Animal Body Systems Section 27.2

Important Functions: Digestion Sponges digest their food inside their cells  the food cannot be larger than the cell All other animals digest food outside their cells – extracellular digestion  food can be larger Simple animals have a digestive system with one opening – gastrovascular cavity Complex animals have a digestive tract with 2 openings – mouth and anus “Tube within a tube” plan – allows for specialization

Important Functions, con’t: Respiration In simple animals, O 2 & CO 2 are exchanged by diffusion across moist skin Aquatic animals use gills – rich in blood vessels, provide a large surface area, must be moist to work Lungs function on land – do not require as much moisture

Important Functions, con’t: Circulation Larger animals must have some way of transporting O 2 and nutrients Two types of circulatory systems:  Open circulatory system – heart pumps blood through the open spaces of the body cavity; not very efficient  Closed circulatory system – heart pumps blood through blood vessels; blood is not in direct contact with cells – materials diffuse through vessel walls

Important Functions, con’t: Conduction of nerve impulses Needed to coordinate activities All animals except sponges have nerves Simple animals have a nerve net – all cells are similar and there is little coordination Bilaterally symmetrical animals have clusters of nerves – ganglia In simple animals, ganglia at the anterior end form brain- like structures Cephalized animals – with heads – have complex brains and sensory organs

Important Functions, con’t: Support Skeleton provides support and a way for the animal to move Three types of skeletons: 1. Hydrostatic – water under pressure inside the body cavity; found in soft-bodied invertebrates 2. Exoskeleton – a rigid external skeleton; found in some invertebrates 3. Endoskeleton – hard material, such as cartilage or bone, inside the animal

Important Functions, con’t: Excretion The removal of wastes made by cells These wastes are toxic – poisonous Aquatic animals can dilute wastes with water Land animals need to save water, so they may produce urea, which is less toxic Kidneys then filter urea from the blood and produce urine

Important Functions, con’t: Reproduction Asexual reproduction – only 1 cell Parthenogenesis – new individual from an unfertilized egg; some insects & fish Sexual reproduction – 2 cells that join Hermaphrodites – one animal produces both sex cells; usually does not self-fertilize; can mate with any other External fertilization – the egg is fertilized outside the female; must be laid in water to keep moist Internal fertilization – egg is fertilized inside the female & then may given a shell & laid on land or develop inside the mother