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L_0365 | evolution and classification of plants | T_1951 | Modern nonvascular plants are called bryophytes. There are about 17,000 bryophyte species. They include liver- worts, hornworts, and mosses. Mosses are the most numerous group of bryophytes. You can see an example of moss in Figure 10.19. Like the moss in the figure, most bryophytes are small. They lack not only vascular tissues. They also lack true roots, leaves, seeds, and flowers. Bryophytes live in moist habitats. Without the adaptations of vascular plants, bryophytes are not very good at absorbing water. They also need water to reproduce. | text | null |
L_0365 | evolution and classification of plants | T_1952 | Todays vascular plants are called tracheophytes. Their vascular tissue is specialized to transport fluid. This allows them to grow tall and take advantage of sunlight high up in the air. It also allows them to live in drier habitats. Most modern plants are tracheophytes. There are hundreds of thousands of species of them. Seedless vascular plants include plants such as ferns. You can see a fern in Figure 10.20. Ferns reproduce with spores instead of seeds. The black dots on the back of the fern leaf in Figure 10.20 are spores. | text | null |
L_0365 | evolution and classification of plants | T_1953 | Seed plants are vascular plants that reproduce with seeds. Modern seed plants are called spermatophytes. Seeds allow the plants to reproduce without water. Most vascular plants today are seed plants. Modern seed plants include gymnosperms and angiosperms. Gymnosperms are seed plants that produce naked seeds in cones. There are about 1000 species of gym- nosperms. Conifers are the most common group of gymnosperms. The spruce tree in Figure 10.21 is an example of a conifer. Angiosperms are seed plants that produce seeds in the ovaries of flowers. Today, they are by far the most diverse type of seed plants. In fact, the vast majority of all modern plants are angiosperms. There are hundreds of thousands of species of them. The apple tree in Figure 10.21 is an example of a common angiosperm. | text | null |
L_0366 | plant responses and special adaptations | T_1954 | Instead of fleeing, a plants primary way of responding is to change how it is growing. One way is by tropisms. | text | null |
L_0366 | plant responses and special adaptations | T_1955 | A tropism is a turning toward, or away from, a stimulus in the environment. Examples of tropisms in plants include gravitropism and phototropism. You can see both tropisms in action in this amazing time-lapse video: MEDIA Click image to the left or use the URL below. URL: Gravitropism is a response to gravity. Plant roots always grow downward because of the pull of Earths gravity. Specialized cells in the tips of plant roots detect and respond to gravity in this way. Phototropism is a response to light. Plant stems and leaves grow toward a light source. The house plant in Figure 10.23 shows the effects of phototropism. The plant receives light mainly from the left so it grows in that direction. | text | null |
L_0366 | plant responses and special adaptations | T_1956 | Plants also detect and respond to the daily cycle of light and darkness. For example, some plants open their leaves during the day to collect sunlight and then close their leaves at night to prevent water loss. Many plants respond to the days growing shorter in the fall by going dormant. They suspend growth and development in order to survive the extreme coldness and dryness of winter. Part of this response causes the leaves of many trees to change color and then fall off (see Figure 10.24). Dormancy ensures that plants will grow and produce seeds only when conditions are favorable. | text | null |
L_0366 | plant responses and special adaptations | T_1957 | Plants dont have an immune system, but they do respond to disease. Typically, their first line of defense is the death of cells surrounding infected tissue. This prevents the infection from spreading. Many plants also produce hormones and toxins to fight pathogens. For example, willow trees, like the one in Figure Exciting new research suggests that plants may even produce chemicals that warn other, nearby plants of threats to their health. The warnings allow nearby plants to prepare for their own defense. As these and other responses show, plants may be rooted in place, but they are far from helpless. | text | null |
L_0366 | plant responses and special adaptations | T_1958 | Plants live just about everywhere on Earth. To live in so many different habitats, they have evolved adaptations that allow them to survive and reproduce under a diversity of conditions. Some plants have evolved special adaptations that let them live in extreme environments. | text | null |
L_0366 | plant responses and special adaptations | T_1959 | All plants are adapted to live on land. Or are they? All living plants today have land-plant ancestors. But some plants now live in the water. They have had to evolve new adaptations for their watery habitat. Modern plants that live in water are called aquatic plants. Living in water has certain advantages for plants. One advantage is, well, the water. Theres plenty of it and its all around. Therefore, most aquatic plants do not need adaptations for absorbing, transporting, and conserving water. They can save energy and matter by not growing extensive root systems, vascular tissues, or thick cuticle on leaves. Support is also less of a problem because of the buoyancy of water. As a result, adaptations such as strong woody stems and deep anchoring roots are not necessary for most aquatic plants. Living in water does present challenges to plants, however. For one thing, pollination by wind or animals isnt feasible under water. Sunlight also cant penetrate very far below the water surface. Thats why some aquatic plants have adaptations that help them keep their flowers and leaves above water. An example is the water lily, shown in Figure 10.26. The water lily has bowl-shaped flowers and broad, flat leaves that float. Plants that live in moving water, such as streams or rivers, may have different adaptations. For example, the cattails shown in Figure 10.26 have narrow, strap-like leaves that reduce their resistance to moving water. | text | null |
L_0366 | plant responses and special adaptations | T_1959 | All plants are adapted to live on land. Or are they? All living plants today have land-plant ancestors. But some plants now live in the water. They have had to evolve new adaptations for their watery habitat. Modern plants that live in water are called aquatic plants. Living in water has certain advantages for plants. One advantage is, well, the water. Theres plenty of it and its all around. Therefore, most aquatic plants do not need adaptations for absorbing, transporting, and conserving water. They can save energy and matter by not growing extensive root systems, vascular tissues, or thick cuticle on leaves. Support is also less of a problem because of the buoyancy of water. As a result, adaptations such as strong woody stems and deep anchoring roots are not necessary for most aquatic plants. Living in water does present challenges to plants, however. For one thing, pollination by wind or animals isnt feasible under water. Sunlight also cant penetrate very far below the water surface. Thats why some aquatic plants have adaptations that help them keep their flowers and leaves above water. An example is the water lily, shown in Figure 10.26. The water lily has bowl-shaped flowers and broad, flat leaves that float. Plants that live in moving water, such as streams or rivers, may have different adaptations. For example, the cattails shown in Figure 10.26 have narrow, strap-like leaves that reduce their resistance to moving water. | text | null |
L_0366 | plant responses and special adaptations | T_1960 | Plants that live in extremely dry environments have the opposite problem: how to get and keep water. Plants that are adapted to very dry environments are called xerophytes. Their adaptations may help them increase water intake, decrease water loss, or store water when its available. The saguaro cactus pictured in Figure 10.27 has adapted in all three ways. When it was still a very small plant, just a few inches high, its shallow roots already reached out as much as 2 meters (7 feet) from the base of the stem. By now, its root system is much more widespread. It allows the cactus to gather as much moisture as possible from rare rainfalls. The saguaro doesnt have any leaves to lose water by transpiration. It also has a large, barrel-shaped stem that can store a lot of water. Thorns protect the stem from thirsty animals that might try to get at the water inside. | text | null |
L_0366 | plant responses and special adaptations | T_1961 | Plants called epiphytes grow on other plants. They obtain moisture from the air instead of the soil. Most epiphytes are ferns or orchids that live in rainforests. Host trees provide support for the plants. They allow epiphytes to get air and sunlight high above the forest floor. This lets the plants get out of the shadows on the forest floor so they can get enough light for photosynthesis. Being elevated may also reduce the risk of being eaten by herbivores. In addition, it may increase the chances of pollination by wind. | text | null |
L_0366 | plant responses and special adaptations | T_1962 | Carnivorous plants are plants that get some or most of their nutrients (but not energy or carbon compounds) from other organisms. They trap and digest insects or other small animals or protozoa. However, they still need sunlight in order to make food by photosynthesis. Carnivorous plants have adapted to grow in places where the soil is thin or poor in nutrients. They are found in places such as bogs and rock outcroppings. Venus fly traps, like those in Figure in action: . MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0367 | what are animals | T_1963 | Animals are multicellular eukaryotes in the Animal Kingdom. All animals are heterotrophs. They eat other living things because they cant make their own food. All animals also have specialized cells that can do different jobs. Most animals have higher levels of organization as well. They may have specialized tissues, organs, and even organ systems. Having higher levels of organization allows animals to perform many complex functions. For a visual introduction to what makes a living thing an animal, watch this short video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0367 | what are animals | T_1964 | Like the cells of all eukaryotes, animal cells have a nucleus and other membrane-bound organelles. Unlike the cells of eukaryotes in the Plant and Fungus Kingdoms, animal cells lack a cell wall. This gives animal cells flexibility. It lets them take on different shapes. This in turn allows them to become specialized for particular jobs. The human nerve cell in Figure 11.2 is a good example of a specialized animal cell. Its shape suits it for its function of sending nerve signals to other cells. A nerve cell couldnt take this shape if it were surrounded by a rigid cell wall. | text | null |
L_0367 | what are animals | T_1965 | With their specialized cells and higher levels of organization, animals can do several things that other eukaryotes cannot. Animals can detect and quickly respond to a variety of stimuli. They have specialized nerve cells that can detect light, sound, touch, or other stimuli. Most animals also have a nervous system that can direct the body to respond to the stimuli. All animals can move, at least during some stage of their life cycle. Specialized muscle and nerve tissues work together to allow movement. Being able to move lets animals actively search for food and mates. It also helps them escape from predators and other dangers. Virtually all animals have internal digestion of food. Animals consume other organisms and may use special tissues and organs to digest them. (Other heterotrophs, such as fungi, absorb nutrients directly from the environment.) | text | null |
L_0367 | what are animals | T_1966 | Many animals have a relatively simple life cycle. A general animal life cycle is shown in Figure 11.3. Most animals spend the majority of their life as diploid organisms. Just about all animals reproduce sexually. Diploid adults undergo meiosis to produce haploid sperm or eggs. Fertilization occurs when a sperm and an egg fuse. The diploid zygote that forms develops into an embryo. The embryo eventually develops into an adult, often going through one or more larval stages on the way. A larva (larvae, plural) is a distinct juvenile form that many animals go through before becoming an adult. The larval form may be very different from the adult form. For example, a caterpillar is the larval form of an insect that becomes a butterfly as an adult. | text | null |
L_0367 | what are animals | T_1967 | The Animal Kingdom is one of four kingdoms in the Eukarya Domain. The Animal Kingdom, in turn, is divided into almost 40 phyla. Table 11.1 lists the 9 animal phyla that contain the largest numbers of species. Each phylum in the table has at least 10,000 species. Phylum Porifera Animals It Includes sponges Cnidaria jellyfish, corals Platyhelminthes flatworms, tapeworms, flukes Nematoda roundworms Mollusca snails, clams, squids Phylum Annelida Animals It Includes earthworms, leeches, marine worms Arthropoda insects, spiders, crustaceans, cen- tipedes Echinodermata sea stars, sea urchins, sand dollars, sea cucumbers Chordata tunicates, lancelets, fish, amphib- ians, reptiles, birds, mammals One basic way to divide animals is between invertebrates and vertebrates. Invertebrates are animals that lack a vertebral column, or backbone. All the phyla in Table 11.1, except the Phylum Chordata, consist only of invertebrates. Even the Phylum Chordata includes some invertebrate taxa. Invertebrates make up about 95 percent of all animal species. Vertebrates are animals that have a backbone. All of them are placed in the Phylum Chordata. Modern vertebrates include fish, amphibians, reptiles, birds, and mammals. Only about 5 percent of animal species are vertebrates. | text | null |
L_0368 | how animals evolved | T_1968 | The partial geologic time scale in Figure 11.5 shows when some of the major events in animal evolution took place. The oldest animal fossils are about 630 million years old, so presumably animals evolved around that time or somewhat earlier. The earliest animals were aquatic invertebrates. The first vertebrates evolved around 550 million years ago. By 500 million years ago, most modern phyla of animals had evolved. The first terrestrial animals evolved about 50 million years after that. | text | null |
L_0368 | how animals evolved | T_1969 | Animals evolved many important traits that set them apart from other eukaryotes. The traitsand the order in which they evolvedinclude: multicellularity and cell specialization; tissues and higher levels of organization; body symmetry; third embryonic cell layer (mesoderm); digestive system; fluid-filled body cavity (coelom); segmented body; and notochord. Each of these traits is described below. All of them evolved in invertebrates. Each major trait to evolve led to a new stage in animal evolution. The phyla in Table 11.1 represent modern animals at each of these major stages. Refer back to the table as you read about the evolution of these traits. | text | null |
L_0368 | how animals evolved | T_1970 | The first animal trait to evolve was multicellularity. This is the presence of multiple cells in a single organism. Scientists think that the earliest animals with multiple cells evolved from animal-like protists that lived in colonies. Some of the cells in the colonies became specialized for different jobs. After a while, the specialized cells came to need each other for survival. Thus, the first multicellular animals evolved. Multicellularity was highly adaptive. Multiple cells could do different jobs. They could evolve special adaptations that allowed them to do a particular job really well. Modern animals that represent this stage of animal evolution are sponges. They are placed in Phylum Porifera (see Table 11.1). They have multiple specialized cells, but their cells are not organized into tissues. | text | null |
L_0368 | how animals evolved | T_1971 | The next major stage of animal evolution was the evolution of tissues. It was the first step in the evolution of organs and organ systems. At first, invertebrates developed tissues from just two embryonic cell layers. There was an outer cell layer called ectoderm and an inner cell layer called endoderm. The two cell layers allowed different types of tissues to form. Modern animals that represent this stage of evolution include jellyfish. They are placed in Phylum Cnidaria. | text | null |
L_0368 | how animals evolved | T_1972 | Another trait that evolved early was symmetry. A symmetrical organism can be divided into two identical halves. Both the coral and the beetle in Figure 11.6 have symmetry, while the sponge lacks symmetry. There are two types of symmetry: radial and bilateral. Radial symmetry is demonstrated by the coral in Figure 11.6. It can be divided into identical halves along any diameter, just like a circular pie. Radial symmetry was the first type of symmetry to evolve. Animals with radial symmetry, such as cnidarians, have no sense of left or right. This makes controlled movement in these directions impossible. Bilateral symmetry is demonstrated by the beetle in Figure 11.6. It can be divided into identical halves just down the middle from top to bottom. Bilateral symmetry could come about only after animals evolved a distinctive head region where nerve tissue was concentrated. The concentration of nerve tissue in the head region was the first step in the evolution of a brain. Animals with bilateral symmetry can tell left from right. This gives them better control over the direction of their movements. | text | null |
L_0368 | how animals evolved | T_1973 | The next major trait to evolve was mesoderm. This is a third embryonic layer of cells between the ectoderm and the endoderm. Modern animals that represent this stage of evolution are the flatworms. They are placed in Phylum Platyhelminthes. You can see the mesoderm in a flatworm in Figure 11.7. Evolution of this new cell layer allowed animals to develop new types of tissues, such as muscle tissue. | text | null |
L_0368 | how animals evolved | T_1974 | Even early invertebrates had a digestive system. However, the earliest digestive system was incomplete. There was just one opening for food to enter the body and waste to leave the body. In other words, the same opening was both mouth and anus. A modern jellyfish has this type of digestive system, as shown in Figure 11.8. Eventually a complete digestive system with two body openings evolved, as shown in Figure 11.8. With a separate mouth and anus, food could move through the body in just one direction. This made digestion more efficient. An animal could keep eating while digesting food and getting rid of waste. Different parts of the digestive tract could also become specialized for different digestive functions. This led to the evolution of digestive organs. Modern animals that represent this stage of evolution are roundworms. They are placed in Phylum Nematoda. | text | null |
L_0368 | how animals evolved | T_1974 | Even early invertebrates had a digestive system. However, the earliest digestive system was incomplete. There was just one opening for food to enter the body and waste to leave the body. In other words, the same opening was both mouth and anus. A modern jellyfish has this type of digestive system, as shown in Figure 11.8. Eventually a complete digestive system with two body openings evolved, as shown in Figure 11.8. With a separate mouth and anus, food could move through the body in just one direction. This made digestion more efficient. An animal could keep eating while digesting food and getting rid of waste. Different parts of the digestive tract could also become specialized for different digestive functions. This led to the evolution of digestive organs. Modern animals that represent this stage of evolution are roundworms. They are placed in Phylum Nematoda. | text | null |
L_0368 | how animals evolved | T_1975 | The next major animal trait to evolve was a body cavity filled with fluid. At first, this was just a partial body cavity, called a pseudocoelom. A pseudocoelom isnt completely enclosed by mesoderm. However, it still allows room for internal organs to develop. The fluid in the cavity also cushions the internal organs. The pressure of the fluid provides stiffness as well. It gives the body internal support. Modern invertebrates with a pseudocoelom include roundworms. Flatworms lack this trait. This difference explains why roundworms are round whereas flatworms are flat. Later, a true coelom evolved. This is a fluid-filled body cavity that is completely enclosed by mesoderm. The coelom lies between the digestive cavity and body wall. You can see it in the invertebrate in Figure 11.9. Modern invertebrates with a coelom include mollusks (Phylum Mollusca) and annelids (Phylum Annelida). | text | null |
L_0368 | how animals evolved | T_1976 | Segmentation evolved next. Segmentation is the division of the body into multiple parts, or segments. Both the earthworm (Phylum Annelida) in Figure 11.10 and ant (Phylum Arthropoda) in Figure 11.11 have segmented bodies. The earthworm has many small segments. The ant has three larger segments. Segmentation increases an animals flexibility. It allows a wider range of motion. Different segments can also be specialized for different functions. All modern annelids and arthropods are segmented. Arthropods also evolved jointed appendages. For example, they evolved jointed legs for walking and jointed feelers (antennae) for sensing. Notice the ants jointed legs and antennae in Figure 11.11 . | text | null |
L_0368 | how animals evolved | T_1976 | Segmentation evolved next. Segmentation is the division of the body into multiple parts, or segments. Both the earthworm (Phylum Annelida) in Figure 11.10 and ant (Phylum Arthropoda) in Figure 11.11 have segmented bodies. The earthworm has many small segments. The ant has three larger segments. Segmentation increases an animals flexibility. It allows a wider range of motion. Different segments can also be specialized for different functions. All modern annelids and arthropods are segmented. Arthropods also evolved jointed appendages. For example, they evolved jointed legs for walking and jointed feelers (antennae) for sensing. Notice the ants jointed legs and antennae in Figure 11.11 . | text | null |
L_0368 | how animals evolved | T_1977 | Some invertebrates evolved a rigid rod along the length of their body. This rod is called a notochord. You can see the notochord in the tunicates in Figure 11.12. The notochord gives the body support and shape. It also provides a place for muscles to attach. It can counterbalance the pull of the muscles when they contract. Animals with a notochord are called chordates. All of them are placed in Phylum Chordata. Some early chordates eventually evolved into vertebrates. | text | null |
L_0368 | how animals evolved | T_1978 | The earliest vertebrates evolved around 550 million years ago. It happened when some chordates evolved a backbone to replace the notochord after the embryo stage. They also evolved a cranium, or bony skull. The cranium enclosed and protected the brain. The earliest vertebrates probably looked like the hagfish in Figure 11.13. | text | null |
L_0368 | how animals evolved | T_1979 | Invertebrates were the first animals to colonize the land. The move to land occurred about 450 million years ago. It required new adaptations. For example, animals needed a way to keep their body from drying out. They also needed a way to support their body on dry land without the buoyancy of water. | text | null |
L_0368 | how animals evolved | T_1980 | One way early land invertebrates solved these problems was with an exoskeleton. This is a non-bony skeleton that forms on the outside of the body. It supports the body and helps it retain water. As the organism grows, it sheds its old exoskeleton and grows a new one. Figure 11.14 shows the discarded exoskeleton of a dragonfly. | text | null |
L_0368 | how animals evolved | T_1981 | The first vertebrates moved onto land about 365 million years ago. They were early amphibians. They were the first animals to have true lungs and limbs for life on land. However, they still had to return to the water to reproduce. Thats because their eggs lacked a waterproof covering and would dry out on land. | text | null |
L_0368 | how animals evolved | T_1982 | The first vertebrates to live fully on land were amniotes. Amniotes are animals that produce eggs with waterproof membranes. The membranes let gases but not water pass through. They allow embryos to breathe without drying out. Amniotic eggs were the first eggs that could be laid on land. The earliest amniotes evolved about 350 million years ago. Amniotes would eventually evolve into modern reptiles, mammals, and birds. | text | null |
L_0372 | insects and other arthropods | T_2010 | Arthropods are invertebrates in Phylum Arthropoda. There are more than a million known species of arthropods. However, scientists estimate that only about a tenth of all arthropod species have been identified. In addition to insects, arthropods include animals such as spiders, centipedes, and lobsters. You can see why arthropods were successful both in the water and on land, by watching these excellent videos: MEDIA Click image to the left or use the URL below. URL: MEDIA Click image to the left or use the URL below. URL: There are several traits shared by all arthropods. Arthropods have a complete digestive system. They also have a circulatory system and a nervous system. In addition, they have special organs for breathing and excreting wastes. Other traits of arthropods include: segmented body; hard exoskeleton; and jointed appendages. | text | null |
L_0372 | insects and other arthropods | T_2011 | Most arthropods have three body segments. The segments are the head, thorax, and abdomen. You can see the three segments in a range of arthropods in Figure 12.21. In some arthropods, the head and thorax are joined together. | text | null |
L_0372 | insects and other arthropods | T_2012 | The exoskeleton (or external skeleton) of an arthropod consists of several layers of cuticle. The exoskeleton prevents water loss. It also protects and supports the body. In addition, it acts as a counterforce for the contraction of muscles. The exoskeleton doesnt grow larger as the animal grows. Eventually, it must be shed and replaced with a new one. This happens periodically throughout an arthropods life. The shedding of the exoskeleton is called molting. You can see a time-lapse video of an insect molting at this link: http://commons.wikimedia.org/wiki/File:Cicada_moltin | text | null |
L_0372 | insects and other arthropods | T_2013 | Because arthropod appendages are jointed, they can bend. This makes them flexible. Jointed appendages on the body are usually used as legs for walking or jumping. Jointed appendages on the head may be modified for other purposes. Head appendages often include upper and lower jaws. Jaws are used for eating and may also be used for defense. Sensory organs such as eyes and antennae are also found on the head. You can see some of these head appendages on the bee in Figure 12.22. | text | null |
L_0372 | insects and other arthropods | T_2014 | Arthropods reproduce sexually. Male and female adults produce gametes. If fertilization occurs, eggs hatch into offspring. After hatching, most arthropods go through one or more larval stages before reaching adulthood. The larvae may look very different from the adults. They change into the adult form in a process called metamorphosis. During metamorphosis, the arthropod is called a pupa. It may or may not spend this stage inside a special container called a cocoon. A familiar example of arthropod metamorphosis is the transformation of a caterpillar (larva) into a butterfly (adult) (see Figure 12.23). Distinctive life stages and metamorphosis are highly adaptive. They allow functions to be divided among different life stages. Each life stage can evolve adaptations to suit it for its specific functions without affecting the adaptations of the other stages. In some arthropods, newly hatched offspring look like small adults. These arthropods dont go through larval stages. They just grow larger until they reach adult size. This type of life cycle is called incomplete metamorphosis. You can see incomplete metamorphosis in a grasshopper in Figure 12.24. | text | null |
L_0372 | insects and other arthropods | T_2014 | Arthropods reproduce sexually. Male and female adults produce gametes. If fertilization occurs, eggs hatch into offspring. After hatching, most arthropods go through one or more larval stages before reaching adulthood. The larvae may look very different from the adults. They change into the adult form in a process called metamorphosis. During metamorphosis, the arthropod is called a pupa. It may or may not spend this stage inside a special container called a cocoon. A familiar example of arthropod metamorphosis is the transformation of a caterpillar (larva) into a butterfly (adult) (see Figure 12.23). Distinctive life stages and metamorphosis are highly adaptive. They allow functions to be divided among different life stages. Each life stage can evolve adaptations to suit it for its specific functions without affecting the adaptations of the other stages. In some arthropods, newly hatched offspring look like small adults. These arthropods dont go through larval stages. They just grow larger until they reach adult size. This type of life cycle is called incomplete metamorphosis. You can see incomplete metamorphosis in a grasshopper in Figure 12.24. | text | null |
L_0372 | insects and other arthropods | T_2015 | The majority of arthropods are insects (Class Insecta). In fact, more than half of all known organisms are insects. There may be more than 10 million insect species in the world, although most of them have not yet been identified. In terms of their numbers and diversity, insects clearly are the dominant animals in the world. | text | null |
L_0372 | insects and other arthropods | T_2016 | Like other arthropods, insects have three body segments and many jointed appendages. The abdomen contains most of the internal organs. Six legs are attached to the thorax. There are several appendages on the insects head: The head has a pair of antennae. Insects use their antennae to smell and taste chemicals. Some insects can also use their antennae to hear sounds. The head generally has several simple eyes and a pair of compound eyes. Simple eyes have a single lens, like the human eye. Compound eyes have many lenses. For feeding, the insect head contains one pair of lower jaws and two pairs of upper jaws. Insects have also evolved a wide range of specialized mouthparts for eating certain foods. You can see some examples in Figure | text | null |
L_0372 | insects and other arthropods | T_2017 | The main reason that insects have been so successful is their ability to fly. Insects are the only invertebrates that can fly. They were also the first animals to evolve flight. The ability to fly is highly adaptive. Its a guaranteed means of escape from nonflying predators. Its also useful for finding food and mates. Insects that fly have wings, like the dragonfly in Figure 12.26. Insects generally have two pairs of wings. They are attached to the thorax. The wings form from the exoskeleton. You can learn how insects flyand how scientists study insect flightby watching this short video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0372 | insects and other arthropods | T_2018 | Most humans interact with insects every day. Many of these interactions are harmless and often go unnoticed. However, insects can also cause humans a lot of harm. Some insects are vectors for human diseases. The mosquito in Figure 12.27 is a vector for malaria. Malaria kills millions of people each year. Many other insects feed on food crops. Growers may need to apply chemical pesticides to control them. On the other hand, without insects to pollinate them, many flowering plants, including important food crops, could not reproduce. | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2019 | Echinoderms are invertebrates in Phylum Echinodermata. All of them are ocean dwellers. They can be found in marine habitats from the equator to the poles. They live at all depths of water. There are about 6000 living species of echinoderms. Besides sea urchins and sea cucumbers, they include sea stars (starfish), feather stars, and sand dollars. Learn more about the amazing world of echinoderms and why they are called the ultimate animal by watching this video: http://shapeoflife.org/video/echinoderms-ultimate-animal MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2020 | The term echinoderm means spiny skin. An echinoderms spines arent actually made of skin. They are part of the animals endoskeleton and just covered with a thin layer of skin. Most adult echinoderms have radial symmetry. This is clear from the sea star pictured in Figure 12.29. However, echinoderms evolved from an ancestor with bilateral symmetry. You can tell because echinoderm larvae have bilateral symmetry and only develop radial symmetry as adults. Another unique trait of echinoderms is a network of internal canals. Most of the canals have projections called tube feet. The end of each tube foot has a sucker. The suckers can stick to surfaces and help the animal crawl. The suckers can also be used to pry open the shells of prey. You can see suckers on the sea star in Figure 12.29. Although echinoderms have a well-developed coelom and complete digestive system, they lack a centralized nervous system and do not have a heart. Some echinoderms have simple eyes that can sense light. Like annelids, echinoderms can regrow a missing body part. In fact, a complete starfish can regrow from a single arm. | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2021 | Some echinoderms can reproduce asexually by fission. However, most echinoderms reproduce sexually. They generally have separate sexes that produce sperm and eggs. Fertilization typically occurs outside the body in the water. Eggs hatch into larvae that have bilateral symmetry and can swim. The larvae undergo metamorphosis to change into the adult form. During metamorphosis, their bilateral symmetry changes to radial symmetry. | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2022 | Chordates are animals in Phylum Chordata. They are animals that have a notochord and certain other traits. The notochord is a rigid rod that runs down the back of the body. Phylum Chordata is a large and diverse phylum. It includes at least 60,000 species, including the human species. For a visual introduction to chordates, watch this video: http://video.about.com/animals/What-Is-Phylum-Chordata-.htm | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2023 | Chordates have three embryonic cell layers: endoderm, mesoderm, and ectoderm. They also have a segmented body with a complete coelom and bilateral symmetry. In addition, chordates have a complete digestive system, central nervous system, and circulatory system. | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2024 | There are four traits that are unique to chordates and define Phylum Chordata. The four traits are a post-anal tail, dorsal hollow nerve cord, notochord, and pharyngeal slits. You can see the four traits in Figure 12.30. 1. The post-anal tail is at the end of the organism opposite the head. It extends beyond the anus. 2. The hollow nerve cord runs along the top (dorsal) side of the animal. (In nonchordate animals, the nerve cord is solid and runs along the bottom side.) 3. The notochord lies between the dorsal nerve cord and the digestive tract. It provides stiffness to counterbalance the pull of muscles. 4. The pharyngeal slits are located in the pharynx. The pharynx is the tube that joins the mouth to the digestive and respiratory tracts. In some chordates, all four of these defining traits last throughout life and have important functions. For example, in some chordates, pharyngeal slits are used to filter food out of water. In many chordates, however, including humans, all four traits are present only in the embryo. After that, some of the traits disappear or develop into other structures. For example, in humans, pharyngeal slits are present in the embryo but later develop into parts of the ear. | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2025 | Living chordates are mainly vertebrates. In vertebrates, the notochord develops into a backbone, or vertebral column, after the embryonic stage. A small percentage of chordates are invertebrates. Their notochord never develops into a backbone. Invertebrate chordates include tunicates and lancelets. Both groups of animals are small and relatively primitive. They are probably similar to the earliest chordates that evolved more than 500 million years ago. | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2026 | Tunicates are invertebrate chordates that lose some of the four defining chordate traits by adulthood. Tunicates are also called sea squirts. There are about 3000 living species of tunicates. All are ocean dwellers and live in shallow water. You can see examples of tunicates in Figure 12.31. As larvae, tunicates can swim freely to find food. As adults, tunicates lack a post-anal tail and notochord, and they can no longer swim. Instead, they remain in one place and are filter feeders. Tunicates can reproduce both sexually and asexually. The same adults produce sperm and eggs. However, fertilization always involves gametes from different parents. Asexual reproduction is by budding. | text | null |
L_0373 | echinoderms and invertebrate chordates | T_2027 | Lancelets are invertebrate chordates that retain all four defining chordate traits as adults. There are only about 25 species of living lancelets. Lancelets resemble tunicates in several ways. For example: lancelets live in shallow ocean water; lancelet larvae can swim to find food; and lancelet adults are filter feeders that can no longer swim. Adult lancelets spend most of their time buried in sand on the ocean floor. Lancelets reproduce sexually, with separate sexes producing sperm and eggs. | text | null |
L_0376 | amphibians | T_2047 | Amphibians are vertebrates that live part of the time in fresh water and part of the time on land. They were the first vertebrates to evolve four legs and colonize the land. They most likely evolved from lobe-finned fish. Modern amphibians include frogs, toads, salamanders, newts, and caecilians. They are ectotherms, so they have little control over their body temperature. This allows them to be active in warm weather, but they become sluggish when the temperature cools. | text | null |
L_0376 | amphibians | T_2048 | Amphibians have moist skin without scales. The skin is kept moist by mucus, which is secreted by mucous glands. In some species, the mucous glands also secrete toxins that make the animal poisonous to predators. The blue poison-dart frogs in Figure 13.12 are a good example. The toxin in their mucus is used by native people in South America to poison the tips of their hunting arrows. Amphibian skin contains keratin, a protein that is also found in the outer covering of most other four-legged vertebrates. The keratin in amphibians is not too tough to allow gases and water to pass through their skin. Most amphibians breathe with gills as larvae and with lungs as adults. However, extra oxygen is absorbed through the skin. | text | null |
L_0376 | amphibians | T_2049 | All amphibians have digestive, excretory, and reproductive systems. All three of these organ systems use a single body cavity, called the cloaca. Wastes enter the cloaca from the digestive and excretory systems. Gametes enter the cloaca from the reproductive system. A single external opening in the cloaca allows the wastes and gametes to exit the body. (Many other four legged vertebrates also have a cloaca.) Amphibians have relatively complex circulatory and nervous systems. They have sensory organs for smelling and tasting, as well as eyes and ears. Frogs also have a larynx, or voice box, that allows them to make sounds. The purpose of frog calls varies. Some calls are used to attract mates, some are used to scare off other frogs, and some are signals of distress.You can hear a collection of frog calls at this link: http://animaldiversity.ummz.umich.edu/co | text | null |
L_0376 | amphibians | T_2050 | Amphibians reproduce sexually. Fertilization may take place inside or outside the body. Amphibians are oviparous. Embryos develop in eggs outside the mothers body. | text | null |
L_0376 | amphibians | T_2051 | Amphibians do not produce amniotic eggs with waterproof membranes. Therefore, they must lay their eggs in water. The eggs are usually covered with a jelly-like substance that helps keep them moist and offers some projection from predators. You can see a mass of frog eggs in jelly in Figure 13.13. Amphibians generally lay large numbers of eggs. Often, many adults lay eggs in the same place at the same time. This helps ensure that the eggs will be fertilized. Once eggs are laid, amphibian parents typically provide no parental care. | text | null |
L_0376 | amphibians | T_2052 | Most amphibians go through a larval stage that is different from the adult form. In frogs, for example, the early larval stage resembles a fish, as you can see in Figure 13.14. Frogs at this stage of development are called tadpoles. Tadpoles live in the water. They lack legs and have a long tail that helps them swim. They also have gills, which absorb oxygen from the water. During metamorphosis, the tadpole changes to the form of an adult frog. It grows legs, loses its tail, and develops lungs. All of these changes prepare it to live on the land. In Figure 13.15, you can see how a frog larva looks as it changes to the adult form. | text | null |
L_0376 | amphibians | T_2052 | Most amphibians go through a larval stage that is different from the adult form. In frogs, for example, the early larval stage resembles a fish, as you can see in Figure 13.14. Frogs at this stage of development are called tadpoles. Tadpoles live in the water. They lack legs and have a long tail that helps them swim. They also have gills, which absorb oxygen from the water. During metamorphosis, the tadpole changes to the form of an adult frog. It grows legs, loses its tail, and develops lungs. All of these changes prepare it to live on the land. In Figure 13.15, you can see how a frog larva looks as it changes to the adult form. | text | null |
L_0376 | amphibians | T_2053 | There are only about 6200 known species of amphibians. They are placed in three orders: frogs, salamanders, and caecilians. Table 13.4 shows a picture of an amphibian in each order. It also provides additional information about the orders. Class Frogs Distinguishing Traits The frog order also includes toads. Unlike other amphibians, frogs and toads lack a tail by adulthood. Their back legs are also longer because they are specialized for jumping. Frogs can jump as far as 20 times their body length. Thats like you jumping more than the length of a basketball court! Example red-eyed tree frog Class Salamanders Caecilians Distinguishing Traits The salamander order also includes newts. Salamanders and newts keep their tails as adults. They have a long body with short legs. They are adapted for walking and swim- ming rather than jumping. Unlike other vertebrates, salamanders can regrow legs or other body parts if they are bitten off by a predator. The caecilian order is the amphib- ian order with the fewest species. Caecilians are closely related to salamanders. They have a long, worm-like body. They are the only amphibians without legs. Caecil- ians evolved from a four-legged an- cestor but lost their legs later in their evolution. As adults, they often bur- row into the soil. Thats one reason why Caecilians tend to be less well known than other amphibians. Example smooth newt microcaecilia | text | null |
L_0376 | amphibians | T_2054 | Amphibians live in freshwater and moist-soil habitats throughout the world. The only continent that lacks amphib- ians is Antarctica. Amphibians are especially common in temperate lakes and ponds and in tropical rainforests. | text | null |
L_0376 | amphibians | T_2055 | Amphibians are the prey of many other vertebrates, including birds, snakes, raccoons, and fish. Amphibians are also important predators. As larvae, they may eat water insects and algae. As adults, they typically eat invertebrates, including worms, snails, and insects. You can watch a frog catching an invertebrate in the slow-motion video at the following link. At its real speed, you would barely see it because it happens so quickly. MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0376 | amphibians | T_2056 | Why are so many amphibian species threatened by extinction, and why should you care? The second question is easy. Amphibians control pests, may be a source of new medicines, and help feed many other animals. The nature of amphibian skin may help explain why so many amphibian species are at risk. Their skin easily absorbs substances from the environment, such as pollutants in water or air. Therefore, they may suffer from poor environmental quality before other animals do. As such, they may provide an early-warning system of environmental damage. What can you do to help save amphibians? Protect the natural environment. For example, reduce your use of energy to curb greenhouse gases and global warming. Avoid the use of garden pesticides. Poisoned insects may be eaten by amphibians that are also harmed by the poison. Make a backyard habitat. A small pond surrounded by native vegetation provides a place for amphibians to live. Help raise awareness. Start a letter-writing campaign to politicians, asking them to support conservation activities for amphibians. For more ideas about what you can do to help save amphibians, check out this website: | text | null |
L_0377 | reptiles | T_2057 | Reptiles are ectothermic, four-legged vertebrates that produce amniotic eggs. The reptile class is one of the largest classes of vertebrates. Besides turtles, it includes crocodiles, alligators, lizards, and snakes. Although some turtles and other reptiles now live mainly in the water, reptiles evolved many adaptations for life on land. For an amusing overview of reptiles, watch this Bill Nye the Science Guy reptile video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0377 | reptiles | T_2058 | Reptiles were the first vertebrates to lay amniotic eggs. This freed them from returning to the water to reproduce. In addition to amniotic eggs, reptiles have several other adaptations for living on land. For example, reptile skin is covered with scales. You can see how the scales overlap and cover the snake in Figure 13.17. Reptile scales are made of very tough keratin. They help protect reptiles from injury as well as loss of water. Because of their tough scales, reptiles cant absorb oxygen through their skin as amphibians can. However, reptiles have more efficient lungs for breathing air. They also have various ways of moving air into and out of their lungs. For example, their chest muscles contract to push air out of the lungs. The muscles relax to allow air to rush into the lungs. Another muscle, called the diaphragm, which lies below the lungs, also helps move air into and out of the lungs. (Mammals also have a diaphragm for breathing air.) | text | null |
L_0377 | reptiles | T_2059 | Reptiles have a circulatory system with a heart that pumps blood. Reptiles also have a centralized nervous system with a brain. Their brain is relatively small, but the parts of the brain that control the senses and learning are larger than in amphibians. Reptiles have good senses of sight and smell. They use their tongue to smell scents. Thats what the blue-tongued lizard in Figure 13.18 is doing. Some reptiles also have a heat-sensing organ that helps them locate the warm bodies of prey animals such as birds and small mammals. | text | null |
L_0377 | reptiles | T_2059 | Reptiles have a circulatory system with a heart that pumps blood. Reptiles also have a centralized nervous system with a brain. Their brain is relatively small, but the parts of the brain that control the senses and learning are larger than in amphibians. Reptiles have good senses of sight and smell. They use their tongue to smell scents. Thats what the blue-tongued lizard in Figure 13.18 is doing. Some reptiles also have a heat-sensing organ that helps them locate the warm bodies of prey animals such as birds and small mammals. | text | null |
L_0377 | reptiles | T_2060 | Most reptiles have sexual reproduction with internal fertilization. Reptiles have a body cavity called a cloaca that is involved in reproduction. Sperm or eggs are released into an adult reptiles cloaca. Males have one or two penises that pass sperm from their cloaca to the eggs in the cloaca of a female, where fertilization takes place. In most reptile species, once fertilized the eggs leave the body through an opening in the cloaca. These reptiles are oviparous. Eggs develop and hatch outside the mothers body. Young reptiles, like the baby alligator in Figure 13.19, look like smaller versions of the adults. They dont have a larval stage as most amphibians do. Baby reptiles are able to move and search for food but are at high risk of predation. Adult reptiles rarely provide any care for their offspring once the eggs are laid. The only exceptions are female alligators and crocodiles. They defend their eggs and hatchlings from predators and help them reach the water. | text | null |
L_0377 | reptiles | T_2061 | There are over 8200 living species of reptiles. They are classified in four orders, called Crocodilia, Sphenodontia, Squamata, and Testudines. Table 13.4 shows a picture of a reptile in each order. It also provides additional information about the orders. For an online gallery of amazing photos of reptiles, go to this link: http://video MEDIA Click image to the left or use the URL below. URL: Class Crocodilia Distinguishing Traits Reptiles in the Crocodilia Order are called crocodilians. They include crocodiles, alligators, caimans, and gharils. They have four sprawling legs that allow them to run surpris- ingly fast. They have strong jaws and replace their teeth throughout life. Crocodilians have relatively complex brains and greater intelli- gence than other reptiles. Example crocodile Class Sphenodontia Distinguishing Traits The Sphenodontia Order includes only tuataras like the one in this photo. They resemble lizards but are the least specialized of all living reptiles. Their brain is similar to the amphibian brain. Example tuatara Squamata The Squamata order includes lizards and snakes. Lizards have four legs for running or climbing, and they can also swim. Many change their color when threatened. Snakes do not have legs, although they evolved from a four-legged ancestor. They have a very flexible jaw for swallowing large prey whole. Some inject poison into their prey through fangs. The Testudines Order includes tur- tles, tortoises, and terrapins. They have four legs for walking. They have a hard shell covering most of their body. lizard Testudines terrapin | text | null |
L_0377 | reptiles | T_2062 | Modern reptiles live in many different habitats. They can be found on every continent except Antarctica. | text | null |
L_0377 | reptiles | T_2063 | Many turtles are aquatic. They may live in the ocean or in fresh water. Other turtles are terrestrial and live on land. All lizards are terrestrial. Their habitats may range from deserts to rainforests. They may live in a range of places, from underground burrows to the tops of trees. Most snakes are terrestrial, but some are aquatic. Crocodilians live in and around swamps or bodies of water. The water may be fresh or salty, depending on the species of crocodilian. | text | null |
L_0377 | reptiles | T_2064 | All reptiles are heterotrophs, and the majority eats other animals. Heterotrophs that eat only or mainly animals are called carnivores. Large carnivorous reptiles such as crocodilians are the top predators in their ecosystems. They prey on large birds, fish, deer, turtles, and sometimes farm livestock. Their powerful jaws are strong enough to crush bones and turtle shells. Smaller carnivorous reptilesincluding tuataras, snakes, and many lizardsare lower-level predators. They prey on small animals such as insects, frogs, birds, and mice. Most terrestrial turtles eat plants. Heterotrophs that eat only or mainly plants are called herbivores. Herbivorous turtles graze on grasses, leaves, flowers, and fruits. Marine turtles and some lizards feed on both plants and animals. Heterotrophs that eat a variety of foods including both plants and animals are called omnivores. | text | null |
L_0378 | birds | T_2065 | Birds are four-limbed, endothermic vertebrates. The upper pair of limbs are wings that most birds use for flying. The lower pair of limbs are legs with feet that birds use for walking. Because birds walk on two legs, they are called bipedal. (Humans are bipedal too.) Birds also have feathers and beaks, and they produce amniotic eggs. Of all vertebrate classes, birds are the most numerous, even though they evolved most recently. Why have birds been so successful? The answer is flight. Being able to fly opened up a whole new world to birds: the world of the air above the land and water. Other than insects, virtually no other animals can inhabit the airy world. Flying is a sure-fire way to escape from all but the quickest nonflying predators. Flying also gives birds a good view for finding food and mates. | text | null |
L_0378 | birds | T_2066 | Wings and feathers are two adaptations for flight that evolved in birds. Both are clearly displayed in the flying gull in Figure 14.2. Wings evolved from the front limbs of a four-legged ancestor. The wings are controlled by large flight muscles in the chest. Feathers also help birds fly. They provide air resistance and lift. In addition, they provide insulation and serve other roles. | text | null |
L_0378 | birds | T_2067 | To keep their flight muscles well supplied with oxygen, birds evolved specialized respiratory and circulatory systems. Birds have special air sacs for storing extra air and pumping it into the lungs. They also have a relatively large heart and a rapid heart rate. These adaptations keep plenty of oxygenated blood circulating to the flight muscles. | text | null |
L_0378 | birds | T_2068 | Birds have relatively big brains for their body size. This is reflected in their high level of intelligence and complex behavior. Some birds, including crows, are more intelligent than many mammals. They are smart enough to use tools to solve problems. You can see this in the video below. However, the part of the brain that is most developed in birds is the part that controls flying. This is another adaptation for flight. MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0378 | birds | T_2069 | Birds reproduce sexually and have separates sexes. Fertilization occurs internally, so males and females must mate. Many bird species have special behaviors, such as unique songs or visual displays, for attracting mates. These special behaviors are called courtship. The white peacock in Figure 14.3 is putting on a stunning display of his amazing tail feathers to court a mate. | text | null |
L_0378 | birds | T_2070 | After mating and fertilization occur, eggs are laid, usually in a nest. Most birds build nests for their eggs and hatchlings, and each species has a certain way of doing it. You can see examples of different types of bird nests in Figure 14.4. Nests range from little more than a depression in the ground (killdeer) to elaborately built structures (weaver bird). You can see how skillful a weaver bird is at weaving its nest by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0378 | birds | T_2070 | After mating and fertilization occur, eggs are laid, usually in a nest. Most birds build nests for their eggs and hatchlings, and each species has a certain way of doing it. You can see examples of different types of bird nests in Figure 14.4. Nests range from little more than a depression in the ground (killdeer) to elaborately built structures (weaver bird). You can see how skillful a weaver bird is at weaving its nest by watching this video: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0378 | birds | T_2071 | In most species, one or both parents take care of the eggs. They sit on the eggs to keep them warm until they hatch. This is called incubation. After the eggs hatch, the parents generally continue their care. They feed the hatchlings until they are big enough to feed on their own. This is usually at a younger age in ground-nesting birds such as ducks than in tree-nesting birds such as robins. | text | null |
L_0378 | birds | T_2072 | There are about 10,000 living species of birds. Almost all of them can fly. Very few birds are flightless. | text | null |
L_0378 | birds | T_2073 | Birds that can fly are classified in 29 orders. Birds in the different orders vary in their physical traits and how they behave. You can see seven of the most common orders of flying birds in Table 14.1. The majority of flying birds are perching birds, described in the last row of the table. There are more species in this order than in all other bird orders combined. Many perching birds are familiar songbirds such as the mockingbird. You can hear a mockingbirds amazing and complex song in this video: http://youtu.be/NNNX3f3_svo Order Landfowl: pheasants Description They are large in size; they spend most of their time on the ground; they usually have a thick neck and short, rounded wings; their flight tends to be brief and close to the ground. Example turkey Waterfowl: ducks, geese, swans They are large in size; they spend most of their time on the water sur- face; they have webbed feet and are good swimmers; most are strong flyers. ducks Shorebirds: puffins, gulls, plovers They range from small to large; most live near the water, and some are sea birds; they have webbed feet and are good swimmers; most are strong flyers. puffin Diurnal Raptors: hawks, falcons, eagles They range from small to large; they are active during the day and sleep during the night; they have a sharp, hooked beak and strong legs with clawed feet; they hunt by sight and have excellent vision. hawk Nocturnal Raptors: burrowing owls, barn owls, horned owls They range from small to large; they are active during the night and sleep during the day; they have a sharp, hooked beak and strong legs with clawed feet; they have large, forward-facing eyes; they have ex- cellent hearing and can hunt with their sense of hearing alone. burrowing owl turkeys, chickens, Order Parrots: cockatoos, parrots, para- keets Description They range from small to large; they are found in tropical regions; they have a strong, curved bill; they stand upright on strong legs with clawed feet; many are brightly col- ored; they are very intelligent. Example cockatoo Perching Birds: honeyeaters, spar- rows, crows They are small in size; they perch above the ground in trees and on buildings and wires; they have four toes for grasping a perch; many are songbirds. honeyeater | text | null |
L_0378 | birds | T_2074 | Some birds lost the ability to fly during their evolution. They include the ostrich, pictured above in Figure 14.1, as well as the kiwi, rhea, cassowary, and moa. All of these birds have long legs that are adapted for running. Penguins, like the one pictured in Figure 14.5, are also flightless, but they have a very different body shape. They are adapted for swimming instead of running. | text | null |
L_0378 | birds | T_2075 | Birds are endothermic. They can maintain a warm body temperature even in a cold climate. Therefore, they can live in a wider range of habitats than ectothermic vertebrates such as amphibians and reptiles. | text | null |
L_0378 | birds | T_2076 | Birds live and breed in most terrestrial habitats on Earth. They can be found on all seven continents, from the Arctic to Antarctica. However, the majority of bird species are native to tropical areas of the planet. | text | null |
L_0378 | birds | T_2077 | Birds may be specialists or generalists in terms of what they eat. Generalists are organisms that eat many different types of food. Birds that are generalists include the red-winged blackbird in Figure 14.6. It has a basic beak that can eat many different foods. Red-winged blackbirds are omnivores. They may eat a wide variety of seeds as well as insects and other small animals such as snails and frogs. Specialists are organisms that eat just one type of food. Birds that are specialists include ospreys, which eat only live fish. You can see an osprey in Figure 14.7. The ospreys feet are very well-adapted for catching fish. Its eyes are also well-adapted for seeing fish under the water. Its beak is well suited for gripping and ripping into fish flesh. Ospreys are so well-adapted to catching fish that they cant catch anything else! | text | null |
L_0379 | mammals | T_2078 | Mammals are endothermic vertebrates with four limbs. Examples of mammals include bats, whales, mice, and humans. Clearly, mammals are a very diverse group. Nonetheless, they share several traits that set them apart from other vertebrates. | text | null |
L_0379 | mammals | T_2079 | Two traits are used to define the mammal class. They are fur or hair and mammary glands in females. All mammals have fur or hair on their skin. It provides insulation and helps keep the body warm. It also can be used for sensing. For example, cats can feel with their whiskers. All female mammals have mammary glands. Mammary glands are glands that produce milk after the birth of offspring. Producing milk for offspring is called lactation. The colt in Figure 14.9 is getting milk from its mother. | text | null |
L_0379 | mammals | T_2079 | Two traits are used to define the mammal class. They are fur or hair and mammary glands in females. All mammals have fur or hair on their skin. It provides insulation and helps keep the body warm. It also can be used for sensing. For example, cats can feel with their whiskers. All female mammals have mammary glands. Mammary glands are glands that produce milk after the birth of offspring. Producing milk for offspring is called lactation. The colt in Figure 14.9 is getting milk from its mother. | text | null |
L_0379 | mammals | T_2080 | Most mammals share several other traits. These include: a large, complex brain and relatively great intelligence; ears with specialized structures that make them extremely good at hearing; four different types of teeth (reptiles have just one type), allowing them to eat a wide range of foods; tiny air sacs called alveoli (alveolus, singular) in the lungs for enhanced gas exchange; and glands in the skin that produce sweat, a salty fluid that helps cool down the body. | text | null |
L_0379 | mammals | T_2081 | Mammals are noted for the many ways they can move. Some mammals are well known for their speed. The fastest land animal is a mammal, the cheetah. It can race at speeds of up to 112 kilometers (70 miles) per hour. The limbs of most mammals are specialized for a particular way of moving. They may be specialized for running, jumping, climbing, flying, gliding, or swimming. The limbs of some mammals are even specialized for swinging through tree tops. You can see mammals with some of these specializations in Figure 14.10. | text | null |
L_0379 | mammals | T_2082 | Mammals have a variety of ways to keep their body temperature stable. | text | null |
L_0379 | mammals | T_2083 | Mammals stay warm in cool weather in two general ways. One way is by generating more heat. The other way is by conserving the heat that is generated. Mammals generate heat mainly by maintaining a high rate of metabolism. Compared with the cells of other animals, the cells of mammals have more mitochondria. Mitochondria are the cell organelles that generate energy. Mammals may also produce little bursts of heat by shivering. Shivering occurs when many muscles all contract slightly at the same time. The muscle contractions generate a small amount of heat. Mammals conserve heat with their hair or fur. It works like the layer of insulation in the walls of a house. It traps warm air next to the skin so it cant escape into the environment. Like the squirrel in Figure 14.11, most mammals can make their hair or fur stand up from the skin. This makes it a better insulator. Mammals also have a layer of insulating fat beneath their skin. Other vertebrates lack this layer of fat. | text | null |
L_0379 | mammals | T_2084 | In hot weather, mammals may need to lose excess body heat. One way they do this is by increasing blood flow to the body surface. The increased blood flow warms the skin, which gives off heat to the environment. Most mammals also sweat to lose excess heat. Sweating wets the skin. Evaporation of the sweat requires heat. The heat comes from the body and cools it down. Animals with fur, like the dogs in Figure 14.12, may pant instead of sweat to lose body heat. Water evaporates from the tongue and other moist surfaces of the mouth, using heat from the body. Watch this video to learn about some unique ways that elephants lose excess heat: MEDIA Click image to the left or use the URL below. URL: | text | null |
L_0379 | mammals | T_2085 | Generating body heat to stay warm takes a lot of energy. Mammals are heterotrophs that get their energy by eating other organisms. Mammals eat a wide range of different foods. Except for leaf litter and wood, almost any kind of organic matter is consumed by some type of mammal. The organic matter typically comes from plants, other animals, or some mix of these sources. | text | null |
L_0379 | mammals | T_2086 | Many mammals are herbivores. Herbivores are heterotrophs that eat only or mainly plant foods (or algae). Depend- ing on the species of mammals, they may eat leaves, shoots, stems, roots, seeds, nuts, fruits, flowers, and/or grasses. Some mammals even eat conifer needles or tree bark. Mammals that are herbivores include rabbits, mice, sheep, zebras, deer, kangaroos, and monkeys. The manatee in Figure 14.13 is also a herbivorous mammal. It eats mainly kelp (seaweed). | text | null |
L_0379 | mammals | T_2086 | Many mammals are herbivores. Herbivores are heterotrophs that eat only or mainly plant foods (or algae). Depend- ing on the species of mammals, they may eat leaves, shoots, stems, roots, seeds, nuts, fruits, flowers, and/or grasses. Some mammals even eat conifer needles or tree bark. Mammals that are herbivores include rabbits, mice, sheep, zebras, deer, kangaroos, and monkeys. The manatee in Figure 14.13 is also a herbivorous mammal. It eats mainly kelp (seaweed). | text | null |
L_0379 | mammals | T_2087 | Some mammals are carnivores. Carnivores are heterotrophs that eat only or mainly animal foods. Depending on their species, carnivorous mammals may eat other mammals, birds, reptiles, amphibians, fish, mollusks, worms, and/or insects. Mammals that are carnivores include anteaters, whales, hyenas, wolves, and seals. The bat in Figure | text | null |
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