4.2 Light-Independent Reactions (CQ - exam)

Question 1

what is the function of the calvin cycle? and which part of the cell are the enzymes for the calvin cycle located?

Answer 1

function of calvin cycle is to convert CO2 into glucose using energy from ATP and NADPH
The enzymes of the Calvin cycle are in the stroma.

Question 2

what role does ribulose-1,5-biphosphate play in the calvin cycle

Answer 2

RuBP is the starting material that joins with CO2 in phase 1.

Question 3

How many G3Ps must be produced in order to make one glucose molecule? What is the function of the other G3P molecules?

Answer 3

2 G3Ps are able to make up one glucose molecule.

Question 4

name the three phases of the Cakin cycle, and state the processes and main function of each phase

Answer 4

1. Fixation of carbon dioxide
   - Rubisco joins CO2 and RuBP, to form an unstable 6C molecule that immediately breaks into two 3C 3-PGA
2. Reduction of 3-phosphoglycerate to G3P
   - 3-PGA is converted into high energy molecule, G3P, using ATP and NADPH
3. Regeneration of RuBP from G3P
   - G3P molecules are converted back into RuBP using ATP

Question 5

list at least 5 different compounds other than glucose that are made from G3Ps

Answer 5

1. Sucrose
2. Starch
3. Substrate for cellulose
4. Plant oils
5. amino acids

Question 6

Explain why all of the G3P synthesized in the Calvin cycle cannot be used to make glucose

Answer 6

The regeneration of RuBP is essential for the Calvin cycle to continue

Question 7

Name the two types of high-energy molecules that are used to drive the Calvin cycle, and state the number of each needed to synthesize one molecule of glucose.

Answer 7

1. ATP
   - 18
2. NADPH
   - 12

Question 8

Define photorespiration, and explain how it affects the Calvin cycle.

Answer 8

• If stomata are closed for water conservation, O2 builds up in the plant and rubisco binds to O2 instead of CO2
• Rubisco binds to whatever is of the highest concentration
• Rubisco binding to Oxygen, creates non high energy molecule and uses ATP
• Photorespiration reduces the output of the calvins cycle by consuming a lot of energy and releases CO2

Question 9

ln the leaves of CAM plants, carbon dioxide fixation and the Calvin cycle occur inside the same cell. How, then, do CAM plants minimize the photorespiration?

Answer 9

• Both occur in mesophyll
• Open at night during cold due to desert
• Take in CO2
• Convert it to 4C molecule
• No bundle sheath cell
• Makes the 4C molecule CO2
• And use during day

Question 10

In an experiment, a suspension of chloroplasts is carrying out photosynthesis under a bright light. if the light were suddenly turned off would the concentration of ribulose-1,5-bisphosphate or 3-phosphoglycerate change first? Explain your reasoning.

Answer 10

• Calvin cycle would continue
• however does need ATP and NADH from light dependent reaction
• RuBP needs ATP and NADH, so RuBP would be used first
• Especially because RuBP is needed to make 3-PGA

Question 11

Describe the difference in the leaf structure of a C4 plant compared to a C3 plant. Explain how the leaf structure of the C4 plant helps to reduce the amount of photorespiration that occurs in the leaves, even when the air is hot and dry.

Answer 11

Photorespiration is reduced by bundle sheath cells being exposed to more CO2 than O2 gas

C4 plants
- CO2 comes in at night and needs to be stored when it is unsafe to open it, converted into 4C molecule for storing in the mesophyll
- Builds up and uses it in the calvin cycle

C3 plants
- When CO2 comes in, goes into mesophyll turns it into 3C molecule

Question 12

Under cool, moist conditions, why are C4 and CAM plants less efficient than C3 plants?

Answer 12

• CAM and C4 plants are inefficient in cool climates because they use energy to drive reactions that store CO2
• wastes energy that could be put towards better causes