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Photosynthesis
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8.1 Energy and Life
Energy –
Living things must obtain and use
energy, even when at rest.
Where does that energy come from?
Chemical Energy and ATP
– One of the most important compounds that cells
use to store and release
– energy is adenosine triphosphate (ATP).
– ATP consists of adenine, a 5-carbon sugar
called ribose, and three phosphate groups.
ATP-ADP Cycle
ATP to
ADP + P
= energy
released
ADP + P
to ATP =
energy
stored
Using Biochemical Energy
– Energy from ATP powers the synthesis of
proteins and responses to chemical signals at
the cell surface.
Heterotrophs and Autotrophs
– Organisms that obtain food by consuming
other living things are known as
heterotrophs.
– Some heterotrophs get their food by eating
plants.
– Other heterotrophs, such as this cheetah,
obtain food from plants indirectly by feeding
on plant-eating animals.
– Still other heterotrophs, such as
mushrooms, obtain food by decomposing
other organisms.
Heterotrophs and Autotrophs
– Organisms that make their own food are
called autotrophs.
– Plants, algae, and some bacteria are able to
use light energy from the sun to produce food.
The process by which autotrophs use the
energy of sunlight to produce high-energy
carbohydrates that can be used for food is
known as photosynthesis.
8.2 Photosynthesis Light
– Energy from the sun travels to Earth in the
form of light.
– Sunlight is a mixture of different
wavelengths, many of which are visible to our
eyes and make up the visible spectrum.
Pigments
Plants gather the sun’s energy with light
absorbing molecules called pigments.
The plants main pigment is chlorophyll.
Chlorophyll a and b absorb blue-violet
and red. They do not absorb green.
Pigments
– The two types of chlorophyll found in plants,
chlorophyll a and chlorophyll b, absorb light
very well in the blue-violet and red regions of
the visible spectrum, but not in the green
region, as shown in the graph.
– Leaves reflect green light, which is why
plants look green.
Pigments
– Plants also contain red and orange pigments
such as carotene that absorb light in other
regions of the spectrum.
Chloroplast
Draw and label
Energy Collection
– Because light is a form of energy, any
compound that absorbs light absorbs energy.
Chlorophyll absorbs visible light especially
well.
– When chlorophyll absorbs light, a large
fraction of the light energy is transferred to
electrons. These high-energy electrons make
photosynthesis work.
Light dependent reaction
•Occurs in the thylakoid membrane
•Produces
ATP
energy
NADPH
source
O2 released (from water)
Light independent reaction
•Calvin cycle C3
•Occurs in the stroma
•CO2 is fixed
•Uses ATP and NADPH (from above) to
make glucose
An Overview of
Photosynthesis
– Photosynthesis uses the energy of sunlight to
convert water and carbon dioxide into highenergy sugars and oxygen.
– In symbols:
– 6 CO2 + 6 H2O  C6H12O6 + 6 O2
– In words:
– Carbon dioxide + Water  Sugars + Oxygen
8.3 The End Results
– The two sets of photosynthetic reactions work
together—the light-dependent reactions trap the
energy of sunlight in chemical form, and the lightindependent reactions use that chemical energy to
produce stable, high-energy sugars from carbon
dioxide and water.
– In the process, animals, including humans, get
food and an atmosphere filled with oxygen.
Factors Affecting Photosynthesis
The most important factors affecting
photosynthesis are
* Temperature-0 C -35 C are the
temperatures enzymes work the best
* Light- light intensity increases the rate to a
point, then levels off
* Water- raw material needed in the process
Photosynthesis under extreme
conditions
In hot, dry areas plants need to conserve
water. They usually do this by closing the
small openings in their leaves (stomata)
that allow carbon dioxide to enter.
C4 Photosynthesis
– C4 plants have a specialized chemical
pathway that allows them to capture even very
low levels of carbon dioxide and pass it to the
Calvin cycle (Dark reaction or light-independent
reaction)
– The name “C4 plant” comes from the fact that
the first compound formed in this pathway
contains 4 carbon atoms.
– The C4 pathway requires extra energy in the
form of ATP to function.
– C4 organisms include crop plants like corn,
sugar cane, and sorghum.
CAM Plants
– Members of the Crassulacae family, such
as cacti and succulents, incorporate carbon
dioxide into organic acids during
photosynthesis in a process called
Crassulacean Acid Metabolism (CAM).
CAM Plants
– CAM plants admit air into their leaves
only at night, where carbon dioxide is
combined with existing molecules to
produce organic acids, “trapping” the
carbon within the leaves.
– During the daytime, when leaves are
tightly sealed to prevent water loss, these
compounds release carbon dioxide,
enabling carbohydrate production.
– CAM plants include pineapple trees,
many desert cacti, and “ice plants”.