WHAT IS AN ANIMAL? CH. 26 WHAT ARE ANIMALS? • Animals are multicellular Eukaryotes, heterotrophic organisms with cells that lack cell walls. INVERTEBRATES VS. VERTEBRATES • Invertebrate: no vertebrate; without a backbone • Vertebrate: having a backbone/spinal column ANIMAL BODY SYSTEMS SUPPORT • An animal’s skeleton supports the animal’s body and helps with movement. • Hydrostatic (water - standing)- body cavity that is filled with water & helps with support • Exoskeleton (outside – skeleton): hard, external supporting structure. • Endoskeleton (inside – skeleton): internal skeleton made of bone & cartilage WHAT SKELETON DO I HAVE? BODY SYSTEMS • Digestive & Excretory Systems: • Digestive system – extracts (takes) energy and nutrients from the food • Excretory system – removes waste products from the body • Gastrovascular (Stomach – vascular) cavity: cavity for digestive & circulatory purpose in cnidarians NERVOUS SYSTEMS • Nervous system – carries information about the environment through the body & coordinates responses & behaviors. • Nerve net – simplest arrangement of nerves • Ganglia – cluster of nerve cells that coordinate responses • ADVANCED: true brain with sensory structures BODY CAVITIES • Bilateral symmetry – 3 basic kinds of internal body plans • Coelom – fluid-filled space found between the body wall and the gut • Acoelomate (no body cavity) • Pseudocoelom (false coelom) • Coelomate (True coelom) – lined with mesoderm and wraps around the gut CIRCULATORY SYSTEM • Transports gases, nutrients, and other substances within the body. • Open circulatory system: fluid leaves the blood vessels; washes the tissues • Closed circulatory system: blood remains inside the blood vessels; small vessels in body tissues REPRODUCTION • Asexual reproduction: (no-sex) • Sexual reproduction: male gametes (sperm) & female gametes (eggs) BODY SYMMETRY • How can an animal’s body be divided into similar pieces? • Asymmetrical (a=no; symmetry=regularity of form) • Radial symmetry – body parts arranged around a central axis • Bilateral symmetry: mirror-image halves • Cephalization – concentration of nerve tissue & sensory organs at the anterior end of an organism SO WHAT IS AN ANIMAL?