Tutorial #23: Energy IV- The Light-Independent Reactions of Photosynthesis (Calvin Cycle)

The light reactions of photosynthesis produce ______, which provides Calvin Cycle with the necessary energy. In addition, the _______ produced by the light reactions provides the reducing power to put glucose together.

1. ATP

2. NADPH

input molecules of calvin cycle

CO2, ATP, NADPH

output molecules of calvin cycle

sugar, ADP, NADP+, inorganic phosphate

Phase 1 of Calvin Cycle

carbon fixation

5-carbon compound (RuBP) joined with 1 CO2 to produce unstable 6-carbon compound

- splits into 2 = 3 C compounds (2)

phase 2 of calvin cycle

Reduction of the Two, Three-Carbon Compounds

3-carbon molecules reduced to G3P

- electrons added from NADPH

- some G3P leaves to become sugar or regenerate RuBP

phase 3 of calvin cycle

regeneration of G3P to RuBP

*for every 3 CO2 fixed, 3 RuBP were needed

convert remaining G3P to RuBP to start process again

what enzyme catalyzes the fixation of CO2 to RuBP in phase 1 of Calvin Cycle?

rubisco

during phase 2, the molecule that can be used to make sugars (G3P) is produced. where does the energy to form these chemical bonds come from?

ATP + NADPH produced in the light-dependent reactions of photosynthesis

During phase 3, ______ is regenerated from G3P.

RuBP

If you applied an herbicide that affected the ability of NADPH to be oxidized, which aspect of photosynthesis would be most immediately affected?

the calvin cycle

The reactions of the Calvin Cycle are not directly dependent on light, but they usually do not occur at night. Why?

the calvin cycle depends on products of light reactions

a mutations occurs in the chloroplasts of a lettuce plant, causing its thylakoid membrane to become freely permeable to hydrogen ions (H+). How might this mutation affect the calvin cycle?

fewer carbohydrates would be produced by calvin cycle because less ATP = less NADPH = calvin cycle slowing down = fewer carbs produced

can plants use sugar they produce during photosynthesis to directly power the work of the plant cell?

plants do not use the sugars they produce directly as they need ATP to power the work they needed

sugars are transported to all cells of a plant and then, when energy is needed, the sugars are broken down through cellular respiration in their mitochondria to produce ATP to power any cellular work needed

- store energy as starch