must be able to maintain the proper balances necessary
for life in a somewhat hostile world. Every organism must be able
to coordinate its life processes, acquire food and oxygen, circulate
that food and oxygen, eliminate waste, and reproduce. As organisms
have evolved from single-celled to multicellular, they have developed
increasingly sophisticated organ systems to accomplish these crucial
tasks. Each organ system, such as the nervous system or circulatory
system, is made up of a number of organs that work
in concert to carry out one or a number of vital body processes.
Each organ, in turn, is made up a number of tissues.
A tissue is a conglomeration of specialized cells that all perform
a common function necessary to an organ’s larger efforts. During
the billions of years that life has existed on Earth, different
organisms have developed various systems of meeting the needs of
their bodies. Oak trees and alligators, for instance, have very
different ways of getting food and nutrients and circulating those
nutrients within their bodies.
The SAT II Biology Test focuses its many questions about
organismal biology on the structure and function of humans and plants.
This chapter on organismal biology is therefore split into two parts.
The first deals with the structure and function of animals, the
second with plants.