Table of Contents – pages iv-v

Unit 1: What is Biology?Unit 2: EcologyUnit 3: The Life of a CellUnit 4: GeneticsUnit 5: Change Through TimeUnit 6: Viruses, Bacteria, Protists, and FungiUnit 7: PlantsUnit 8: InvertebratesUnit 9: VertebratesUnit 10: The Human Body

Unit 1: What is Biology?

Chapter 1: Biology: The Study of LifeUnit 2: Ecology Chapter 2: Principles of Ecology Chapter 3: Communities and Biomes Chapter 4: Population Biology Chapter 5: Biological Diversity and ConservationUnit 3: The Life of a Cell Chapter 6: The Chemistry of Life Chapter 7: A View of the Cell Chapter 8: Cellular Transport and the Cell Cycle Chapter 9: Energy in a Cell

Unit 4: Genetics

Chapter 10: Mendel and Meiosis

Chapter 11: DNA and Genes

Chapter 12: Patterns of Heredity and Human Genetics

Chapter 13: Genetic Technology

Unit 5: Change Through Time Chapter 14: The History of Life Chapter 15: The Theory of Evolution Chapter 16: Primate Evolution Chapter 17: Organizing Life’s Diversity

Unit 6: Viruses, Bacteria, Protists, and Fungi

Chapter 18: Viruses and Bacteria

Chapter 19: Protists

Chapter 20: Fungi

Unit 7: Plants

Chapter 21: What Is a Plant?

Chapter 22: The Diversity of Plants

Chapter 23: Plant Structure and Function

Chapter 24: Reproduction in Plants

Unit 8: Invertebrates

Chapter 25: What Is an Animal?

Chapter 26: Sponges, Cnidarians, Flatworms, and

Roundworms

Chapter 27: Mollusks and Segmented Worms

Chapter 28: Arthropods

Chapter 29: Echinoderms and Invertebrate

Chordates

Unit 9: Vertebrates Chapter 30: Fishes and Amphibians

Chapter 31: Reptiles and Birds

Chapter 32: Mammals

Chapter 33: Animal Behavior

Unit 10: The Human Body

Chapter 34: Protection, Support, and Locomotion

Chapter 35: The Digestive and Endocrine Systems

Chapter 36: The Nervous System

Chapter 37: Respiration, Circulation, and Excretion

Chapter 38: Reproduction and Development

Chapter 39: Immunity from Disease

Invertebrates

What is an animal?

Sponges, Cnidarians, Flatworms and Roundworms

Mollusks and Segmented Worms

Arthropods

Echinoderms and Invertebrate Chordates

Chapter 25 What is an animal?

25.1: Typical Animal Characteristics

25.1: Section Check

25.2: Body Plans and Adaptations

25.2: Section Check

Chapter 25 Summary

Chapter 25 Assessment

What You’ll Learn

You will identify animal characteristics and distinguish them from those of other life forms.

You will identify cell differentiation in the developmental stages of animals.

You will identify and interpret body plans of animals.

• Identify the characteristics of animals.

Section Objectives:

• Identify cell differentiation in the development of a typical animal.

• Sequence the development of a typical animal.

• Animals are eukaryotic, multicellular organisms with ways of moving that help them reproduce, obtain food, and protect themselves.

Characteristics of AnimalsCharacteristics of Animals

• Most animals have specialized cells that form tissues and organs—such as nerves and muscles.

Characteristics of AnimalsCharacteristics of Animals

• Animals are composed of cells that do not have cell walls.

• One characteristic common to all animals is that they are heterotrophic, meaning they must consume food to obtain energy and nutrients.

Animals obtain foodAnimals obtain food

• All animals depend either directly or indirectly on autotrophs for food.

• Scientists hypothesize that animals first evolved in water.


• In water, some animals, such as barnacles and oysters, do not move from place to place and have adaptations that allow them to capture food from their water environment.


• Organisms that are permanently attached to a surface are called sessile.

• Most adults are sessile and attach themselves to rocks or other objects.


• Some aquatic animals, such as corals and sponges move about only during the early stages of their lives.

• Land animals use more oxygen and expend more energy to find food.


• There is little suspended food in the air.

• Some of the food that an animal consumes and digests is stored as fat or glycogen, a polysaccharide, and used when other food is not available.

Animals digest foodAnimals digest food

• In some animals, digestion is carried out within individual cells; in other animals, digestion takes place in an internal cavity.

Animals digest foodAnimals digest food• In animals such as planarians and earthworms,

food is digested in a digestive tract.

Mouth

Anus

Digestive tract

Digestive tract

Extended pharynx

• Animals have specialized cells that enable them to sense and seek out food and mates, and allow them to identify and protect themselves from predators.

Animal cell adaptationsAnimal cell adaptations

• Most animal cells are differentiated and carry out different functions.

• After fertilization, the zygote of different animal species all have similar, genetically determined stages of development.

Development of AnimalsDevelopment of Animals

• Most animals develop from a fertilized egg cell called a zygote.

• Male animals produce sperm cells and female animals produce egg cells.

FertilizationFertilization• Most animals reproduce sexually.

• The mesoderm cells develop into the muscles, circulatory system, excretory system, and, in some animals, the respiratory system.

Formation of mesodermFormation of mesoderm

• When the opening in the gastrula develops into the mouth, the animal is called a protostome.

• Snails, earthworms, and insects are examples of protostomes.


• In other animals, such as sea stars, fishes, toads, snakes, birds, and humans, the mouth does not develop from the gastrula’s opening.


• An animal whose mouth developed not from the opening, but from cells elsewhere on the gastrula is called a deuterostome.


• Scientists hypothesize that protostome animals were the first to appear in evolutionary history, and that deuterostomes followed at a later time.

• Determining whether an animal is a protostome or deuterostome can help biologists identify its group.


Cell differentiation in Animal DevelopmentCell differentiation in Animal Development

• The fertilized eggs of most animals follow a similar pattern of development. From one fertilized egg cell, many divisions occur until a fluid-filled ball of cells forms.

• The ball folds inward and continues to develop.

Fertilization

First cell division

Additional cell divisions

Cell Differentiation in Animal Development

Cell Differentiation in Animal Development

Formation of a blastula

Gastrulation

Formation of mesoderm

Sperm cells

Egg cell

Endoderm

Mesoderm

Ectoderm

Growth and developmentGrowth and development

• Most animal embryos continue to develop over time, becoming juveniles that look like smaller versions of the adult animal.

• In some animals, such as insects and echinoderms, the embryo develops inside an egg into an intermediate stage called a larva (plural larvae).



• A larva often bears little resemblance to the adult animal.

• Inside the egg, the larva is surrounded by a membrane formed right after fertilization.

• When the egg hatches, the larva breaks through this fertilization membrane.

Adult animalsAdult animals

• Once the juvenile or larval stage has passed, most animals continue to grow and develop into adults.

• This growth and development may take just a few days in some insects, or up to fourteen years in some mammals.

• Eventually the adult animals reach sexual maturity, mate, and the cycle begins again.

Question 1

Which of the following is NOT a characteristic of animals?

D. prokaryotic

C. heterotrophic

B. multicellular

A. eukaryotic

The answer is D.

Sessile animals _______.

D. live only on land

C. are permanently attached to a surface

B. are autotrophs

A. live only underground

Question 2

The answer is C. Sessile animals are permanently attached to a surface.

Ingestion is another word for _______.

D. eating

C. breathing

B. physically responding to a light stimulus

A. digestion

Question 3

The answer is D, eating.

Question 4

Which of the following is NOT true of animal fertilization?

B. forms a haploid zygote

A. occurs when a sperm cell penetrates an egg cell

Question 4

Which of the following is NOT true of animal fertilization?

D. may be internal or external

C. forms a diploid zygote

The answer is B, forms a haploid zygote.

Question 5

When a zygote divides by mitosis and cell division to form two cells, the process is called _______.

D. gastrulation

C. ingestion

B. fertilization

A. cleavage

The answer is A, cleavage.

Cleavage

• Compare and contrast radial and bilateral symmetry with asymmetry.

Section Objectives:

• Trace the phylogeny of animal body plans.

• Distinguish among the body plans of acoelomate, pseudocoelomate, and coelomate animals.

What is symmetryWhat is symmetry

• Symmetry is a term that describes the arrangement of body structures.

• Different kinds of symmetry enable animals to move about in different ways.

AsymmetryAsymmetry

• Animals with no symmetry often are sessile organisms that do not move from place to place.

• Most adult sponges do not move about.

• An animal that is irregular in shape has no symmetry or an asymmetrical body plan.

AsymmetryAsymmetry

• The bodies of most sponges consist of two layers of cells.

• Unlike all other animals, a sponge’s embryonic development does not include the formation of an endoderm and mesoderm, or a gastrula stage.

Radial symmetryRadial symmetry

• Animals with radial symmetry can be divided along any plane, through a central axis, into roughly equal halves.


• Radial symmetry is an adaptation that enables an animal to detect and capture prey coming toward it from any direction.


• The body plan of a hydra can be compared to a sack within a sack.

• These sacks are cell layers organized into tissues with distinct functions.


Inner cell layer

• A hydra develops from just two embryonic cell layers—ectoderm and endoderm.

Outer cell layer

Bilateral symmetryBilateral symmetry

• An organism with bilateral symmetry can be divided down its length into similar right and left halves.


• In bilateral animals, the anterior, or head end, often has sensory organs.

• The posterior of these animals is the tail end.

• Bilaterally symmetrical animals can be divided in half only along one plane.


• The dorsal, or upper surface, also looks different from the ventral, or lower surface.

• Animals with bilateral symmetry can find food and mates and avoid predators because they have sensory organs and good muscular control.

Bilateral Symmetry and Body PlansBilateral Symmetry and Body Plans

• All bilaterally symmetrical animals developed from three embryonic cell layers—ectoderm, endoderm, and mesoderm.

• Some bilaterally symmetrical animals also have fluid-filled spaces inside their bodies called body cavities in which internal organs are found.

• Animals that develop from three cell layers—ectoderm, endoderm, and mesoderm—but have no body cavities are called acoelomate animals.

• They have a digestive tract that extends throughout the body.

AcoelomatesAcoelomates

AcoelomatesAcoelomates• Flatworms are

bilaterally symmetrical animals with solid, compact bodies. Like other acoelomate animals, the organs of flatworms are embedded in the solid tissues of their bodies.

Acoelomate Flatworm

Ectoderm

Mesoderm

Endoderm

Body cavityDigestive tract

• A flattened body and branched digestive tract allow for the diffusion of nutrients, water, and oxygen to supply all body cells and to eliminate wastes.

Acoelomate Flatworm

Ectoderm

Mesoderm

Endoderm


AcoelomatesAcoelomates

PseudocoelomatesPseudocoelomates

• A roundworm is an animal with bilateral symmetry.

• The body of a roundworm has a space that develops between the endoderm and mesoderm.

Ectoderm

Mesoderm

Endoderm


Pseudocoelomate Roundworm

• It is called a pseudocoelom—a fluid-filled body cavity partly lined with mesoderm.

Ectoderm

Mesoderm

Endoderm



Pseudocoelom


• Pseudocoelomates can move quickly.

• Although the roundworm has no bones, it does have a rigid, fluid-filled space, the pseudocoelom.

• Its muscles attach to the mesoderm and brace against the pseudocoelom.


PseudocoelomatesPseudocoelomates• Pseudocoelomates have a one-way digestive

tract that has regions with specific functions.

• The mouth takes in food, the breakdown and absorption of food occurs in the middle section, and the anus expels waste.

MouthIntestine

Round body shape

Anus

CoelomatesCoelomates

• The body cavity of an earthworm develops from a coelom, a fluid-filled space that is completely surrounded by mesoderm.

• The greatest diversity of animals is found among the coelomates.

Ectoderm

Mesoderm

Endoderm

Body cavity

Digestive tract

Coelomate Segmented Worm

Coelom

• In coelomate animals, the digestive tract and other internal organs are attached by double layers of mesoderm and are suspended within the coelom.

• The coelom cushions and protects the internal organs. It provides room for them to grow and move independently within an animal’s body.

CoelomatesCoelomates

• Over time, the development of body cavities resulted in a greater diversity of animal species.

• Some animals, such as mollusks, evolved hard shells that protected their soft bodies.

• Other animals, such as sponges, evolved hardened spicules between their cells that provided support.

Animal Protection and SupportAnimal Protection and Support

• Some animals developed exoskeletons. An exoskeleton is a hard covering on the outside of the body that provides a framework for support.


• Exoskeletons also protect soft body tissues, prevent water loss, and provide protection from predators.


• As an animal grows, it secretes a new exoskeleton and sheds the old one.

• Exoskeletons are often found in invertebrates. An invertebrate is an animal that does not have a backbone.


• Invertebrates, such as sea urchins and sea stars, have an internal skeleton called an endoskeleton. It is covered by layers of cells and provides support for an animal’s body.


• The endoskeleton protects internal organs and provides an internal brace for muscles to pull against.


Animal Protection and SupportAnimal Protection and Support• An endoskeleton may be made of calcium

carbonate, as in sea stars; cartilage, as in sharks; or bone.

Calcium carbonate cartilage

• Bony fishes, amphibians, reptiles, birds, and mammals all have endoskeletons made of bone.

bone


• A vertebrate is an animal with an endoskeleton and a backbone. All vertebrates are bilaterally symmetrical.


Origin of AnimalsOrigin of Animals

• Most biologists agree that animals probably evolved from aquatic, colonial protists.

• Scientists trace this evolution back in time to late in the Precambrian.

Origin of

Animals

Origin of

Animals

Origin of AnimalsOrigin of Animals

• Many scientists agree that all the major animal body plans that exist today were already in existence at the beginning of the Cambrian Period, 543 million years ago.

• All known species have variations of the animal body plans developed during the Cambrian Period.

A sea star exhibits _______.

Question 1

D. bilateral – posterior

C. bilateral – anterior

B. asymmetry

A. radial symmetry

The answer is A, radial symmetry.

Which of the following animals does NOT exhibit radial symmetry?

Question 2

D. sea urchin

C. octopus

B. starfish

A. jellyfish

The answer is C. An octopus exhibits bilateral symmetry.

As you look at the cross sections of animals in the following figure, give the reason why animals with the basic cross section in the middle and on the far right will tend to be larger than animals with the far-left cross section.

Question 3

Question 3

Ectoderm Mesoderm Endoderm Body cavity Digestive tract

Acoelomate Flatworm


Coelomate Segmented Worm

PseudocoelomCoelom

The development of fluid-filled body cavities made it possible for animals to grow larger because it allowed for the efficient circulation and transport of fluids, and support for organs and organ systems.

Which of the following pairs of terms is not related?

Question 4

D. coral – larvae

C. flatworm – coelom

B. mollusk – shell

A. sponge – spicule

The answer is C.

Which of the following is NOT a vertebrate feature?

Question 5

D. pseudocoelom

C. bilaterally symmetrical

B. backbone

A. endoskeleton

The answer is D.

• Animals are multicellular eukaryotes whose cells lack cell walls. Their cells are specialized to perform different functions.

Typical Animal Characteristics

• All animals are heterotrophs that obtain and digest food.

• At some point during its life an animal can move from place to place. Most animals retain this ability.

• Embryonic development of a fertilized egg cell by cell division and differentiation is similar among animal phyla. The sequence of developmental stages is:

1. formation of a blastula—a cell-covered, fluid-filled ball;


2. gastrulation—the inward movement of cells to form two cell layers, the endoderm and ectoderm;

3. formation of the mesoderm—the development of a cell layer between the endoderm and ectoderm.


• Animal adaptations include asymmetry, radial symmetry, or bilateral symmetry.

Body Plans and Adaptations

• Flatworms and other acoelomates have flattened, solid bodies with no body cavities.

• Animals such as roundworms have a pseudocoelom, a body cavity that develops between the endoderm and mesoderm.

• A coelom is a fluid-filled body cavity that supports internal organs. Coelomate animals have internal organs suspended in a body cavity that is completely surrounded by mesoderm.

Body Plans and Adaptations

• Exoskeletons provide a framework of support on the outside of the body. Endoskeletons provide internal support.

Question 1

What is the difference between a blastula and a gastrula?

GastrulaA blastula is a cell-covered, fluid-filled ball. When the cells on one side of the blastula move inward, they form a gastrula, which is a structure made up of two layers of cells with an opening at one end.

Question 2

The layer of cells on the outer surface of the gastrula is called the _______.

D. blastula

C. mesoderm

B. ectoderm

A. endoderm

The answer is B, ectoderm.

Endoderm

Ectoderm

Mesoderm

Which of these organs develops from the endoderm?

D. circulatory system

C. muscles

B. skin

A. digestive system

The answer is A.

Question 3

Question 4

Which of the following is NOT a deuterostome?

D. honey bee

C. frog

B. dolphin

A. shark

The answer is D.

List the following stages in the order of their occurrence.

D. blastula formation

C. fertilization

B. gastrulation

A. embryo formation

Question 5

D. blastula formation

C. fertilization

B. gastrulation

A. embryo formation

The answer is c,a,d,b.

Question 6

Why can an octopus squeeze through spaces much smaller than the width of its body?

An octopus has no endoskeleton or exoskeleton to maintain a rigid shape for the animal. Therefore, it can modify its shape as necessity demands.

Question 7

Which of the following animals does NOT have an exoskeleton?

D. tarantula

C. turtle

B. ant

A. horseshoe crab

The answer is C. A turtle is a vertebrate animal with an internal skeleton.

Question 8

Why are sessile animals more likely to live in water than on land?

Answer

There is little suspended food in the air for these animals to eat.

Question 9

Why are sessile animals more likely to live in vigorously moving water than in still water?

Vigorously moving water is much more likely to bring food particles past sessile animals where they can capture it than water that is standing still. Also, moving water has more oxygen suspended in it than still water.

Question 10

Describe the way somatic cell nuclear transfer produces stem cells.

AnswerThe nucleus is removed from a normal animal egg cell. A somatic cell is placed next to the egg cell without a nucleus and the two cells are made to fuse. The new cell undergoes many cell divisions and forms a blastocyst from which stem cells are taken.

Photo CreditsPhoto Credits

• Digital Stock

• NOAA

• PhotoDisc

• USDA- ARS

• Alton Biggs

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Table of Contents – pages iv-v