1.2a Each system is composed of organs and tissues which perform specific functions
and interact with each other, e.g., digestion, gas exchange, excretion, circulation, loco-
motion, control, coordination, reproduction, and protection from disease.
1.2b Tissues, organs, and organ systems help to provide all cells with nutrients, oxygen,
and waste removal.
1.2c The digestive system consists of organs that are responsible for the mechanical and
chemical breakdown of food. The breakdown process results in molecules that can be
absorbed and transported to cells.
1.2d During respiration, cells use oxygen to release the energy stored in food. The respi-
ratory system supplies oxygen and removes carbon dioxide (gas exchange).
1.2e The excretory system functions in the disposal of dissolved waste molecules, the
elimination of liquid and gaseous wastes, and the removal of excess heat energy.
1.2f The circulatory system moves substances to and from cells, where they are needed
or produced, responding to changing demands.
1.2g Locomotion, necessary to escape danger, obtain food and shelter, and reproduce, is
accomplished by the interaction of the skeletal and muscular systems, and coordinated
by the nervous system.
1.2h The nervous and endocrine systems interact to control and coordinate the bodys
responses to changes in the environment, and to regulate growth, development, and
reproduction. Hormones are chemicals produced by the endocrine system; hormones
regulate many body functions.
1.2i The male and female reproductive systems are responsible for producing sex cells
necessary for the production of offspring.
1.2j Disease breaks down the structures or functions of an organism. Some diseases are
the result of failures of the system. Other diseases are the result of damage by infection
from other organisms (germ theory). Specialized cells protect the body from infectious
disease. The chemicals they produce identify and destroy microbes that enter the body.