Photosynthesis
Photosynthesis
-Primarily in chloroplasts of plants
-Reactions occur inside structures within the
chloroplasts called thylakoids and the stroma.
Chloroplast
Granum
Single
thylakoid
Stroma
Overall Reaction of Photosynthesis
Reactants: carbon dioxide, water, and
energy (sun)
Products: glucose and oxygen
6CO2 + 6H2O + Energy  C6H12O6 + 6O2
Light Reactions
Function:
-Energy from the sun is absorbed by chlorophyll located inside the
thylakoids.
-The light energy is transferred from the chlorophyll to NADP+ to form
NADPH. This occurs in a series of reactions called the electron transport
chain (ETC) across the thylakoid membrane.
-ATP is formed from ADP by chemiosmosis across the thylakoid
membrane. (ADP adds a P group with the help of the protein ATP
Synthase.)
Location: chlorophyll & thylakoid membrane
Reactants: H2O, energy (sun) ADP, and NADP+.
Products: oxygen, ATP, and NADPH.
Photosynthesis
H2O
CO2
Light
NADP+
ADP + P
Lightdependent
reactions
O2
Calvin
cycle
Sugars
Calvin Cycle (Dark Reactions)
Function:
-No sunlight is needed.
-Plants use the energy within ATP and NADPH
to build organic compounds (glucose) which are
sources of nutrients for the plant.
Location: stroma of the chloroplast
Reactants: CO2 (from air), ATP and NADPH
Products: Organic Compounds (Glucose)
Photosynthesis
H2O
CO2
Light
NADP+
ADP + P
Lightdependent
reactions
O2
Calvin
cycle
Sugars
Photosynthesis
• The two sets of photosynthetic reactions
work together.
– The light-dependent reactions trap sunlight
energy in chemical form.
– The light-independent reactions use that
chemical energy to produce stable, high-energy
sugars from carbon dioxide and water.
Alternative Biochemical Pathways
• C4 Pathway – Plants in hot, dry climates. Try to
prevent water loss. Water loss occurs through the
stomata. (Passageway for O2 & CO2 entering and
leaving the plant.)
• CAM Pathway – open stomata only at night.
• C3 , C4 & CAM pathway plants also differ by the
initial product of carbon fixation.
Factors affecting the Rate of
Photosynthesis:
• Light Intensity
• Amount of CO2
• Temperature