Photosynthesis- the Light Independent Reactions of Photosynthesis/ Calvin Cycle

Question 1

Where do the reactions of the Calvin Cycle take place?

Answer 1

In the stroma of the chloroplast

Question 2

Which products of the light dependent reactions are utilized during the Calvin Cycle?

Answer 2

ATP and reduced NADP

Question 3

What are the three important steps of the Calvin Cycle?

Answer 3

1. Carbon dioxide fixation
2. Reduction
3. Regeneration

Question 4

List the events which occur during carbon dioxide fixation.

Answer 4

1. CO2 gas diffuses into the chloroplasts along a diffusion gradient.
2. This carbon dioxide and some water combine with the carbon dioxide acceptor RUBP (ribulose bisphosphate 5C) to form a 6C compound which is unstable.
3. The enzyme RUBISCO (ribulose bisphosphate carboxylase) catalyzes this carboxylation reaction.
4. As fast as the CO2 is accepted by the RUBP, the concentration of CO2 in the stroma decreases allowing a diffusion gradient to be maintained between the outside of the palisade cells and the stroma of the chloroplast.
   GP is the first product of photosynthesis.

Question 5

What is the first product of the Calvin Cycle?

Answer 5

GP (glycerate-3-phosphate)

Question 6

List the events which occur during the reduction stage of the Calvin Cycle?

Answer 6

1. During the reduction phase, the energy of some of the ATP and the reducing power of all of the NADPH are used to convert the GP to TP (triose phosphate) which is the first carbohydrate of photosynthesis.
2. During this reduction phase, oxygen is removed from GP using some energy from ATP and combined with hydrogen provided by NADPH.
3. Water is produced while NADPH becomes oxidized to NADP.

Question 7

What is the first carbohydrate produced during the Calvin Cycle?

Answer 7

Triose Phosphate (TP)

Question 8

What occurs during the regeneration of the carbon dioxide acceptor?

Answer 8

The CO2 acceptor RUBP has to be regenerated for reuse in the Calvin Cycle to enable CO2 to be fixed
1. In order for this, 5/6 of the TP produced and the remainder of the ATP are both needed to regenerate RUP.
2. The TP is converted to ribulose phosphate by the rearrangement of carbon atoms of the TP.
3. The rest of the ATP is then used to convert RUP to RUBP.
This is a process of phosphorylation of the RUP.
4. The formation of other carbohydrates, like glucose, starch and cellulose, lipids and amino acids from TP are produced from 1/6 of every TP molecule.