Characteristics of Life
There are a few aspects of living things that
are common to all living things. These characteristics of living
things include: Are made up of one or more cells, can reproduce,
grow and develop, obtain and use energy, and respond to their
environments. Knowing these characteristics and being able to
identify them in an organism can determine whether or not something
Living things are made up of small self-contained
units called cells. Each cell is a collection of living matter
enclosed by a barrier that separates the cell from its surroundings.
Most cells can perform all the functions we associate with life.
Organisms consisting of only a single cell are called unicellular.
Most of the organisms you are familiar with, however, are multicellular,
meaning they are made up of many cells.
Living things can reproduce, or produce new organisms
of the same type. There are two basic types of reproduction;
sexual reproduction and asexual reproduction. Sexual reproduction
requires the two cells from different individuals unite to produce
the first cell of a new organism. In asexual reproduction a
single organism can reproduce without the aid of another.
All living things at one stage or another are capable of growth.
During growth, most living things go through a cycle of change
called development. Living things obtain energy from their environment
and use that energy to grow, develop, and reproduce. All organisms
require energy to build the substances that make up their cells.
Any process in a living thing that involves putting together
or synthesizing, complex substances from simpler substances
is called anabolism (Photosynthesis). The breaking down of complex
substances into simpler ones, resulting in the release of energy
is called catabolism. The total sum of all chemical reactions
in the body – the balance of anabolism and catabolism
– is called metabolism.
Living things respond to their environments. Anything in the
environment that causes a change is called a stimulus. Organisms
react to many stimuli, including light, temperature, odor, sound,
gravity, heat, water, and pressure. The ability of living things
to react to stimuli is known as irritability (this does not
mean grouchy). The process by which organisms respond to stimuli
in ways that keep conditions in their body suitable for life
is called homeostasis.