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, O2 & CO2 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 O2 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 invertebrates2. Exoskeleton – a rigid external skeleton; found

in some invertebrates3. 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