Horticulture: Photosynthesis - Calvin Cycle & Light Reactions (VOCAB)

Vocabulary flashcards covering key terms related to photosynthesis, Calvin cycle, light reactions, and photorespiration from the lecture notes.

Calvin Cycle

The set of reactions in the chloroplast stroma that fixes CO2 into organic molecules, producing G3P using ATP and NADPH from the light reactions.

Light Reactions

Photosynthetic reactions in the thylakoid membranes that convert light energy into chemical energy (ATP and NADPH) and release O2 from water.

NADP+

Electron carrier that accepts electrons and H+ during the light reactions to form NADPH.

NADPH

Reduced form of NADP+; provides electrons and reducing power for the Calvin cycle.

ATP

Energy-carrying molecule produced by the light reactions and used to power the Calvin cycle.

RuBP (Ribulose-1,5-bisphosphate)

Five-carbon molecule that combines with CO2 in carbon fixation to form 3-PGA.

Rubisco (RuBP carboxylase/oxygenase)

Enzyme that fixes CO2 to RuBP; can also fix O2, leading to photorespiration.

3-PGA (3-phosphoglyceric acid)

First stable product of carbon fixation; a 3-carbon molecule formed in the Calvin cycle.

G3P (glyceraldehyde-3-phosphate)

Three-carbon sugar produced in the Calvin cycle; one exits to form glucose, others regenerate RuBP.

Glucose

Six-carbon sugar synthesized from two G3P molecules; main carbohydrate product of photosynthesis.

Thylakoid membrane

Membrane within the chloroplast where the light-dependent reactions occur.

Stroma

Fluid surrounding the thylakoids in the chloroplast; location of the Calvin cycle.

Carbon fixation

Phase 1 of the Calvin cycle; CO2 is fixed to RuBP to form 3-PGA.

Reduction

Phase 2 of the Calvin cycle; 3-PGA is phosphorylated and reduced to G3P using ATP and NADPH.

Regeneration

Phase 3 of the Calvin cycle; most G3P is used to regenerate RuBP so the cycle can continue.

C3 pathway

Standard photosynthetic pathway used by most plants; CO2 is fixed directly by RuBP in the Calvin cycle.

C4 pathway

CO2-concentrating pathway where CO2 is fixed in mesophyll cells and transported to bundle-sheath cells; reduces photorespiration.

CAM pathway

Crassulacean acid metabolism; stomata open at night to fix CO2 into malate, stored until daytime.

Photorespiration

Wasteful process when Rubisco fixes O2 instead of CO2, reducing photosynthetic efficiency.

Stomata

Leaf pores that regulate gas exchange; open to admit CO2 and close to prevent water loss.

CO2

Carbon dioxide; substrate for the Calvin cycle; concentration affects fixation efficiency.

O2

Oxygen; produced by the light reactions and can be fixed by Rubisco, causing photorespiration.

H2O

Water; split during the light reactions to provide electrons and protons and to release O2.

Bundle-sheath cell

Cell type in C4 plants where CO2 is released for the Calvin cycle; helps exclude O2.

Malate

Four-carbon compound formed in CAM (and C4) pathways as a CO2 carrier stored at night and used during the day.

RuBP regeneration

Process of converting G3P back into RuBP to continue the Calvin cycle.

O2 exclusion

In C4 plants, spatial separation prevents O2 from binding Rubisco, reducing photorespiration.