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1. PHOTOSYNTHESIS

2. Photosynthesis
process by which plants
synthesize starch out of
carbon dioxide, water and
sunlight.

3. Photosynthesis nourishes almost the
entire living world directly or
indirectly. An organism acquires the
organic compound it uses for energy
and carbon skeletons by one of two
major modes: autotrophic nutrition
or heterotrophic nutrition.

4. AUTOTROPHS are “self-feeders”.
They sustain themselves without eating
anything derived from other organism.
Autotrophs produce their organic
molecule from CO2 and another
inorganic raw materials obtained from
the environment.

5. Almost all plants are
autotrophs. The only nutrients
they require are water and
minerals from the soil and
carbon dioxide from the air.

6. HETEROTROPHS obtain their
organic material by the second
major mode of nutrition. Unable to
make their own food, they live on
compounds produced by other
organism. Heterotrophs are
biosphere’s consumer.

7. Chloroplasts: The site of
photosynthesis in plants
All green plants, including green
stem and unriped fruit have
chloroplasts, but the leaves are the
major sites of photosynthesis in
most plants.

9. The color of the leaf is from chlorophyll, the
green pigment located within chloroplast. It
is the light energy absorbed by the
chlorophyll that drives the synthesis of
organic molecules in the chloroplast. Carbon
dioxide enters the leaf, and oxygen exist by
the way of microscopic pores called stomata.

10. In some places, thykaloid sacs
are stacked in columns called
grana. Chlorophyll resides in
the thykaloid membranes.

11. Two stages of
photosynthesis

12. Photosynthesis is not a single process,
but two processes, each with a
multiple steps. These two stages of
photosynthesis are known as the
Light Reaction (the photo part of the
photosynthesis and the Calvin Cycle
(the synthesis part)

13. The light reaction are the steps of
photosynthesis that convert solar energy to
chemical energy.
Light absorbed by chlorophyll drives a
transfer of electrons and hydrogen from water
to an acceptor called NADP+ (niotinamide
adenine dinucleotide phosphate), which
temporarily store the energized electrons.
Water is split in the process, and thus it is the
light reaction of photosynthesis that give off
Oxygen as a by product.

14. The electron acceptor of the light
reaction, NADP+, is first cousin to
NAD+, which function as an electron
carrier in cellular respiration; the two
molecule differ only by the presence
of an extra phosphate group in the
NADP+ molecule.

16. Thus, light energy is converted to chemical
energy in the form of two compounds:
NADPH – a source of energized
electrons;and
ATP – the versatile energy currency of the
cell

17. Notice that the light reaction
produce no sugar, that
happens in the second stage
of photosynthesis, the Calvin
Cycle.

18. The Calvin cycle is named for Melvin
Calvin, who, along with his colleagues,
began to elucidate its steps in the late
1940’s.
The cycle begins by incorporating CO2
from the air into organic molecules
already present in chloroplast.

19. Thus, it is the Calvin cycle that
makes sugar, but it can do so only
with the help of the NADPH and ATP
produced by the light reaction.

21. Light Reaction Calvin cycle
Reaction
Are carried out by
molecules in the thylakoid
membrane
Takes place in the
stroma
Convert light energy to the
chemical energy of ATP
and NADPH
Use ATP and NADPH to
convert CO2 to the sugar
G3P
Split H2O and releases O2
to the atmosphere
Return ADP, inorganic
phosphate, and NADP+ to
the light reaction