1. Photosynthesis

2. Photosynthesis is a metabolic pathway consisting of
light-dependent and light-independent reactions.
Overall, water and carbon dioxide are used to produce
carbohydrates, with oxygen as a waste product.

3. • Photosynthesis is anendergonic process of
carbon reduction
• Cell respiration is anexergonicprocess of
carbon oxidation.
• Photosynthesis can be considered anabolic,
while respiration is catabolic.

4. An Overview
• Light-dependent reactions-
– Occurs in the thylakoids and grana of chloroplasts
– Solar energy is converted to chemical energy
– Chlorophyll drives the transfer of electrons and
hydrogen from water to the electron acceptor
NADP+
– Oxygen is released when water splits (photolysis)
– ATP is formed during the light reactions through
chemiosmosis by photophosphorylation
– Products include: NADPH and ATP

5. An Overview
• Light-independent reactions
– Involves the Calvin Cycle
– Occurs in the stroma
– Carbon dioxide is incorporated into existing organic
compounds by carbon fixation
– These compounds are then reduced to form
carbohydrates
– Reducing power and chemical energy comes from
NADPH and ATP, products of the light-dependent
reactions
– Products include: organic molecules

6. Factors that affect photosynthesis
There are many steps in the reactions of
photosynthesis, each requiring optimal
conditions for maximum activity. Whichever
factor is closest to the minimum is known as
the limiting factor. It will therefore slow the
whole process down.

7. Factors that affect photosynthesis
Factor Effect
Light Intensity Needed for photoactivation of electrons and photolysis of
water.
Low light results in low production of protons, low activity of
proton pumps and low recycling of hydrogen ions
Carbon dioxide Needed for carboxylation of RuBP in the Calvin Cycle.
concentration Low CO2 results in low production of glycerate-3-phospate
(G3P) and therefore low yield of triose phosphate (TP).
Temperature As an enzyme-controlled series of reactions, photosynthesis
has an optimum temperature. Low temperature gives
slower reactions due to lower energy, high temperatures
lead to denaturation of enzymes.

8. Action Spectrum
• The action spectrum of photosynthesis is the
range of wavelengths of light over which
photosynthesis is most active.
• The effectiveness of different wavelengths in
fuelling photosynthesis shows that red and
blue/violet influence the rate more than the
other colors.

9. Absorption Spectrum
• Shows the amount of light that is absorbed by
the different pigments
• Green light is poorly absorbed whereas red
and blue/violet is absorbed well.