Chapter 32Introduction to Animals

Section 1The nature of

animals

Characteristics

• Animals lack cell walls• Vertebrates- have a backbone• Invertebrates- do not have a

backbone• 95% of all animals are invertebrates

Multicellular Organization• Adult humans have 50-100 trillion cells• Specialization- evolutionary adaptation

of a cell for a particular function–Digesting food, removing wastes, or

reproducing• Cells tissues organs organ

systems organism

Heterotrophy• Animals cannot make their own food • Ingestion- animal takes in organic

material

• Animals cannot make their own food • Ingestion- animal takes in organic

material

Sexual Reproduction & Development

• Asexual and sexual reproduction• Zygote- diploid cell that results from the

fusion of the gametes, then undergoes mitotic divisions• Differentiation- cells become specialized

and become different from each other

Movement • Most animals move in some way

throughout their environment• Nervous and muscle tissue are

responsible for allowing animals to move• Neurons conduct electrical signals that

initiate a response.

Origin & Classification• Animals are theorized to have come

from the sea• Unicellular multicellular specialized

functions• Phylogenetic diagram shows how

animals are related through evolution• Separated by phylum

Invertebrates• Do not have a backbone• Make up the greatest number of

animal species

Chordates• Chordate- refers to animals with a

notochord- a firm flexible rod of tissue located in the dorsal part of the body

Chordates• During development, all chordates

have a notochord, a dorsal nerve cord, pharygeal pouches, and a postanal tail• Pharygeal pouches- small outpockets

of digestion tract• Dorsal nerve cord- hollow tube above

notochord

Chordates• In vertebrates, the dorsal nerve cord

becomes the brain & spinal cord, and the notochord is replaced by the backbone• In aquatic vertebrates, the pharyngeal

pouches have evolved into gills

Body Structure• Some animals lack

true tissues and body symmetry, while others have organized tissues and consistent body shape

Patterns of Symmetry• Body plans- describe animal’s shape,

symmetry, & internal organization• Symmetry- body arrangement in

which parts that lie on opposite sides of an axis are identical• Radial symmetry- body plan

organized in a circle around axis

Radial Symmetry

Patterns of Symmetry• Dorsal- back• Ventral- abdomen side (front)• Anterior- toward the head• Posterior- toward the tail• Bilateral symmetry- two similar

halves on either side

Patterns of Symmetry• Bilaterally symmetrical animals tend

to exhibit cephalization- concentration of sensory and brain structures in the anterior end of an animal

Germ Layers• Germ layers- tissue layers in the embryos

of all animals except sponges, which have no true tissues• Organs and tissues arise from germ layers• Ctenophores & cnidarians have two germ

layers, and all other animals have three

Body Cavities• Most animals have a fluid-filled cavity

between their digestive tract and outer wall of the body during development.• Roundworms have a fluid-filled body

cavity that helps them move

Body Cavities

REVIEW!!!• Explain how the first animals may

have evolved from unicellular organisms.• Identify four features only found in

chordates.• What are the two types of tissue for

allowing animals to move?