Chapter 32 Introduction to Animals Section 1 The 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?