Energy for Life
4.5-4.7
The Sun and Photosynthesis: How
We Get Energy
 All activities by living things require
energy.
 Consumers get their energy from the
foods that they eat, but where do the
producers get their energy?
 Organisms can’t use light energy
directly as a source of food.
 Photosynthesis convert light energy
from the sun into chemical energy
that is stored in sugar molecules.
 This energy can be used by plants
themselves or organisms that eat the
plant.
 First, the plant must absorb light
energy using chlorophyll, a green
pigment that gives plants their color.
 CO2 and water is also absorbed.
 Light energy breaks down the water
into hydrogen and oxygen.
 The hydrogen then combines with the
CO2 to form sugar molecules.
 The oxygen is released into the air.
 The energy used to form the sugar is
stored in chemical bonds.
 When the bonds are broken, energy
is release.
 Energy is used to carry out the cells
activities.
Energy is Released as Food is
Broken Down
 The major energy releasing process is
cellular respiration.
 During this process sugar is broken
down and energy is released.
 The chemical energy in food is also
released by chemical reactions.
ATP, the Cell’s Currency for Energy
Transfer
 Cellular respiration converts the
energy stored in complex molecules
into chemical energy stored in ATP,
adenosine triphosphate.
 Each ATP molecule is made up of a
sugar complex attached to three
phosphates.
 Energy is stored in ATP until it is
released by reactions that remove
one of the phosphates.
 Each ATP molecule releases energy
whenever a phosphate is broken off
or transferred to another molecule.
 The molecule that remains has only
two phosphate groups and is called
ADP, adenosine diphosphate.