Answer 1:
All molecules are made up of
atoms which are joined together by bonds.
The bonds which join atoms contain energy.
Because different atoms have different
properties, the bonds between different atoms
will vary in their strength and amount of
energy.
The cells in your body
function by manipulating and rearranging
molecules to form new bonds or break old ones,
in a process called metabolism. By
controlling the formation and breakage of
particular chemical bonds your cell can control
the energy present in the bonds.
Basically, everything that happens in your body
is the result of these controlled chemical
reactions that are occurring in your cells.
Some chemical reactions release energy when
they occur. Others require energy. Your cell is
able to use chemical reactions that release energy
in order to achieve desired reactions that consume
energy. It accomplishes this through an
intermediary molecule called ATP. ATP is a
molecule that contains three phosphates, and
the bond between two of the phosphates contains
a lot of energy.
Your cells use the energy released
from an energy-releasing chemical reaction to
produce ATP (by joining the molecule ADP with
another phosphate molecule). By coupling these
reactions the cell has effectively captured some
energy in the bonds of the ATP. (This is just one
way of producing ATP, called substrate-level
phosphorylation. But there are other ways
that cells can produce ATP too-- for example,
through aerobic respiration or
photosynthesis!).
Later, when the cell needs energy to perform
another chemical reaction, it can use the energy
released by breaking the phosphate bond in ATP
(again separating the ADP and phosphate molecules)
to make the reaction go.
Some organic molecules contain a lot more
energy in their bonds, due to the types of bonds
they possess. This makes them rich stores of
chemical energy. Keep in mind, though, that it's
not just the energy in the bonds that is important
to your body! The bonds must also be of the
right type for your body to use in its chemical
reactions!
If you want to know why, exactly, some bonds
contain more energy than others, that is something
that unfortunately I do not understand. I hope a
chemist or a physicist can help explain that to
you! | 
