Photosynthesis: Light Reactions and the Calvin Cycle

Photosynthesis

Process by which plants make their own food.

Anabolic Reaction

Builds complex molecules from simpler ones.

Endergonic Reaction

Requires energy input to proceed.

Water

Enters roots via osmosis for photosynthesis.

Stomata

Tiny openings for gas exchange in leaves.

Chloroplasts

Organelles where photosynthesis occurs in plants.

Thylakoids

Membrane-enclosed compartments within chloroplasts.

Stroma

Fluid-filled space surrounding thylakoids in chloroplasts.

Light Reactions

Convert light energy into ATP and NADPH.

Calvin Cycle

Uses ATP and NADPH to synthesize glucose.

Photons

Packets of light energy that drive photosynthesis.

Pigments

Molecules that absorb specific wavelengths of light.

Chlorophyll A

Most abundant pigment in plants, absorbs light.

Photosystems

Complexes of pigments that initiate light reactions.

Electron Transport Chain (ETC)

Series of reactions transferring electrons in thylakoids.

Concentration Gradient

Difference in proton concentration across thylakoid membrane.

ATP Synthase

Enzyme that produces ATP using proton flow.

NADP+

Oxidized form, final electron acceptor in photosynthesis.

NADPH

Reduced form, carries electrons for Calvin cycle.

Carbon Fixation

Incorporation of CO2 into organic compounds.

3-Phosphoglycerate (3PG)

First stable product of carbon fixation.

Glyceraldehyde 3-Phosphate (G3P)

Intermediate formed from 3PG, can become glucose.

Rubisco

Enzyme that catalyzes CO2 fixation in Calvin cycle.

RuBP

5-carbon molecule that reacts with CO2.

Photorespiration

Process where Rubisco uses O2 instead of CO2.

Autotrophs

Organisms that produce their own food.

Heterotrophs

Organisms that obtain energy from others.

Efficiency of Photosynthesis

Only about 5% of sunlight converted to sugars.

Climate Change Impact

High temperatures affect CO2/O2 balance in plants.

Oxygen Release

Byproduct of water splitting during light reactions.