Process of
Photosynthesis
Photosynthesis Equation
 Photosynthesis is the process of
capturing light energy and
converting it into chemical
energy, (usually in the form of
carbohydrates)
 6 CO2 + 6 H2O + Light 
C6H12O6 + 6O2
Photosynthesis is broken
down into two reactions.
 Light Dependent Reaction energy from light makes the
reaction happen
 Light Independent Reaction
(Calvin Cycle; Dark Reaction)
Doesn’t need direct light
energy, but it does need the
high-energy products from the
Light Rx. ATP and NADPH
Light Dependent ReactionsIn the Chloroplast
1. Light energy is
pigments
absorbed by _________
in the thylakoid
membranes of the
chloroplast (pigments
are located in
Photosystem I & II)
2. In Photosystem II the
electrons become
energized
________________or
“excited”.
3. The excited electrons
are passed down a
series of molecules
called the
____________________
Electron Transport
_________.
Chain
4. To replace the
electrons that are lost,
some are stolen from
water . This breaks the
water molecule apart
like this:
+
2H2O  4H + O2
5.As electrons move
down the chain, their
energy is used to
ATP (a highmake ______
energy molecule)
6. The electrons now go
to Photosystem I. Light
energizes new
electrons in PI and they
combine with NADP+ to
make ________
NADPH
(another high-energy
molecule).
LIGHT RX
http://www.cnr.vt.edu/DENDRO/forestbiology/photosynthesi
s.swf
The final products of the
light reaction
At the end of the light
reaction we have made:
1. ATP
2. NADPH
3. O2
Reactants used during the
light reaction:
1. Water
2. Also used sunlight
Light independent
reaction ( Calvin Cycle)
A. Needs: CO2 , ATP, NADPH
B. Where do they come from?
 Light Reaction- ATP NADPH
 Air-CO2
C. Where do they go?
 Calvin Cycle
 Location stroma
 Enzymes are found in the stroma
Calvin cycle (dark reaction):
 doesn’t need light
- Uses the ATP and NADPH “charged”
by the light reactions to link CO2
together to build C6H12O6
Reactant: 6CO2
Product: C6H12O6
What happens to the glucose?
1. Move to the mitochondria to be converted
into ATP through Cell respiration
2. Go through dehydration synthesis to build
a big starch chain and be stored for future
use
Photosynthesis: An Overview
Chloroplast
Chloroplast
Light
CO2
H2O
NADP+
ADP + P
Calvin
Cycle
LightDependent
Reactions
ATP
NADPH
O2
Sugars
Factors affecting Photosynthesis:
 Light Intensity: the rate of
increases
photosynthesis _________as
light
intensity_________,
increases then levels off
 CO2 levels: the rate of
increases as CO2
photosynthesis _________
increases then levels off
_________,
What causes the rate to
level off in each case?
 With more light, the plant is
limited by the amount of CO2
available.
 Don’t forget that the wavelength of
light matters!!!
 With more CO2, the plant is
limited by the amount light
energy available.
 Temperature: increasing the
temperature, _________the
increases
rate
of photosynthesis, then the rate
decreases
peaks and ____________.
Why does the rate decrease
after a certain temperature?
 The enzymes and other
molecules controlling the
reaction start to break
down after that
temperature.
Alternative Pathways
hot
 Some plants that live in ____,
dry environments have
____
modified internal structures and
use alternative carbon fixation
pathways.
water loss
 Better at preventing _________.
Leaf structure
Stoma (stomata pl.)
 How does a plant stop
water loss?
Close the stomata.
 But what problem does that
cause?
Run out of CO2 and too
much O2 builds up.
C4 pathway
 The C4 pathway uses a
four
special ____-carbon
compound to “fix” carbon into
glucose.
 This is more efficient when
the level of CO2 is low.
Examples:
corn, crab grass, sugar cane
CAM pathways
Opens stomata at
________
night to store CO2.
Close stomata in the day,
which prevents water loss.
Examples:
pineapple, cacti
Exceptions to the Rules:
 Autotrophic Bacteria:
Example: Cyanobacteria
(“Blue” bacteria)
Exceptions to the Rules:
 Autotrophic Protists:
Example: Algae and
Euglena
Exceptions to the Rules:
 Heterotrophic plants: some plants
get food from other organisms
Mistletoe: makes food AND
takes sap (high in sugar) from
other trees
Exceptions to the Rules:
Venus Flytrap: traps and digests
insects as a food source
Photosynthesis Summary
Light
Reaction
Location
Reactants
Products
Calvin
Cycle
Photosynthesis Summary
Location
Reactants
Products
Light
Reaction
Thylakoid
Calvin
Cycle
Photosynthesis Summary
Location
Reactants
Products
Light
Reaction
Thylakoid
Calvin
Cycle
Stroma
Photosynthesis Summary
Location
Light
Reaction
Thylakoid
Reactants Light, H2O
Products
Calvin
Cycle
Stroma
Photosynthesis Summary
Location
Light
Reaction
Thylakoid
Reactants Light, H2O
Products
Calvin
Cycle
Stroma
CO2, ATP,
NADPH
Photosynthesis Summary
Location
Light
Reaction
Thylakoid
Reactants Light, H2O
Products ATP, NADPH,
O2
Calvin
Cycle
Stroma
CO2, ATP,
NADPH
Photosynthesis Summary
Location
Light
Reaction
Thylakoid
Reactants Light, H2O
Calvin
Cycle
Stroma
CO2, ATP,
NADPH
Products ATP, NADPH, Glucose
O2
Photosynthesis: An Overview
Chloroplast
Chloroplast
Light
CO2
H2O
NADP+
ADP + P
Calvin
Cycle
LightDependent
Reactions
ATP
NADPH
O2
Sugars
Concept Map
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
use
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
NADPH
O2
takes place in
Stroma
uses
ATP
NADPH
of
to produce
Chloroplasts
High-energy
sugars