1. Characteristics of Animals Section 27.1

2. Features of Animals: # 1: Heterotrophy & Mobility Animals cannot make their own food Most animals move to find food Food is digested internally Animals have the ability to make rapid, complex movements

3. Features of Animals, con’t: # 2: Multicellularity & Tissues All animals are made of many specialized cells Animals are the only multicellular group without cell walls All cells are roughly the same size, regardless of the size of the animal Similar cells are organized into functional groups called tissues

4. Features of Animals, con’t: # 3: Diploidy & Sexual Reproduction Adults cells are diploid – have 2 copies of each chromosome, 1 from each parent Haploid gametes (sex cells with 1 set of chromosomes) unite to form offspring The zygote (fertilized egg) is diploid This allows for genetic diversity

5. Features of Animals, con’t: # 4: Blastula Formation The zygote divides to form a hollow ball – the blastula Cells in the blastula develop three layers which then develop into different structures: Ectoderm: skin, nervous system Endoderm: digestive & respiratory systems Mesoderm: skeleton, muscular, circulatory, reproductive & excretory systems

6. Animal Body Plans: # 1: Symmetry Asymmetrical – irregular in shape (sponges) Radial symmetry – like the spokes of a wheel (sea anemone) Bilateral symmetry – two equal sides (humans) right & left sides dorsal (back) & ventral (belly) anterior (head) & posterior (tail)  cephalization

7. Animal Body Plans, con’t: # 2: Internal Body Cavity Found in bilaterally symmetrical animals Coelom – the body cavity – fluid-filled space between body wall & gut; protects the internal organs Three plans: Acoelomate – no coelom Pseudocoelomate – body cavity between the mesoderm and endoderm – “false coelom” Coelomate – cavity within mesoderm; allows for greater movement

8. Animal Body Plans, con’t: # 3: Segmentation Segments are repeating body units All higher animals have some degree of segmentation (vertebrae)

9. Kinds of Animals 35 phyla Often divided into 2 major groups: Invertebrates (without backbones) Vertebrates (with backbones)