Chapter 4
Cells and Energy
ATP and Photosynthesis
Work
Is done when anything is moved
Life processes rearrange molecules, ions,
and atoms
Requires energy
Energy
Is the ability to do work
Comes from food
Food is broken down into small molecules
that can enter cells
Cells break down molecules to release the
energy
Energy from molecules
Is not all used at one time
Used to balance supply and demand
Energy not used right away is stored in a
molecule called ATP
ATP releases the energy when the cell
needs it
Cells die without ATP
ATP
Adenosine triphosphate
– Sugar (ribose)
– Adenine
– 3 phosphate groups
– Energy is stored in the phosphate-phosphate
bonds
– When a phosphate is removed, energy is
released to the cell
– ADP is left
ADP
Adenosine diphosphate
– Sugar (ribose)
– Adenine
– 2 phosphate groups
– Is recycled by adding another phosphate to
store energy
– Putting another phosphate on ADP converts it
back to ATP
ATP / ADP Cycle
Energy cycle
ADP + P + energy = ATP
ATP
– Energy available for work is free energy
– Energy stored in molecules is potential energy
– ATP is the energy link between energy-using
and energy-releasing reactions
Autotrophs
Trap energy from sunlight for
photosynthesis
Most plants are green because of
chlorophyll (green pigment)
Chlorophyll reflects green light
Energy from sun is trapped inside
thylakoid membrane of chloroplast
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Photosynthesis
2 groups of reactions: light reactions and
Calvin cycle (dark reactions)
Light reactions
– Light converted to chemical energy
– Photo part
– Split water and give hydrogen to Calvin cycle
Calvin cycle
– Forms sugar from CO2 and H (from water)
– Synthesis part
Light reactions
Electrons in chlorophyll absorb light
energy
Electrons leave chlorophyll and are
passed through electron transport chain
Extra energy is stored as ATP
Water is split into O2 and H+ (photolysis)
H + electron picked up by NADP+
(electron carrier)
O2 given off as waste
Photolysis
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Calvin Cycle
Enzyme adds C from CO2 to a 5-carbon
molecule
C is not fixed to an organic molecule
(carbon fixation-coverts gaseous CO2 to a
useable form for living things: sugars,
starch, cellulose)
Called dark reactions because light does
not have to be available for fixation
(CO2)
The Calvin
Cycle
(Unstable intermediate)
(RuPB)
ADP +
ATP
ATP
ADP +
NADPH
NADP+
(PGAL)
(PGAL)
(Sugars and other carbohydrates)
(PGAL)
Life without light
Some organisms are chemosynthetic
(bacteria)
Obtain energy by converting inorganic
compounds into useable forms
Usually final participants in decomposition
processes