Chapter 27Introduction to Animals

I. Characteristics of AnimalsA. Heterotrophy•Unable to make food• Food is eaten and then digested in a cavity

inside the animal’s body

B. Mobility• Move by means of muscle cells• Animals can swim, crawl, walk, run, and fly

C. Multicellularity• The size of most of the cells that make up animals

are roughly the same size• The number of cells or each animal are drastically

different

D. Diploidy• With few exceptions, adult animals are diploid,

meaning their body cells have two copies of each chromosome• Only gametes are haploid• Permits an animal to exchange genes between

the two copies of a set of chromosomes, creating new combinations of genes

E. Sexual ReproductionF. Absence of a Cell Wall• Allows animals mobility• Allows cells to move around in your body

G. Blastula Formation• A blastula is a hallow ball of cells that arises

from the zygote

• Develop into three primary tissue layers – ectoderm, endoderm, and mesoderm

- Give rise to all of the tissues and organs of the adult body

H. Tissues• Groups of cells with a common structure that

work together to perform a specific functionExamples

1. The cells of muscle tissue are specialized to contract, producing movement

2. The cells of nerve tissue are specialized to conduct signals

I. Body Symmetry• Each animal has its own body plan that

describes an animal’s shape, symmetry, and internal organization• Plan results from information carried by

animal’s genes which have been the result of natural selection

1. Asymmetrical• Sponges show a symmetrical body plan, they

have irregular shapes that are often dependent on where they are growing

2. Radial Symmetry• Body parts arranged

around a central axis• A plane that passes

through the central axis divides the organism into roughly equal halves• Today’s radially

symmetrical animals are aquatic• Move slowly or drift in

ocean currents

3. Bilateral Symmetry• A body design in which there are distinct right

and left halves• A plane that passes through the animal’s

midline divides the animals into mirror image halves

• Four distinct body surfaces1.Dorsal - top2.Ventral – bottom3.Anterior – front4.Posterior - back

• Enabled different parts of the body to become specialized in different ways•Most bilateral animals have also developed an

anterior concentration of sensory structures and nerves in a process called cephalization

J. Internal Body Cavity• A coelom is a fluid-filled space found between

the body wall and the digestive tract• Animals with no body cavity are called

acoelomates

• Other animals, called pseudocoelomates, have a body cavity located between the mesoderm and endoderm

• Coelomates have a true coelom, a body cavity located entirely within the mesoderm- Provides an internal space

where mesoderm and endoderm can be in contact with each other during embryonic development

- Aided in the evolution of complex organs made of more than one type of tissue

K. Body Segmentation• Segmented animals are composed of a series

of repeating, similar units called segments• In vertebrates, segments are not visible

externally• Segments are not totally independent of each

otheri.e. a circulatory system connects all segments,

nerves also connect each segment to a brain

II. Kinds of Animals• 35 major divisions

called phyla that show an extraordinary range of body forms, internal body systems, and behaviors• Organized into a

phylogenetic tree that shows how animals are related through evolution

• Clues to animal relationships can be found in the fossil record and by comparing the anatomy and physiology of living animals• The most direct evidence of evolutionary

relationships comes from comparing the DNA in the genes of various animal species

III. Tissues and Organs• Specialized to perform specific functionsA. Digestion• Sponges digest their food within their body

cells so their food cannot be larger than their individual cells

• Other organisms digest their food within a digestive cavity that contains digestive enzymes- Allows them to prey on organisms larger than

their body cells

• Simple animals have a gastrovascular cavity, a digestive cavity with only one opening• Other animals have a digestive tract (gut) with

two openings- Allows for specialization

B. Respiration• Simple animals exchange oxygen and carbon

dioxide with the environment by diffusion

• Diffusion does not supply complex animals with sufficient oxygen• Aquatic animals use gills to respire

• Gills are not suitable for most terrestrial animals because they do not function unless they are kept moist

C. Circulation• A circulatory system delivers oxygen and

nutrients throughout the body

• In an open circulatory system, a heart pumps fluid containing oxygen and nutrients through a series of vessels out into the body cavity- Fluid washes across body’s tissues- Fluid collects in open spaces and flows back

to the heart

• In a closed circulatory system, a heart pumps blood through a system of blood vessels- Blood remains in the

vessels and does not come in contact with the body’s tissues

- Materials pass into and out of the blood by diffusion through the walls of the blood vessels

D. Conduction of Nerve Impulses• Neurons are specialized for carrying messages in

the form of electrical impulses (conduction)• These cells coordinate the activities in an animal’s

body allowing it to respond to its environment

• In simple animals, nerves cells are similar and are linked to one another in a web• Bilaterally symmetric animals have clusters of

neurons called ganglia• Complex animals have brains with sensory

structures, such as eyes, that allow them to interact with their environment in more-complex ways

E. Support• An animal’s skeleton

gives support and allows movement1. Hydrostatic skeleton•Most soft-bodied

invertebrates have a hydrostatic skeleton that consists of water that is contained under pressure in a closed cavity

2. Exoskeleton• Other invertebrates have an exoskeleton, a

rigid external skeleton that encases the body of an animal

3. Endoskeleton• Composed of a hard material, such as bone,

embedded within an animal

F. Excretion• The removal of wastes produced by cellular

metabolism• A toxic waste product produced is ammonia• Ammonia dissolves in body fluids and

becomes less toxic

• It is inefficient to get rid of all the fluid with dissolved ammonia so mammal’s have kidneys that convert ammonia to a less toxic urea and filter it from fluid, allowing the animal to maintain its water balance while getting rid of waste

IV. Reproductive StrategiesA. Asexual Reproduction• Reproduction that does not involve the

fusion of two gametes

B. Sexual Reproduction• A new individual is formed by the union of a

male and a female gamete• Gametes are produced in the sex organs• Hermaphrodites have male and female

organs, however their gametes are produced at different times so self-fertilization does not occur