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L_0536 | habitat destruction | T_2984 | A habitat that is quickly being destroyed is the wetland. By the 1980s, over 80% of all wetlands in parts of the U.S. were destroyed. In Europe, many wetland species have gone extinct. For example, many bogs in Scotland have been lost because of human development. Another example of species loss due to habitat destruction happened on Madagascars central highland plateau. From 1970 to 2000, slash-and-burn agriculture destroyed about 10% of the countrys total native plants. The area turned into a wasteland. Soil from erosion entered the waterways. Much of the river ecosystems of several large rivers were also destroyed. Several fish species are almost extinct. Also, some coral reef formations in the Indian Ocean are completely lost. | text | null |
L_0554 | human uses of fungi | T_3036 | Fungi are extremely important to the ecosystem because they are one of the major decomposers of organic material. Decomposing organic material is how fungi acquire energy. But fungi have other roles in addition to being decom- posers. How do fungi help people? They are used to help prepare food and beverages, and they have many other uses. | text | null |
L_0554 | human uses of fungi | T_3037 | Yeasts are crucial for the fermentation process that makes beer, wine, and bread. Fermentation occurs in the absence of oxygen and allows the first step of cellular respiration, glycolysis, to continue. Some fungi are used in the production of soy sauce and tempeh, a source of protein used in Southeast Asia. Fungi can produce antibiotics, such as penicillin. Antibiotics are important medicines that kill bacteria, and penicillin was the first identified cure against many deadly bacterial species. Antibiotics only treat bacterial diseases; they can not be used to treat viral or fungal diseases. Mushrooms are fungi that are eaten by people all over the globe. The video Bread Mold Kills Bacteria at explains Alexander Flemings famous discovery that lead to the discovery of the antibiotic penicillin. Antibiotics are used to kill Saccharomyces cerevisiae, a single-celled fungus called brewers or bakers yeast, is used in the baking of bread and in making wine and beer through fermentation. harmful bacteria. See Alexander Fleming 1881 - 1955 at Click image to the left or use the URL below. URL: | text | null |
L_0554 | human uses of fungi | T_3038 | Some of the best known types of fungi are mushrooms, which can be edible or poisonous ( Figure 1.2). Many species are grown commercially, but others are harvested from the wild. When you order a pizza with mushrooms or add them to your salad, you are most likely eating Agaricus bisporus, known as white or button mushrooms, the most commonly eaten species. Other mushroom species are gathered from the wild for people to eat or for commercial sale. Many mushroom species are poisonous to humans. Some mushrooms will simply give you a stomachache, while others may kill you. Some mushrooms you can eat when they are cooked but are poisonous when raw. So if you find mushrooms in the wild, dont eat them until you are certain they are safe! Have you ever eaten blue cheese? Do you know what makes it blue? You guessed it. A fungus. For certain types of cheeses, producers add fungal spores to milk curds to promote the growth of mold, which makes the cheese blue. Molds used in cheese production are safe for humans to eat. Some fungi are poisonous and must be avoided. | text | null |
L_0555 | human vision | T_3039 | Think about all the ways that students use their sense of sight during a typical school day. As soon as they open their eyes in the morning, they might look at the clock to see what time it is. Then, they might look out the window to see what the weather is like. They probably look in a mirror to comb their hair. In school, they use their eyes to read the board, their textbooks, and the expressions on their friends faces. After school, they might keep their eye on the ball while playing basketball ( Figure 1.1). Then, they might read their homework assignment and text messages from their friends. Sight, or vision, is the ability to see light. It depends on the eyes detecting light and forming images. It also depends on the brain making sense of the images, so that we know what we are seeing. Human beings and other primates depend on vision more than many other animals. Its not surprising, then, that we have a better sense of vision than many other animals. Not only can we normally see both distant and close-up objects clearly, but we can also see in three dimensions and in color. But humans do not have the best vision. You may think you see things fairly clearly. Imagine if you could see even better. How about 8 times better? Raptors, or birds of prey, including the eagles, hawks and falcons can see up to 8 times more clearly than the sharpest human eye. A golden eagle for example can see a rabbit from a mile away. Why do you think they have such a good sense of vision? Other animals also have much better night vision then us. | text | null |
L_0555 | human vision | T_3040 | Did you ever use 3-D glasses to watch a movie, like the boy pictured below ( Figure 1.2)? If you did, then you know that the glasses make people and objects in the movie appear to jump out of the screen. They make images on the flat movie screen seem more realistic because they give them depth. Thats the difference between seeing things in two dimensions and three dimensions. We are able to see in three dimensions because we have two eyes facing the same direction but a few inches apart. As a result, we see objects and people with both eyes at the same time but from slightly different angles. Hold up a finger a few inches away from your face, and look at it, first with one eye and then with the other. Youll notice that your finger appears to move. Now hold up your finger at arms length, and look at it with one eye and then the other. Your finger seems to move less than it did when it was closer. Although you arent aware of it, your brain constantly uses such differences to determine the distance of objects. | text | null |
L_0555 | human vision | T_3041 | For animals like us that see in color, it may be hard to imagine a world that appears to be mainly shades of gray. You can get an idea of how many other animals see the world by looking at a black-and-white picture of colorful objects. For example, look at the apple on the tree pictured below ( Figure 1.3). In the top picture, they appear in color, the way you would normally see them. In the bottom picture they appear without color, in shades of gray ( Figure 1.4). Humans with color vision see the apple on this tree; the bright red color of the apple stands out clearly from the green background of leaves. This black-and-white picture gives an idea of how many animals see the world. Dogs and cats would see the green and red colors as shades of gray; they are able to see blue, but red and green appear the same to them. Many animals see just one or two colors. Some see colors that we cannot see. Apes and chimps see the same colors as us. But whereas many animals cannot see colors, some animals see colors that we cannot. The range of color vision of bees and butterflies for example, extends beyond the visible spectrum of light we can see. The leaves of the flowers they pollinate have special ultraviolet patterns which guide the insects deep into the flower. | text | null |
L_0555 | human vision | T_3041 | For animals like us that see in color, it may be hard to imagine a world that appears to be mainly shades of gray. You can get an idea of how many other animals see the world by looking at a black-and-white picture of colorful objects. For example, look at the apple on the tree pictured below ( Figure 1.3). In the top picture, they appear in color, the way you would normally see them. In the bottom picture they appear without color, in shades of gray ( Figure 1.4). Humans with color vision see the apple on this tree; the bright red color of the apple stands out clearly from the green background of leaves. This black-and-white picture gives an idea of how many animals see the world. Dogs and cats would see the green and red colors as shades of gray; they are able to see blue, but red and green appear the same to them. Many animals see just one or two colors. Some see colors that we cannot see. Apes and chimps see the same colors as us. But whereas many animals cannot see colors, some animals see colors that we cannot. The range of color vision of bees and butterflies for example, extends beyond the visible spectrum of light we can see. The leaves of the flowers they pollinate have special ultraviolet patterns which guide the insects deep into the flower. | text | null |
L_0555 | human vision | T_3042 | Why do you think primates, including humans, evolved the ability to see in three dimensions and in color? To answer that question, you need to know a little about primate evolution. Millions of years ago, primate ancestors lived in trees. To move about in the trees, they needed to be able to judge how far away the next branch was. Otherwise, they might have a dangerous fall. Being able see in depth was important. It was an adaptation that would help tree-living primates survive. Primate ancestors also mainly ate fruit. They needed to be able to spot colored fruits in the leafy background of the trees ( Figure 1.5). They also had to be able to judge which fruits were ripe and which were still green. Ripe fruits are usually red, orange, yellow, or purple. Being able to see in color was important for finding food. It was an adaptation that would help fruit-eating primates survive. | text | null |
L_0556 | humans and primates | T_3043 | The great apes are the members of the biological family Hominidae, which includes four living genera: chimpanzees, gorillas, orangutans and humans. Among these four genera are just seven species, two of each except humans, which has only one species, Homo sapiens. | text | null |
L_0556 | humans and primates | T_3044 | The Great Apes are large, tailless primates, ranging in size from the pygmy chimpanzee, at 66-88 pounds in weight, to the gorilla, at 300-400 pounds ( Figure 1.1). In all species, the males are, on average, larger and stronger than the females. A Western Lowland gorilla, member of the great apes. The gorilla is the largest of the hominids, weighing up to 309-397 lbs. Most living primate species are four-footed, but all are able to use their hands for gathering food or nesting materials. In some cases, hands are used as tools, such as when gorillas use sticks to measure the depth of water ( Figure 1.2). Chimpanzees sharpen sticks to use as spears in hunting; they also use sticks to gather food and to fish for termites. Most primate species eat both plants and meat ( omnivorous), but fruit is the preferred food among all but humans. In contrast, humans eat a large amount of highly processed, low fiber foods, and unusual proportions of grains and vertebrate meat. As a result of our diets, human teeth and jaws are markedly smaller for our size than those of other apes. Humans may have been eating cooked food for a million years or more, so perhaps our teeth adapted to eating cooked food. Gorillas and chimpanzees live in family groups of approximately five to ten individuals, although larger groups are sometimes observed. The groups include at least one dominant male, and females leave the group when they can mate. Orangutans, however, generally live alone. | text | null |
L_0556 | humans and primates | T_3044 | The Great Apes are large, tailless primates, ranging in size from the pygmy chimpanzee, at 66-88 pounds in weight, to the gorilla, at 300-400 pounds ( Figure 1.1). In all species, the males are, on average, larger and stronger than the females. A Western Lowland gorilla, member of the great apes. The gorilla is the largest of the hominids, weighing up to 309-397 lbs. Most living primate species are four-footed, but all are able to use their hands for gathering food or nesting materials. In some cases, hands are used as tools, such as when gorillas use sticks to measure the depth of water ( Figure 1.2). Chimpanzees sharpen sticks to use as spears in hunting; they also use sticks to gather food and to fish for termites. Most primate species eat both plants and meat ( omnivorous), but fruit is the preferred food among all but humans. In contrast, humans eat a large amount of highly processed, low fiber foods, and unusual proportions of grains and vertebrate meat. As a result of our diets, human teeth and jaws are markedly smaller for our size than those of other apes. Humans may have been eating cooked food for a million years or more, so perhaps our teeth adapted to eating cooked food. Gorillas and chimpanzees live in family groups of approximately five to ten individuals, although larger groups are sometimes observed. The groups include at least one dominant male, and females leave the group when they can mate. Orangutans, however, generally live alone. | text | null |
L_0556 | humans and primates | T_3045 | Gorillas, chimpanzees, and humans have more than 97% of their DNA sequence in common. This means that a similar percent of the amino acid sequences of the proteins will be the same, resulting in many proteins with similar or identical functions. All organisms in the Hominidae communicate with some kind of language. They can also create simple cultures beyond the family or group of animals. Having a culture means that knowledge and behaviors can be passed on from generation to generation. | text | null |
L_0556 | humans and primates | T_3046 | Specialized features of Homo sapiens include the following: small front teeth (canines and incisors) and very large molars relative to other primate species, a fully upright posture resulting in bipedalism (walking on two limbs instead of four), shortening of the arms relative to the legs, increased usefulness (dexterity) of the hands, increase in brain size, especially in the frontal lobes and a decrease in bone mass of the skull and face. See Communication - the Jane Goodall Institute at , Com- paring the Human and Chimpanzee Genomes at http://wrl.it/show/197403/12898478 , and Discovering Gibbons at Click image to the left or use the URL below. URL: | text | null |
L_0558 | importance of arthropods | T_3048 | Have you ever been startled by a bee landing on a flower? Or surprised by a swarm of pill bugs when you overturned a rock? These arthropods might seem a little scary to you, but they are actually performing important roles in the environment. Arthropods are important to the ecosystem and to humans in many ways. | text | null |
L_0558 | importance of arthropods | T_3049 | Many species of crustaceans, especially crabs, lobsters ( Figure 1.1), shrimp, prawns, and crayfish, are consumed by humans, and are now farmed on a large commercial scale. Nearly 10,000,000 tons of arthropods as food were produced in 2005. Over 70% by weight of all crustaceans caught for consumption are shrimp and prawns. Over 80% is produced in Asia, with China producing nearly half the worlds total. Insects and their grubs are at least as nutritious as meat, and are eaten both raw and cooked in many cultures. Beetles, locusts, butterflies, ants, and stinkbugs (which have an apple flavor) are insects that are regularly eaten by people in dozens of countries. In fact, there are more than 1,900 edible insect species on Earth, hundreds of which are already part of the diet of about two billion people worldwide. This is just under one of every three people worldwide, and this number should continue to grow in the future. The intentional cultivation of arthropods and other small animals for human food, referred to as minilivestock, is now emerging in animal husbandry as an ecologically sound concept. However, the greatest contribution of arthropods to human food supply is by pollination. Three-fourths of the worlds flowering plants and about 35% of the worlds food crops depend on animal pollinators to reproduce and increase crop yields. More than 3,500 species of native bees pollinate crops. Some scientists estimate that one out of every three bites of food we eat exists because of animal pollinators, including birds and bats and arthropods like bees, butterflies and moths, and beetles and other insects. Lobsters are one kind of arthropod food source. | text | null |
L_0558 | importance of arthropods | T_3050 | Humans use mites to prey on unwanted arthropods on farms or in homes. Other arthropods are used to control weed growth. Populations of whip scorpions added to an environment can limit the populations of cockroaches and crickets. Millipedes also control the harmful growth of destructive fungi and bacteria. When the numbers of millipedes is low, the imbalance between predator and prey can cause harmful microorganisms to flourish, and it can became difficult to manage plagues and diseases through natural processes. Cockroaches, spiders, mites, ticks and all other insects considered as carnivorous, prey on smaller species to maintain ecological balance. Thus, communities that have a good balance of these arthropods tend to have better pest control. | text | null |
L_0558 | importance of arthropods | T_3051 | Many arthropods have extremely important roles in ecosystems. Arthropods are of ecological importance because of their sheer numbers and extreme diversity. As mentioned above, bees, wasps, ants, butterflies, moths, flies and beetles are invaluable agents of pollination. Pollens and grains became accidentally attached to their chests and legs and are transferred to other agricultural crops as these animals move about, either by walking or flying. Most plants actually produce scents to send signals to insects that food (in the form of nectar) is available. Mites, ticks, centipedes, and millipedes are decomposers, meaning they break down dead plants and animals and turn them into soil nutrients. This is an important role because it supplies the plants with the minerals and nutrients necessary for life. It also keeps dead material from accumulating in the environment. Plants then pass along those minerals and nutrients to the animals that eat the plants. | text | null |
L_0558 | importance of arthropods | T_3052 | Arthropods are also invaluable to humans, as they are used in many different human-made products. Examples are: Bees produce honey and their honeycombs contain beeswax, widely used for making candles, furniture wax and polishes, waxed papers, antiseptics, and fillings for surgical uses. The pollens stored in honeycombs were discovered to have a rich mixture of vitamins, enzymes, and amino acids that could provide medical benefits. They were used as ingredients for supplements and medications that could provide relief for colds, asthma, and hay fever. Silk produced by arthropods, like those produced by caterpillars to protect their cocoons, is strong enough to use and be woven into fabrics, a discovery first used in ancient Chinas silk industry. The spiders web was discovered as an additional material that could provide strength, and has became essential raw materials for Kevlar vests, fishing nets, surgical sutures, and adhesives, as they contained natural antiseptics. | text | null |
L_0559 | importance of biodiversity | T_3053 | Biodiversity is a measurement of the amount of variation of the species in a given area. More specifically, biodi- versity can be defined as the variety of life and its processes, including the variety of living organisms, the genetic differences among them, and the communities and ecosystems in which they occur. A place such as a coral reef has many different species of plants and animals. That means the coral reef is a ecosystem with high biodiversity ( Figure 1.1). Because of its biodiversity, the rainforest shown above is an ecosystem with extreme importance. Why is biodiversity so important? In addition to maintaining the health and stability of the ecosystem, the diversity of life provides us with many benefits. Extinction is a threat to biodiversity. Does it matter if we are losing thousands of species each year? The answer is yes. It matters even if we consider not only the direct benefits to humans, but also the benefits to the ecosystems. The health and survival of ecosystems is related to that ecosystems biodiversity. Coral reefs are one of the biomes with the highest biodiversity on Earth. | text | null |
L_0559 | importance of biodiversity | T_3054 | Economically, there are many direct benefits of biodiversity. As many as 40,000 species of fungi, plants, and animals provide us with many varied types of clothing, shelter, medicines and other products. These include poisons, timber, fibers, fragrances, papers, silks, dyes, adhesives, rubber, resins, skins, furs, and more. According to one survey, 57% of the most important prescription drugs come from nature. Specifically, they come from bacteria, fungi, plants, and animals ( Figure 1.2). But only a small amount of species with the ability to give us medicines have been explored. The loss of any species may mean the loss of new medicines, which will have a direct effect on human health. Aspirin originally came from the bark of the white willow tree, pictured here. | text | null |
L_0559 | importance of biodiversity | T_3055 | Nature has inspired many technologies in use today. Bionics, also known as biomimetics or biomimicry, uses organisms to inspire technology or engineering projects. By studying animals and their traits, we are able to gain valuable information that we can put to use to help us. For example, rattlesnake heat-sensing pits helped inspire the development of infrared sensors. Zimbabwes Eastgate Centre ( Figure 1.3) was inspired by the air-conditioning efficiency of a termite mound ( Figure 1.4). Design of the Eastgate Centre (brown building), in Zimbabwe, which requires just 10% of the energy needed for a con- ventional building of the same size, was inspired by a biological design. | text | null |
L_0559 | importance of biodiversity | T_3056 | Biodiversity also has many benefits to ecosystems. High biodiversity makes ecosystems more stable. What can happen to an ecosystem if just one species goes extinct? What if that one species was a producer or decomposer? Would the loss of a producer have an effect on all the organisms that relied on that producer? If a decomposer vanishes, are there other decomposers to fill the void? Maybe the resulting species will adapt. Other species may fill in the niche left by the extinct species. But the extinction of one species could have a "domino" effect, resulting in the extinction of other species. This could greatly effect the stability of the whole ecosystem. The air-conditioning efficiency of this ter- mite mound was the inspiration for the Eastgate Centre. One important role of biodiversity is that it helps keep the nutrients, such as nitrogen, in the soil. For example, a diversity of organisms in the soil allows nitrogen fixation and nutrient recycling to happen. Biodiversity also allows plants to be pollinated by different types of insects. And of course, different species of fungi are necessary to recycle wastes from dead plants and animals. These are just a few of the many examples of how biodiversity is important for ecosystems. | text | null |
L_0560 | importance of birds | T_3057 | You are probably familiar with birds as food. People have always hunted birds for food. People eventually discovered that certain wild fowl (ducks, chickens, turkeys) could be tamed. This discovery led to the development of poultry, which is domesticated fowl that farmers raise for meat and eggs. Chickens are probably the oldest kinds of poultry. Chickens were domesticated in Asia at least 3,000 years ago. Since then, farmers have developed other poultry, including ducks, geese, guineafowl, pheasants, and turkeys. Around the world, people consume all these birds, and even more exotic birds, like ostriches. Today, chickens rank as the most widely raised poultry by far. Farmers throughout the world produce hundreds of millions of chickens annually for meat and eggs. Ducks and turkeys rank second and third in production worldwide. Ducks are raised for both meat and eggs. Turkeys are raised mainly for meat. Can you think of other ways that birds are important? | text | null |
L_0560 | importance of birds | T_3058 | 1. In agriculture, humans harvest bird droppings for use as fertilizer. These droppings have a high content of nitrogen, phosphate, and potassium, three nutrients essential for plant growth. 2. Chickens are also used as an early warning system of human diseases, such as West Nile virus. Mosquitoes carry the West Nile virus, bite young chickens and other birds, and infect them with the virus. When chickens or other birds become infected, humans may also become infected in the near future. 3. Birds have important cultural relationships with humans. Birds are common pets in the Western world. Common bird pets include canaries, parrots, finches, and parakeets. Sometimes, people act cooperatively with birds. For example, the Borana people in Africa use birds to guide them to honey that they use in food. 4. Birds also play prominent and diverse roles in folklore, religion, and popular culture. They have been featured in art since prehistoric times, when they appeared in early cave paintings. Many young child know of Big Bird, a very large canary of Sesame Street fame. 5. Feathers are also used all over the world to stuff pillows, mattresses, sleeping bags, coats, and quilting. Goose feathers are preferred because they are soft. Manufacturers often mix goose feathers with down feathers to provide extra softness. | text | null |
L_0560 | importance of birds | T_3059 | Birds are obviously important members of many ecosystems. They are integral parts of food chains and food webs. In a woodland ecosystem for example, some birds get their food mainly from plants. Others chiefly eat small animals, such as insects or earthworms. Birds and bird eggs, in turn, serve as food for such animals as foxes, raccoons, and snakes. The feeding relationships among all the animals in an ecosystem help prevent any one species from becoming too numerous. Birds play a vital role in keeping this balance of nature. In addition to being important parts of food webs, birds play other roles within ecosystems. 1. Birds eat insects. They are a natural way to control pests in gardens, on farms, and other places. A group of birds gliding through the air can easily eat hundreds of insects each day. Insect eating birds include warblers, bluebirds and woodpeckers. 2. Nectar-feeding birds are important pollinators, meaning they move the pollen from flower to flower to help fertilize the sex cells and create new plants. Hummingbirds, sunbirds, and the honey-eaters are common pollinators. 3. Many fruit-eating birds help disperse seeds. After eating fruit, they carry the seeds in their intestines and deposit them in new places. Fruit-eating birds include mockingbirds, orioles, finches and robins. 4. Birds are often important to island ecology. In New Zealand, the kereru and kokako are important browsers, or animals that eat or nibble on leaves, tender young shoots, or other vegetation ( Figure 1.1). Seabirds add nutrients to soil and to water with their production of guano, their dung. The kereru (left) and the kokako (right) are important browser species in New Zealand | text | null |
L_0561 | importance of echinoderms | T_3060 | Echinoderms are important for the ecosystem. They are also a source of food and medicine for humans. | text | null |
L_0561 | importance of echinoderms | T_3061 | Echinoderms play numerous ecological roles. Sand dollars and sea cucumbers burrow into the sand, providing more oxygen at greater depths of the sea floor. This allows more organisms to live there. In addition, starfish prevent the growth of algae on coral reefs. This allows the coral to filter-feed more easily. And many sea cucumbers provide a habitat for parasites such as crabs, worms, and snails. Echinoderms are also an important step in the ocean food chain. Echinoderms are the staple diet of many animals, including the sea otter. On the other hand, echinoderms eat seaweed and keep its growth in check. Recall that the sea urchin is a grazer, mainly feeding on algae on the coral and rocks. Recently, some marine ecosystems have been overrun by seaweed. Excess seaweed can destroy entire reefs. Scientists believe that the extinction of large quantities of echinoderms has caused this destruction ( Figure 1.1). A large die-off of the sea urchin, Diadema antillarum, in the Caribbean Sea coin- cided with increases in algal growth in some areas but not others. | text | null |
L_0561 | importance of echinoderms | T_3062 | In some countries, echinoderms are considered delicacies. Around 50,000 tons of sea urchins are captured each year for food. They are consumed mostly in Japan, Peru, Spain and France. Both male and female gonads of sea urchins are also consumed. The taste is described as soft and melting, like a mixture of seafood and fruit. Sea cucumbers are considered a delicacy in some southeastern Asian countries. In China they are used as a basis for gelatinous soups and stews. | text | null |
L_0561 | importance of echinoderms | T_3063 | Echinoderms are also used as medicine and in scientific research. For example, some sea cucumber toxins slow down the growth rate of tumor cells, so there is an interest in using these in cancer research. Sea urchins are also model organisms used in developmental biology research. Sea urchins have been used to study the mechanisms of fertilization and egg activation, physiological processes that occur during early development, and the regulation of differentiation in the early embryo. In addition, the molecular basis of early development was studied in sea urchins. Gametes can be obtained easily, sterility is not required, and the eggs and early embryos of many commonly used species are beautifully transparent. In addition, the early development of sea urchin embryos is a highly conserved process. When a batch of eggs is fertilized, all of the resulting embryos typically develop at the same time. This makes biochemical and molecular studies of early embryos possible in the sea urchin, and has led to a number of major discoveries. | text | null |
L_0561 | importance of echinoderms | T_3064 | The hard skeleton of echinoderms is used as a source of lime by farmers in some areas where limestone is unavailable. Lime is added to the soil to allow plants to take up more nutrients. About 4,000 tons of the animals are used each year for this purpose. | text | null |
L_0562 | importance of insects | T_3065 | Many insects are considered to be pests by humans. However, insects are also very important for numerous reasons. | text | null |
L_0562 | importance of insects | T_3066 | Insects can be found in every environment on Earth. While a select few insects, such as the Arctic Wooly Bear Moth, live in the harsh Arctic climate, the majority of insects are found in the warm and moist tropics. Insects have adapted to a broad range of habitats, successfully finding their own niche, because they will eat almost any substance that has nutritional value. Insects are crucial components of many ecosystems, where they perform many important functions. They aerate the soil, pollinate blossoms, and control insect and plant pests. Many insects, especially beetles, are scavengers, feeding on dead animals and fallen trees, thereby recycling nutrients back into the soil. As decomposers, insects help create top soil, the nutrient-rich layer of soil that helps plants grow. Burrowing bugs, such as ants and beetles, dig tunnels that provide channels for water, benefiting plants. Bees, wasps, butterflies, and ants pollinate flowering plants ( Figure 1.1). Gardeners love the big-eyed bug and praying mantis because they control the size of certain insect populations, such as aphids and caterpillars, which feed on new plant growth. Finally, all insects fertilize the soil with the nutrients from their droppings. Bees are important pollinators of flower- ing plants. | text | null |
L_0562 | importance of insects | T_3067 | Insects have tremendous economic importance. Some insects produce useful substances, such as honey, wax, lacquer, and silk. Honeybees have been raised by humans for thousands of years for honey. The silkworm greatly affected human history. When the Chinese used worms to develop silk, the silk trade connected China to the rest of the world. Adult insects, such as crickets, as well as insect larvae, are also commonly used as fishing bait. | text | null |
L_0562 | importance of insects | T_3068 | Insects, of course, are not just eaten by people. Insects are the sole food source for many amphibians, reptiles, birds, and mammals, making their roles in food chains and food webs extremely important. It is possible that food webs could collapse if insect populations decline. In some parts of the world, insects are used for food by humans. Insects are a rich source of protein, vitamins, and minerals, and are prized as delicacies in many third-world countries. In fact, it is difficult to find an insect that is not eaten in one form or another by people. Among the most popular are cicadas, locusts, mantises, grubs, caterpillars, crickets, ants, and wasps. Many people support this idea to provide a source of protein in human nutrition. From South America to Japan, people eat roasted insects, like grasshoppers or beetles. | text | null |
L_0562 | importance of insects | T_3069 | Insects have also been used in medicine. In the past, fly larvae ( maggots) were used to treat wounds to prevent or stop gangrene. Gangrene is caused by infection of dead flesh. Maggots only eat dead flesh, so when they are placed on the dead flesh of humans, they actually clean the wound and can prevent infection. Some hospitals still use this type of treatment. | text | null |
L_0563 | importance of mammals | T_3070 | Mammals play many important roles in ecosystems, and they also benefit people. | text | null |
L_0563 | importance of mammals | T_3071 | Mammals have important roles in the food webs of practically every ecosystem. Mammals are important members of food chains and food webs, as grazers and predators. Mammals can feed at various levels of food chains, as herbivores, insectivores, carnivores and omnivores. Mammals also interact with other species in many symbiotic relationships. For example, bats have established mutually beneficial relationships with plants. Nectar-feeding bats receive a tasty treat from each flower, and, in return, they pollinate the flowers. That means they transfer pollen from one flower to another, allowing the plant to reproduce. Non-flying mammalian pollinators include marsupials, primates, and rodents. In most cases, these animals visit flowers to eat their nectar, and end up with pollen stuck to their bodies. When the animal visits another flower to eat the nectar, the pollen is transferred to that flower. Fruit-eating bats ( Figure 1.1) also receive food from plants. In return, they help these plants spread their seeds. When bats consume fruit, they also consume the seeds within the fruit. Then they carry the seeds in their guts to far-away locations. Zebras have been known to befriend ostriches. In this symbiotic relationship, both species benefit. The ostrich, with its terrible senses of smell and hearing and the zebra with its poor eyesight, are both able to warn the other when danger is near. The zebra can smell or hear certain dangers approaching, while the ostrich can see other dangers. Both are prepared to warn one another at a moments notice so they can each flee when necessary. Baboons and impala have a similar relationship. Impala are one of the most common prey species for all predators and need to be constantly alert. Impala have good hearing and eyesight, raising an alarm when danger is near. Baboons use trees to check for danger and bark an alarm when danger is sensed. What do the baboons receive? Male baboons sometimes prey on young impala soon after birth. So, though both alert others to dangers, sometimes this is not the best of relationships for young impala. Zebra and wildebeest are found together on the African savanna grazing different parts of the same grass. The zebra grazes the tougher parts of the plant, saving the softer parts for the wildebeest. A zebra will move into an area of tall grass before other herbivores and graze the grass down to the area that the wildebeest prefers. Bats, like this Egyptian fruit bat, play an important role in seed dispersal. | text | null |
L_0563 | importance of mammals | T_3072 | We see examples of mammals (other than people!) serving our needs everywhere. We have pets that are mammals, such as dogs and cats. Mammals are also used around the world for transport. For example, horses, donkeys, mules, or camels ( Figure 1.2) may be the primary means of transport in some parts of the world. Mammals also do work for us. Service dogs can be trained to help the disabled. These include guide dogs, which are assistance dogs trained to lead blind and visually impaired people around obstacles. Horses and elephants can carry heavy loads. Humans also use some mammals for food. For example, cows and goats are commonly raised for their milk and meat. Mammals more highly developed brains have made them ideal for use by scientists in studying such things as learning, as seen in maze studies of mice and rats. | text | null |
L_0563 | importance of mammals | T_3073 | Mammals have also played a significant role in different cultures folklore and religion. For example, the grace and power of the cougar have been admired in the cultures of the native peoples of the Americas. The Inca city of Cuzco is designed in the shape of a cougar, and the thunder god of the Inca, Viracocha, has been associated with the animal. In North America, mythological descriptions of the cougar have appeared in the stories of several American Indian tribes. Important mammals include Dolly the sheep, Lassie the dog, and flipper the dolphin. Dolly was the first mammal to be cloned from an adult somatic (body) cell, using the process of nuclear transfer. Lassie was a collie dog who appeared in seven full length feature films in the 1940s and 1950s, starting with Lassie Come Home in 1943. Additional Lassie movies were made as recently as 2005. Between 1954 and 1973, the Lassie television series aired, with plenty of additional productions as recently as 2007. Flipper was a bottle nose dolphin that starred in a television series between 1964 and 1967. The most famous mammal may be King Kong, the giant gorilla that terrorized New York City in 1933 in the movie of the same name. | text | null |
L_0564 | importance of mollusks | T_3074 | Mollusks are important in a variety of ways; they are used as food, for decoration, in jewelry, and in scientific studies. They are even used as roadbed material and in vitamin supplements. | text | null |
L_0564 | importance of mollusks | T_3075 | Edible species of mollusks include numerous species of clams, mussels, oysters, scallops, marine and land snails, squid, and octopuses. Many species of mollusks, such as oysters, are farmed in order to produce more than could be found in the wild ( Figure 1.1). Today, fisheries in Europe, Japan, and the US alone produce over 1 billion pounds of oyster meat each year. Abalone (a marine gastropod mollusk), a great delicacy, can fetch up to three hundred dollars per pound. Eating mollusks is associated with a risk of food poisoning from toxins that accumulate in molluscs under certain conditions, and many countries have regulations to reduce this risk. At certain times of the year, (usually the warmer months) many species of saltwater mollusks become very poisonous due to an algal bloom known as "red tide." The mollusks filter feed on the tiny creatures (called dinoflagellates in the bloom) that produce the toxins. Eating shellfish during a red tide can cause serious illness and even death to humans. Tastes in molluscan food vary tremendously from one person to the next and from culture to culture; however, when it comes to a question of survival, most mollusks are edible. Some are considered delicacies such as oysters and escargot (a snail that lives in trees), while others such as the clams and mussels of freshwater ponds and streams are less likely to be consumed due to taste, but none-the-less are very edible. Land-based mollusks are also eaten. France alone consumes 5 million pounds of escargot every year. Of course, some people are allergic to mollusks and need to be careful about consuming any kind of shelled animals. | text | null |
L_0564 | importance of mollusks | T_3076 | Two natural products of mollusks used for decorations and jewelry are pearls and nacre. A pearl is the hard, round object produced within the mantle of a living shelled mollusk. Pearls are produced by many bivalves when a tiny particle of sand or grit is trapped between the mantle and the shell. Its as if the mollusk has a splinter. The mollusk forms a protective covering around the irritant. Most pearls used as jewelry are made by pearl oysters and freshwater mussels; most of the ones sold are cultured and not wild. Natural pearls have been highly valued as gemstones and objects of beauty for many centuries. The most desirable pearls are produced by oysters and river mussels. The substance used to form the pearl covering is made from the mother of pearl material that lines the interior of the shell. Mother of pearl is also known as nacre. Nacre is the iridescent inner shell layer. It can be found in buttons, watch faces, knives, guns, and jewelry. It is also used to decorate various musical instruments. | text | null |
L_0564 | importance of mollusks | T_3077 | Several mollusks are ideal subjects for scientific investigation of the nervous system. The giant squid has a sophis- ticated nervous system and a complex brain for study. The California sea slug, also called the California sea hare, is used in studies of learning and memory because it has a simple nervous system, consisting of just a few thousand large, easily identified neurons. These neurons are responsible for a variety of learning tasks. Some slug brain studies have even allowed scientists to better understand human brains. Some octopuses and squid are incredibly smart. They are capable of learning to solve problems and do mazes. | text | null |
L_0565 | importance of protists | T_3078 | Humans could not live on Earth if it were not for protists. Why? Plant-like protists produce almost one-half of the oxygen on the planet through photosynthesis. Other protists decompose and recycle nutrients that humans need to live. All protists make up a huge part of the food chain. Humans use protists for many other reasons: Many protists are also commonly used in medical research. For example, medicines made from protists are used in treatment of high blood pressure, digestion problems, ulcers, and arthritis. Other protists are used in scientific studies. For example, slime molds (including D. discoideum, a soil-living protist) are used to analyze the chemical signals in cells. Protists are also valuable in industry. Look on the back of a milk carton. You will most likely see carrageenan, which is extracted from red algae. This is used to make puddings and ice cream solid ( Figure 1.1). Chemicals from other kinds of algae are used to produce many kinds of plastics. | text | null |
L_0566 | importance of reptiles | T_3079 | Reptiles play an important role in the life of humans. In addition to playing an important role in many food chains, which keep the populations of small animals under control, reptiles serve as food, pets, and have played roles in art and culture for thousands of years. | text | null |
L_0566 | importance of reptiles | T_3080 | Reptiles are important as food sources for people: Green iguanas, a type of large lizard, are eaten in Central America. The tribals of Irulas from Andhra Pradesh and Tamil Nadu in India are known to eat some of the snakes they catch. Cantonese snake soup is consumed by local people in the fall to prevent colds. The soup is believed to warm up their body of those who eat it. Cooked rattlesnake meat is commonly consumed in parts of the Midwestern United States. You can eat rattlesnake meat without worry of the poisonous venom. Other snake meat is consumed throughout the world. Turtle soup is consumed throughout the world. | text | null |
L_0566 | importance of reptiles | T_3081 | Reptiles also make good pets. In the Western world, some snakes, especially less aggressive species, like the ball python or corn snake, are kept as pets. Turtles, particularly small land-dwelling and freshwater turtles, are also common pets. Among the most popular are Russian tortoises, Greek spur-thighed tortoises, and terrapins. Large constrictor snakes like pythons, boa constrictors, and anacondas are powerful wild animals capable of killing an adult human, and they are commonly kept as pets. Many people dont think this is a wise idea, as these reptiles pose dangerous threats to people, especially children. Reptiles are capable of recognizing people by voice, sight and smell; many are capable of learning. Some species actually benefit from interaction with humans. When cared for properly, all live as long or longer than mammalian pets of similar size. Having a reptile as a pet, you get to learn about everything from adaptation, behavior and the environment, to nutrition, camouflage and reproductive strategies. Learning about the natural history and proper captive care of these animals just might change your world outlook and get you thinking more about the environment as a whole. Keep in mind that if you want to have a snake as a pet, that there are no herbivorous snakes, and you must be willing to feed it a proper diet. Be prepared to feed your snake, or other reptile, mice, rats, birds eggs, insects, or fish. And these need to be served raw. Of course, the herbivorous reptiles, such as the green iguanas and some tortoises, are much easier to feed. They eat foods such as chopped collard greens, romaine lettuce, chopped squash and bananas. | text | null |
L_0566 | importance of reptiles | T_3082 | Finally, reptiles play a significant role in folklore, religion, and popular culture. The Moche people of ancient Peru worshipped reptiles and often put lizards in their art. Snakes or serpents are connected to healing and to the Devil. Since snakes shed and then heal again, they are a symbol of healing and medicine, as shown in the Rod of Asclepius ( Figure 1.1). In Egyptian history, the Nile cobra is found on the crown of the pharaoh. This snake was worshiped as one of the gods. Reptiles have also played roles in more recent popular culture. Unforgettable reptiles include Leonardo, Donatello, Michaelangelo, and Raphael, otherwise known as the Teenage Mutant Ninja Turtles, and Godzilla, one of the most famous movie reptiles who has been terrorizing Japanese cities for years. Dino, from The Flintstones is one of the more lovable television reptiles. On the other hand is Nagini from the Harry Potter series. This tremendously long snake (roughly 12 feet) is difficult to forget as she was very important to Lord Voldemort. Though her appearances are far and few between, her unwavering loyalty to the Dark Lord makes her one of the more infamous reptiles. | text | null |
L_0567 | importance of seedless plants | T_3083 | Seedless plants have been tremendously useful to humans. Without these plants evolving millions of years ago, life as we know it would be very different. | text | null |
L_0567 | importance of seedless plants | T_3084 | The greatest influence seedless plants have had on human society is in the formation of coal millions of years ago. When the seedless plants died, became buried deep in the Earth, and were exposed to heat and pressure, coal formed. Coal is essentially made of the fossilized carbon from these plants. Now coal is burned to provide energy, such as electricity. | text | null |
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 |
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