10.3 chemical energy trapped in photosynthesis is used to synthesize carbohydrates

Question 1

CO2 Fixation

Answer 1

• CO2 is reduced to carbohydrates using energy from ATP and NADPH.
• Occurs in the stroma of chloroplasts.
• Calvin and Benson used 14C radioisotope to show the CO2 fixation pathway.

Question 2

Calvin Cycle Overview

Answer 2

• The Calvin cycle fixes CO2 into carbohydrates.
• Initial compound formed is 3-phosphoglycerate (3PG), a sugar phosphate.
• Pathway involves fixation of CO2 to 3PG, reduction to glyceraldehyde 3-phosphate (G3P), and regeneration of RuBP.

Question 3

Calvin Cycle Steps

Answer 3

• Fixation of CO2 to 3PG.
• Reduction of 3PG to G3P.
• Regeneration of RuBP, the CO2 acceptor.
• One CO2 is fixed and one RuBP is regenerated per cycle.

Question 4

Glyceraldehyde 3-phosphate (G3P)

Answer 4

• Product of the Calvin cycle.
• Some G3P is exported to the cytoplasm and converted to glucose and fructose, serving as energy sources.
• Others are used to synthesize glucose and starch within the chloroplast.

Question 5

G3P Utilization

Answer 5

• Some G3P is stored as sucrose and transported to other parts of the plant.
• Stored starch is utilized at night when plants cannot produce energy.

Question 6

Calvin and Benson

Answer 6

• Scientists who used 14C radioisotope to determine the sequence of reactions in CO2 fixation.
• Their work led to the understanding of the Calvin cycle.

Question 7

Calvin Cycle Stimulation

Answer 7

• The Calvin cycle is stimulated by light.
• Light-induced electron transport activates Calvin cycle enzymes by reducing disulfide bonds, mediated by ferredoxin and thioredoxin.

Question 8

RuBP Regeneration

Answer 8

• RuBP is regenerated in the Calvin cycle to continue fixing CO2.
• Regeneration ensures the cycle’s continuous operation.

Question 9

3-phosphoglycerate (3PG)

Answer 9

• Initial compound formed in the Calvin cycle.
• 3PG is a sugar phosphate that serves as a precursor for carbohydrate synthesis.

Question 10

Carbon Fixation Pathway

Answer 10

• The Calvin cycle is the primary carbon fixation pathway in plants.
• It converts atmospheric CO2 into organic compounds, crucial for plant growth and metabolism.