Calvin Cycle, C4, and Pathways

Mitochondria

An organelle where protons are pumped into the intermembrane space to drive ATP synthesis as they diffuse back into the [answer] matrix.

Chloroplast

An organelle where protons are pumped into the thylakoid space to drive ATP synthesis as they diffuse back into the stroma.

Chemiosmosis

The process in which the diffusion of hydrogen ions from the thylakoid space back to the stroma, down their concentration gradient, powers ATP synthase to produce ATP.

C3 Plants

These represent approximately 80% of plants on earth. They use the Calvin cycle for carbon fixation, which occurs entirely in the stroma.

6 Turns

18 ATP

12 NADPH

Carbon Fixation Requirement

To produce one molecule of glucose, the Calvin cycle requires [answer] turns, utilizing [answer] ATP and [answer] NADPH molecules.

Carbon Fixation

Phase 1 of the Calvin Cycle (C3 Pathway)

6 Molecules

Ribulose bisphosphate

12 Molecules

Phosphoglycerate

Phase 1: [Number] molecules of carbon dioxide are captured by [Answer] (RuBP). This results in an unstable intermediate that immediately breaks into [Number] molecules of [Answer] (PGA).

Carbon Reduction

Phase 2 of the Calvin Cycle (C3 Pathway)

PGA

ATP

NADPH

12 Molecules

Glyceraldehyde-3-phosphate G3P

Phase 2: [Answer] is phosphorylated by [Answer] and reduced by [Answer] to form [Number] molecules of [Answer].

12 G3P Molecules

2 Molecules

Glucose

Phase 2.5: Out of the [Number] G3P molecules produced, [Number] molecules exit the cycle to be used for [Answer] and other carbohydrate synthesis.

RuBP Regeneration

Phase 3 of the Calvin Cycle (C3 Pathway)

10 Molecules

6 Molecules

Ribulose Phosphate

RuBP

Phase 3: The remaining [Number] molecules of G3P are rearranged through a series of reactions to regenerate [Number] molecules of [Answer] (RP), which then becomes [Answer] to restart the cycle.

25%

The percentage in which Rubisco accounts for of the nitrogen in photosynthetic cells.

Rubisco

Short for Ribulose-1,5-bisphosphate carboxylase/oxygenase. It is the enzyme that initiates carbon fixation but can also act as an oxygenase.

Carboxylase Activity

(Activity) Rubisco initiates the standard carbon fixation reactions of the Calvin cycle.

Oxygenase Activity

(Activity) Under conditions of low carbon dioxide, Rubisco catalyzes a reaction between RuBP and oxygen.

Photorespiration

A process triggered by Rubisco's oxygenase activity. It occurs in the light, consumes oxygen, produces carbon dioxide, and uses ATP without producing sugar. Can reduce the photosynthetic efficiency of the Calvin cycle by up to 50%.

C4 Pathway (Hatch-Slack Pathway)

A mechanism used by certain plants to minimize photorespiration costs by physically separating carbon fixation and the Calvin cycle.

C4 Leaves

C3 vs. C4

Carbon dioxide is first fixed into four-carbon compounds in the mesophyll cells. These compounds are then transferred to specialized bundle sheath cells, where the Calvin cycle occurs.

C3 Leaves

C3 vs. C4

The Calvin Cycle occurs in mesophyll cells, while the bundle sheath cells are nonphotosynthetic.

C4 Plants

Found in hot, moist environments. 15% of plants (grass, corn, sugarcane). Divides photosynthesis spatially. Light rection in the mesophyll cells while Calvin cycle in the bundle sheath cells.

PEP Carboxylase

An enzyme used in C4 and CAM plants that adds carbon dioxide to phosphoenolpyruvate (PEP) to form oxaloacetate. It has a higher affinity for carbon dioxide than Rubisco.

Crassulacean Acid Metabolism (CAM)

A pathway where plants minimize photorespiration and water loss by fixing carbon at night. Carbon dioxide is stored as organic acids in vacuoles and released to the Calvin cycle during the day.

CAM Pathway

Happen in hot, dry environments, where stomates close during the day and open at night. Light-reaction in the day and Calvin cycle when CO2 is present.

CO2

Malate

Malic Acid

CAM plants open their stomata at night, and CO2 enters [Answer]. In these cells, the CO2 is converted into [Answer], which is stored in cell vacuoles as [Answer] acid.

Malate

Chloroplasts

In CAM Plants, during the day, when stomata are closed. CO2 is removed from [Answer] and becomes available to be fixed into sugar by the Calvin cycle in the [Answer] (located in the cytoplasm).