Energy is defined as the ability
to do work; all living things
require some level of energy
to keep them alive. The source
of energy is from the sun as
we are part of the solar
system. Living things have
different abilities in using this
energy in what is known as
metabolism activity. This
represents a sum of all
chemical reactions that take
place in living organisms and
result in the energy process. This energy can be used for all
different activities including growth, movements, and
Metabolism is composed of catabolic and anabolic reactions.
Catabolic means the breakdown of macromolecules into
basic building blocks. Anabolic means using the materials
that resulted from the breakdown to rebuild the new
Living things are divided regarding metabolism into different
1. Autotroph – represents those organisms that can
produce their own food, because; they have the ability
to perform photosynthesis capturing the sunlight and
converted into stored chemical energy in food.
2. Heterotroph – organisms that can’t make photosynthesis
and depend on produced foods.
3. Decomposers – the last group that is responsible to
recycle all the materials.
The energy level is conserved between these three levels of