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L_0379 | mammals | T_2088 | Some mammals are omnivores. Omnivores are heterotrophs that eat a mix of plant and animal foods. Mammals that are omnivores include bears, foxes, rats, pigs, and human beings. The chimpanzees in Figure 14.15 are also omnivorous mammals. In the wild, they eat mainly plant foods, but they supplement plants with birds, bird eggs, insects, small monkeys, and other small mammals. Their favorite and most common food, however, is fruit. Animals that eat mainly fruit are called frugivores. | text | null |
L_0379 | mammals | T_2089 | Mammals have separate sexes and reproduce sexually. They produce eggs or sperm and must mate in order for fertilization to occur. A few mammals are oviparous. They lay eggs, which later hatch. These mammals are called monotremes. Most mammals are viviparous and give birth to live young. These mammals are either placental mammals or marsupials. Placental mammals give birth to relatively large and well-developed fetuses. Marsupials give birth to smaller, less-developed embryos. In both placental and marsupial mammals, the young grow and develop inside the mothers body in an organ called the uterus. At birth, they pass through a tube-like organ called the birth canal, or vagina. | text | null |
L_0379 | mammals | T_2090 | Placental mammals get their name from the placenta. This is a spongy structure that develops during pregnancy only in placental mammals. You can see where a human placenta forms in Figure 14.16. The placenta sustains the fetus while it grows inside the mothers uterus. It consists of membranes and blood vessels from both mother and fetus. It allows substances to pass between the mothers blood and that of the fetus. The fetus gets oxygen and nutrients from the mother. It passes carbon dioxide and other wastes to the mother. The placenta permits a long period of fetal growth. As a result, the fetus can become relatively large and mature before birth. This increases its chances of survival. On the other hand, supporting a growing fetus may be difficult for the mother. She has to eat more while pregnant and may become less mobile as the fetus grows larger. Giving birth to a large infant is also risky. | text | null |
L_0379 | mammals | T_2091 | By giving birth to tiny embryos, marsupial mothers are at less risk. However, the tiny newborn marsupial may be less likely to survive than a newborn placental mammal. The marsupial embryo completes its growth and development outside the mothers body in a pouch. It gets milk by sucking on a nipple in the pouch. There are very few living species of marsupials. They include kangaroos, koalas, and opossums. You can see a baby koala peeking out of its mothers pouch in Figure 14.17. | text | null |
L_0379 | mammals | T_2092 | There are very few living species of monotremes, or egg-laying mammals. They include the echidna and platypus, both pictured in Figure 14.18. Monotremes are found only in Australia and the nearby island of New Guinea. Female monotremes lack a uterus and vagina. Instead, they have a cloaca with one external opening, like the cloaca of reptiles and birds. The opening is used to excrete wastes as well as lay eggs. The eggs of monotremes have a leathery shell, like the eggs of reptiles. Female monotremes have mammary glands but not nipples. They secrete milk to feed their young from a patch on their belly. This form of reproduction is least risky for the mother but most risky for the offspring. | text | null |
L_0379 | mammals | T_2092 | There are very few living species of monotremes, or egg-laying mammals. They include the echidna and platypus, both pictured in Figure 14.18. Monotremes are found only in Australia and the nearby island of New Guinea. Female monotremes lack a uterus and vagina. Instead, they have a cloaca with one external opening, like the cloaca of reptiles and birds. The opening is used to excrete wastes as well as lay eggs. The eggs of monotremes have a leathery shell, like the eggs of reptiles. Female monotremes have mammary glands but not nipples. They secrete milk to feed their young from a patch on their belly. This form of reproduction is least risky for the mother but most risky for the offspring. | text | null |
L_0379 | mammals | T_2093 | Mammals are a class in Phylum Chordata. Monotremes, marsupials, and placental mammals are subclasses of mammals. Almost all living mammals are placental mammals. Placental mammals, in turn, are divided into many orders. Some of the larger orders are described in Table 14.2. Order Insectivora Example mole Sample Trait small sharp teeth Chiroptera bat digits support membranous wings Order Carnivora Example coyote Sample Trait long pointed canine teeth Rodentia mouse incisor teeth grow continuously Lagomorpha rabbit chisel-like incisor teeth Artiodactyla deer even-toed hooves Cetacea whale paddle-like forelimbs Primates monkey five digits on hands and feet The orders in Table 14.2 are still widely used, but ideas about mammal classification are constantly changing. Traditional classifications are based on similarities and differences in physical traits. More recent classifications are based on similarities and differences in DNA. The latter are more useful for determining how mammals evolved. | text | null |
L_0380 | primates | T_2094 | A primate is a mammal in the Primate Order of placental mammals. In addition to human beings, this order consists of lemurs, tarsiers, monkeys, and apes. It includes mammals that range in size from the tiny mouse lemur, which weighs only 30 g (about an ounce), to the majestic gorilla, an ape that may weigh as much as 200 kg (440 lb). Both a mouse lemur and gorilla are pictured in Figure 14.19. | text | null |
L_0380 | primates | T_2095 | Primates are generally divided into prosimian and non-prosimian primates. Primates called prosimians are generally smaller. There are also far fewer of them. Prosimians include lemurs, such as the mouse lemur in Figure 14.19, and lorises. Prosimians are thought to be more similar to the earliest primates. All other primates are non-prosimian primates. They are placed in groups that include tarsiers, New World (Central and South America) monkeys, Old World (Africa and Asia) monkeys, apes, and humans. You can see examples of non-prosimian primates in Figure 14.20. | text | null |
L_0380 | primates | T_2095 | Primates are generally divided into prosimian and non-prosimian primates. Primates called prosimians are generally smaller. There are also far fewer of them. Prosimians include lemurs, such as the mouse lemur in Figure 14.19, and lorises. Prosimians are thought to be more similar to the earliest primates. All other primates are non-prosimian primates. They are placed in groups that include tarsiers, New World (Central and South America) monkeys, Old World (Africa and Asia) monkeys, apes, and humans. You can see examples of non-prosimian primates in Figure 14.20. | text | null |
L_0380 | primates | T_2096 | A number of traits set primates apart from other orders of placental mammals. Primates evolved from tree-living, or arboreal, ancestors. As a result, many primate traits are adaptations for life in the trees. Living in trees requires good grasping ability. Being able to judge distances is also important. Primates have five digits (fingers or toes) on each extremity. Unlike the hooves of horses or the paddles of whales, the digits of primates are relatively unspecialized. Therefore, they can be used to do a variety of tasks, including grasping branches and holding tools. Most primates have opposable thumbs. An opposable thumb can be brought into opposition with the other fingers of the same hand. This allows the hand to grasp and hold things. Primates usually rely more on the sense of vision rather than the sense of smell, which is the dominant sense in many other mammals. The importance of vision in primates is reflected by the bony socket that surrounds and protects the primate eye. Primates have widely spaced eyes in the same plane that give them stereoscopic (3-D) vision, needed for judging distances. Some primates, including humans, have also evolved color vision. Primates tend to have bigger brains for their body size than other mammals. This is reflected in their relatively high level of intelligence and their ability to learn new behaviors. Primates have slower rates of development than other mammals their size. They reach maturity later and have longer lifespans. Being dependent on adults for a long maturation period gives young primates plenty of time to learn from their elders. | text | null |
L_0380 | primates | T_2097 | Except for humans and a few other species, most modern primates still live in trees at least some of the time. They live primarily in tropical rain forests of Central and South America, Africa, and South Asia. Some primates, such as the gibbon in Figure 14.21, have long arms and curving fingers that allow them to swing from branch to branch high up in trees. This way of traveling is called brachiation. You can watch a gibbon brachiating in this amazing video: MEDIA Click image to the left or use the URL below. URL: Fruit is the preferred food for almost all primates except humans. However, most primate species are omnivorous and consume a variety of plant and animal foods. For example, they may eat leaves, seeds, bird eggs, insects, and other small animals. Chimpanzees may band together and hunt for animals to kill and eat. They may even sharpen sticks and use them as spears when they hunt. Watch this video to see the incredible teamwork of a group of chimpanzees hunting a monkey: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0381 | understanding animal behavior | T_2098 | Why do animals behave in the ways pictured in Figure 15.1? The specific answer depends on what the behavior is. Male flamingoes put on a noisy group show in order to attract females for mating. Frogs call out to attract mates or to warn other frogs to stay away from their territory. Baby ducks follow their mother to stay close to her for protection and survival. Male elephant seals fight to defend their hunting territory from each other. All of these behaviors have the purpose of promoting reproduction or survival. Like the animals pictured above, all animals have behaviors that help them achieve these basic ends. Behaviors that help animals reproduce or survive increase their fitness. Animals with greater fitness have a better chance of passing their genes to the next generation. If genes control behaviors that increase fitness, the behaviors become more common in the species. In other words, they evolve by natural selection. | text | null |
L_0381 | understanding animal behavior | T_2099 | All of the animal behaviors pictured in Figure 15.1 are ways that animals act without being taught to act in these ways. Such behaviors are called innate. An innate behavior is any behavior that occurs naturally in all the 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 doesnt have to practice the behavior in order to get it right or to become better at doing it. Innate behaviors are also predictable. All members of a species perform an innate behavior in the same way. | text | null |
L_0381 | understanding animal behavior | T_2100 | There are many other examples of innate behaviors in animals. Even behaviors that seem complex and difficult may be innate. For example, honeybees perform dances in order to communicate about food sources. When a honeybee, like the one in Figure 15.2, finds a food source, it returns to its hive and does a dance, 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. Watch this video to see the waggle dance and find out what it communicates: http://video.nationalgeographic.com/video/weirdest-bees-dance MEDIA Click image to the left or use the URL below. URL: Three other examples of innate behavior are pictured in Figure 15.3. If an animal were to perform such behaviors incorrectly, it might be less likely to survive or reproduce. Can you explain why each behavior pictured in the figure is important for reproduction or survival? | text | null |
L_0381 | understanding animal behavior | T_2100 | There are many other examples of innate behaviors in animals. Even behaviors that seem complex and difficult may be innate. For example, honeybees perform dances in order to communicate about food sources. When a honeybee, like the one in Figure 15.2, finds a food source, it returns to its hive and does a dance, 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. Watch this video to see the waggle dance and find out what it communicates: http://video.nationalgeographic.com/video/weirdest-bees-dance MEDIA Click image to the left or use the URL below. URL: Three other examples of innate behavior are pictured in Figure 15.3. If an animal were to perform such behaviors incorrectly, it might be less likely to survive or reproduce. Can you explain why each behavior pictured in the figure is important for reproduction or survival? | text | null |
L_0381 | understanding animal behavior | T_2101 | Innate behaviors occur in all animals. However, the more intelligent a species is, the fewer innate behaviors it generally has. The human species is the most intelligent animal species, and it has very few innate behaviors. The only innate behaviors in humans are reflex behaviors. A reflex behavior is a simple response that always occurs when a certain stimulus is present. Human reflex behaviors occur mainly in babies. You may have seen a baby exhibit the grasp reflex shown in Figure this way from birth to about 6 months of age. Its easy to see why this might help a baby survive. Grabbing onto something could keep a baby from falling and being injured. | text | null |
L_0381 | understanding animal behavior | T_2102 | Other than infant reflexes, human behaviors are mainly learned rather than innate behaviors. Learned behavior is behavior that occurs only after experience or practice. Did you ever teach a dog to sit on command? Thats an example of a learned behavior. The dog wasnt born knowing that it should sit when it hears the word sit. The dog had to learn the behavior. Most animals are capable of learning, but animals that are more intelligent are better at learning and depend more on learned behaviors. The big advantage of learned behaviors over innate behaviors is that learned behaviors are flexible. They can be changed to suit changing conditions. Human beings depend on learned behaviors more than any other species. Think about some of the behaviors you have learned. They might include making a bed, riding a bicycle, using a computer, and playing a sport, to name just a few. You may have learned each of the behaviors in different ways. There are several different ways in which animals learn. They include habituation, observational learning, conditioning, learning through play, and insight learning. | text | null |
L_0381 | understanding animal behavior | T_2103 | One of the simplest ways of learning that occurs in just about all animals is habituation. Habituation means learning to get used to something after being exposed to it repeatedly. It usually involves getting used to something that is frightening or annoying but not dangerous. Look at the crows in Figure 15.5. They are no longer afraid of the scarecrow. They have gotten used to a human in this location and know that it wont hurt them. Habituation lets animals ignore things that wont harm them. It allows them to avoid wasting time and energy escaping from things that arent really dangerous. | text | null |
L_0381 | understanding animal behavior | T_2104 | Do you remember how you learned to tie your shoe laces? You may have watched and copied the behavior of your mom or an older sibling. Learning by watching and copying the behavior of someone else is called observational learning. Human children learn many behaviors this way. Other animals also learn through observational learning. For example, the wolves in Figure 15.6 learned how to hunt in a group by watching and copying the hunting behaviors of older wolves in their pack. | text | null |
L_0381 | understanding animal behavior | T_2104 | Do you remember how you learned to tie your shoe laces? You may have watched and copied the behavior of your mom or an older sibling. Learning by watching and copying the behavior of someone else is called observational learning. Human children learn many behaviors this way. Other animals also learn through observational learning. For example, the wolves in Figure 15.6 learned how to hunt in a group by watching and copying the hunting behaviors of older wolves in their pack. | text | null |
L_0381 | understanding animal behavior | T_2105 | Conditioning is a way of learning that involves a reward or punishment. If you ever trained a dog to obey a command, you probably gave the dog a tasty treat each time he performed the desired behavior. It may not have been very long before the dog would reliably follow the command in order to get the treat. This is an example of conditioning that involves a reward. Conditioning does not always involve a reward. It can involve a punishment instead. For example, a dog might be scolded each time she jumps up on the sofa. After repeated scolding, she may learn to stay off the sofa. Conditioning occurs in nature as well. Here are just two examples: Bees learn to find nectar in certain types of flowers because they have found nectar in those types of flowers before. In this case, the behavior is learned because it is rewarded with nectar. Many birds learn to avoid eating monarch butterflies, like the one pictured in Figure 15.7. Monarch butterflies taste bad and make birds sick. In this case, the behavior is learned because it is punished with a nasty taste and illness. | text | null |
L_0381 | understanding animal behavior | T_2106 | Many animals, especially mammals, spend a lot of time playing when they are young. Although playing is fun, its likely that animals play for other reasons as well. Learning behaviors that will be important in adulthood is one likely outcome of play. Bear cubs, like the two bear cubs in Figure 15.8, frequently play together. They often pretend to be fighting. By play fighting they may be learning skills such as fighting and hunting that they will need as adults. Other young animals may play in different ways. For example, young deer play by running and kicking up their hooves. This may help them learn how to escape from predators. Human children learn by playing as well. For example, playing games and sports may help them learn how to follow rules and work with others. | text | null |
L_0381 | understanding animal behavior | T_2107 | Insight learning is learning from past experiences and reasoning. It generally 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 it to invent the wheel to land astronauts on the moon. Think about problems you have solved. You may have 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 recent decades, however, there have been many observations of other animal species using tools. They range from monkeys and chimpanzees to crows. You can see a monkey using a stone tool in Figure 15.9. She is using the stone to crack open the shells of marine invertebrates such as oysters. Chimpanzees have been observed using sticks to fish for termites in a termite mound. Crows have been seen bending wire to form a hook in order to pull food out of a tube. Behaviors such as these show that other species of animals besides humans can use their experience and reasoning to solve problems. They can learn through insight. | text | null |
L_0382 | types of animal behavior | T_2108 | Communication is any way that animals share information. Many animals live in social groups. For these animals, being able to communicate is essential. Communicating increases the ability of group members to cooperate and avoid conflict. Communication may help animals work together to find food and defend themselves from predators. It also helps them find mates and care for their offspring. In addition, communication helps adult animals teach the next generation learned behaviors. Therefore, communication generally improves the chances of animals surviving and reproducing. | text | null |
L_0382 | types of animal behavior | T_2109 | Different animal species use a range of senses for communicating. They may communicate using hearing, sight, or smell. Animals that communicate by making and hearing sounds include frogs, birds, and monkeys. Frogs call out to attract mates. Birds may use calls to warn other birds to stay away or to tell them to flock together. Monkeys use warning calls to tell other troop members that a predator is near. Animals may communicate by sight with gestures, body postures, or facial expressions. Look at the cat in Figure 15.11. Theres no mistaking the meaning of its arched back, standing hair, and exposed fangs. Its clearly saying stay away, or else! Bees communicate with a waggle dance. They use it to tell other bees where food is located. A wide range of animals communicate by releasing chemicals they can smell or detect in some other way. They include animals as different as ants and dogs. An ant, for example, releases chemicals to mark the trail to a food source. Other ants in the nest can detect the chemicals with their antennae and find the food. Look at the dog in Figure 15.12. Its marking its territory with a chemical that it releases in urine. It does this to keep other dogs out of its yard. | text | null |
L_0382 | types of animal behavior | T_2110 | Humans communicate with each other in a variety of ways. Chiefly, however, we use sound and sight to share information. The most important way that humans communicate is with language. Language is the use of symbols to communi- cate. In human languages, the symbols are words. Words may stand for things, people, actions, feelings, or ideas. By combining words in sentences, language can be used to express very complex thoughts. Another important way that humans communicate is with facial expressions. Look at the facial expressions of the girl in Figure 15.13. You can probably tell what emotion she is trying to convey with each expression. From left to right, she looks happy, sad, and angry. Humans also commonly use gestures and body postures to communicate. You might answer a question by shrugging your shoulders, which means I dont know. You might use a thumbs-up gesture when a friend scores a goal to mean Good job. Can you think of other gestures you commonly use to communicate with others? | text | null |
L_0382 | types of animal behavior | T_2110 | Humans communicate with each other in a variety of ways. Chiefly, however, we use sound and sight to share information. The most important way that humans communicate is with language. Language is the use of symbols to communi- cate. In human languages, the symbols are words. Words may stand for things, people, actions, feelings, or ideas. By combining words in sentences, language can be used to express very complex thoughts. Another important way that humans communicate is with facial expressions. Look at the facial expressions of the girl in Figure 15.13. You can probably tell what emotion she is trying to convey with each expression. From left to right, she looks happy, sad, and angry. Humans also commonly use gestures and body postures to communicate. You might answer a question by shrugging your shoulders, which means I dont know. You might use a thumbs-up gesture when a friend scores a goal to mean Good job. Can you think of other gestures you commonly use to communicate with others? | text | null |
L_0382 | types of animal behavior | T_2110 | Humans communicate with each other in a variety of ways. Chiefly, however, we use sound and sight to share information. The most important way that humans communicate is with language. Language is the use of symbols to communi- cate. In human languages, the symbols are words. Words may stand for things, people, actions, feelings, or ideas. By combining words in sentences, language can be used to express very complex thoughts. Another important way that humans communicate is with facial expressions. Look at the facial expressions of the girl in Figure 15.13. You can probably tell what emotion she is trying to convey with each expression. From left to right, she looks happy, sad, and angry. Humans also commonly use gestures and body postures to communicate. You might answer a question by shrugging your shoulders, which means I dont know. You might use a thumbs-up gesture when a friend scores a goal to mean Good job. Can you think of other gestures you commonly use to communicate with others? | text | null |
L_0382 | types of animal behavior | T_2111 | Without communication, animals would not be able to live together in groups. Animals that live in groups with other members of their species are called social animals. Social animals include many species of insects, birds, and mammals. Specific examples are ants, bees, crows, wolves, and human beings. | text | null |
L_0382 | types of animal behavior | T_2112 | Some species of animals are very social. In these species, members of the group depend completely on one another. Thats because different animals within the group have different jobs. Therefore, group members must work together for the good of all. Most species of bees and ants are highly social animals. Look at the honeybees in Figure 15.14. Honeybees live in colonies that may consist of thousands of individual bees. Generally, there are three types of adult bees in a colony: workers, a queen, and drones. Most of the adult bees in a colony are workers. They cooperate to build the hive, collect food, and care for the young. Each worker has a specific task to perform, depending on its age. Young worker bees clean the hive and feed the offspring. Older worker bees build the waxy honeycomb or guard the hive. The oldest worker bees leave the hive to find food. Each colony usually has one queen. Her only job is to lay eggs. The colony also has a relatively small number of male drones. Their only job is to mate with the queen. | text | null |
L_0382 | types of animal behavior | T_2113 | Bees and other social animals must cooperate to live together successfully. Cooperation means working together with others. Members of the group may cooperate by dividing up tasks, defending each other, and sharing food. The ants in Figure 15.15 are sharing food. One ant is transferring food directly from its mouth to the mouth of another colony member. Besides social insects, animals in many other species also cooperate. For example, in meerkat colonies, young female meerkats act as babysitters. They take care of the baby meerkats while their parents are out looking for food. | text | null |
L_0382 | types of animal behavior | T_2114 | Some of the most important behaviors in animals involve reproduction. They include behaviors to attract mates and behaviors for taking care of the young. | text | null |
L_0382 | types of animal behavior | T_2115 | Mating is the pairing of an adult male and an adult female for the purpose of reproduction. In many animal species, females choose the males they will mate with. For their part, males try to show females that they would be better mates than other males. To be chosen as mates, males may perform courtship behaviors. These are special behaviors that help attract a mate. Male courtship behaviors are meant to get the attention of females and show off a males traits. Different species of animals have different courtship behaviors. An example of courtship behavior in birds is shown in Figure 15.16. The bird in the picture is a male sharp-tailed grouse, and hes doing a courtship dance. Each year in the spring, as many as two dozen grouse males gather in a grassy area to perform their courtship dance. Female grouse watch the dance and then mate with the males that put on the best display. You can see a group of male grouse performing their courtship dance in this short video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0382 | types of animal behavior | T_2116 | In most species of birds and mammals, one or both parents care for the young. This may include building a nest or other shelter. It may also include feeding the young and protecting them from predators. Caring for the young increases their chances of surviving. This, in turn, increases the parents fitness, so such behaviors evolve by natural selection. Emperor penguins make great sacrifices to take care of their young. After laying an egg, a penguin mother returns to the sea for two months to feed. Her mate stays behind to keep the egg warm. He balances the egg on top of his feet to keep it warm for the entire time the mother is away. During this time, he goes without food. To survive the cold, he huddles together with other males. If the chick hatches before the mother returns, the father feeds it with a high-protein, high-fat substance he produces just for this purpose. You can see an emperor penguin father feeding his chick in Figure 15.17. | text | null |
L_0382 | types of animal behavior | T_2116 | In most species of birds and mammals, one or both parents care for the young. This may include building a nest or other shelter. It may also include feeding the young and protecting them from predators. Caring for the young increases their chances of surviving. This, in turn, increases the parents fitness, so such behaviors evolve by natural selection. Emperor penguins make great sacrifices to take care of their young. After laying an egg, a penguin mother returns to the sea for two months to feed. Her mate stays behind to keep the egg warm. He balances the egg on top of his feet to keep it warm for the entire time the mother is away. During this time, he goes without food. To survive the cold, he huddles together with other males. If the chick hatches before the mother returns, the father feeds it with a high-protein, high-fat substance he produces just for this purpose. You can see an emperor penguin father feeding his chick in Figure 15.17. | text | null |
L_0382 | types of animal behavior | T_2117 | Some species of animals are territorial. This means that they defend an area that typically includes their nest and enough food for themselves and their offspring. Animals generally dont fight to defend their territory. Instead, they are more likely to put on a defensive display. For example, male gorillas may pound on their chest and thump the ground to warn other male gorillas to stay away from their territory. This gets the message across without physical conflict, which would be riskier and take more energy. You can see a male gorilla putting on a defensive display in this video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0382 | types of animal behavior | T_2118 | Many animal behaviors occur in repeated cycles. Some cycles of behavior repeat each year. Other cycles of behavior repeat each day. | text | null |
L_0382 | types of animal behavior | T_2119 | Examples of behaviors with annual cycles include migration and hibernation. Both are innate behaviors. They are triggered by changes in the environment, such as the days growing shorter in the fall. Migration is the movement of animals from one place to another. Migration is most common in birds, fish, and insects. In the Northern Hemisphere, many species of birds, such as finches and swallows, travel south for the winter. They migrate to areas where it is warmer and where more food is available. They return north in the spring. Migrating animals generally follow the same route each year. They may be guided by the position of the sun, Earths magnetic field, or other clues in the environment. Hibernation is a state in which an animals body processes slow down and its body temperature falls. A hibernating animal uses less energy than usual. This helps it survive during a time of year when food is scarce. Hibernation may last for weeks or even months. Examples of animals that hibernate include some species of bats, squirrels, snakes, and insects (see Figure 15.18). | text | null |
L_0382 | types of animal behavior | T_2120 | Many animals go through daily cycles. Daily cycles of behavior are called circadian rhythms. For example, most animals go to sleep when the sun sets down and wake up when the sun rises. These animals are active during the day and called diurnal. Other animals go to sleep when the sun rises and wake up when the sun sets. These animals are active during the night and called nocturnal. Many owls, like the owls in Figure 15.19, are nocturnal. Like some other nocturnal animals, they have large eyes that are specially adapted for seeing when light levels are low. In many species, including the human species, circadian rhythms are controlled by a tiny structure called the biological clock. It is located in the hypothalamus, which is a gland at the base of the brain. The biological clock sends signals to the body. The signals cause regular changes in behavior and body processes. The biological clock, in turn, is controlled by changes in the amount of light entering the eyes. Thats why the biological clock causes changes that repeat every 24 hours. | text | null |
L_0388 | choosing healthy foods | T_2164 | MyPlate is a diagram that shows you how to balance foods at each meal. It represents the relative amounts of five food groups that you should put on your plate (and in your cup). You can see MyPlate in Figure 17.6. The five food groups in MyPlate are: 1. 2. 3. 4. 5. Grains, such as whole-grain bread, pasta, and cereal. Vegetables, such as spinach, broccoli, and carrots. Fruits, such as oranges, strawberries, and bananas. Dairy, such as milk, yogurt, and cheese. Protein, such as meat, fish, and beans Follow these guidelines for using MyPlate: Enjoy your food, but eat less. Avoid oversized portions. Make half your plate fruits and vegetables, including both green and yellow or orange vegetables. Make at least half your grains whole grains. Choose fat-free or low-fat milk. Avoid high-sodium foods. Drink water instead of sugary drinks. Youll notice that there is no food group on MyPlate for foods like ice cream, cookies, and potato chips. These foods have little nutritional value. They may also be high in fats, sugars, or salt. They should be eaten only sparingly if at all. | text | null |
L_0388 | choosing healthy foods | T_2165 | How do you know which foods contain whole grain and which are low in fat and sodium? Thats where food labels come in. In the U.S., packaged foods must be labeled with nutritional information. A nutrition facts label shows the main nutrients in one serving of the food. Packaged foods must also be labeled with their ingredients. An ingredient is a specific item that a food contains. | text | null |
L_0388 | choosing healthy foods | T_2166 | Look at the nutrition facts label in Figure 17.7. Instructions at the right of the label tell you what to look for. At the top of the label, look for the serving size. The serving size tells you how much of the food you should eat to get the nutrients listed on the label. For this food, 1 cup is a serving. The Calories in one serving are listed next. In this food, there are 250 Calories per serving. Next on the nutrition facts label, look for the percent daily values (% DV) of several nutrients. The percent daily value shows what percent of daily needs for a given nutrient that the food provides (based on a 2000- Calorie-per-day diet). A food is low in a nutrient if the %DV is 5% or less. This particular food is low in fiber, vitamin A, vitamin C, and iron. A food is high in a nutrient if the %DV is 20% or more. This food is high in sodium, potassium, and calcium. To learn more about nutrition facts labels and how to use them, watch this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0388 | choosing healthy foods | T_2167 | The food label in Figure 17.8 represents a different food and includes the list of ingredients. The main ingredient is always listed first. The main ingredient is the ingredient that is present in the food in the greatest amount. As you go down the list, the ingredients are present in smaller and smaller amounts. Reading the ingredients lists on food labels can help you choose the healthiest foods. At the top of the list, look for ingredients such as whole grains, vegetables, fruits, and low-fat milk. Ingredients such as these are needed in the greatest amounts for balanced eating. Avoid foods that list fats, oils, sugar, or salt near the top of the list. For good health, you should avoid getting too much of these ingredients. Be aware that ingredients such as corn syrup are sugars. You should also use moderation when eating foods that contain ingredients such as white flour or white rice. These ingredients have been processed, and processing removes nutrients. The word enriched is a clue that an ingredient has been processed. Ingredients are enriched with added nutrients to replace those lost during processing. Even so, they are still likely to have fewer nutrients than unprocessed ingredients. | text | null |
L_0388 | choosing healthy foods | T_2168 | Physical activity is an important part of balanced eating. It helps you use up any extra Calories in the foods you eat. You should try to get at least an hour of exercise just about every day (see Figure 17.9). Exercise has many health benefits in addition to balancing the energy in food. For example, it strengthens the bones and muscles and may improve your mood. | text | null |
L_0388 | choosing healthy foods | T_2169 | What happens if you dont get enough exercise to balance the food you eat? Any unused energy in the food is stored as fat. If you take in more energy than you use day after day, you will store more and more fat and become overweight. Eventually, you may become obese. Obesity is diagnosed in people who have a high percentage of body fat. A measure called Body Mass Index, or BMI, is often used to diagnose obesity. You can learn more about BMI by watching this video: MEDIA Click image to the left or use the URL below. URL: Obesity is associated with many health problems, including high blood pressure and diabetes. People that remain obese during their entire adulthood usually do not live as long as people that stay within a healthy weight range. The current generation of young people in the U.S. is the first generation in our history that may have a shorter life span than their parents because of obesity and the health problems associated with it. | text | null |
L_0388 | choosing healthy foods | T_2170 | You can avoid gaining too much weight and becoming obese. Choose healthy foods and balance the energy in food with exercise. To choose healthy foods, use MyPlate and nutrition facts labels. On food labels, pay attention to Calories as well as nutrients. Keep in mind that the average 1113 year old needs about 2000 Calories a day. To balance energy with exercise, aim to get about an hour of physical activity each day. You can use an online calculator like this one to find the number of Calories you use in a wide range of activities: | text | null |
L_0411 | communities | T_2375 | Predation is a relationship in which members of one species consume members of another species. The consuming species is called the predator. The species that is consumed is called the prey. In Figure 23.8, the wolves are predators, and the moose is their prey. | text | null |
L_0411 | communities | T_2376 | A predator-prey relationship tends to keep the populations of both species in balance. Look at the graph in Figure population also increases. As the number of predators increases, more prey are captured. This causes the prey population to decrease, followed by the predator population decreasing again. | text | null |
L_0411 | communities | T_2377 | Some predator species play a special role in their community. They are called keystone species. When the population size of a keystone species changes, the populations of many other species are affected. Prairie dogs, pictured in Figure 23.10, are an example of a keystone species. Their numbers affect most of the other species in their community. Prairie dog actions improve the quality of soil and water for plants, upon which most other species in the community depend. | text | null |
L_0411 | communities | T_2378 | Both predators and prey have adaptations to predation that evolve through natural selection. Predator adaptations help them capture prey. Prey adaptations help them avoid predators. A common adaptation in both predator and prey species is camouflage. You can see an example in Figure 23.11. You can also see some amazing examples in this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0411 | communities | T_2378 | Both predators and prey have adaptations to predation that evolve through natural selection. Predator adaptations help them capture prey. Prey adaptations help them avoid predators. A common adaptation in both predator and prey species is camouflage. You can see an example in Figure 23.11. You can also see some amazing examples in this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0411 | communities | T_2379 | Competition is a relationship between organisms that depend on the same resources. The resources might be food, water, or space. Competition can occur between organisms of the same species or between organisms of different species. Competition within a species is called intraspecific competition. It leads to natural selection within the species, so the species becomes better adapted to its environment. Competition between different species is called interspecific competition. It might lead to the less well-adapted species going extinct. Or it might lead to one or both species evolving specialized adaptations. For example, competing species might evolve adaptations that allow them to use different food sources. You can see an example in Figure 23.12. | text | null |
L_0411 | communities | T_2380 | Symbiosis is a close relationship between two species in which at least one species benefits. For the other species, the relationship may be beneficial, harmful, or neutral. There are three types of symbiosis: mutualism, parasitism, and commensalism. | text | null |
L_0411 | communities | T_2381 | Mutualism is a symbiotic relationship in which both species benefit. An example of mutualism is pictured in Figure can inject poison in the anemones prey. The clownfish is protected from the stingers by mucus that covers its body. How do the two species benefit from their close relationship? The anemone provides the clownfish with a safe place to live by keeping away predatory fish. The clownfish also feeds on the remains of the anemones prey. In return, the clownfish helps the anemone catch food by attracting prey with its bright colors. Its feces also provide nutrients to the anemone. | text | null |
L_0411 | communities | T_2382 | Parasitism is a symbiotic relationship in which one species benefits and the other species is harmed. The species that benefits is called the parasite. The species that is harmed is called the host. Many species of animals are parasites, at least during some stage of their life cycle. Most animal species are also hosts to one or more parasites. A parasite generally lives in or on its host. An example of a parasite that lives in its host is the hookworm. Figure from their host, which is harmed by the loss of nutrients and blood. Some parasites kill their host, but most do not. Its easy to see why. If a parasite kills its host, the parasite may also die. Instead, parasites usually cause relatively minor damage to their host. | text | null |
L_0411 | communities | T_2383 | Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected. An example is the relationship between birds called cattle egrets and cattle (see Figure 23.15). Cattle egrets feed on insects. They follow cattle herds around to take advantage of the insects stirred up by the feet of the cattle. The egrets get ready access to food from the relationship, whereas the cattle are not affected. | text | null |
L_0412 | ecosystems | T_2384 | Ecosystems need a constant input of energy to supply the needs of their organisms. Most ecosystems get energy from sunlight. A few ecosystems get energy from chemical compounds. Unlike energy, matter doesnt need to be constantly added to ecosystems. Instead, matter is recycled through ecosystems. Water and elements such as carbon and nitrogen that living things need are used over and over again. | text | null |
L_0412 | ecosystems | T_2385 | Two important concepts associated with the ecosystem are niche and habitat. | text | null |
L_0412 | ecosystems | T_2386 | Niche is the role that a particular species plays in its ecosystem. This role includes all the ways that the species interacts with the biotic and abiotic factors in the ecosystem. A major aspect of any niche is how the species obtains energy and matter. Look at Figure 23.16. The grass in the figure obtains energy from sunlight and uses it to convert carbon dioxide and water to sugar by photosynthesis. The deer in the figure gets matter and energy by consuming and digesting the grass. Each species has a different and distinctive niche. | text | null |
L_0412 | ecosystems | T_2387 | Another important aspect of a species niche is its habitat. Habitat is the physical environment in which a species lives and to which it has adapted. Features of a habitat depend mainly on abiotic factors, such as temperature and rainfall. These factors influence the traits of the organisms that live there. | text | null |
L_0412 | ecosystems | T_2388 | A given habitat may contain many different species. However, each species in the same habitat must have a different niche. Two different species cannot occupy the same niche in the same habitat at the same time. This is called the competitive exclusion principle. What do you think would happen if two species were to occupy the same niche in the same habitat? The two species would compete for everything they needed in the environment. One species might outcompete and replace the other. Or, both species might evolve different specializations so they can fill slightly different niches. | text | null |
L_0414 | flow of energy | T_2397 | Living things can be classified based on how they obtain energy. Some use the energy in sunlight or chemical compounds directly to make food. Some get energy indirectly by consuming other organisms, either living or dead. | text | null |
L_0414 | flow of energy | T_2398 | Producers are living things that produce food for themselves and other organisms. They use energy and simple inorganic molecules to make organic compounds. Producers are vital to all ecosystems because all organisms need organic compounds for energy. Producers are also called autotrophs. There are two basic types of autotrophs: photoautotrophs and chemoautotrophs. Photoautotrophs use energy in sunlight to make organic compounds by photosynthesis. They include plants, algae, and some bacteria (see Figure 24.1). Chemoautotrophs use energy in chemical compounds to make organic compounds. This process is called chemosynthesis. Chemoautotrophs include certain bacteria and archaea. | text | null |
L_0414 | flow of energy | T_2399 | Consumers are organisms that depend on other living things for food. They take in organic compounds by eating or absorbing other living things. Consumers include all animals and fungi. They also include some bacteria and protists. Consumers are also called heterotrophs. There are several different types of heterotrophs depending on exactly what they consume. They may be herbivores, carnivores, or omnivores. Herbivores are heterotrophs that consume producers such as plants or algae. Examples include rabbits and snails. Carnivores are heterotrophs that consume animals. Examples include lions and frogs. Omnivores are heterotrophs that consume both plants and animals. They include crows and human beings. The grizzly bears pictured in Figure 24.2 are also omnivores. | text | null |
L_0414 | flow of energy | T_2400 | Decomposers are heterotrophs that break down the wastes of other organisms or the remains of dead organisms. When they do, they release simple inorganic molecules back into the environment. Producers can then use the inorganic molecules to make new organic compounds. For this reason, decomposers are essential to every ecosystem. Imagine what would happen if there were no decomposers. Organic wastes and dead organisms would pile up everywhere, and their nutrients would no longer be recycled. Decomposers are classified by the type of organic matter they break down. They may be scavengers, detritivores, or saprotrophs. Scavengers are decomposers that consume the soft tissues of dead animals. Examples of scavengers include hyenas and cockroaches. Detritivores are decomposers that consume dead leaves, animal feces, and other organic debris that collects on the ground or at the bottom of a body of water. Examples of detritivores include earthworms and catfish. You can see another example in Figure 24.3. Saprotrophs are decomposers that feed on any remaining organic matter that is left after other decomposers do their work. Examples of saprotrophs include fungi and protozoa. | text | null |
L_0414 | flow of energy | T_2400 | Decomposers are heterotrophs that break down the wastes of other organisms or the remains of dead organisms. When they do, they release simple inorganic molecules back into the environment. Producers can then use the inorganic molecules to make new organic compounds. For this reason, decomposers are essential to every ecosystem. Imagine what would happen if there were no decomposers. Organic wastes and dead organisms would pile up everywhere, and their nutrients would no longer be recycled. Decomposers are classified by the type of organic matter they break down. They may be scavengers, detritivores, or saprotrophs. Scavengers are decomposers that consume the soft tissues of dead animals. Examples of scavengers include hyenas and cockroaches. Detritivores are decomposers that consume dead leaves, animal feces, and other organic debris that collects on the ground or at the bottom of a body of water. Examples of detritivores include earthworms and catfish. You can see another example in Figure 24.3. Saprotrophs are decomposers that feed on any remaining organic matter that is left after other decomposers do their work. Examples of saprotrophs include fungi and protozoa. | text | null |
L_0414 | flow of energy | T_2401 | Energy flows through ecosystems from producers, to consumers, to decomposers. Food chains and food webs are diagrams that model this flow of energy. They represent feeding relationships by showing who eats whom. | text | null |
L_0414 | flow of energy | T_2402 | A food chain is a diagram that represents a single pathway through which energy flows through an ecosystem. Food chains are generally simpler than what really happens in nature. Thats because most organisms consume and are consumed by more than one species. You can see examples of terrestrial and aquatic food chains in Figure 24.4. See if you can construct a food chain of each type by playing the animation at this link: | text | null |
L_0414 | flow of energy | T_2403 | A food web is a diagram that represents many pathways through which energy flows through an ecosystem. It includes a number of intersecting food chains. Food webs are generally more similar to what really happens in nature. They show that most organisms consume and are consumed by multiple species. You can see an example of a food web in Figure 24.5. | text | null |
L_0414 | flow of energy | T_2404 | Each food chain or food web has organisms at different trophic levels. A trophic level is a feeding position in a food chain or web. The trophic levels are identified in the food web in Figure 24.5. All food chains and webs have at least two or three trophic levels, but they rarely have more than four trophic levels. The trophic levels are: 1. 2. 3. 4. Trophic level 1 = producers that make their own food Trophic level 2 = primary consumers that eat producers Trophic level 3 = secondary consumers that eat primary consumers Trophic level 4 = tertiary consumers that eat secondary consumers Many consumers feed at more than one trophic level. For example, the bivalves in Figure 24.5 eat both producers and primary consumers. Therefore, they feed at trophic levels 2 and 3. | text | null |
L_0414 | flow of energy | T_2405 | Energy is passed up a food chain or web from lower to higher trophic levels. However, only about 10 percent of the energy at one level is passed up the next level. This is represented by the ecological pyramid in Figure 24.6. The other 90 percent of energy at each trophic level is used for metabolic processes or given off to the environment as heat. This loss of energy explains why there are rarely more than four trophic levels in a food chain or web. There isnt enough energy left to support additional levels. It also explains why ecosystems need a constant input of energy. You can learn more about ecological pyramids in this video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0414 | flow of energy | T_2406 | Biomass is the total mass of organisms at a trophic level. With less energy at higher trophic levels, there are usually fewer organisms as well. This is also represented in the pyramid in Figure 24.6. Organisms tend to be larger in size at higher trophic levels. However, their smaller numbers result in less biomass. | text | null |
L_0416 | ecosystem change | T_2416 | Primary succession occurs in an area that has never before been colonized by living things. Generally, the area is nothing but bare rock. | text | null |
L_0416 | ecosystem change | T_2417 | Secondary succession occurs in a formerly inhabited area that was disturbed. | text | null |
L_0416 | ecosystem change | T_2418 | This type of environment could come about when: a landslide uncovers bare rock a glacier retreats and leaves behind bare rock lava flows from a volcano and hardens into bare rock (see Figure 24.12) Secondary succession could result from a fire, flood, or human action such as farming. For example, a forest fire might kill all the trees and other plants in a forest, leaving behind only charred wood and soil. | text | null |
L_0416 | ecosystem change | T_2419 | The first few species to colonize a disturbed area are called pioneer species. In primary succession, pioneer species must be organisms that can live on bare rock. They usually include bacteria and lichens (see Figure 24.12). Along with wind and water, the pioneer species help weather the rock and form soil. Once soil begins to form, plants can move in. The first plants are usually grasses and other small plants that can grow in thin, poor soil. As more plants grow and die, organic matter is added to the soil. This improves the soil and helps it hold water. The improved soil allows shrubs and trees to move into the area. Secondary succession is faster than primary succession. The soil is already in place. After a forest fire, for example, the pioneer species are plants such as grasses and fireweed. You can see a forest in this stage of recovery in Figure area. You can see the amazing real-world story of secondary succession on Mount St. Helens by watching this short video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0416 | ecosystem change | T_2419 | The first few species to colonize a disturbed area are called pioneer species. In primary succession, pioneer species must be organisms that can live on bare rock. They usually include bacteria and lichens (see Figure 24.12). Along with wind and water, the pioneer species help weather the rock and form soil. Once soil begins to form, plants can move in. The first plants are usually grasses and other small plants that can grow in thin, poor soil. As more plants grow and die, organic matter is added to the soil. This improves the soil and helps it hold water. The improved soil allows shrubs and trees to move into the area. Secondary succession is faster than primary succession. The soil is already in place. After a forest fire, for example, the pioneer species are plants such as grasses and fireweed. You can see a forest in this stage of recovery in Figure area. You can see the amazing real-world story of secondary succession on Mount St. Helens by watching this short video: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0416 | ecosystem change | T_2420 | Does a changing ecosystem ever stop changing? Does its community of organisms ever reach some final, stable state? Scientists used to think that ecological succession always ended at a stable state, called a climax community. Now their thinking has changed. Theoretically, a climax community is possible. But continued change is probably more likely for real-world ecosystems. Most ecosystems are disturbed too often to ever develop a climax community. | text | null |
L_0420 | biodiversity and extinction | T_2447 | Biodiversity refers to the variety of life and its processes. It includes the variation in living organisms, the genetic differences among them, and the range of communities and ecosystems in which they live. Scientists have identified about 1.9 million species alive today, but they are discovering new species all the time. How many species actually exist in the world? No one knows for sure because only a small percentage of them have already been discovered. Estimates range from 5 to 30 million total species currently in existence. Many of them live on coral reefs and in tropical rainforests (see Figure 25.14). These two ecosystems have some of the greatest biodiversity on the planet. | text | null |
L_0420 | biodiversity and extinction | T_2448 | Biodiversity is important to human beings for many reasons. For one thing, biodiversity has direct economic benefits. Here are a few of the economic benefits of biodiversity: Besides food, diverse living things provide us with many different products. Some examples include dyes, rubber, fibers, paper, adhesives, and timber. Living things are an invaluable source of medical drugs. More than half of the most important prescription drugs come from wild species. However, only a fraction of species have yet been studied for their medical potential. Certain species may warn us of toxins in the environment. Amphibians are particularly sensitive to toxins be- cause of their permeable skin. Their current high rates of extinction serve as an early warning of environmental damage and danger to us all. Wild organisms maintain a valuable pool of genetic variation. This is important because most domestic species have been bred to be genetically uniform. This puts domestic crops and animals at great risk of dying out due to disease. Some living things provide inspiration for technology. For example, water strider insects like the one in Figure water quality, among other useful purposes. | text | null |
L_0420 | biodiversity and extinction | T_2448 | Biodiversity is important to human beings for many reasons. For one thing, biodiversity has direct economic benefits. Here are a few of the economic benefits of biodiversity: Besides food, diverse living things provide us with many different products. Some examples include dyes, rubber, fibers, paper, adhesives, and timber. Living things are an invaluable source of medical drugs. More than half of the most important prescription drugs come from wild species. However, only a fraction of species have yet been studied for their medical potential. Certain species may warn us of toxins in the environment. Amphibians are particularly sensitive to toxins be- cause of their permeable skin. Their current high rates of extinction serve as an early warning of environmental damage and danger to us all. Wild organisms maintain a valuable pool of genetic variation. This is important because most domestic species have been bred to be genetically uniform. This puts domestic crops and animals at great risk of dying out due to disease. Some living things provide inspiration for technology. For example, water strider insects like the one in Figure water quality, among other useful purposes. | text | null |
L_0420 | biodiversity and extinction | T_2449 | Biodiversity is important for healthy ecosystems. It generally increases ecosystem productivity and stability. It helps ensure that at least some species will survive environmental change. Biodiversity also provides many other ecosystem services. For example: Plants and algae maintain Earths atmosphere. They add oxygen to the air and remove carbon dioxide when they undertake photosynthesis. Plants help protect the soil. Their roots grip the soil and keep it from washing or blowing away. When plants die, their organic matter improves the soil as it decomposes. Microorganisms purify water in rivers and lakes. They also decompose organic matter and return nutrients to the soil. Certain bacteria fix nitrogen and make it available to plants. Predator species such as birds and spiders control insect pests. They reduce the need for chemical pesticides, which are expensive and may be harmful to human beings and other organisms. Animals, like the bee in Figure below, pollinate flowering plants. Many crop plants depend on pollination by wild animals. | text | null |
L_0420 | biodiversity and extinction | T_2450 | Extinction is the complete dying out of a species. Once a species goes extinct, it can never return. More than 99 percent of all the species that ever lived on Earth have gone extinct. Five mass extinctions have occurred in Earths history. They were caused by major geologic and climatic events. The fifth mass extinction wiped out the dinosaurs 65 million years ago. | text | null |
L_0420 | biodiversity and extinction | T_2451 | Evidence shows that a sixth mass extinction is happening right now. Species are currently going extinct at the fastest rate since the dinosaurs died out. Dozens of species are going extinct every day. If this rate continues, as many as half of all remaining species could go extinct by 2050. Why are so many species going extinct today? Unlike previous mass extinctions, the sixth mass extinction is due mainly to human actions. | text | null |
L_0420 | biodiversity and extinction | T_2452 | The single biggest cause of the sixth mass extinction is habitat loss. A habitat is the area where a species lives and to which it has become adapted. When a habitat is disturbed or destroyed, it threatens all the species that live there with extinction. More than half of Earths land area has been disturbed or destroyed by farming, mining, forestry, or the development of cities, suburbs, and golf courses. Habitats that are rapidly being destroyed include tropical rainforests. They are being cut and burned, mainly to clear the land for farming. Half of Earths mature tropical forests have already been destroyed. At current rates of destruction, they will all be gone by 2090. In the U.S., half of the wetlands and almost all of the tall-grass prairies (see Figure 25.17) have already been destroyed for farming. | text | null |
L_0420 | biodiversity and extinction | T_2453 | There are several other causes of the sixth mass extinction. Most of them contribute to habitat destruction. The burning of fossil fuels has increased the greenhouse effect and caused global climate change. Increasing temperatures are changing basic climate factors of habitats, and rising sea levels are covering them with water. These changes threaten many species. Pollution of air, water, and soil makes habitats toxic to many organisms. A well-known example is the near extinction of the peregrine falcon in the mid-1900s due to the pesticide DDT. Humans have over-harvested trees, fish, and other wild species. This threatens not only their survival but the survival of all the other species that depend on them. Humans have introduced exotic species into new habitats. These are species that are not native to the habitat where they are introduced. They may lack predators in the new habitat so they can out-compete native species and drive them extinct. Exotic species may also carry new diseases, prey on native species, and disrupt local food webs. You can read about an example of an exotic species in Figure 25.18. | text | null |
L_0420 | biodiversity and extinction | T_2453 | There are several other causes of the sixth mass extinction. Most of them contribute to habitat destruction. The burning of fossil fuels has increased the greenhouse effect and caused global climate change. Increasing temperatures are changing basic climate factors of habitats, and rising sea levels are covering them with water. These changes threaten many species. Pollution of air, water, and soil makes habitats toxic to many organisms. A well-known example is the near extinction of the peregrine falcon in the mid-1900s due to the pesticide DDT. Humans have over-harvested trees, fish, and other wild species. This threatens not only their survival but the survival of all the other species that depend on them. Humans have introduced exotic species into new habitats. These are species that are not native to the habitat where they are introduced. They may lack predators in the new habitat so they can out-compete native species and drive them extinct. Exotic species may also carry new diseases, prey on native species, and disrupt local food webs. You can read about an example of an exotic species in Figure 25.18. | text | null |
L_0420 | biodiversity and extinction | T_2454 | Government policies and laws are needed to protect biodiversity. Such actions have been shown to work in the past. For example, peregrine falcons made an incredible recovery after laws were passed banning the use of DDT. Individuals can also play a role in protecting biodiversity. What can you do? Here are a few suggestions: Start a compost pile to recycle organic wastes. Use the compost to enrich yard and garden soil. It will reduce the need for chemical fertilizers and added water. Make your backyard welcoming to native wildlife. Plant native plants that will provide food and shelter for native animals such as birds and amphibians. Add a water source, such as a fountain or bird bath. Avoid the introduction of exotic species to local habitats. Avoid the use of herbicides and pesticides. In addition to killing garden weeds and pests, they may harm native organisms, such as wildflowers, honey bees, and song birds. Conserve natural resources, including energy resources. Always reduce, reuse, or recycle. Learn more about biodiversity and how to protect it. Then pass on what you learn to others. | text | null |
L_0429 | mendels discoveries | T_2547 | Mendel was an Austrian Monk who lived in the 1800s. You can see his picture in Figure 6.1. | text | null |
L_0429 | mendels discoveries | T_2548 | Mendel didnt call himself a scientist. But he had all the traits of good scientist. He was observant and curious, and he asked a lot of questions. He also tried to find answers to his questions by doing experiments. Working alone in his garden in the mid-1800s, he grew thousands of pea plants over many years. He carefully crossed plants with different traits. Then he observed what traits showed up in their offspring. He repeated each experiment many times. | text | null |
L_0429 | mendels discoveries | T_2549 | Pea plants were a good choice to study for several reasons. One reason is that they are easy to grow. They also grow quickly. In addition, peas have many traits that are easy to observe, and each trait exists in two different forms. Figure 6.2 shows the traits that Mendel studied in pea plants. For example, one trait is flower color. Flowers may be either white or violet. Another trait is stem length. Plants may be either tall or short. Pea plants reproduce sexually. The male gametes are released by tiny grains of pollen. The female gametes lie deep within the flowers. Fertilization occurs when pollen from one flower reaches the female gametes in the same or a different flower. This is called pollination. Mendel was able to control which plants pollinated each other. He transferred pollen by hand from flower to flower. | text | null |
L_0429 | mendels discoveries | T_2550 | At first, Mendel studied one trait at a time. This was his first set of experiments. These experiments led to his first law, the law of segregation. Then Mendel studied two traits at a time. This was his second set of experiments. These experiments led to his second law, the law of independent assortment. | text | null |
L_0429 | mendels discoveries | T_2551 | An example of Mendels first set of experiments is his research on flower color. He transferred pollen from a plant with white flowers to a plant with violet flowers. This is called cross-pollination. Then Mendel observed flower color in their offspring. The offspring formed the first generation (F1). You can see the outcome of this experiment in Figure 6.3. All of the F1 plants had violet flowers. Mendel wondered, "What happened to the white form of the trait?" "Did it disappear?" If so, the F1 plants should have only violet-flowered offspring. Mendel let the FI plants pollinate themselves. This is called self-pollination. Then he observed flower color in their offspring. These offspring formed the second generation (F2). Surprisingly, the trait of white flowers showed up in the F2 plants. One out of every four F2 plants had white flowers. The other three out of four had violet flowers. In other words, F2 plants with violet flowers and F2 plants with white flowers had a 3:1 ratio. Mendel repeated this experiment with each of the other traits. For each trait, he got the same results. One form of the trait seemed to disappear in the F1 plants. Then it showed up again in the F2 plants. Moreover, the two forms of the trait always showed up in the F2 plants in the same 3:1 ratio. | text | null |
L_0429 | mendels discoveries | T_2552 | Based on these results, Mendel concluded that each trait is controlled by two factors. He also concluded that one of the factors for each trait dominates the other. He described the dominating factor as dominant. He used the term recessive to describe the other factor. If both factors are present in an individual, only the dominant factor is expressed. This explains why one form of a trait always seems to disappear in the F1 plants. These plants inherit both factors for the trait, but only the dominant factor shows up. The recessive factor is hidden. When F1 plants reproduce, the two factors separate and go to different gametes. This is Mendels first law, the law of segregation. It explains why both forms of the trait show up again in the F2 plants. One out of four F2 plants inherits two of the recessive factors for the trait. In these plants, the recessive form of the trait is expressed. | text | null |
L_0429 | mendels discoveries | T_2553 | Mendel wondered whether different traits are inherited together. For example, are seed form and seed color passed together from parents to offspring? Or do the two traits split up in the offspring? To answer these questions, Mendel studied two traits at a time. For example, he crossed plants that had round, yellow seeds with plants that had wrinkled, green seeds. Then he observed how the two traits showed up in their offspring (F1). You can see the results of this cross in Figure 6.4. All of the F1 plants had round, yellow seeds. The wrinkled and green forms of the traits seemed to disappear in the F1 plants. Then Mendel let the F1 plants self-pollinate. Their offspring, the F2 plants, had all possible combinations of the two traits. You can see this in Figure 6.5. For example there were plants that had round, green seeds, as well as plants that had wrinkled, yellow seeds. In this case the ratios were 9:3:3:1. The ratios are shown across the bottom of Figure 6.5. Mendel repeated this experiment with other combinations of two traits. In each case, he got the same results. One form of each trait seemed to disappear in the F1 plants. Then these forms reappeared in the F2 plants in all possible combinations. Moreover, the different combinations of traits always occurred in the same 9:3:3:1 ratio. | text | null |
L_0429 | mendels discoveries | T_2553 | Mendel wondered whether different traits are inherited together. For example, are seed form and seed color passed together from parents to offspring? Or do the two traits split up in the offspring? To answer these questions, Mendel studied two traits at a time. For example, he crossed plants that had round, yellow seeds with plants that had wrinkled, green seeds. Then he observed how the two traits showed up in their offspring (F1). You can see the results of this cross in Figure 6.4. All of the F1 plants had round, yellow seeds. The wrinkled and green forms of the traits seemed to disappear in the F1 plants. Then Mendel let the F1 plants self-pollinate. Their offspring, the F2 plants, had all possible combinations of the two traits. You can see this in Figure 6.5. For example there were plants that had round, green seeds, as well as plants that had wrinkled, yellow seeds. In this case the ratios were 9:3:3:1. The ratios are shown across the bottom of Figure 6.5. Mendel repeated this experiment with other combinations of two traits. In each case, he got the same results. One form of each trait seemed to disappear in the F1 plants. Then these forms reappeared in the F2 plants in all possible combinations. Moreover, the different combinations of traits always occurred in the same 9:3:3:1 ratio. | text | null |
L_0429 | mendels discoveries | T_2554 | The results of Mendels two-trait experiments led to the law of independent assortment. This law states that factors controlling different traits go to gametes independently of each other. This explains why F2 plants have all possible combinations of the two traits. | text | null |
L_0429 | mendels discoveries | T_2555 | You might think that Mendels discoveries would have made him an instant science rock star. Hed found the answers to age-old questions about heredity. In fact, Mendels work was largely ignored until 1900. Thats when three other scientists independently arrived at Mendels laws. Only then did people appreciate what a great contribution to science Mendel had made. Mendels discoveries form the basis of the modern science of genetics. Genetics is the science of heredity. For his discoveries, Mendel is now called the "father of genetics." Watch this entertaining, upbeat video for an excellent review of Mendels life and work. Its also a good introduction to the next lesson, "Introduction to Genetics." MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0430 | introduction to genetics | T_2556 | Today we know that the traits of organisms are controlled by genes on chromosomes. A gene can be defined as a section of a chromosome that contains the genetic code for a particular protein. The position of a gene on a chromosome is called its locus. Each gene may have different versions. The different versions are called alleles. Figure 6.6 shows an example in pea plants. It shows the gene for flower color. The gene has two alleles. There is a purple-flower allele and a white-flower allele. Different alleles account for most of the variation in the traits of organisms within a species. In sexually reproducing species, chromosomes are present in cells in pairs. Chromosomes in the same pair are called homologous chromosomes. They have the same genes at the same loci. These may be the same or different alleles. During meiosis, when gametes are produced, homologous chromosomes separate. They go to different gametes. Thus, the alleles for each gene also go to different gametes. | text | null |
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