3.5.1.2 - Photosynthesis (Calvin Cycle)

Question 1

The diagram shows Melvin Calvin’s Lollipop experiment for identifying the products of the Calvin Cycle. Why was radioactive hydrogen carbonate supplied to the algae?

Answer 1

So that the substances into which the CO2 is incorporated can be identified.

Question 2

Describe the Calvin Cycle

Answer 2

1. CARBON FIXATION - Rubisco enzyme catalyses the reaction of RuBP with CO₂ to produce 2x Glycerate-3-Phosphate (G-3-P).
2. REDUCTION - NADPH reduces G-3-P into 2x Triose Phosphate (TP) with energy being provided by ATP.
3. REGENERATION - 2 x TP are converted into orgnaic compounds e.g. glucose OR ATP is used to convert TP into RuBP for more turns of the Calvin cycle.

Question 3

How many carbon aotms in Ribulose Bisphosphate (RuBP)?

Answer 3

5

Question 4

Name the enzyme that catalyses the fixation of carbon dioxde into RuBP to produce glycerate-3-phosphate.

Answer 4

Rubisco

Question 5

How many turns of the calvin cycle take place to produce 1 molecule of glucose?

Answer 5

6

Question 6

How many carbon atoms in glycerate-3-phosphate?

Answer 6

3

Question 7

What are the proudcts of every 6 turns of the carbon cycle?

Answer 7

1 x glucose molecule

5 x RuBP

Question 8

What are the light independent reactions of photosynthesis sometimes referred to as?

Answer 8

The Calvin Cycle

Question 9

What are the products of the Calvin cycle (LIR)?

Answer 9

Organic compounds e.g. glucose, amino acids, lipids

RuBP (Ribulose Bisphosphate)

Question 10

How many carbon atoms in triose phosphate?

Answer 10

3

Question 11

The diagram shows Melvin Calvin’s Lollipop experiment for identifying the products of the Calvin Cycle. Why is a fast flow tap used in this experiment?

Answer 11

To terminate the reactions immediately.

Question 12

The diagram shows Melvin Calvin’s Lollipop experiment for identifying the products of the Calvin Cycle. Why is hot methanol supplied to the algae?

Answer 12

High temp will denature enzymes that catalyse reactions.

Methonal could denature the enzymes.

Question 13

Does the Calvin Cycle require light to function?

Answer 13

No

BUT

The reactions will stop eventually in the absence of light because essential ATP and NADPH from light reactions will run out.

Question 14

During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how. (6 marks)

Answer 14

1. Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. Produces two glycerate-3-phosphate / GP;
3. GP reduced to triose phosphate / TP;
4. Using reduced NADP; and…
5. …Using energy from ATP;
6. Triose phosphate converted to glucose / RuBP / ribulose bisphosphate

Question 15

Heat stress decreases the LDR - why does this lead to a decrease in the LIDR?

Answer 15

Less ATP

Less reduced NADP

Question 16

A decrease in the activity of the enzyme rubisco would limit photosynthesis - why?

Answer 16

Less carbon dioxide reacts with RuBP

so

Less GP

Question 17

where is rubisco found?

Answer 17

stroma (of chloroplast)