27 animal - savvas

27 Animal Systems I

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Red-billed oxpeckers are carnivores that have a mutualistic relationship with zebras. These birds eat ticks and insects that feed on the zebras, freeing them of these parasites.

(NEAR) DEATH BY SALT WATERIt started as an adventure. Some college buddies tried their own version of a “survivor” experience. During summer vacation, they were dropped off on an uninhabited tropical island, with minimal supplies. They would be picked up in a few days.

The island was hot and dry, and they discovered that there was no fresh water. They knew that coconuts could provide fluids in the form of coconut “milk.” But one group member hated coconuts. He figured he’d get his fluids by drinking salt water. At first, he was fine—although he was thirstier than his friends. Then, he became nauseated and weak. His condition worsened quickly. Soon he was seriously ill—with dizziness, headaches, and an inability to concentrate. His friends began to panic. What was happening? As you read the chapter, look for clues to help you explain the reason for the survivalist’s illness. Then, solve the mystery.

Never Stop Exploring Your World.Finding out what happened to the survivalist is only the beginning. Take a video field trip with the ecogeeks of Untamed Science to see where the mystery leads.

TEKS

FO

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Texas Essential Knowledge and Skills

READINESS TEKS: 10A Describe the interactions that occur among systems that perform the functions of regulation, nutrient absorption, reproduction, and defense from injury or illness in animals. 12A Interpret relationships, including predation, parasitism, commensalism, mutualism, and competition among organisms.

SUPPORTING TEKS: 9C Identify and investigate the role of enzymes. 12B Compare variations and adaptations of organisms in different ecosystems.

TEKS: 3D Evaluate the impact of research on scientific thought, society, and the environment. Also covered: TEKS 3B.

Animal Systems I 781

BUILD Vocabulary

27.1 Feeding and Digestion

Key Questions

How do animals obtain food?

How does digestion occur in animals?

How are mouthparts adapted for different diets?

Vocabularyintracellular digestion extracellular digestion gastrovascular cavity digestive tract rumen

Taking NotesOutline Before you read, use the headings in this lesson to outline the ways animals obtain and digest food. As you read, add details to your outline.

Obtaining Food How do animals obtain food?

There’s an old saying that “You are what you eat.” We can rephrase that as “How you look and act depends on what and how you eat.” In formal biological language, evolutionary adaptations for feeding on different foods in different ways have shaped the body structures and adaptations of animals, such as those in Figure 27–1.

Filter Feeders Filter feeders strain their food from water. Most filter feeders catch algae and small animals by using modified gills or other structures as nets that filter food items out of water. Many invertebrate filter feeders are small or colonial organisms, like worms and sponges, that spend their adult lives in a single spot. Some ver-tebrate filter feeders, such as blue whales, are huge, and feed while swimming.

Detritivores Detritus is made up of decaying bits of plant and animal material. Detritivores feed on detritus, often obtaining extra nutrients from the bacteria, algae, and other microorganisms that grow on and around it. Detritivores are essential members of many food webs.

Carnivores Carnivores eat other animals. Mammalian carni-vores, such as wolves, use teeth, claws, and speed or stealthy hunting tactics to capture prey. Many carnivorous invertebrates would be as menacing as tigers if they were larger. Some cnidarians paralyze prey with poison-tipped darts, while some spiders immobilize their victims with venomous fangs.

Herbivores Herbivores eat plants or parts of plants or algae. Leaves don’t have much nutritional content, are tough to digest, and can contain poisons or hard particles that wear down teeth. Other her-bivores specialize in eating seeds or fruits, which are often filled with energy-rich compounds.

WORD ORigiNs The word part -vore comes from the Latin verb vorare, which means “to devour.”

THiNK ABOUT iT From tiny insects that dine on our blood, to bison that feed on prairie grasses, to giant blue whales that feed on plankton, all animals are heterotrophs that obtain nutrients and energy from food. Feeding adaptations are a large part of what makes animals interesting.

In this lesson you will learn about the various feeding relationships among animals (TEKs 12A), as well as the interactions of various body systems during digestion and the absorption of nutrients (TEKs 10A). You will also learn about the role of enzymes in digestion (TEKs 9C).

TEKs 12A

Read with a partner the Key Questions. As you read the lesson together, work out some possible responses to each Key Question. Then, pair up with another group of two. Ask one another the Key Questions. Respond to the ques-tions, using your notes.

ELPS 4.G.3

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Carnivore – Orca Herbivore – Sea Slug

Filter Feeders – Barnacles Detritivore – Cleaner Shrimp

Nutritional Symbionts Recall that a symbiosis is the dependency of one species on another. Symbionts are the organisms involved in a symbio-sis. Many animals rely upon symbiosis for their nutritional needs.

Parasitic Symbionts Parasites live within or on a host organism, where they feed on tissues or on blood and other body fluids, disrupt-ing the health of their hosts. Some parasites are just nuisances, but many cause serious diseases in humans, livestock, and crop plants. Parasitic flatworms and roundworms afflict millions of people, par-ticularly in the tropics.

Mutualistic Symbionts Mutualistic nutritional relationships benefit both participants, and are often important in maintaining the health of organisms. Reef-building corals depend on symbiotic algae that live within their tissues for most of their energy. Those algae capture solar energy, recycle nutrients, and help corals lay down calcium carbonate skeletons. The algae, in turn, obtain nutrients from the corals’ wastes.

Many animals have close relationships with symbiotic microor-ganisms that live within their digestive tracts. Animals that eat wood or plant leaves rely on microbial symbionts to break down cellulose, which no animal can digest on its own. Recent research has shown that microorganisms living in human intestines play vital roles in maintaining health. These gut microorganisms help in digestion and nutrient absorption, manufacture some essential vitamins, and help protect the host from other potentially harmful microorganisms.

Figure 27–1 Obtaining Food The orca, sea slug, barnacles, and cleaner shrimp obtain their food in different ways.


Cnidarian

Mouth/Anus

Gastrovascularcavity

Sponge Water andwastes out

Incurrent PoreWater and food

particles in

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BA C D FE G H I

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ge o

f Eg

g W

hite

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este

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Time (hours)

Rate of Digestion

128 16 20

100

80

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40

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Processing Food How does digestion occur in animals?

Obtaining food is just the first step. Food must then be broken down, or digested, and absorbed to make energy and nutrients available to body tissues. Some invertebrates break down food primarily by intracellular digestion, but many animals use extracellular digestion to break down food. A variety of digestive systems are shown in Figure 27–2.

Intracellular Digestion Animals have evolved many ways of digest-ing and absorbing food. The simplest animals, such as sponges, digest food inside specialized cells that pass nutrients to other cells by diffu-sion. This digestive process is known as intracellular digestion.

Extracellular Digestion Most more-complex animals rely on extra-cellular digestion. Extracellular digestion is the process in which food is broken down outside cells in a digestive system and then absorbed.

Gastrovascular Cavities Some animals have an interior body space with tissues that carry out digestive and circulatory functions. Some invertebrates, such as cnidarians, have a gastrovascular cavity with a single opening through which they both ingest food and expel wastes. Some cells lining the cavity secrete enzymes and absorb diges ted food. Other cells surround food particles and digest them in vacuoles. Nutrients are then transported to cells throughout the body.

Digestive Tracts Many invertebrates and all vertebrates, such as birds, digest food in a tube called a digestive tract, which has two openings. Food moves in one direction, entering the body through the mouth. Wastes leave through the anus.

Protein DigestionA scientist performed an experiment to determine the amount of time needed for a certain carnivorous animal to digest animal protein. He placed pieces of hard-boiled egg white (an animal protein) in a test tube containing hydrochloric acid, water, and the enzyme pepsin, which digests protein. The graph shows the rate at which the egg white was “digested” over a 24-hour period. 1. Interpret Graphs Describe the trend in the amount of protein digested over time.

2. Analyze Data About how many hours did it take for half of the protein to be digested?

3. Draw Conclusions How would you expect the rate of meat digestion to differ in an animal whose digestive tract had less of the enzyme pepsin?

TEKS 9C, 10A

TEKS 2G, 9C

784 Chapter 27 • Lesson 1

Canines Canines are pointed teeth. Carnivores use them for piercing, gripping, and tearing. In herbivores, canines are reduced or absent.

Incisors Chisel-like incisors are used for cutting, gnawing, and grooming.

Carnivore

Molars and Premolars Broad, flattened molars and premolars are adapted for grinding tough plants, like two pieces of sandpaper wearing down wood.

Herbivore

Molars and Premolars The sharp edges of these teeth slice and dice meat into small pieces. These teeth have ridges that interlock during chewing like the blades of scissors.

Jaw joint

Jaw joint

Bird

MouthEsophagus

Crop

Stomach

GizzardIntestine

Anus

BA C D FE G H I

Figure 27–2 Digesting Food Animals have different digestive structures with different functions.

BA C D FE G H I The sponge (previous page) has one digestive opening and uses intracellular digestion to process its food. BA C D FE G The cnidarian (previous page) processes its food by extracellular digestion in a gastrovascular cavity. BA C D FE G The bird has a one-way digestive tract with two openings.

One-way digestive tracts often have specialized structures, such as a stomach and intestines, that perform different tasks as food passes through them. You can think of a digestive tract as a kind of “disassembly line” that breaks down food one step at a time. In some animals, the mouth secretes digestive enzymes that start the chemical digestion of food. Then, mechanical digestion may occur as specialized mouthparts or a muscular organ called a gizzard breaks food into small pieces. Then, chemical digestion begins or continues in a stomach that secretes digestive enzymes. Chemical breakdown continues in the intestines, sometimes aided by secretions from other organs such as a liver or pancreas. Intestines also absorb the nutrients released by digestion.

Solid Waste Disposal No matter how efficiently an animal breaks down food and extracts nutrients, some indigestible material will always be left. These solid wastes, or feces, are expelled either through the single digestive opening or through the anus.

Specializations for Different Diets

How are mouthparts adapted for different diets?The mouthparts and digestive systems of animals have evolved many adaptations to the physical and chemical characteristics of different foods, as shown in Figure 27–3. As a window into these specializations, we’ll examine adaptations to two food types that are very different physically and chemically: meat and plant leaves.

Specialized Mouthparts Carnivores and leaf-eating herbivores usually have very different mouthparts. These differences are typically related to the different physical characteristics of meat and plant leaves.

SPECIALIZED TEETHFigure 27–3 Mouthparts The specialized jaws and teeth of animals are well adapted to their diets.

TEKS 10A


1. a. Review What types of food do herbivores eat? What are nutritional symbionts?

b. Relate Cause and Effect How might a coral be affected if all its symbiotic algae died?

2. a. Review What are two types of digestion animals use to break down and absorb food?

b. Compare and Contrast What is a major structural difference between gastrovascular cavities and digestive tracts?

3. a. Review Describe the adaptations of the mouthparts and digestive systems of leaf-eaters and meat-eaters.

b. Interpret Describe the relation-ship between a ruminant and its microbial symbionts in terms of “teamwork.”

Summary4. Describe the process of a cow’s

digestion of grass, from the cow’s uprooting of the grass to its reswallowing of it. Use the terms molar, rumen, symbiont, and cud.

Eating Meat Carnivores typically have sharp mouth-parts or other structures that can capture food, hold it, and “slice and dice” it into small pieces. Carnivorous mammals, such as wolves, have sharp teeth that grab, tear, and slice food like knives and scissors would. The jaw bones and muscles of carni-vores are adapted for up-and-down movements that chop meat into small pieces.

Eating Plant Leaves Herbivores have mouthparts adapt-ed to rasping or grinding to tear plant cell walls and expose their contents. Many herbivorous invertebrates, from mollusks to insects, have mouthparts that grind and pulverize plant or algal tissues. Herbivorous mammals, such as the horse in Figure 27–4, have front teeth and muscular lips adapted to grabbing and pull-ing leaves, and flattened molars that grind leaves to a pulp. The jaw bones and muscles of mammalian herbivores are also adapted for side-to-side “grinding” movements.

Specialized Digestive Tracts Carnivorous invertebrates and vertebrates typically have short digestive tracts that produce fast acting, meat-digesting enzymes. These enzymes can digest most cell types found in animal tissues.

No animal produces digestive enzymes that can break down the cellulose in plant tissue, however. Some herbivores have very long intestines or specialized pouches in their digestive tracts that harbor microbial symbionts that help digest tough plant tissues and help maintain the health of their hosts. Animals called rumi-nants, such as cattle, have a pouchlike extension of their esopha-gus called a rumen (plural: rumina), in which symbiotic bacteria digest cellulose. Ruminants regurgitate food that has been partially digested in the rumen, chew it again, and reswallow it. This pro-cess is called “chewing the cud.”

figure 27–4 Eating Plant Leaves The teeth and jaws of herbivores, such as horses, are adapted for pulling, rasping, and grinding plant leaves.

27.1 Review Key Concepts TEKS 10A, 12A


Respiration

Key Questions

What characteristics do the respiratory structures of all animals share?

How do aquatic animals breathe?

What respiratory structures enable land animals to breathe?

Vocabularygill • lung • alveolus

Taking NotesConcept Map Draw a concept map showing the characteristics of the lung structures of vertebrates.

Gas Exchange What characteristics do the respiratory structures of all

animals share?Despite all the amazing things living cells can do, no cell can actively pump oxygen or carbon dioxide across membranes. Yet, in order to breathe, all animals must exchange oxygen and carbon dioxide with their surroundings. How do they do it? One way that animals have adapted to different environments is by evolving respiratory structures that promote the movement of these gases in the required directions by passive diffusion.

Gas Diffusion and Membranes Recall that substances diffuse from an area of higher concentration to an area of lower concentration. Gases diffuse most efficiently across a thin, moist membrane that is permeable to those gases. The larger the surface area of that mem-brane, the more diffusion can take place, just as a bumpy paper towel absorbs more liquid than a smooth one does. These physical principles create a set of requirements that respiratory systems must meet, one way or another.

Requirements for Respiration Because of the behavior of gases, all respiratory systems share certain basic characteris-tics. Respiratory structures provide a large surface area of moist, selectively permeable membrane. Respiratory struc-tures maintain a difference in the relative concentrations of oxygen and carbon dioxide on either side of the respiratory membrane, promoting diffusion.

Figure 27–5 Requirements for Respiration Respiratory surfaces are moist, so exhaled air contains a lot of moisture. That exhaled moisture condenses into visible “fog“ if outside air is cold.

THINK ABOUT IT Cellular respiration requires oxygen and pro-duces carbon dioxide as a waste product. So all animals must obtain oxygen from their environment and get rid of carbon dioxide. In other words, all animals need to “breathe.” Humans can drown because our lungs can’t extract oxygen from water. Most fishes have the opposite problem; out of water, their gills don’t work. How are these different respiratory systems adapted to their different environments?

27.2In this lesson you will learn about the processes of respiration and gas exchange in animals (TEKS 10A).

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Mouth A muscular pump pulls water in through the mouth and pushes it back across the gills.

Gill Filaments Water is pumped past thousands of threadlike gill filaments, which are rich with capillaries. Filaments absorb oxygen from water and release carbon dioxide.

Operculum Water carryingcarbon dioxide is pumpedout behind the operculum, or gill cover.

Breathing in Clams and Crayfishes2 1 3 4 65 7 8 9 Do not touch the clam or crayfish. Put a drop

of food coloring in the water near a clam’s siphons. Observe what happens to the coloring.

2 1 3 4 65 7 8 9 Put a drop of food coloring in the water near the middle of a crayfish. CAUTION: Keep your fingers away from the crayfish’s pincers. Observe what happens to the coloring.Analyze and Conclude1. Observe Describe what happened to the coloring in step 1. How does water move through a clam’s gills?

2. Infer What is the clam’s main defense? How is the location of the clam’s siphons related to this defense?

3. Compare and Contrast What happened in step 2? Compare the flow of water through the gills of clams and crayfishes.

4. Infer Unlike many other arthropods, crayfishes have gills. Why do crayfishes need gills?

Respiratory Surfaces of Aquatic Animals

How do aquatic animals breathe?Some aquatic invertebrates, such as cnidarians and some flatworms, are relatively small and have thin-walled bodies whose outer surfaces are always wet. These animals rely on diffusion of oxygen and carbon dioxide through their outer body covering. A few aquatic chordates, including lancelets, some amphibians, and even some sea snakes, rely to varying extents on gas exchange by diffusion across body surfaces.

For large, active animals, however, skin respiration alone is not enough. Many aquatic invertebrates and most aquatic chor-dates other than reptiles and mammals exchange gases through gills. As shown in Figure 27–6, gills are feathery structures that expose a large surface area of thin, selectively permeable membrane to water. Inside the gill membranes is a network of tiny, thin-walled blood vessels called capillaries. Many animals, including aquatic mol-lusks and fishes, actively pump water over their gills as blood flows through inside. This helps maintain differences in oxygen and carbon dioxide concentration that promote diffusion. Aquatic reptiles and aquatic mammals such as whales breathe with lungs and must hold their breath underwater. Lungs are organs that exchange oxy-gen and carbon dioxide between blood and air. You will learn more about lungs shortly.

Figure 27–6 Respiration With Gills Many aquatic animals, such as fishes, respire with gills, which are thin, selectively permeable membranes. As water passes over the gills, gas exchange is completed within the gill capillaries.

TEKS 10A


SpiderTracheal tubes

Insect

Spiders respire using organs called book lungs, which are made of parallel, sheetlike layers of thin tissues that contain blood vessels.

In most insects, a system of tracheal tubes extends throughout the body. Air enters and leaves the system through openings in the body surface called spiracles. In some insects, oxygen and carbon dioxide diffuse through the tracheal system, and in and out of body fluids. In other insects, body movements help pump air in and out of the tracheal system.

AirflowSpiracles

Book lung

BUILD VocabularyMUlTIplE MEANINGS The biological term respiration has different, though related, meanings. In animals, it can refer to gas exchange, the intake of oxygen and release of waste gases, or to cellular respiration, the cell process that releases energy by breaking down food molecules in the presence of oxygen. Because cellular respiration requires oxygen, the two processes are related.

Figure 27–7 Respiratory Structures of Terrestrial Invertebrates Terrestrial invertebrates have a wide variety of respiratory structures, including skin, mantle cavities, book lungs, and tracheal tubes. These structures must stay moist even in the driest of conditions in order to function properly.

Respiratory Surfaces of Terrestrial Animals

What respiratory structures enable land animals to breathe?Terrestrial animals must keep their respiratory membranes moist in dry environments. They must also carry oxygen and carbon dioxide back and forth between those surfaces and the rest of their bodies. Interactions among several body systems are essential for this process.

Respiratory Surfaces in land Invertebrates The many body plans found among terrestrial invertebrates include very different strategies for respiration. Respiratory structures in terrestrial invertebrates include skin, mantle cavities, book lungs, and tracheal tubes. Some land invertebrates, such as earthworms, live in moist environments and can respire across their skin if it stays moist. Other invertebrates, such as land snails, respire using a mantle cavity lined with moist tissue and blood vessels. Insects and spiders have more complex respira-tory systems, as you can see in Figure 27–7.

lung Structure in Vertebrates Terrestrial vertebrates display a wide range of breathing adaptations. But all terrestrial vertebrates—reptiles, birds, mammals, and the land stages of most amphibians—breathe with lungs. Although lung structure in these animals varies, the processes of inhaling and exhaling are similar. Inhaling brings oxygen-rich air through the trachea (tray kee uh), or airway, into the lungs. Inside the lungs, oxygen diffuses into the blood through lung capillaries. At the same time, carbon dioxide diffuses out of capillaries into the lungs. Oxygen-poor air is then exhaled.

Online Journal Would you expect dolphins to breathe with gills or lungs? Explain your answer.

TEKS 10A


Lung

Nostrils, mouth, and throatTrachea

Amphibian Reptile Mammal

1. a. Review In what ways are the respiratory structures of all animals similar?

b. Apply Concepts Explain why it is impor-tant that respiratory surfaces are moist and permeable.

2. a. Review Which groups of aquatic animals breathe with gills? With lungs?

b. Relate Cause and Effect Why do some ani-mals actively pump water over their gills?

3. a. Review How do terrestrial invertebrates and terrestrial vertebrates breathe?

b. Interpret Visuals Contrast the structures of amphibian, reptilian, and mammalian lungs, as shown in Figure 27–8.

Description4. Describe the events that occur when a

mammal respires, including the path of air through its lungs.

Figure 27–8 lungs Terrestrial vertebrates breathe with lungs. Lungs with a larger surface area can take in more oxygen and release more carbon dioxide. Mammals have the greatest lung surface area among animals. Infer Why do mammals require a large surface area with which to process oxygen?

Amphibian, Reptilian, and Mammalian Lungs The internal surface area of lungs increases from amphibians to reptiles to mam-mals, as shown in Figure 27–8. A typical amphibian lung is little more than a sac with ridges. Reptilian lungs are often divided into chambers that increase the surface area for gas exchange. Mammalian lungs branch extensively, and air passages branch and re-branch, ending in bubblelike structures called alveoli (al vee uh ly; singular: alveolus). Alveoli provide an enormous surface area for gas exchange. Alveoli are surrounded by a network of capillaries in which blood picks up oxygen and releases carbon dioxide. Mammalian lung structure helps take in the large amounts of oxygen required by high metabolic rates. When mammals and most other vertebrates breathe, air moves in and out through the same air passages, and some stale, oxygen-poor air remains. In humans, this stale air is typically equivalent to about one third of the air inhaled in a normal breath.

Bird Lungs In birds, the lungs are structured so that air flows mostly in only one direction. No stale air gets trapped in the system. A unique system of tubes and air sacs in birds’ respiratory systems enables this one-way airflow. Thus, gas exchange surfaces are continuously in con-tact with fresh air. This highly efficient gas exchange helps birds obtain the oxygen they need to power their flight muscles at high altitudes for long periods of time.

27.2 Review Key Concepts


Sinusesand organs

Heart

Hearts

Blood vessels

Insect: OpenCirculatory System

Circulation

Key Questions How do open and closed

circulatory systems compare?

How do the patterns of circulation in vertebrates compare?

Vocabularyheart open circulatory system closed circulatory system atrium ventricle

Taking NotesCycle Diagram As you read, draw a cycle diagram showing a five-step sequence in which blood pumps through a closed, two-loop circulatory system.

Figure 27–9 Open Circulatory System In an open circulatory system, blood is not entirely contained within blood vessels. Grasshoppers, for example, have open circulatory systems in which blood leaves vessels and moves through sinuses before returning to a heart.

Open and Closed Circulatory Systems

How do open and closed circulatory systems compare?Many animals move blood through their bodies using one or more hearts. A heart is a hollow, muscular organ that pumps blood around the body. A heart can be part of either an open or a closed circulatory system.

Open Circulatory Systems Arthropods and most mollusks have open circulatory systems, such as the one in Figure 27–9.

In an open circulatory system, blood is only partially contained within a system of blood vessels as it travels through the body. One or more hearts or heartlike organs pump blood through vessels that empty into a system of sinuses, or spongy cavities. There, blood comes into direct contact with body tis-sues. Blood then collects in another set of sinuses and eventually makes its way back to the heart.

ThiNK AbOuT iT When you eat food, your digestive tract breaks it down. But how do energy and nutrients from food get to your cells? How does oxygen from your lungs get to other tissues? How do carbon dioxide and wastes get eliminated? Some aquatic animals with bodies only a few cells thick rely solely on diffusion to transport materials. But in most animals, oxygen, carbon dioxide, nutrients, and wastes are transported through a circulatory system that inter-acts with other body systems.

27.3In this lesson you will learn about the process of circulation in animals.

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Heartlike structure

Small vesselsin tissues

Blood vessels

Heartlikestructures

Annelid: ClosedCirculatory System

BUILD Vocabulary

Lung capillariesGill capillaries

1 ventricle

1 atrium

2 ventricles

2 atria

Body capillaries

Heart

Heart

Body capillaries

Closed Circulatory Systems Many larger, more active invertebrates, including annelids and some mollusks, and all vertebrates, have closed circulatory systems, such as the one shown in Figure 27–10.

In a closed circulatory system, blood circulates entirely within blood vessels that extend throughout the body. A heart or heartlike organ forces blood through these vessels. Nutrients and oxygen reach body tissues by diffusing across thin walls of capillaries, the smallest blood vessels. Blood that is completely contained within blood ves-sels can be pumped under higher pressure, and thus can be circulated more efficiently, than can blood in an open system.

Single- and Double-Loop Circulation

How do the patterns of circulation in vertebrates compare?As chordates evolved, they developed more-complex organ systems and more-efficient channels for internal transport. You can see two main types of circulatory systems of vertebrates in Figure 27–11.

Single-Loop Circulation Most vertebrates with gills have a single-loop circulatory system with a single pump that forces blood around the body in one direction. In fishes, for example, the heart consists of two chambers: an atrium and a ventricle. The atrium (plural: atria) receives blood from the body. The ventricle then pumps blood out of the heart and to the gills. Oxygen-rich blood then travels from the gills to the rest of the body and returns, oxygen-poor, to the atrium.

Double-Loop Circulation As terrestrial vertebrates evolved into larger and more active forms, their capillary networks became larger. Using a single pump to force blood through the entire system would have been increasingly difficult. This issue was avoided as the lineage of vertebrates that led to reptiles, birds, and mammals evolved. Most verte-brates that use lungs for respiration have a double-loop, two-pump circulatory system.

MuLtipLe MeaningS The word atrium has different but parallel meanings in everyday usage and in biology. In everyday usage, it means a large entrance hall. In biology, it means a heart chamber through which blood from the body enters the heart.

Figure 27–10 Closed Circulatory System Annelids, such as earthworms, and many more-complex animals have closed circulatory systems. Blood stays within the vessels of a closed circulatory system.

Figure 27–11 Single- and Double-Loop Circulation Most vertebrates that use gills for respiration have a single-loop circulatory system that forces blood around the body in one direction (left). Vertebrates that use lungs have a double-loop system (right). (Note that in diagrams of animals’ circulatory systems, blood vessels carrying oxygen-rich blood are red, while blood vessels carrying oxygen-poor blood are blue.)


The first loop, powered by one side of the heart, forces oxygen-poor blood from the heart to the lungs. After the blood picks up oxygen (and drops off carbon dioxide) in the lungs, it returns to the heart. Then, the other side of the heart pumps this oxygen-rich blood through the second circulatory loop to the rest of the body. Oxygen-poor blood from the body returns to the heart, and the cycle begins again.

Mammalian Heart-Chamber Evolution Four-chambered hearts like those in modern mammals are actually two separate pumps work-ing next to one another. But where did the second pump come from? During chordate evolution, partitions evolved that divided the origi-nal two chambers into four. Those partitions transformed one pump into two parallel pumps. The partitions also separated oxygen-rich blood from oxygen-poor blood. We can get an idea of how the parti-tions evolved by looking at other modern vertebrates.

Amphibian hearts usually have three chambers: two atria and one ventricle. The left atrium receives oxygen-rich blood from the lungs. The right atrium receives oxygen-poor blood from the body. Both atria empty into the ventricle. Some mixing of oxygen-rich and oxygen-poor blood in the ventricle occurs. However, the internal structure of the ventricle directs blood flow so that most oxygen-poor blood goes to the lungs, and most oxygen-rich blood goes to the rest of the body.

Reptilian hearts typically have three chambers. However, most reptiles have a partial partition in their ventricle. Because of this partition, there is even less mixing of oxygen-rich and oxygen-poor blood than there is in amphibian hearts.

1. a. Review Describe an open circulatory system. Describe a closed circulatory system.

b. Explain Which groups of animals tend to have each type of circulatory system?

c. Relate Cause and Effect How does having a closed circulatory system benefit a large, active animal?

2. a. Review What are two different patterns of circulation found in vertebrates?

b. Compare and Contrast What is the major structural dif-ference between vertebrates that have single-loop circulatory systems and those that have double-loop systems?

3. Infer Do you think large, active vertebrates could have evolved with open circulatory systems? Explain your reasoning.

Figure 27–12 Reptilian Heart Under the armor-like hide of this crocodile lies a heart with two atria and one ventricle.

27.3 Review Key Concepts


27.4 Excretion

Key Questions

How do animals eliminate toxic nitrogenous waste?

What adaptations enable organisms in aquatic ecosystems to eliminate wastes?

What adaptations enable animals in terrestrial ecosystems to eliminate wastes while con-serving water?

Vocabularyexcretion • kidney • nephridium • Malpighian tubule

Taking NotesPreview Visuals Note three questions you have about Figure 27–15. As you read, try to answer your questions.

The Ammonia Problem How do animals eliminate toxic nitrogenous waste?

When cells break down proteins, they produce a nitrogen-containing, or nitrogenous, waste: ammonia. This is a problem, because ammo-nia is poisonous! Even moderate concentrations of ammonia can kill most cells. Animal systems address this difficulty in one of two ways.

Animals either eliminate ammonia from the body quickly or convert it into other nitrogenous compounds that are less toxic. The elimination of metabolic wastes, such as ammonia, is called excretion. Some small animals that live in wet environments rid their bodies of ammonia by allowing it to diffuse out of their body fluids across their skin. Most larger animals, and even some smaller ones that live in dry environments, have excretory systems that process ammonia and eliminate it from the body.

Storing Nitrogenous Wastes Animals that cannot dispose of ammonia as it is produced have evolved ways to hold, or “store,” nitrogenous wastes until they can be eliminated. In most cases, ammonia is too toxic to be stored in body fluids. Insects, reptiles, and birds typi-cally solve this problem by converting ammonia into a sticky white compound called uric acid, which you can see in Figure 27–14. Uric acid is much less toxic than ammonia and is also less soluble in water. Mammals and some amphibians, on the other hand, convert ammonia to a different nitrogenous compound—urea. Like uric acid, urea is less toxic than ammonia, but unlike uric acid, urea is highly soluble in water.

figure 27–13 Ammonia Some aquatic animals, such as this zebra flatworm, release ammonia as soon as they produce it.

THINK ABOUT IT The first three lessons in this chapter discussed respiratory and digestive systems that exchange gases, absorb nutrients and get rid of indigestible waste. But cellular metabolism generates other kinds of wastes that are released into body fluids and that must be elimi-nated from the body. What are these wastes and how do animals get rid of them? The answers involve interactions between the digestive, respiratory, and circulatory systems, and an excretory system that eliminates wastes.

In this lesson you will learn how various animals get rid of wastes and how the excretory system interacts with other body systems (TEKS 10A). In addition, you will learn about the various adaptations that have developed for the process of excretion in different environments (TEKS 12B).

TEKS 10A

794

Figure 27–14 Other Nitrogenous Compounds Many animals, like these seagulls, convert ammonia to uric acid and excrete it as sticky white guano.

Maintaining Water Balance Getting rid of any type of nitrogenous waste involves water. For that reason, excretory systems interact with other systems involved in regulating water balance in blood and body tissues. In some cases, excretory systems eliminate excess water along with nitrogenous wastes. In other cases, excretory systems must elimi-nate nitrogenous wastes while conserving water.

Many animals use kidneys to separate wastes and excess water from blood in a fluid called urine. Kidneys must perform this func-tion despite a serious limitation: No living cell can actively pump water across a membrane. You may recall that cells can pump ions across their membranes. Kidney cells pump ions from dissolved salts in blood in ways that create an osmotic gradient. Water then “follows” those ions passively by osmosis. This process can get rid of nitrog-enous wastes and retain water, but leaves kidneys with one weakness: They usually cannot excrete excess salt.

Online Journal Explain how kidneys remove excess water from the blood.

Excretion in Aquatic Animals What adaptations enable organisms in aquatic ecosystems to

eliminate wastes? Aquatic animals have an advantage in getting rid of nitrogenous wastes because they are surrounded by water. In general, aquatic animals can allow ammonia to diffuse out of their bodies into surrounding water, which dilutes the ammonia and carries it away. But aquatic animals still face excretory challenges. Many have adaptations that either eliminate water from their bodies or conserve it, depending on whether they live in fresh or salt water ecosystems, as summarized in Figure 27–15 on the next page.

TEKS 12B


The bodies of freshwater animals, such as �shes, contain a higher concentra-tion of salt than the water they live in.

So water moves into their bodies by osmosis, mostly across the gills. Salt di�uses out. If they didn’t excrete water, they’d look like water balloons with eyes!

So they excrete water through kidneys that produce lots of watery urine. They don't drink, and they actively pump salt in across their gills.

The bodies of saltwater animals, such as �shes, contain a lower concentration of salt than the water they live in.

So they lose water through osmosis, and salt di�uses in. If they didn’t conserve water and eliminate salt, they’d shrivel up like dead leaves.

So they conserve water by producing very little concentrated urine. They drink, and they actively pump salt out across their gills.

Fres

h W

ater

Salt

Wat

er

Salt

Urine

Urine

Water

Water

Water

Water

More waterLess salt

Less waterMore salt

More saltLess water

More waterLess salt

Do

drink

Salt

Don’t drink

Salt

Salt

EXCRETION IN AQUATIC ANIMALSFigure 27–15 All animals must rid their bodies of ammonia while maintaining appropriate water balance. Freshwater and saltwater animals face very different challenges in this respect. Interpret Visuals What are two ways freshwater fishes avoid looking like “water balloons with eyes”?

Freshwater Animals Many freshwater invertebrates lose ammonia to their environment by simple diffusion across their skin. Many freshwa-ter fishes and amphibians eliminate ammonia by diffusion across the same gill membranes they use for respiration.

But invertebrates and fishes that live in freshwater must excrete wastes while managing an osmotic challenge. The concentration of water surrounding their bodies is higher than the concentration of water in their body fluids. So water moves passively into their bodies by osmosis, and salt leaves by diffusion. To help maintain water balance, flatworms have adaptations involving specialized cells called flame cells that remove excess water from body fluids. That water travels through excretory tubules and leaves through pores in the skin. Adaptations in amphibians and freshwater fishes typically involve excreting excess water in very dilute urine, and pumping salt actively inward across their gills.

Saltwater Animals Marine invertebrates and vertebrates typically release ammonia by diffusion across their body surfaces or gill mem-branes. Many marine invertebrates have body fluids with water concen-trations similar to that of the seawater around them. For that reason, these animals have less of a problem with water balance than do fresh-water invertebrates. Marine fishes, however, tend to lose water to their surroundings because their bodies are less salty than the water they live in. These animals actively excrete salt across their gills. Their kidneys also produce small quantities of very concentrated urine—an adapta-tion that conserves water.


Excretorypore

BladderUrethra

Nephrostome

Kidneys

MalpighiantubulesArthropod

VertebrateAnnelid

Nephridia

figure 27–16 Excretion in Terrestrial Animals Some terrestrial invertebrates, such as annelids, rid their bodies of ammonia by releasing urine created in their nephridia (left). Some insects and arachnids have Malpighian tubules, which absorb uric acid from body fluids and combine it with digestive wastes (above). In vertebrates, such as humans, excretion is carried out mostly by the kidneys (right).

Excretion in Terrestrial Animals What adaptations enable animals in terrestrial ecosystems to

eliminate wastes while conserving water?Land animals also face challenges. In dry environments, they can lose large amounts of water from respiratory membranes that must be kept moist. In addition, they must eliminate nitrogenous wastes in ways that require disposing of water—even though they may not be able to drink water. Figure 27–16 shows the excretory systems of some terrestrial animals.

Terrestrial Invertebrates Some terrestrial invertebrates, including annelids and mollusks, produce urine in nephridia. Nephridia (singular: nephridium) are tubelike excretory structures that filter body fluid. Typically, body fluid enters the nephridia through openings called nephrostomes and becomes more concentrated as it moves along the tubes. Urine leaves the body through excretory pores.

Other terrestrial invertebrates, such as insects and arachnids, convert ammonia into uric acid. Nitrogenous wastes, such as uric acid, are absorbed from body fluids by structures called Malpighian tubules. These wastes are added to digestive wastes traveling through the gut. As water is absorbed from these wastes, they crystallize and form a thick paste, which leaves the body through the anus. This paste contains little water, so these adaptations minimize water loss.

Terrestrial Vertebrates In terrestrial vertebrates, excretion is car-ried out mostly by the kidneys. Mammals and land amphibians convert ammonia into urea, which is excreted in urine. In most reptiles and birds, ammonia is converted into uric acid. Reptiles and birds pass uric acid through ducts into a cavity that also receives diges-tive wastes from the gut. The walls of this cavity absorb most of the water from the wastes, causing the uric acid to separate out as white crystals. The result is a thick, milky-white paste that you would recog-nize as “bird droppings.”

Water and Nitrogen Excretion

2 1 3 4 65 7 8 9 Label one test tube Urea and the other Uric Acid. Place 2 grams of urea in the one labeled Urea. Place 2 grams of uric acid in the one labeled Uric Acid. 2 1 3 4 65 7 8 9 Add 15 mL of water to each

test tube. Stopper and shake the test tubes for 3 minutes.

2 1 3 4 65 7 8 9 Observe each test tube. Record your observations.Analyze and Conclude1. Observe Which substance—urea or uric acid—is less soluble in water? Explain.2. Infer Reptiles excrete nitrogenous wastes in the form of uric acid. How does this adaptation help reptiles survive on land?

TEKS 12B

TEKS 12B


1. a. Review Why does the metabolic waste ammonia pose a problem for all animals?

b. Explain How do insects, reptiles, and birds eliminate ammonia? How do mammals and some amphibians eliminate it?

c. Apply Concepts How do kidneys help main-tain homeostasis while processing nitrogenous wastes?

2. a. Review In general, how do aquatic animals address the ammonia problem?

b. Compare and Contrast How do the differing water balance needs of freshwater animals and saltwater animals explain the difference in their excretion of nitrogenous wastes?

4. The Greek word ouron, meaning “urine,” has led to the root uro-, of urea and uric (acid). Why is it appropriate that these two words are each formed from a root word meaning “urine”?

3. a. Review In what form do (a) annelids and mollusks, (b) insects and arachnids, (c) mam-mals and land amphibians, and (d) reptiles and birds excrete nitrogenous wastes?

b. Relate Cause and Effect Explain how differing water balance needs relate to an animal’s conver-sion of ammonia to either urea or uric acid.

Adaptations to Extreme Environments The kidneys of most ter-restrial vertebrates are remarkable organs, but the way they operate results in some limitations. Most vertebrate kidneys, for example, cannot excrete concentrated salt. That’s why most vertebrates cannot survive by drinking seawater. All that extra salt would overwhelm the kidneys, and the animal would die of dehydration. Some marine rep-tiles and birds, such as the petrel in Figure 27–17, have evolved adap-tations in the form of specialized glands in their heads that excrete very concentrated salt solutions. Another excretory adaptation is found in the kangaroo rats of the American southwest. The kidneys of these desert rodents produce urine that is 25 times more concentrated than their blood! In addition, their intestines are so good at absorbing water that their feces are almost dry.

Figure 27–17 Excretion Adaptations Some terrestrial animals that must drink salt water, such as this petrel, have evolved special adaptations to excrete excess salt. Specialized salt glands produce a concentrated salt solution, which can sometimes been seen dripping out of their elongated nostrils.

27.4 Review Key Concepts TEKS 4B, 12B


Testing for Heart DiseaseEver-improving imaging techniques make it pos-sible for doctors to diagnose heart disease and disorders quickly and without the risk of invasive procedures. None of these tests involves inserting instruments into the body, but they reveal the inner workings of the heart with remarkable accuracy.

Computed Tomography AngiographyA patient is injected with an iodine-based dye. Then the CT scanner rotates over the patient and takes multiple X-rays of the heart, which a computer uses to form three-dimensional images. The test can show if parts of blood vessels are blocked or damaged. The results can be used to determine what further tests are needed or as a guide for planning surgery.

EchocardiographyHigh-frequency sound waves, transmitted through the chest, are fed into a computer, which analyzes the “echoes” to produce moving images of the heart. This is an especially safe test because it doesn’t involve radiation or dyes. The test allows doctors to see the heart in action. It can reveal an enlarged heart, reduced pump-ing action, and structural problems.

Find two published journal articles about one of the techniques mentioned. In a couple of paragraphs, communicate your findings.

Magnetic Resonance Imaging (MRI)MRI uses powerful magnets to produce images that are particularly good for examining muscle and other soft tissue. Professionals analyzing MRI images can see the difference between healthy tissue and unhealthy tissue. MRI does not involve radiation or iodine-based dyes. It can be used to assess heart muscle damage caused by a heart attack, birth defects, or ab-normal growths.

TEKS 3B, 3D

Technology and Biology 799

(Near) Death by Salt waterLuckily, the pick-up the group arranged arrived earlier than planned. They rushed the sick man to a hospital, where he was diagnosed with severe dehydration and given water and intravenous fluids. If he had gone much longer without treatment, doctors told his friends, he would have died. What had happened? Why didn’t his friends suffer the same problems? As sailors have known for centuries, humans can’t drink seawater for any length of time. But why can’t we drink seawater? Because seawater is saltier than human blood and body fluids, drinking it loads the body with excess salt. Human kidneys cannot produce urine with salt concentrations high enough to get rid of that salt efficiently. So the kidneys are forced to excrete more water in urine than the amount of salt water consumed. Cells and tissues begin to dehydrate, and fatal kidney failure can result.

1. explain Why did the castaway who drank salt water become dehydrated quicker than his fellow “survivors?”

2. Infer Human blood needs to circulate through very small capillaries. What might happen if the water content of a person’s blood were to drop too low?

3. explain Using terms such as osmosis and diffu-sion, explain why your cells and tissues would dehydrate quickly if you were flooding your body with salt water by drinking it.

4. Propose a Solution If you were marooned on an island that had no fresh water, what would be your plan for getting some?

5. Compare and Contrast While the group mem-ber who drank seawater became seriously ill, the other group members experienced some water stress as well. In general, what was going on in their circulatory and excretory systems, and why was it not as serious?

6. Investigate Although humans can’t safely drink salt water and can’t exist without fresh water, many marine birds and reptiles can do either or both. Using the Web, research the different strate-gies other animals use to regulate salt content and water balance.

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800 Chapter 27 • Solve the Chapter Mystery

27 TEKS PracticeReview Content 1. Animals that obtain food by ingesting decaying

bits of plant and animal material are called a. herbivores. c. detritivores. b. carnivores. d. filter feeders.

2. Algae that live in the bodies of reef-building corals are

a. parasitic symbionts. b. mutualistic symbionts. c. occupants that have no effect on the coral animals. d. consumed as food by the coral animals.

3. In order for the exchange of oxygen and carbon dioxide to take place, an animal’s respiratory surfaces must be kept

a. cold. c. hot. b. dry. d. moist.

4. In a closed circulatory system, blood a. comes in direct contact with tissues. b. remains within blood vessels. c. empties into sinuses. d. does not transport oxygen.

5. Most chordates that have gills for respiration have a(n)

a. double-loop circulatory system. b. accessory lung. c. single-loop circulatory system. d. four-chambered heart.

6. The composition and levels of body fluids in mammals are controlled by the

a. lungs. c. intestine. b. kidneys. d. heart.

7. The elimination of metabolic wastes from the body is called

a. excretion. c. respiration. b. circulation. d. digestion.

Understand Concepts 8. Compare the processes of intracellular and extra-

cellular digestion. 9. Describe the differences between the canine

and molar teeth of herbivorous and carnivorous mammals.

10. How do vertebrate filter feeders obtain food? 11. With what respiratory structures do aquatic

reptiles and aquatic mammals breathe? What inconvenience does this cause when they are underwater?

12. Describe the circulatory system of a mammal as open or closed, and state the number of loops and the number of heart chambers.

13. Compare single-loop circulation and double-loop circulation.

14. Why do most animals convert ammonia into urea or uric acid?

15. What is the difference in kidney function of fresh-water fishes and saltwater fishes?

Think Critically 16. Classify You are observing an animal that has a

digestive tract. Does this animal practice intracel-lular digestion or extracellular digestion? Explain your answer.

17. Pose Questions Hummingbirds eat high-energy foods, such as nectar. Many ducks eat insects and other small animals. What are some research questions you could investigate to discover more about the diet of a bird species and its energy needs?

18. Describe Describe the interactions that occur among systems that perform the function of nu-trient absorption in animals.

19. Predict During heavy rains, earthworms often emerge from their burrows. What might happen to an earthworm if it does not return to its burrow when the rain stops and the air becomes dry?

20. Infer Land snails have a respiratory structure called a mantle cavity, which is covered with mu-cus. What might the purpose of the mucus be?

21. Apply Concepts How do the interactions be-tween a fish’s respiratory and circulatory systems work together to maintain homeostasis in the body as a whole?

22. Describe In what way do the digestive and respi-ratory systems depend on the circulatory system to carry out the functions of obtaining nutrients?

TEKS 10A, 10C, 11A, 12B

801

23. Relate How do the lungs work together with the circulatory system? Relate the levels of organiza-tion in biological systems to each other.

24. Infer The excretory systems of terrestrial inverte-brates, such as earthworms, convert ammonia to less toxic substances. Explain why this change is unnecessary in small aquatic invertebrates, such as planarians.

25. Apply Concepts Of all the nitrogenous wastes eliminated by animals, uric acid requires the least water to excrete. Why is the production of uric acid an advantage to animals that live on land?

Use Science GraphicsA student conducts an experiment to measure the effect of caffeine on the heart rate of a small pond- water crustacean called Daphnia. The heart of this ani-mal is visible through its transparent shell. With the help of a dissecting microscope, the student counts the heartbeats per minute before and after adding increas-ing amounts of coffee to the water surrounding the animal. Each data point in the graph at the top right represents the average of five trials. Use the graph to answer questions 26 and 27.

Daphnia Heart Rate and Caffeine

Hea

rt R

ate

(bea

ts p

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inut

e)

10 5Drops of Coffee Added

Daphnia Heart Rate and Caffeine

32 4

190

180

170

160

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1200

26. Interpret Graphs Describe the effect of caffeine on the heart rate of Daphnia.

27. Predict What would be your prediction of the effect of five or more drops of coffee on the heart rate of Daphnia?

Biology Chapter 27

Lesson 1In Lesson 27.1, you learned about the different ways that animals obtain nutrients. Once an animal obtains food, that food must be digested by either intracellular digestion or extracellular digestion. Animals have mouthparts and digestive systems that are adapted to the foods that they eat.

Lesson 2In Lesson 27.2, you learned about the process of respiration in animals. All animals, regardless of how they get oxygen, must have respiratory structures with a large surface area. Respiratory structures must be kept moist and must have membranes that permit the diffusion of oxygen and carbon dioxide.

Lesson 3Lesson 27.3 discusses the circulatory system. The circulatory system transports nutrients from the digestive system and oxygen from the respiratory system to body cells. Animals have either an open circulatory system or a closed circulatory system. In an open circulatory system, the blood is only partially contained within blood vessels. In a closed circulatory system, the blood is entirely contained within blood vessels.

Lesson 4In Lesson 27.4, you learned about the excretory system. Animals must eliminate ammonia from the body quickly in order to maintain homeostasis. Aquatic animals allow ammonia to diffuse out of their bodies into the surrounding water. Terrestrial animals have various adaptations to release ammonia.

TEKS Practice TEKS

REVI

EW THE

Readiness TEKS: 10A, 12A Supporting TEKS: 9C

Readiness TEKS: 10A Supporting TEKS: 12B

Readiness TEKS: 10A

802 Chapter 27 • TEKS Practice

★TEKS Practice: Chapter Review

1 Most animals have a circulatory system that moves blood around the body. Circulatory systems can be categorized as open circulatory systems or closed circulatory systems. How are these two categories of circulatory systems similar?

A Both can be double-loop or single-loop.

B Both have blood contained in blood vessels.

C Both deliver nutrients and oxygen by diffusion through capillary walls.

D None of the above

2 In animals, the excretory system rids the body of wastes produced by body tissues. The graphic organizer below lists information about how the excretory system functions to maintain homeostasis in a salt water animal.

Aquatic Animal

Salt actively transported through gills

Concentrated urine is excreted to conserve water

Ammonia diffuses through skin

What is a limitation of this graphic organizer?

F It can be used to learn about water balance but not salt balance.

G It can be used to learn about salt balance but not water balance.

H It can be used to learn about saltwater animals but not freshwater animals.

J It can be used to learn about freshwater animals but not saltwater animals.


3 The figure shows the skulls of two different mammals.

Incisors

Canines

Molars and premolars

Mammal 1 Mammal 2

Which observation provides the best evidence to support the explanation that Mammal 1 and Mammal 2 do not compete with one another for food?

A Mammals 1 and 2 have canines that differ in shape.

B Mammals 1 and 2 both have canines, incisors, molars, and premolars.

C Mammals 1 and 2 have incisors that are in the same location within the mouth.

D Mammals 1 and 2 have similar numbers of molars and premolars.

4 Animals do not produce enzymes that can digest cellulose, which is found in leaves and wood. Some animals, such as termites and cows, can obtain nutrients from cellulose due to the enzymes produced by other organisms that live in their digestive systems. The organisms in the cow and termite digestive systems also benefit from the relationship. What is the best classification for these relationships.

F Competition

G Parasitism

H Mutualism

J Predation

804 Chapter 27 • TEKS Practice

★TEKS Practice: Cumulative Review

5 In Arctic food chains, elephant seals are prey of killer whales. Which body systems would most directly enable an elephant seal to notice and swim away from a killer whale?

A Muscular, skeletal, and nervous systems

B Circulatory and excretory systems

C Digestive and nervous systems

D Skeletal and reproductive systems

6 The figure shows relationships among different organisms.

According to the figure, what is true about modern birds?

F Modern birds descended from Archaeopteryx.

G Modern birds share a common ancestor with T. rex.

H Modern birds share most characteristics with dinosaurs.

J All of the above

If You Have Trouble With . . . Question 1 2 3 4 5 6

See Lesson 27.3 27.4 27.1 27.1 25.1 26.2

TEKS 10A 10A, 3E 12A, 3A 12A 10A 7B

Tyrannosaurs(T. rex)CompsognathidsAllosaurs

Oviraptor (Gigantoraptor) Archaeopteryx

Modernbirds


27 animal - savvas

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