7.1a A population consists of all individuals of a species that are found together at a
given place and time. Populations living in one place form a community. The commu-
nity and the physical factors with which it interacts compose an ecosystem.
7.1b Given adequate resources and no disease or predators, populations (including
humans) increase. Lack of resources, habitat destruction, and other factors such as pre-
dation and climate limit the growth of certain populations in the ecosystem.
7.1c In all environments, organisms interact with one another in many ways.
Relationships among organisms may be competitive, harmful, or beneficial. Some
species have adapted to be dependent upon each other with the result that neither could
survive without the other.
7.1d Some microorganisms are essential to the survival of other living things.
7.1e The environment may contain dangerous levels of substances (pollutants) that are
harmful to organisms. Therefore, the good health of environments and individuals
requires the monitoring of soil, air, and water, and taking steps to keep them safe.