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Animals, Part 2 Vertebrates. VERTEBRATES CHORDATA: dorsal, hollow nerve cord CRANIATES: have a skull (hagfish) VERTEBRATES: have a backbone (lampreys)

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Presentation on theme: "Animals, Part 2 Vertebrates. VERTEBRATES CHORDATA: dorsal, hollow nerve cord CRANIATES: have a skull (hagfish) VERTEBRATES: have a backbone (lampreys)"— Presentation transcript:

1 Animals, Part 2 Vertebrates

2 VERTEBRATES CHORDATA: dorsal, hollow nerve cord CRANIATES: have a skull (hagfish) VERTEBRATES: have a backbone (lampreys) GNATHOSTOMES: have jaws (extinct) CHONDRICHTHYANS: cartilage skeleton (sharks and rays) OSTEICHTHYANS: bony skeleton (fishes) TETRAPODS: four feet (amphibians: frogs, salamanders) AMNIOTES: have a yolk egg (reptiles: turtles, snakes, crocodiles, birds) MAMMALS: have hair and produce milk (marsupials, etc)

3 CHORDATA Chordates have a notochord and a dorsal, hollow nerve cord. They are not quite invertebrates, but are more closely related to vertebrates than to invertebrates. A notochord is a long, flexible rod located between the digestive tube and the nerve cord. It provides skeletal support throughout most of the length of the back. It differs from vertebrates in that it is not jointed; the notochord in humans is reduced to discs sandwiched between the vertebrae, known intervertebral discs. A dorsal, hollow nerve cord is unique to chordates. Other animals have solid nerve cords. The nerve cord of a chordate embryo develops into the central nervous system including the brain and spinal cord. Rather than a fully developed brain, chordates have only a slightly swollen tip at the anterior end of their dorsal nerve cord.

4 CRANIATES Craniates are chordates that have a skull. One example is the hagfish, which have a skull made out of cartilage, but they lack jaws and vertebrae. They swim in a snake like fashion by using their muscles. Hagfish have a small brain, eyes, ears, and a nasal opening that connects with the phalanx. They also have tooth like formations made out of protein in their mouth. All species are marine, and measure up to 60 cm in length. Most are bottom dwelling scavengers that feed on worms or sick or dead fish. A hagfish has rows of slime glands that secrete a slime to repulse other scavengers. When a hagfish is attacked, it can produce several liters of slime in less than a minute. This slime coats the gills of an attacking fish, forcing it to retreat or suffocate. Scientists are investigating the properties of hagfish slime in hopes of producing it as a space- filling gel which can be used to stop bleeding during surgery.

5 VERTEBRATES Vertebrates are craniates that have a backbone. They have a more complex nervous system and a more elaborate skeleton, and have become active predators. In most vertebrates, the vertebrae enclose the spinal cord. Aquatic vertebrates also acquired dorsal, ventral, and anal fins which provide thrust and steering control during swimming. They also adapted more efficient gas exchange systems in their gills. Lampreys differ from fishes in that they lack jaws and they lack paired fins. They represent the oldest of the vertebrates. Most are parasites that feed by clamping their round, jawless mouth onto the flank of a live fish. They then use their rasping tong to penetrate the skin of the fish and ingest the fish's blood. Their skeleton mostly consists of cartilage. Collectively, jawless fish are referred to as agnathans (“no jaw”)

6 GNATHOSTOMES Gnathostomes (“jaw mouth”) are vertebrates that have jaws. A jaw is a hinged structure that, with help of the teeth, enables gnathostomes to grip food firmly and slice it up. Their forebrain is enlarged compared to that of other craniates, which allows them enhanced senses of smell and vision. Running the length of each side of the body in aquatic gnathostomes is the lateral line system, a row of microscopic organs sensitive to vibrations in the surrounding water. Additionally, they have a mineralized endoskeleton. All of the vertebrates that we will discuss are descents of this clade; the species that are only gnathostomes are all extinct.

7 CHONDRICHTHYANS Chondrichthyans have a skeleton and that is predominately cartilage, impregnated with calcium. Examples include sharks and rays. They are the biggest and most successful vertebrate predators in the ocean.

8 SHARKS Sharks have hinged jaws, vertebrae, a flexible skeleton made of cartilage, and a lateral line system. A lateral line system is a row of sensory organs running along each side that are sensitive to changes in water pressure and can detect vibrations caused by animals swimming nearby. They have a streamlined body and are swift swimmers, but they do not maneuver very well. Powerful movements of the trunk and tailfin propel them forward. The dorsal fins function mainly as stabilizers. They do not have a swim bladder. A swim bladder is a gas-filled sac that can help keep a fish afloat. Instead, the shark gets buoyancy by storing a large amount of oil in its huge liver, the animal is still denser than water, and if it stops swimming it sinks. Continual swimming also ensures that water flows into the shark’s mouth and out through the gills, where gas exchange occurs. However, some sharks spend a good deal of time resting on the seafloor. When resting, they use muscles of their jaw to pass water over the gills.

9 SHARKS The largest sharks and rays are suspension feeders that consume plankton (algae). Most sharks, however, are carnivores that swallow their prey whole or use their powerful jaws and sharp teeth to tear flesh from animals too large to swallow in one piece. Sharks have several rows of teeth that gradually move to the front of the mouth as old teeth are lost.

10 SHARKS Acute senses are adaptations that go along with the active, carnivorous lifestyle of sharks. Sharks have sharp vision but cannot distinguish colors. The nostrils of sharks function only for smelling, not for breathing. Sharks also have a pair of regions in the skin of their head that can detect electric fields generated by muscle contractions of nearby animals. Like other aquatic vertebrates, sharks have no eardrums to transmit sound waves. Sound reaches a shark through water, and the animal's entire body transmits the sound to the hearing organs of the inner ear.

11 RAYS Rays are closely related to sharks, but they have adapted a very different lifestyle. Most rays are flattened bottom-dwellers that feed by using their jaws to crush mollusks and crustaceans. They use their greatly enlarged pectoral fins like water wings to propel themselves through the water. The tail of many rays is whip-like and in some species, have poisonous barbs that function in defense. Sharks and rays are severely threatened with overfishing. In 2003, sharks in the Northwest Atlantic declined 75% in 15 years.

12 OSTEICHTHYANS Osteichthyan means “bony fish”. They have a bony skeleton made out of calcium phosphate. Informally, we call these “fish”. They breathe by drawing water over four or five pairs of gills located in chambers covered by a protective bony flap called the operculum.

13 OSTEICHTHYANS Most fish control their buoyancy with an air sac known as a swim bladder. Movement of gases from the blood to the swim bladder increases buoyancy, making the animal rise. This skin is often covered by flattened, bony scales that differ in structure and function from the tooth-like scales of sharks. Glands in the skin secrete a slimy mucus over the skin to reduce drag during swimming. Like sharks, boney fish have a lateral line system. There are two main types of fishes: Ray-finned and lobe-fins.

14 Ray-Finned Fishes Ray-finned fishes have an operculum, a lateral line system, a swim bladder, and flattened scales cohering the skin, but they do not have a flexible skeleton made of cartilage. Nearly all of the osteichthyans we are familiar with are among the ray-finned fishes. Examples include bass, trout, perks, tuna, and herring. The fins are modified for maneuvering, defense, and other functions. Ray- finned fishes originated in fresh water and spread to the seas. Some species have returned to fresh water at some point in their evolution.

15 Ray-Finned Fishes Some of them, including salmon and trout, replay their evolutionary round-trip from freshwater to sea water and back to fresh water during their lifecycle. Ray-finned fishes serve as a major source of protein for humans. However, industrial-scale fishing operations now threaten some of the world's biggest fisheries with collapse. Ray- finned fishes also face other pressures from humans, such as the diversion of rivers by dams.

16 Lobe-Fin Fishes The key derived characteristic of lobe-finned fish is a series of rod-shaped bones in their fins surrounded by a thick layer of muscle in their pectoral and pelvic fins. During their evolution, they lived in brackish waters where they probably used their lobed fins to swim and “walk” underwater across the bottom. Today only two main types of lobe-fins survive. One is called the coelacanths, which shifted to the ocean. Scientists once thought that coelacanths had become extinct 75 million years ago, but in 1938, fishermen caught a living coelacanth in the western Indian Ocean. A second species has been discovered in Indonesia.

17 Lobe-Fin Fishes Another lineage of living lobe-fin is a lung fish which are found in the southern hemisphere. They are found only in fresh water stagnant ponds and swamps. They have gills as well as lungs; they surface to pull air into their lungs. They also have gills for additional gas exchange. When ponds shrink during the dry season; they burrow into the mud and wait for conditions to improve.

18 Fish: the Good News and the Bad News Fish is a good source of protein and, unlike fatty meat products, it’s not high in saturated fat. It’s also a good source of omega-3 fatty acids, which benefit heart health. The American Heart Association recommends eating fish at least twice a week. However, some types of fish may contain high levels of mercury and other environmental contaminants. Levels of these substances are generally highest in older, larger, predatory fish and marine mammals.

19 Fish: the Good News and the Bad News Fish with the highest levels of mercury are shark, swordfish, golden bass or golden snapper, and king mackerel. These fish should be avoided by pregnant and nursing women and by young children. Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish. Albacore ("white") tuna has more mercury than canned light tuna; you may eat up to 6 ounces (one average meal) of albacore tuna per week. Fish sticks and "fast-food" sandwiches are commonly made from fish that are low in mercury.

20 TETRAPODS Tetrapods (“ four feet ”) are gnathostomes that have limbs and feet which evolved from the fins of lobe-fin fish. Once tetrapods moved onto land, they eventually took on many new forms, from leaping frogs to flying eagles. The limbs can support their weight on land and their feet allow them to walk. They do not have gills slits. The ears are adapted to the detection of airborne sounds. Some species developed wings, while others, such as whales, retained the shape of a fish. The first tetrapods to evolve were amphibians, represented by salamanders (with tails), frogs (tail-less), and caecilians (legless).

21 TETRAPODS Most salamanders that live on land walk with a side to side bending of the body. Adult frogs use their powerful hind legs to hop along the terrain. A frog nabs insects by flicking out its long, sticky tongue, which is attached to the front of the mouth. Frogs display a great variety of adaptations that help them avoid being eaten by larger predators. Their skin glands secrete distasteful or even poisonous mucus. Many poisonous species have bright coloration, which predators apparently associated with danger. Other frogs have caller patterns that camouflage. Caecilians are legless and nearly blind, and superficially they resembled earthworms. They inhabit tropical areas and burrow in moist forest soil.

22 Amphibians Amphibians were the first terrestrial vertebrates. Most amphibian life cycles include a metamorphosis, and larval amphibians have a lateral line system resembling that in fishes. Amphibian means “ two lives ”. The larval stage of a frog, called a tadpole, is an aquatic herbivore with a long tail. Larval amphibians have a lateral line system like bony fishes and sharks. The tadpole initially lacks legs and swims by its tail. During the metamorphosis that leads to the second life, the tadpole develops legs, lungs, a pair of external eardrums, and a digestive system adapted to a carnivorous diet. At the same time, the gills disappear. The young frog crawls onto shore and becomes a terrestrial hunter. Lungs and appendages for support did NOT evolve first in amphibians. Lungs evolved from the swim bladders of fish, and appendages evolved from their fins.

23 Amphibians Most amphibians are found in damp habitats such as swamps and rain forests. Even those that are adapted to drier habitats spend much of their time in burrows or under moist leave, where the humidity is high. Amphibians generally rely heavily on their moist skin for gas exchange with the environment.

24 Amphibians They usually lay their eggs in water. Fertilization is external and most amphibians; the male grasps the female and spills his sperm over the eggs as the female sheds them. Adults display various types of parental care. Depending on the species, either males or females may house eggs on their back, in their mouths, or even in their stomach. Some species make nests, and others abandon their eggs in water or in moist environments on land.

25 Amphibians Many amphibians exhibit complex and diverse social behaviors, especially during their breeding seasons. Frogs are usually quiet, but the males of many species vocalize to defend their breeding territory or to attract females.

26 Amphibians Over the past 25 years, there has been a rapid decline in amphibian populations throughout the world. There appears to be several causes, including habitat degradation, fungal pathogens, and acid rain. One difference between an amphibian and a reptile is that amphibians do not have an amniotic egg.

27 AMNIOTES Amniotes have an amniotic (yolk) egg, such as reptiles (including birds). An amniotic egg is one that contains specialized membranes that protect the embryo. They function in gas exchange, waste storage, and the transfer of storage nutrients to the embryo. The amnion is the layer that contains fluid and acts as a shock absorber. In contrast to the shell-less eggs of amphibians, the amniotic eggs of most reptiles and some mammals have a shell.

28 AMNIOTES The shells of bird eggs are made of breakable calcium carbonate, while the shells of many reptile eggs are leathery and flexible. The shell significantly slows dehydration of the egg in the air, an adaptation that allowed amniotes to occupy a wider range of terrestrial habitats than amphibians. Most mammals no longer have a shell, and the embryo develops within the mother. Amniotes also acquired other adaptations to terrestrial life, including less permeable skin and the ability to use the rib cage to ventilate the lungs. They also walk with a more elevated stance.

29 Reptiles Reptiles include snakes, lizards, turtles, crocodiles, and birds. Reptiles have scales, amniotic eggs, and waterproof skin, but no lateral line system in larvae. Unlike amphibians, reptiles have scales that contain the protein keratin. Scales create a waterproof area that helps prevent dehydration in dry air. Scales prevent reptiles from breathing through their skin like amphibians; most reptiles rely on their lungs alone for gas exchange. Turtles are the exception to this rule; many turtles also use the moist surfaces of their skin for gas exchange.

30 Reptiles Reptiles include snakes, lizards, turtles, crocodiles, and birds. Reptiles have scales, amniotic eggs, and waterproof skin, but no lateral line system in larvae. Unlike amphibians, reptiles have scales that contain the protein keratin. Scales create a waterproof area that helps prevent dehydration in dry air. Scales prevent reptiles from breathing through their skin like amphibians; most reptiles rely on their lungs alone for gas exchange. Turtles are the exception to this rule; many turtles also use the moist surfaces of their skin for gas exchange.

31 Reptiles The adaptation of an amniotic egg allowed reptiles to complete their life cycles on land. Most reptiles lay shelled eggs on land. Fertilization must occur internally, before the shell is secreted. Many species of snakes and lizards are viviparous ; they're amniotic membranes form a placenta that enables the embryo to obtain nutrients from its mother.

32 Reptiles Many reptiles are sometimes said to be “cold-blooded” because they do not is their metabolism to control their body temperature. However, they do regulate their body temperature by using behavioral adaptations. For example, many lizards bask in the sun when the air is cool and seek the shade when the air is too warm. A more accurate description of these reptiles is to say they are ectothermic. By heating their bodies directly with solar energy rather than through metabolic breakdown of food, an ectothermic reptile can survive on less than 10% of the food required by a mammal of the same size. Ectothermic animals include frogs, lizards, turtles, and alligators.

33 Snakes A snake is a scaly, limbless, elongate reptile. Snakes descended from an extinct lizard-like ancestor that was venomous. All snakes are carnivorous. Some snakes have a venomous bite, which they use to kill their prey before eating it. Other snakes kill their prey by constriction. Still others swallow their prey whole and alive. A snake smells by using its forked tongue to collect airborne particles then passing them to an organ in their mouth to examine them. The term poisonous snake is false - poison is inhaled or ingested whereas venom is injected. Snake venom is used in biotechnology to rapidly stop excessive bleeding during vascular surgery and major trauma.

34 Lizards Lizards normally possess four legs, external ear openings and movable eyelids. They can range in size from a few centimeters (geckos) to nearly three meters (Komodo Dragons).

35 Turtles Turtles are the most distinctive group of reptiles alive today. All turtles had a box like shell made of upper and lower shields that are fused to the vertebrae. In most species, the shell is hard, providing excellent defense against predators. The earliest turtles could not retract their heads into their shell; mechanisms for doing so evolved independently in two separate branches of turtles. The side-necked turtles fold their neck horizontally, while the vertical-neck turtles fold their neck vertically.

36 Turtles Some turtles have adapted to deserts, and others live almost entirely in ponds and rivers. Still others have returned to the sea. Sea turtles have a reduced shell and enlarged forelimbs that function as flippers. They are the largest living turtles and can weigh over 1500 kg. They feed on jellyfish and dive as deep as 60 m. They are endangered by fishing boats that accidentally catch them in their nets, as well as by the humans’ development of the beaches where turtles lay their eggs.

37 Alligators and Crocodiles Alligators and crocodiles are collectively called crocodilians. They are confined to the warmer regions of the world. Alligators in the United States have made a strong comeback after spending years on the endangered species list.

38 Birds Birds are in the same category as reptiles; they evolved from dinosaurs when they developed hollow bones, then some feathers, then flight feathers, then two toes in front and two in back. Although they are reptiles, their reptilian anatomy has undergone adaptations that are weight saving modifications to make flying more efficient. Adaptations for flight include the absence of teeth, very short tail bones, large breast muscles, efficient lungs, lack of a urinary bladder, an extremely high rate of metabolism, and the females of most species only have one ovary. The skull is especially light and the bones are hollow, although a bird skeleton as a whole is no lighter in relation to body weight than the skeleton of a mammal of similar size.

39 Birds Birds also have relatively large brains and possibly the best vision of all vertebrates. Although most birds are fabulous flyers, some birds are flightless. Birds generally display very complex behaviors, particularly during breeding season, when they engage in elaborate courtship rituals. Fertilization is internal and the amniotic egg of birds has a hard outer shell. Male and female frequently share responsibility for the incubation and care of the young. Although their general body form is similar, different species can be distinguished by their body profile, flying style, behavior, feather colors, beak shape, and foot structure.

40 MAMMALS Mammals evolved from reptiles. Mammals have hair and have mammary glands which produce milk. All mammalian mothers nurse their young with milk, a balanced diet rich in fats, sugars, proteins, minerals, and vitamins. Hair and a fat layer under the skin help to retain the body heat. Like birds, mammals are endothermic, and most have a high metabolic rate. This is supported by an efficient respiratory system with a diaphragm and efficient circulatory system, including a four-chambered heart. Live births are not limited to mammals (some reptiles have live births), and some mammals lay eggs.

41 MAMMALS Mammals generally have a larger brain than other vertebrates of equivalent size. A relatively long duration of parental care extends the time for offspring to learn important survival skills by observing their parents.

42 MAMMALS Mammals are endothermic (warm-blooded). They use heat generated by metabolism to maintain a warm, steady body temperature. Differentiation of teeth is another important mammalian trait. The teeth of mammals come in a variety of sizes and shapes adapted for chewing many types of food. Humans, for example, have teeth modified for shearing and for crushing and grinding. The three major groups of mammals are the monotremes, marsupials, and eutherians.

43 Monotremes Monotremes are found only in Australia and New Guinea and are represented by the platypus and spiny anteater. Like all mammals, monotremes have hair and produce milk, but they lay eggs and they lack nipples; the baby sucks milk from the mother’s fur.

44 Marsupials Examples are opossums, kangaroos, and koalas. A marsupial is born very early in its development and completes its development while nursing in a maternal pouch called a marsupium. A red kangaroo is about the size of a honey bee at its birth, just 33 days after fertilization. Its hind legs are merely buds, but it's forelegs are strong enough for it to crawl from the exit of its mother's reproductive tract to a pouch that opens to the front of her body, a journey that lasts a few minutes.

45 Marsupials Australia has not been in contact with another continent for about 65 million years. Most marsupials evolved after South America and Australia broke off from the other landmasses. That is why kangaroos and koalas are only found in Australia. Australia’s native species face serious challenges from introduced, alien species.

46 Eutherians Eutherians (placental mammals) Eutherians are commonly called placental mammals because their placentas are more complex than those of marsupials and they have a longer period of pregnancy. Eutherians complete their embryonic development within the uterus. The major order of eutherians we will discuss is the Primates.

47 Primates This order includes the lemurs, the tarsiers, the monkeys, and the apes. Humans are members of the ape group. Most primates have hands and feet adapted for grasping, and their digits have flat nails instead of claws. Additionally, the fingers have skin ridges (fingerprints). Primates have a larger brain than other mammals, and short jaws, giving them a flat face. There have forward-looking eyes that are close together on the front of the face. Primates also have relatively well-developed parental care and complex social behavior.

48 Primates The earliest primates were probably tree dwellers, and many of the characteristics of primates are adaptation to the demands of living in trees. All modern primates, except humans, have a big toe that is widely separated from the other toes, enabling them to grasp branches with their feet. All primates have a thumb that is relatively mobile and separate from the fingers, but only monkeys, apes, and humans have a fully opposable thumb; that is, they can touch the tip of all four fingers with the fingerprint surface of the thumb of the same hand. In humans, a distinctive bone structure at the base of the thumb allows it to be used for more precise manipulation. Having two eyes facing forward causes and overlapping of visual fields, which enhances depth perception.

49 Primates There are three main groups of living primates: the lemurs of Madagascar, the tarsiers of South East Asia, and the anthropoids, which include monkeys, apes, and humans. After South America and Africa a drifted apart, South America is called the New World and Africa and Asia are called the Old World. New World monkeys and Old World monkeys underwent separate adaptive evolutions. All species of New World monkeys live in trees, have prehensile tails, and nostrils that open to the sides. Old World monkeys include ground dwelling as well as tree-dwelling species, lack a prehensile tail, and their nostrils open downward. Most monkeys in both groups are active during the day and usually live in bands held together by social behavior.

50 Primates The other group of anthropoids, the hominoids, consists of primates informally called the apes. This group includes gibbons, orangutans, gorillas, chimpanzees, and humans. Hominoids have relatively long arms, short legs, no tail, and a larger brain in proportion to their body size than other primates.

51 Humans “ Homo sapiens ” (wise or rational man) is the genus and species for humans. Humans are the only living members of the Homo genus. A number of characteristics distinguish humans from other hominoids. Humans have a much larger brain, and are capable of written language, symbolic thought, and they can manufacture and use complex tools. Humans also have reduced jawbones and jaw muscles and a shorter digestive tract. Humans are 99% genetically identical to chimpanzees, but that 1% translates into a large number of differences in a genetic sequence that contains 3 billion genes.

52 Humans The characteristics of humans have been reconsidered recently; a gorilla named Coco demonstrated knowledge and use of sign language. An African gray parrot named Alex has also demonstrated an understanding of spoken vocabulary, and not just mimicry. And many species of mammals make their own tools to obtain food, however they are not complex tools that humans make.

53 Other Orders of Eutherians (not on the exam) Proboscidea : elephants Sirenia : manatees Xenarthra: sloths, anteaters, armadillos Lagomorpha : rabbits Carnivora : dogs, wolves, bears, cats, weasels, otters, seals, walruses Artiodactyls : sheep, pigs, cattle, deer, giraffes Cetaceans : whales, dolphins, porpoises Rodentia : squirrels, beavers, rats, porcupines, mice Perissodactyla: horses, zebras, rhinoceroses

54 ANIMAL FORM AND FUNCTION Structure Fits Function in the Animal Body Anatomy is the study of an organism's structures; physiology is the study of the function of an organism's structures. The structure of an organism fits its adaptive function. For instance, a gecko’s anatomy includes tiny hairs on its feet that allow it to climb vertical walls; a physiologist would study the functioning of these hairs in order to understand how they work.

55 ANIMAL FORM AND FUNCTION Another example is the flight apparatus of birds. Feathers give the wing its broad shape without adding much weight to the body. They remain dry because they are lightly coated with oil, and they also trap air, which provides insulation that helps a bird to maintain its high body temperature and metabolism. The function of feathers results from their unique structure. Feathers consist entirely of nonliving material, mainly the protein keratin. A flight feather has a hollow shaft that provides a central support with minimum weight. Small flat rods called barbs extend from both sides of the shaft. Still finer rods called barbules extend from the sides of the barbs. Each barbule has tiny hooks that interlock with adjacent barbules. This gives a feather a particular shape and rigidity that support flight. When a bird preens, it draws its feathers through its beak, hooking the barbules back together like zipping up a zipper.

56 ANIMAL FORM AND FUNCTION The muscles and bones in a bird wing also show the relationship between structure and function. Muscles provide power, and the bones provide support for flight. The flight muscles are situated on the breast and around the base of the wings, keeping most of the weight off the wings and helping maintain the birds balance in flight.

57 ANIMAL FORM AND FUNCTION The bones in a bird wing are similar to those in a human arm, but the number of the bones is fewer. The bird wing only has three fingers, and only the middle one has a complete set of bones. This adaptation helps make the wing lighter but less flexible than a human hand. This reduced flexibility stabilizes the wing and helps it function as a unit in flight.

58 Animal Structure Has a Hierarchy Just as there is a progression from atoms to molecules to cells, the progression continues within an animal. Cells connect with other cells of similar function in and coordinate themselves, making up a tissue. For instance, cardiac muscle cells are branched and can communicate with each other. A tissue is a group of similar cells that perform a specific function, for instance, cardiac tissue. An organ is a group of tissues that work together to perform a specific task, for example, the heart.

59 Animal Structure Has a Hierarchy An organ system consists of multiple organs that together perform a vital bodily function, for instance, the circulatory system consists of the heart and blood vessels. An organism contains a number of organ systems, each specialized for certain functions and all functioning together as a coordinated unit. For example, the pelican’s circulatory system cannot function without the oxygen supplied by the respiratory system and nutrients supplied by the digestive system. And it takes the coordination of muscle and bone systems to enable the bird to fly.

60 ORGAN SYSTEMS Digestive System: ingests and breaks down food to be absorbed. Respiratory System : exchanges gases with the environment, supplies blood with oxygen Circulatory System : delivers oxygen into the body cells Immune System: Defends the body against infections Lymphatic System : filters and cleans the fluid that leaks out from blood vessels. Excretory System : removes waste products Endocrine System : secretes hormones that regulate body activities Nervous System : coordinates body activities Integumentary System : protects against injury, infection, temperature, and dryness Skeletal System : supports the body and protects internal organs Muscular System : produces movement of the body, maintains posture Reproductive System : produces gametes and sex hormones.


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