Photosynthesis

Photosynthesis

-Primarily in chloroplasts of plants-Reactions occur inside structures within the chloroplasts called thylakoids and the stroma.

Chloroplast

Singlethylakoid

Granum

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 membraneReactants: H2O, energy (sun) ADP, and NADP+.

Products: oxygen, ATP, and NADPH.

PhotosynthesisLight

H2O

O2

CO2

Sugars

NADP+

ADP + P

Light- dependen

t reactions

Calvin cycle

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 chloroplastReactants: CO2 (from air), ATP and NADPH Products: Organic Compounds (Glucose)

PhotosynthesisLight

H2O

O2

CO2

Sugars

NADP+

ADP + P

Light- dependen

t reactions

Calvin cycle

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