tall) while the recessive factor is represented by a lowercase letter (t). For the T and t factors, three combinations are possible: TT, Tt, and tt. TT plants will be tall, while plants with tt will be short. Since T is dominant to t, plants that are Tt will be tall because the dominant factor masks the recessive factor. In this example, we are crossing a TT tall plant with a tt short plant. As each parent gives one factor to the F1 generation, all of the F1 generation will be Tt tall plants. When the F1 generation (Tt) is allowed to self-pollinate, each parent will give one factor (T or t) to the F2 generation. So the F2 offspring will have four possible combinations of factors: TT, Tt, tT, or tt. According to the laws of probability, 25% of the offspring would be tt, so they would appear short. And 75% would have at least one T factor and would be tall. | text | null |
L_0598 | mendels pea plants | T_3170 | What does the word "inherit" mean? You may have inherited something of value from a grandparent or another family member. To inherit is to receive something from someone who came before you. You can inherit objects, but you can also inherit traits. For example, you can inherit a parents eye color, hair color, or even the shape of your nose and ears! Genetics is the study of inheritance. The field of genetics seeks to explain how traits are passed on from one generation to the next. In the late 1850s, an Austrian monk named Gregor Mendel ( Figure 1.1) performed the first genetics experiments. To study genetics, Mendel chose to work with pea plants because they have easily identifiable traits ( Figure 1.2). For example, pea plants are either tall or short, which is an easy trait to observe. Furthermore, pea plants grow quickly, so he could complete many experiments in a short period of time. Mendel also used pea plants because they can either self-pollinate or be cross-pollinated. Self-pollination means that only one flower is involved; the flowers own pollen lands on the female sex organs. Cross pollination is done by hand by moving pollen from one flower to the stigma of another (just like bees do naturally). As a result, one plants sex cells combine with another plants sex cells. This is called a "cross." These crosses produce offspring Gregor Mendel, the "father" of genetics. Characteristics of pea plants. (or "children"), just like when male and female animals mate. Since Mendel could move pollen between plants, he could carefully control and then observe the results of crosses between two different types of plants. He studied the inheritance patterns for many different traits in peas, including round seeds versus wrinkled seeds, white flowers versus purple flowers, and tall plants versus short plants. Because of his work, Mendel is considered the "Father of Genetics." | text | null |
L_0598 | mendels pea plants | T_3170 | What does the word "inherit" mean? You may have inherited something of value from a grandparent or another family member. To inherit is to receive something from someone who came before you. You can inherit objects, but you can also inherit traits. For example, you can inherit a parents eye color, hair color, or even the shape of your nose and ears! Genetics is the study of inheritance. The field of genetics seeks to explain how traits are passed on from one generation to the next. In the late 1850s, an Austrian monk named Gregor Mendel ( Figure 1.1) performed the first genetics experiments. To study genetics, Mendel chose to work with pea plants because they have easily identifiable traits ( Figure 1.2). For example, pea plants are either tall or short, which is an easy trait to observe. Furthermore, pea plants grow quickly, so he could complete many experiments in a short period of time. Mendel also used pea plants because they can either self-pollinate or be cross-pollinated. Self-pollination means that only one flower is involved; the flowers own pollen lands on the female sex organs. Cross pollination is done by hand by moving pollen from one flower to the stigma of another (just like bees do naturally). As a result, one plants sex cells combine with another plants sex cells. This is called a "cross." These crosses produce offspring Gregor Mendel, the "father" of genetics. Characteristics of pea plants. (or "children"), just like when male and female animals mate. Since Mendel could move pollen between plants, he could carefully control and then observe the results of crosses between two different types of plants. He studied the inheritance patterns for many different traits in peas, including round seeds versus wrinkled seeds, white flowers versus purple flowers, and tall plants versus short plants. Because of his work, Mendel is considered the "Father of Genetics." | text | null |
L_0598 | mendels pea plants | T_3171 | In one of Mendels early experiments, he crossed a short plant and a tall plant. What do you predict the offspring of these plants were? Medium-sized plants? Most people during Mendels time would have said medium-sized. But an unexpected result occurred. Mendel observed that the offspring of this cross (called the F1 generation) were all tall plants! Next, Mendel let the F1 generation self-pollinate. That means the tall plant offspring were crossed with each other. He found that 75% of their offspring (the F2 generation) were tall, while 25% were short. Shortness skipped a generation. But why? In all, Mendel studied seven characteristics, with almost 20,000 F2 plants analyzed. All of his results were similar to the first experimentabout three out of every four plants had one trait, while just one out of every four plants had the other. For example, he crossed purple flowered-plants and white flowered-plants. Do you think the colors blended? No, they did not. Just like the previous experiment, all offspring in this cross (the F1 generation) were one color: purple. In the F2 generation, 75% of plants had purple flowers and 25% had white flowers ( Figure 1.3). There was no blending of traits in any of Mendels experiments. The results of Mendels experiment with purple flowered and white flowered-plants numerically matched the results of his experiments with other pea plant traits. | text | null |
L_0600 | microevolution and macroevolution | T_3173 | Does evolution only happen gradually through small changes? Or is it possible that drastic environmental changes can cause new species to evolve? Or can both small and large changes occur? Evolutionary changes can be both big and small. Some evolutionary changes do not create new species, but result in changes at the population level. A population is a group of organisms of the same species that live in the same area ( Figure 1.1). But what exactly is the definition of a species? A species is a group of organisms that have similar characteristics (they are genetically similar) and can mate with one another to produce fertile offspring. This school of fish are considered mem- bers of the same species because they are able to mate with one another. They are also considered a population because they live in the same part of the ocean. | text | null |
L_0600 | microevolution and macroevolution | T_3174 | You already know that evolution is the change in species over time. Most evolutionary changes are small and do not lead to the creation of a new species. When populations change in small ways over time, the process is called microevolution. Microevolution results in changes within a species. An example of microevolution is the evolution of mosquitoes that cannot be killed by pesticides, called pesticide- resistant mosquitoes. Imagine that you have a pesticide that kills most of the mosquitoes in your state. Through a random mutation, some of the mosquitoes have resistance to the pesticide. As a result of the widespread use of this pesticide, most of the remaining mosquitoes are the pesticide-resistant mosquitoes. When these mosquitoes repro- duce the next year, they produce more mosquitoes with the pesticide-resistant trait. Soon, most of the mosquitoes in your state are resistant to the pesticide. This is an example of microevolution because the number of mosquitoes with this trait changed. However, this evolutionary change did not create a new species of mosquito because the pesticide-resistant mosquitoes can still reproduce with other non-pesticide-resistant mosquitoes. | text | null |
L_0600 | microevolution and macroevolution | T_3175 | Macroevolution refers to much bigger evolutionary changes that result in new species. Macroevolution may happen: 1. When microevolution occurs repeatedly over a long period of time and leads to the creation of a new species. 2. As a result of a major environmental change, such as a volcanic eruption, earthquake, or an asteroid hitting Earth, which changes the environment so much that natural selection leads to large changes in the traits of a species. After thousands of years of isolation from each other, Darwins finch populations have experienced both microevo- lution and macroevolution. These finch populations cannot breed with other finch populations when they are brought together. Since they do not breed together, they are classified as separate species. | text | null |
L_0604 | modern genetics | T_3184 | Mendel laid the foundation for modern genetics, but there were still a lot of questions he left unanswered. What exactly are the dominant and recessive factors that determine how all organisms look? And how do these factors work? Since Mendels time, scientists have discovered the answers to these questions. Genetic material is made out of DNA. It is the DNA that makes up the hereditary factors that Mendel identified. By applying our modern knowledge of DNA and chromosomes, we can explain Mendels findings and build on them. In this concept, we will explore the connections between Mendels work and modern genetics. | text | null |
L_0604 | modern genetics | T_3185 | Recall that our DNA is wound into chromosomes. Each of our chromosomes contains a long chain of DNA that encodes hundreds, if not thousands, of genes. Each of these genes can have slightly different versions from individual to individual. These variants of genes are called alleles. Each parent only donates one allele for each gene to an offspring. For example, remember that for the height gene in pea plants there are two possible factors. These factors are alleles. There is a dominant allele for tallness (T) and a recessive allele for shortness (t). | text | null |
L_0604 | modern genetics | T_3186 | Genotype is a way to describe the combination of alleles that an individual has for a certain gene ( Table 1.1). For each gene, an organism has two alleles, one on each chromosome of a homologous pair of chromosomes (think of it as one allele from Mom, one allele from Dad). The genotype is represented by letter combinations, such as TT, Tt, and tt. When an organism has two of the same alleles for a specific gene, it is homozygous (homo means "same") for that gene. An organism can be either homozygous dominant (TT) or homozygous recessive (tt). If an organism has two different alleles (Tt) for a certain gene, it is known as heterozygous (hetero means different). Genotype Homozygous Heterozygous Homozygous dominant Homozygous recessive Definition Two of the same allele One dominant allele and one reces- sive allele Two dominant alleles Two recessive alleles Example TT or tt Tt TT tt Phenotype is a way to describe the traits you can see. The genotype is like a recipe for a cake, while the phenotype is like the cake made from the recipe. The genotype expresses the phenotype. For example, the phenotypes of Mendels pea plants were either tall or short, or they were purple-flowered or white-flowered. Can organisms with different genotypes have the same phenotypes? Lets see. What is the phenotype of a pea plant that is homozygous dominant (TT) for the tall trait? Tall. What is the phenotype of a pea plant that is heterozygous (Tt)? It is also tall. The answer is yes, two different genotypes can result in the same phenotype. Remember, the recessive phenotype will be expressed only when the dominant allele is absent, or when an individual is homozygous recessive (tt) ( Figure 1.1). Different genotypes (AA, Aa, aa or TT, Tt, tt) will lead to different phenotypes, or different appearances of the organism. | text | null |
L_0605 | molecular evidence for evolution | T_3187 | Arguably, some of the best evidence of evolution comes from examining the molecules and DNA found in all living things. Beginning in the 1940s, scientists studying molecules and DNA have confirmed conclusions about evolution drawn from other forms of evidence. Molecular clocks are used to determine how closely two species are related by calculating the number of differences between the species DNA sequences or amino acid sequences. These clocks are sometimes called gene clocks or evolutionary clocks. The fewer the differences, the less time since the species split from each other and began to evolve into different species ( Figure 1.1). A chicken and a gorilla will have more differences between their DNA and amino acid sequences than a gorilla and an orangutan. That means the chicken and gorilla had a common ancestor a very long time ago, while the gorilla and orangutan shared a more recent common ancestor. This provides additional evidence that the gorilla and orangutan are more closely related than the gorilla and the chicken. Which pair of organisms would have more molecular differences, a mammal and a bird, a mammal and a frog, or a mammal and a fish? On the other hand, animals may look similar but can have very different DNA sequences and evolutionary ancestry. Which would have more DNA sequences in common, a whale and a horse, or a whale and a shark? Almost all organisms are made from DNA with the same building blocks. The genomes (all of the genes in an organism) of all mammals are almost identical. The genomes, or all the DNA sequences of all the genes of an organism, have been determined for many different organisms. The comparison of genomes provides new information about the relationships among species and how evolution occurs ( Figure 1.2). Molecular evidence for evolution also includes: 1. The same biochemical building blocks, such as amino acids and nucleotides, are found in all organisms, from bacteria to plants and animals. Recall that amino acids are the building blocks of proteins, and nucleotides are the building blocks of DNA and RNA. 2. DNA and RNA determine the development of all organisms. 3. The similarities and differences between the genomes confirm patterns of evolution. | text | null |
L_0611 | natural selection | T_3204 | The theory of evolution by natural selection means that the inherited traits of a population change over time. Inherited traits are features that are passed from one generation to the next. For example, your eye color is an inherited trait. You inherited your eye color from your parents. Inherited traits are different from acquired traits, or traits that organisms develop over a lifetime, such as strong muscles from working out ( Figure 1.1). Natural selection explains how organisms in a population develop traits that allow them to survive and reproduce. Natural selection means that traits that offer an advantage will most likely be passed on to offspring; individuals with those traits have a better chance of surviving. Evolution occurs by natural selection. Take the giant tortoises on the Galpagos Islands as an example. If a short-necked tortoise lives on an island with fruit located at a high level, will the short-necked tortoise survive? No, it will not, because it will not be able to reach the food it needs to survive. If all of the short necked tortoises die, and the long-necked tortoises survive, then, over time, only the long-necked trait will be passed down to offspring. All of the tortoises with long-necks will be Human earlobes may be attached or free. You inherited the particular shape of your earlobes from your parents. Inherited traits are influenced by genes, which are passed on to offspring and future genera- tions. Things not influenced by genes are not passed on to your offspring. Natural selection only operates on traits like ear- lobe shape that have a genetic basis, not on traits that are acquired, like a summer tan. "naturally selected" to survive. Organisms that are not well-adapted, for whatever reason, to their environment, will naturally have less of a chance of surviving and reproducing. Every plant and animal depends on its traits to survive. Survival may include getting food, building homes, and attracting mates. Traits that allow a plant, animal, or other organism to survive and reproduce in its environment are called adaptations. Natural selection occurs when: 1. There is some variation in the inherited traits of organisms within a species. Without this variation, natural selection would not be possible. 2. Some of these traits will give individuals an advantage over others in surviving and reproducing. 3. These individuals will be likely to have more offspring. Imagine how in the Arctic, dark fur makes a rabbit easy for foxes to spot and catch in the snow. Therefore, white fur is a beneficial trait that improves the chance that a rabbit will survive, reproduce, and pass the trait of white fur on to its offspring ( Figure 1.2). Through this process of natural selection, dark fur rabbits will become uncommon over time. Rabbits will adapt to have white fur. In essence, the selection of rabbits with white fur - the beneficial trait - is a natural process. | text | null |
L_0611 | natural selection | T_3205 | Scientists estimate that there are between 5 million and 30 million species on the planet. But why are there so many? Different species are well-adapted to live and survive in many different types of environments. As environments change over time, organisms must constantly adapt to those environments. Diversity of species increases the chance that at least some organisms adapt and survive any major changes in the environment. For example, if a natural disaster kills all of the large organisms on the planet, then the small organisms will continue to survive. | text | null |
L_0617 | nonvascular plants | T_3218 | Nonvascular seedless plants, as their name implies, lack vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. As they lack vascular tissue, they also do not have true roots, stems, or leaves. Nonvascular plants do often have a leafy appearance, though, and they can have stem-like and root-like structures. These plants are very short because they cannot move nutrients and water up a stem. Nonvascular seedless plants, also known as bryophytes, are classified into three phyla: 1. Mosses 2. Hornworts 3. Liverworts | text | null |
L_0617 | nonvascular plants | T_3219 | Mosses are most often recognized as the green fuzz on damp rocks and trees in a forest. If you look closely, you will see that most mosses have tiny stem-like and leaf-like structures. This is the gametophyte stage. Remember that a gametophyte is haploid, having only one set of chromosomes. The gametophyte produces the gametes that, after fertilization, develop into the diploid sporophyte with two sets of chromosomes. The sporophyte forms a capsule, called the sporangium, which releases spores ( Figure 1.1). Sporophytes sprout up on stalks from this bed of moss gametophytes. Notice that both the sporophytes and gametophytes exist at the same time. | text | null |
L_0617 | nonvascular plants | T_3220 | Hornworts are named for their appearance. The "horn" part of the name comes from their hornlike sporophytes, and wort comes from the Anglo-Saxon word for herb. The hornlike sporophytes grow from a base of flattened lobes, which are the gametophytes ( Figure 1.2). They usually grow in moist and humid areas. In hornworts, the horns are the sporo- phytes that rise up from the leaflike ga- metophyte. | text | null |
L_0617 | nonvascular plants | T_3221 | Liverworts have two distinct appearances: they can either be leafy like mosses or flattened and ribbon-like. Liver- worts get their name from the type with the flattened bodies, which can resemble a liver ( Figure 1.3). Liverworts can often be found along stream beds. Liverworts with a flattened, ribbon-like body are called thallose liverworts. | text | null |
L_0620 | organization of living things | T_3228 | When you see an organism that you have never seen before, you probably put it into a group without even thinking. If it is green and leafy, you probably call it a plant. If it is long and slithers, you probably call it as a snake. How do you make these decisions? You look at the physical features of the organism and think about what it has in common with other organisms. Scientists do the same thing when they classify, or put into categories, living things. Scientists classify organisms not only by their physical features, but also by how closely related they are. Lions and tigers look like each other more than they look like bears, but are lions and tigers related? Evolutionarily speaking, yes. Evolution is the change in a species over time. Lions and tigers both evolved from a common ancestor. So it turns out that the two cats are actually more closely related to each other than to bears. How an organism looks and how it is related to other organisms determines how it is classified. | text | null |
L_0620 | organization of living things | T_3229 | People have been concerned with classifying organisms for thousands of years. Over 2,000 years ago, the Greek philosopher Aristotle developed a classification system that divided living things into several groups that we still use today, including mammals, insects, and reptiles. Carolus (Carl) Linnaeus (1707-1778) ( Figure 1.1) built on Aristotles work to create his own classification system. He invented the way we name organisms today, with each organism having a two word name. Linnaeus is considered the inventor of modern taxonomy, the science of naming and grouping organisms. In the 18th century, Carl Linnaeus invented the two-name system of naming organisms (genus and species) and introduced the most complete classification system then known. Linnaeus developed binomial nomenclature, a way to give a scientific name to every organism. In this system, each organism receives a two-part name in which the first word is the genus (a group of species), and the second word refers to one species in that genus. For example, a coyotes species name is Canis latrans. Latrans is the species and Canis is the genus, a larger group that includes dogs, wolves, and other dog-like animals. Here is another example: the red maple, Acer rubra, and the sugar maple, Acer saccharum, are both in the same genus and they look similar ( Figure 1.2). Notice that the genus is capitalized and the species is not, and that the whole scientific name is in italics. Tigers (Panthera tigris) and lions (Panthera leo) have the same genus name, but are obviously different species. The names may seem strange, but the names are written in a language called Latin. These leaves are from two different species of trees in the Acer, or maple, genus. The green leaf (far left) is from the sugar maple, and the red leaf (center ) are from the red maple. One of the character- istics of the maple genus is winged seeds (far right). | text | null |
L_0620 | organization of living things | T_3229 | People have been concerned with classifying organisms for thousands of years. Over 2,000 years ago, the Greek philosopher Aristotle developed a classification system that divided living things into several groups that we still use today, including mammals, insects, and reptiles. Carolus (Carl) Linnaeus (1707-1778) ( Figure 1.1) built on Aristotles work to create his own classification system. He invented the way we name organisms today, with each organism having a two word name. Linnaeus is considered the inventor of modern taxonomy, the science of naming and grouping organisms. In the 18th century, Carl Linnaeus invented the two-name system of naming organisms (genus and species) and introduced the most complete classification system then known. Linnaeus developed binomial nomenclature, a way to give a scientific name to every organism. In this system, each organism receives a two-part name in which the first word is the genus (a group of species), and the second word refers to one species in that genus. For example, a coyotes species name is Canis latrans. Latrans is the species and Canis is the genus, a larger group that includes dogs, wolves, and other dog-like animals. Here is another example: the red maple, Acer rubra, and the sugar maple, Acer saccharum, are both in the same genus and they look similar ( Figure 1.2). Notice that the genus is capitalized and the species is not, and that the whole scientific name is in italics. Tigers (Panthera tigris) and lions (Panthera leo) have the same genus name, but are obviously different species. The names may seem strange, but the names are written in a language called Latin. These leaves are from two different species of trees in the Acer, or maple, genus. The green leaf (far left) is from the sugar maple, and the red leaf (center ) are from the red maple. One of the character- istics of the maple genus is winged seeds (far right). | text | null |
L_0620 | organization of living things | T_3230 | Modern taxonomists have reordered many groups of organisms since Linnaeus. The main categories that biologists use are listed here from the most specific to the least specific category ( Figure 1.3). All organisms can be classified into one of three domains, the least specific grouping. The three domains are Bacteria, Archaea, and Eukarya. The Kingdom is the next category after the Domain. All life is divided among six kingdoms: Kingdom Bacteria, Kingdom Archaea, Kingdom Protista, Kingdom Plantae, Kingdom Fungi, and Kingdom Animalia. This diagram illustrates the classification categories for organisms, with the broad- est category (kingdom) at the bottom, and the most specific category (species) at the top. We are Homo sapiens. Homo is the genus of great apes that includes modern humans and closely related species, and sapiens is the only living species of the genus. | text | null |
L_0620 | organization of living things | T_3231 | Even though naming species is straightforward, deciding if two organisms are the same species can sometimes be difficult. Linnaeus defined each species by the distinctive physical characteristics shared by these organisms. But two members of the same species may look quite different. For example, people from different parts of the world sometimes look very different, but we are all the same species ( Figure 1.4). So how is a species defined? A species is defined as a group of similar individuals that can interbreed with one another and produce fertile offspring. A species does not produce fertile offspring with other species. | text | null |
L_0622 | origin of species | T_3236 | The creation of a new species is called speciation. Most new species develop naturally. But humans have also artificially created new breeds and species for thousands of years. New species develop naturally through the process of natural selection. Due to natural selection, organisms with traits that better enable them to adapt to their environment will tend to survive and reproduce in greater numbers. Natural selection causes beneficial heritable traits to become more common in a population and unfavorable heritable traits to become less common. For example, a giraffes neck is beneficial because it allows the giraffe to reach leaves high in trees. Natural selection caused this beneficial trait to become more common than short necks. As new changes in the DNA sequence are constantly being generated in a populations gene pool (changing the populations allele frequencies), some of these changes will be beneficial and result in traits that allow adaptation and survival. Natural selection causes evolution of a species as these beneficial traits become more common within a population. Evolution can occur within a species without completely resulting in a new species. Therefore, evolution and speciation are not the same. | text | null |
L_0622 | origin of species | T_3237 | Artificial selection occurs when humans select which plants or animals to breed in order to pass on specific traits to the next generation. For example, a farmer may choose to breed only cows that produce the best milk. Farmers would also avoid breeding cows that produce less milk. In this way, selective breeding of the cows would increase milk quality and quantity. Humans have also artificially bred dogs to create new breeds ( Figure 1.1). Artificial Selection: Humans used artificial selection to create these different breeds. Both dog breeds are descended from the same wolves, and their genes are almost identical. | text | null |
L_0622 | origin of species | T_3238 | There are two main ways that speciation happens naturally. Both processes create new species by reproductively isolating populations of the same species from each other. Organisms can be geographically isolated or isolated by a behavior. Either way, they will no longer be able to mate. Over a long period of time, usually thousands of years, each of the isolated populations evolves in a different direction, forming distinct species. How do you think scientists test whether two populations are separate species? They bring species from two populations back together again. If the two populations do not mate and produce fertile offspring, they are separate species. | text | null |
L_0622 | origin of species | T_3239 | Allopatric speciation occurs when groups from the same species are geographically isolated for long periods. Imagine all the ways that plants or animals could be isolated from each other: Emergence of a mountain range. Formation of a canyon. New rivers or streams. Here are two examples of allopatric speciation: Darwin observed thirteen distinct finch species on the Galpagos Islands that had evolved from the same ancestor. Different finch populations lived on separate islands with different environments. They evolved to best adapt to those particular environments. Later, scientists were able to determine which finches had evolved into distinct species by bringing members of each population together. The birds that could not mate were a separate species. When the Grand Canyon in Arizona formed, two populations of one squirrel species were separated by the giant canyon. After thousands of years of isolation from each other, the squirrel populations on the northern wall of the canyon looked and behaved differently from those on the southern wall ( Figure 1.2). North rim squirrels have white tails and black bellies. Squirrels on the south rim have white bellies and dark tails. They cannot mate with each other, so they are different species. Abert squirrel (left) on the southern rim of the Grand Canyon. Kaibab squirrel (right) found on northern rim of the Grand Canyon. | text | null |
L_0622 | origin of species | T_3240 | Sympatric speciation occurs when groups from the same species stop mating because of something other than physical or geographic separation. The behavior of two groups that live in the same region is an example of such separation. The separation may be caused by different mating seasons, for example. Sympatric speciation is more difficult to identify. Here are two examples of sympatric speciation: Some scientists suspect that two groups of orcas (killer whales) live in the same part of the Pacific Ocean part of the year but do not mate. The two groups hunt different prey species, eat different foods, sing different songs, and have different social interactions ( Figure 1.3). Two groups of Galpagos Island finch species lived in the same space, but each had his or her own distinct mating signals. Members of each group selected mates according to different beak structures and bird calls. The behavioral differences kept the groups separated until they formed different species. | text | null |
L_0631 | plant characteristics | T_3265 | Plants have adapted to a variety of environments, from the desert to the tropical rain forest to lakes and oceans. In each environment, plants have become crucial to supporting animal life. Plants are the food that animals eat. Plants also provide places for animals, such as insects and birds, to live; many birds build nests in plants. From tiny mosses to gorgeous rose bushes to extremely large redwood trees ( Figure 1.1), the organisms in this kingdom, Kingdom Plantae, have three main features. They are all: 1. Eukaryotic. 2. Photosynthetic. 3. Multicellular. Recall that eukaryotic organisms also include animals, protists, and fungi. Eukaryotes have cells with nuclei that contain DNA, and membrane-bound organelles, such as mitochondria. Photosynthesis is the process by which plants capture the energy of sunlight and use carbon dioxide from the air (and water) to make their own food, the carbohydrate glucose. Plants have chloroplasts, the organelle of photosynthesis, and are known as producers and autotrophs. Other organisms are heterotrophic consumers, meaning they must obtain their nutrients from another organism, as these organisms lack chloroplasts. Lastly, plants must be multicellular, composed of more than one cell. There are no single-celled plants. Recall that some protists, such as algae, are eukaryotic and photosynthetic but are not considered plants. Unlike plants, algae is mostly unicellular. | text | null |
L_0632 | plant classification | T_3266 | Plants are formally divided into 12 phyla (plural for phylum), and these phyla are gathered into four groups ( Figure 1. Nonvascular plants evolved first. They are distinct from the algae because they keep the embryo inside of the reproductive structure after fertilization. These plants do not have vascular tissue, xylem or phloem, to transport nutrients, water, and food. Examples include mosses, liverworts, and hornworts. Without vascular tissue, these plants do not grow very tall. 2. Seedless vascular plants evolved to have vascular tissue after the nonvascular plants but do not have seeds. Examples include the ferns, whisk ferns, club mosses, and horsetails. Vascular tissue allowed these plants to grow taller. 3. Gymnosperms evolved to have seeds but do not have flowers. Examples of gymnosperms include the Redwood, Fir, and Cypress trees. Gymnos means "naked" in Greek; the seeds of gymnosperms are naked, not protected by flowers. 4. Flowering plants, or angiosperms, evolved to have vascular tissue, seeds, and flowers. Examples of an- giosperms include magnolia trees, roses, tulips, and tomatoes. The plant kingdom contains a diversity of organisms. | text | null |
L_0633 | plant hormones | T_3267 | Plants may not move, but that does not mean they dont respond to their environment. Plants can sense gravity, light, touch, and seasonal changes. For example, you might have noticed how a house plant bends toward a bright window. Plants can sense and then grow toward the source of light. Scientists say that plants are able to respond to "stimuli," or somethingusually in the environmentthat results in a response. For instance, light is the stimulus, and the plant moving toward the light is the "response." Hormones are special chemical messengers molecules that help organisms, including plants, respond to stimuli in their environment. In order for plants to respond to the environment, their cells must be able to communicate with other cells. Hormones send messages between the cells. Animals, like humans, also have hormones, such as testosterone or estrogen, to carry messages from cell to cell. In both plants and animals, hormones travel from cell to cell in response to a stimulus; they also activate a specific response. | text | null |
L_0633 | plant hormones | T_3268 | Five different types of plant hormones are involved in the main responses of plants, and they each have different functions ( Table 1.1). Hormone Ethylene Gibberellins Cytokinins Abscisic Acid Auxins Function Fruit ripening and abscission Break the dormancy of seeds and buds; promote growth Promote cell division; prevent senescence Close the stomata; maintain dormancy Involved in tropisms and apical dominance | text | null |
L_0633 | plant hormones | T_3269 | The hormone ethylene has two functions. It (1) helps ripen fruit and (2) is involved in the process of abscission, the dropping of leaves, fruits, and flowers. When a flower is done blooming or a fruit is ripe and ready to be eaten, ethylene causes the petals or fruit to fall from a plant ( Figure 1.1 and Figure 1.2). Ethylene is an unusual plant hormone because it is a gas. That means it can move through the air, and a ripening apple can cause another apple to ripen, or even over-ripen. Thats why one rotten apple spoils the whole barrel! Some farmers spray their green peppers with ethylene gas to cause them to ripen faster and become red peppers. You can try to see how ethylene works by putting a ripe apple or banana with another unripe fruit in a closed container or paper bag. What do you think will happen to the unripe fruit? | text | null |
L_0633 | plant hormones | T_3270 | Gibberellins are hormones that cause the plant to grow. When gibberellins are applied to plants by scientists, the stems grow longer. Some gardeners or horticulture scientists add gibberellins to increase the growth of plants. The hormone ethylene causes flower petals to fall from a plant, a process known as abscission. Dwarf plants (small plants), on the other hand, have low levels of gibberellins ( Figure 1.3). Another function of gibberellins is to stop dormancy (resting time) of seeds and buds. Gibberellins signal that its time for a seed to germinate (sprout) or for a bud to open. Dwarf plants like this bonsai tree often have unusually low concentrations of gib- berellins. | text | null |
L_0633 | plant hormones | T_3270 | Gibberellins are hormones that cause the plant to grow. When gibberellins are applied to plants by scientists, the stems grow longer. Some gardeners or horticulture scientists add gibberellins to increase the growth of plants. The hormone ethylene causes flower petals to fall from a plant, a process known as abscission. Dwarf plants (small plants), on the other hand, have low levels of gibberellins ( Figure 1.3). Another function of gibberellins is to stop dormancy (resting time) of seeds and buds. Gibberellins signal that its time for a seed to germinate (sprout) or for a bud to open. Dwarf plants like this bonsai tree often have unusually low concentrations of gib- berellins. | text | null |
L_0633 | plant hormones | T_3271 | Cytokinins are hormones that cause plant cells to divide. Cytokinins were discovered from attempts to grow plant tissue in artificial environments ( Figure 1.4). Cytokinins prevent the process of aging (senescence). So florists sometimes apply cytokinins to cut flowers, so they do not get old and die. Cytokinins promote cell division and are necessary for growing plants in tissue cul- ture. A small piece of a plant is placed in sterile conditions to regenerate a new plant. | text | null |
L_0633 | plant hormones | T_3272 | Abscisic acid is misnamed because it was once believed to play a role in abscission (the dropping of leaves, fruits, and flowers), but we now know abscission is caused by ethylene. The actual role of abscisic acid is to close the stomata, the tiny openings in leaves that allow substances to enter and leave, and to maintain dormancy. When a plant is stressed due to lack of water, abscisic acid tells the stomata to close. This prevents water loss through the stomata. When the environment is not good for a seed to germinate, abscisic acid signals for the dormancy period of the seed to continue. Abscisic acid also tells the buds of plants to stay in the dormancy stage. When conditions improve, the levels of abscisic acid drop and the levels of gibberellins increase, signaling that is time to break dormancy ( Figure | text | null |
L_0633 | plant hormones | T_3273 | Auxins are hormones that play a role in plant growth. Auxins produced at the tip of the plant are involved in apical dominance, when the main central stem grows more strongly than other stems and branches. When the tip of the plant is removed, the auxins are no longer present, and the side branches begin to grow. This is why pruning a plant by cutting off the main branches helps produce a fuller plant with more branches. You actually need to cut branches off of a plant for it to grow more branches! Auxins are also involved in tropisms, responses to stimuli in the environment | text | null |
L_0634 | plant like protists | T_3274 | Plant-like protists are known as algae ( Figure 1.1). They are a large and diverse group. Plant-like protists are autotrophs. This means that they produce their own food. They perform photosynthesis to produce sugar by using carbon dioxide and water, and the energy from sunlight, just like plants. Unlike plants, however, plant-like protists do not have true stems, roots, or leaves. Most plant-like protists live in oceans, ponds, or lakes. Protists can be unicellular (single-celled) or multicellular (many-celled). Seaweed and kelp are examples of multicellular, plant-like protists. Kelp can be as large as trees and form a "forest" in the ocean ( Figure 1.2). Plant-like protists are essential to the ecosystem. They are the base of the marine food chain, and they produce oxygen through photosynthesis for animals to breathe. They are classified into a number of basic groups ( Table Red algae are a very large group of protists making up about 5,0006,000 species. They are mostly multicellular and live in the ocean. Many red algae are seaweeds and help create coral reefs. Macrocystis pyrifera (giant kelp) is a type of multicellular, plant-like protist. Phylum Description Chlorophyta Green algae (related to higher plants) Red algae Brown algae Diatoms, golden-brown algae, yellow-green algae Dinoflagellates Euglenoids Rhodophyta Phaeophyta Chrysophyta Pyrrophyta Euglenophyta Approximate Number of Species 7,500 5,000 1,500 12,000 Chlamydomnas, Volvox Porphyra Macrocystis Cyclotella 4,000 1,000 Gonyaulax Euglena | text | null |
L_0634 | plant like protists | T_3274 | Plant-like protists are known as algae ( Figure 1.1). They are a large and diverse group. Plant-like protists are autotrophs. This means that they produce their own food. They perform photosynthesis to produce sugar by using carbon dioxide and water, and the energy from sunlight, just like plants. Unlike plants, however, plant-like protists do not have true stems, roots, or leaves. Most plant-like protists live in oceans, ponds, or lakes. Protists can be unicellular (single-celled) or multicellular (many-celled). Seaweed and kelp are examples of multicellular, plant-like protists. Kelp can be as large as trees and form a "forest" in the ocean ( Figure 1.2). Plant-like protists are essential to the ecosystem. They are the base of the marine food chain, and they produce oxygen through photosynthesis for animals to breathe. They are classified into a number of basic groups ( Table Red algae are a very large group of protists making up about 5,0006,000 species. They are mostly multicellular and live in the ocean. Many red algae are seaweeds and help create coral reefs. Macrocystis pyrifera (giant kelp) is a type of multicellular, plant-like protist. Phylum Description Chlorophyta Green algae (related to higher plants) Red algae Brown algae Diatoms, golden-brown algae, yellow-green algae Dinoflagellates Euglenoids Rhodophyta Phaeophyta Chrysophyta Pyrrophyta Euglenophyta Approximate Number of Species 7,500 5,000 1,500 12,000 Chlamydomnas, Volvox Porphyra Macrocystis Cyclotella 4,000 1,000 Gonyaulax Euglena | text | null |
L_0636 | plants adaptations for life on land | T_3276 | The first photosynthetic organisms were bacteria that lived in the water. So, where did plants come from? Evidence shows that plants evolved from freshwater green algae, a protist ( Figure 1.1). The similarities between green algae and plants is one piece of evidence. They both have cellulose in their cell walls, and they share many of the same chemicals that give them color. So what separates green algae from green plants? There are four main ways that plants adapted to life on land and, as a result, became different from algae: The ancestor of plants is green algae. This picture shows a close up of algae on the beach. 1. In plants, the embryo develops inside of the female plant after fertilization. Algae do not keep the embryo inside of themselves but release it into water. This was the first feature to evolve that separated plants from green algae. This is also the only adaptation shared by all plants. 2. Over time, plants had to evolve from living in water to living on land. In early plants, a waxy layer called a cuticle evolved to help seal water in the plant and prevent water loss. However, the cuticle also prevents gases from entering and leaving the plant easily. Recall that the exchange of gassestaking in carbon dioxide and releasing oxygenoccurs during photosynthesis. 3. To allow the plant to retain water and exchange gases, small pores (holes) in the leaves called stomata also evolved ( Figure 1.2). The stomata can open and close depending on weather conditions. When its hot and dry, the stomata close to keep water inside of the plant. When the weather cools down, the stomata can open again to let carbon dioxide in and oxygen out. 4. A later adaption for life on land was the evolution of vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. In algae, vascular tissue is not necessary since the entire body is in contact with the water, and the water simply enters the algae. But on land, water may only be found deep in the ground. Vascular tissues take water and nutrients from the ground up into the plant, while also taking food down from the leaves into the rest of the plant. The two vascular tissues are xylem and phloem. Xylem is responsible for the transport of water and nutrients from the roots to the rest of the plant. Phloem carries the sugars made in the leaves to the parts of the plant where they are needed. | text | null |
L_0639 | predation | T_3282 | Predation is another mechanism in which species interact with each other. Predation is when a predator organism feeds on another living organism or organisms, known as prey. The predator always lowers the preys fitness. It does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to maintaining the balance of organisms in an ecosystem. Examples of predator-prey relationships include the lion and zebra, the bear and fish, and the fox and rabbit. There are different types of predation, including: true predation. grazing. parasitism. True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it. Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example, This lion is an example of a predator on the hunt. eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance. Certain traits enable organisms to be effective hunters. These include camouflage, speed, and heightened senses. These traits also enable certain prey to avoid predators. In grazing, the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish. Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species. These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species. Prey also have adaptations for avoiding predators. Prey sometimes avoid detection by using camouflage ( Figure background. Mimicry is a related adaptation in which a species uses appearance to copy or mimic another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey ( Figure 1.3). Parasitism is a type of symbiotic relationship and will be described in the Symbiosis concept. Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards. An example of mimicry, where the Viceroy butterfly (right) mimics the unpleasant Monarch butterfly (left). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry. | text | null |
L_0639 | predation | T_3282 | Predation is another mechanism in which species interact with each other. Predation is when a predator organism feeds on another living organism or organisms, known as prey. The predator always lowers the preys fitness. It does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to maintaining the balance of organisms in an ecosystem. Examples of predator-prey relationships include the lion and zebra, the bear and fish, and the fox and rabbit. There are different types of predation, including: true predation. grazing. parasitism. True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it. Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example, This lion is an example of a predator on the hunt. eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance. Certain traits enable organisms to be effective hunters. These include camouflage, speed, and heightened senses. These traits also enable certain prey to avoid predators. In grazing, the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish. Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species. These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species. Prey also have adaptations for avoiding predators. Prey sometimes avoid detection by using camouflage ( Figure background. Mimicry is a related adaptation in which a species uses appearance to copy or mimic another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey ( Figure 1.3). Parasitism is a type of symbiotic relationship and will be described in the Symbiosis concept. Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards. An example of mimicry, where the Viceroy butterfly (right) mimics the unpleasant Monarch butterfly (left). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry. | text | null |
L_0639 | predation | T_3282 | Predation is another mechanism in which species interact with each other. Predation is when a predator organism feeds on another living organism or organisms, known as prey. The predator always lowers the preys fitness. It does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to maintaining the balance of organisms in an ecosystem. Examples of predator-prey relationships include the lion and zebra, the bear and fish, and the fox and rabbit. There are different types of predation, including: true predation. grazing. parasitism. True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large prey. They tear it apart and chew it before eating it. Others, like bottlenose dolphins or snakes, may eat their prey whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example, This lion is an example of a predator on the hunt. eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance. Certain traits enable organisms to be effective hunters. These include camouflage, speed, and heightened senses. These traits also enable certain prey to avoid predators. In grazing, the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass. The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed) can regrow after being eaten by fish. Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could become dominant over others. Grazers on a grassland keep grass from growing out of control. Predators can be keystone species. These are species that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a detrimental effect on the whole ecosystem. In this example, the wolves would be a keystone species. Prey also have adaptations for avoiding predators. Prey sometimes avoid detection by using camouflage ( Figure background. Mimicry is a related adaptation in which a species uses appearance to copy or mimic another species. For example, a non-poisonous dart frog may evolve to look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry can be used by both predators and prey ( Figure 1.3). Parasitism is a type of symbiotic relationship and will be described in the Symbiosis concept. Camouflage by the dead leaf mantis makes it less visible to both its predators and prey. If alarmed, it lies motionless on the rainforest floor of Madagascar, Africa, camouflaged among the actual dead leaves. It eats other animals up to the size of small lizards. An example of mimicry, where the Viceroy butterfly (right) mimics the unpleasant Monarch butterfly (left). Both butterfly species are avoided by predators to a greater degree than either one would be without mimicry. | text | null |
L_0644 | primates | T_3294 | If primates are mammals, what makes them seem so different from most mammals? Primates, including humans, have several unique features. Some adaptations give primates advantages that allow them to live in certain habitats, such as in trees. Other features have allowed them to adapt to complex social and cultural situations. Primates are mostly omnivorous, meaning many primate species eat both plant and animal material. The order contains all of the species commonly related to lemurs, monkeys, and apes. The order also includes humans ( Figure 1.1). Key features of primates include: Five fingers, known as pentadactyl. Several types of teeth. Certain eye orbit characteristics, such as a postorbital bar, or a bone that runs around the eye socket. An opposable thumb, a finger that allows a grip that can hold objects. (top left) Ring-tailed lemurs. Lemurs be- long to the prosimian group of primates. (top right) One of the New World mon- keys, a squirrel monkey. (bottom left) Chimpanzees belong to the great apes, one of the groups of primates. (bottom right) Reconstruction of a Neanderthal man, belonging to an extinct subspecies of Homo sapiens. This subspecies of humans lived in Europe and western and central Asia from about 100,000 40,000 BCE. Whats the difference between monkeys and apes? The easiest way to distinguish monkeys from the other primates is to look for a tail. Most monkey species have tails, but no apes or humans do. Monkeys are much more like other mammals than apes and humans are. | text | null |
L_0644 | primates | T_3295 | In intelligent mammals, such as primates, the cerebrum is larger compared to the rest of the brain. A larger cerebrum allows primates to develop higher levels of intelligence. Primates have the ability to learn new behaviors. They also engage in complex social interactions, such as fighting and play. | text | null |
L_0644 | primates | T_3296 | Old World species, such as apes and some monkeys ( Figure 1.1 and Figure 1.2), tend to have significant size differences between the sexes. This is known as sexual dimorphism. Males tend to be slightly more than twice as heavy as females. This dimorphism may have evolved when one male had to defend many females. Old World generally refers to monkeys of Africa and Asia. New World refers to monkeys of the Americas. New World species, including tamarins (squirrel-sized monkeys) and marmosets (very small primitive monkeys) ( Figure 1.2), form pair bonds, which is a partnership between a mating pair that lasts at least one season. The pair cooperatively raise the young and generally do not show a significant size difference between the sexes. Old World monkeys do not tend to form monogamous relationships. (left) An Old World monkey, a species of macaque, in Japan. (center ) A New World species of monkey, a tamarin. (right) Another New World species of monkey, the pygmy marmoset. | text | null |
L_0644 | primates | T_3297 | Non-human primates live mostly in Central and South America, Africa, and South Asia. Since primates evolved from animals living in trees, many modern species still live mostly in trees. Other species live on land most of the time, such as baboons ( Figure 1.3) and the Patas monkey. Only a few species live on land all of the time, such as the gelada and humans. Primates live in a diverse number of forested habitats, including rain forests, mangrove forests and mountain forests to altitudes of over 9,800 feet. The combination of opposable thumbs, short fingernails, and long, inward-closing fingers has allowed some species to develop the ability to move by swinging their arms from one branch to another ( Figure 1.4). Another feature for climbing are expanded finger-like parts, such as those in tarsiers, which improve grasping ( Figure 1.4). A few species, such as the proboscis monkey, De Brazzas monkey, and Allens swamp monkey, evolved webbed fingers so they can swim and live in swamps and aquatic habitats. Some species, such as the rhesus macaque and the Hanuman langur, can even live in cities by eating human garbage. (left) A gibbon shows how its limbs are modified for hanging from trees. (right) A species of tarsier, with expanded digits used for grasping branches. | text | null |
L_0644 | primates | T_3297 | Non-human primates live mostly in Central and South America, Africa, and South Asia. Since primates evolved from animals living in trees, many modern species still live mostly in trees. Other species live on land most of the time, such as baboons ( Figure 1.3) and the Patas monkey. Only a few species live on land all of the time, such as the gelada and humans. Primates live in a diverse number of forested habitats, including rain forests, mangrove forests and mountain forests to altitudes of over 9,800 feet. The combination of opposable thumbs, short fingernails, and long, inward-closing fingers has allowed some species to develop the ability to move by swinging their arms from one branch to another ( Figure 1.4). Another feature for climbing are expanded finger-like parts, such as those in tarsiers, which improve grasping ( Figure 1.4). A few species, such as the proboscis monkey, De Brazzas monkey, and Allens swamp monkey, evolved webbed fingers so they can swim and live in swamps and aquatic habitats. Some species, such as the rhesus macaque and the Hanuman langur, can even live in cities by eating human garbage. (left) A gibbon shows how its limbs are modified for hanging from trees. (right) A species of tarsier, with expanded digits used for grasping branches. | text | null |
L_0650 | protist characteristics | T_3312 | Protists are eukaryotes, which means their cells have a nucleus and other membrane-bound organelles. Most, but not all, protists are single-celled. Other than these features, they have very little in common. You can think about protists as all eukaryotic organisms that are neither animals, nor plants, nor fungi. Although Ernst Haeckel set up the Kingdom Protista in 1866, this kingdom was not accepted by the scientific world until the 1960s. These unique organisms can be so different from each other that sometimes Protista is called the junk drawer" kingdom. Just like a junk drawer, which contains items that dont fit into any other category, this kingdom contains the eukaryotes that cannot be put into any other kingdom. Therefore, protists can seem very different from one another. | text | null |
L_0650 | protist characteristics | T_3313 | Most protists are so small that they can be seen only with a microscope. Protists are mostly unicellular (one-celled) eukaryotes. A few protists are multicellular (many-celled) and surprisingly large. For example, kelp is a multicellular protist that can grow to be over 100-meters long ( Figure 1.1). Multicellular protists, however, do not show cellular specialization or differentiation into tissues. That means their cells all look the same and, for the most part, function the same. On the other hand, your cells often are much different from each other and have special jobs. Kelp is an example of a muticellular pro- tist. | text | null |
L_0650 | protist characteristics | T_3314 | A few characteristics are common between protists. 1. 2. 3. 4. They are eukaryotic, which means they have a nucleus. Most have mitochondria. They can be parasites. They all prefer aquatic or moist environments. | text | null |
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