Living things have different levels of
organization. The simplest level of
organization is that of the cell. A group
of cells with a similar function is called a tissue.
Groups of tissues working together to perform a common
function are called organs. An example of this
would include the nervous, muscle, and other tissues which
make up the heart. Groups of organs working
together to perform a common function are referred to as a system
or organ system. The blood vessels, blood,
and the heart are organs which work together to form the
circulatory system. Many different systems
function together to allow a complex organism to function.
the components of the living things, from the cells and the
organelles within them to the organ systems of complex
organisms must interact to maintain a balanced internal
environment within the organism. Organisms possess
many control mechanisms to detect internal and external
changes and make changes to correct any
deviations. This maintenance of a stable
internal environment by an organism is called homeostasis.
Homeostasis in an organism is constantly threatened.
Failure to respond effectively can result in disease or death.