Photosynthesis captures light energy from the sun and uses it to produce carbohydrates that store energy. These energy-rich molecules fuel biochemical pathways that release the stored energy, with some of this energy temporarily stored in ATP molecules. ATP then directly supplies energy to power various cellular activities. When ATP is used as an energy source, its phosphate bond is broken, converting it into ADP.

1. ATP and ADP

2.  Nearly all the energy that fuels
life comes from the sun.
 Each day, light energy is
captured through photosynthesis
and is used to make energy-rich
carbohydrates.

3.  Almost all living things depend
on the products of photosynthesis
to survive.
 The energy stored in food
molecules is gradually released
in a series of chemical reactions
called a biochemical pathway.

4.  Some of the usable form of
energy is stored temporarily in a
molecule called ATP.
 ATP is the molecule that
supplies energy to fuel the
activities of the cell.

5.  When the bond between the two
phosphate groups of ATP is
broken, ATP becomes ADP.

6. 1. What life activities performed by
cells require energy?
ACTIVITY
2. What are biochemical pathways?
3. How does ATP supply energy for
the cell?
4. How does an ATP molecule
become ADP?