Light Independent Reaction

Question 1

What is the light independent reaction also known as?

Answer 1

The Calvin Cycle

Question 2

Where does the light independent reaction occur?

Answer 2

In the chloroplast, specifically the stroma

Question 3

What enzyme is contained in the stroma? What does this enzyme do?

Answer 3

The enzyme RuBisCo is contained in the stroma which catalyses the reaction

Question 4

What is the Calvin cycle sensitive to? How does this “thing” affect the Calvin cycle?

Answer 4

The Calvin Cycle is temperature sensitive due to the fact enzymes are involved and have the potential to denature

Question 5

What are the key molecules used in the Calvin Cycle? What key molecules are formed the light dependent reaction stage?

Answer 5

The key molecules used in the Calvin Cycle are carbon dioxide, ATP and NADPH.

ATP and NADPH are the molecules that derive from the LDR stage

Question 6

What do the key molecules (carbon dioxide, ATP and NADPH) form?

Answer 6

The key molecules come together to form a. hexose sugar (glucose)

Question 7

What is the role of ATP in the LIR stage? How does ATP perform this role?

Answer 7

ATP provides energy for this reaction. ATP becomes hydrolysed into ADP releasing energy to be used in the reaction

Question 8

What is the role of NADPH in the LIR stage? How does NADPH perform this role?

Answer 8

NADPH reduces the GP molecule. NADPH donates a hydrogen to reduce the GP molecule in the cycle

Question 9

Outline the Calvin Cycle:

Answer 9

1. Carbon dioxide diffuses through the stomata on the leaves, reacting with ribulose bisphosphate (RuBP). The enzyme Rubisco catalyses this reactions and forms two molecules of glycerate - 3 phosphate (GP) (3 carbon compound)
2. GP is then reduced to triose phosphate (TP) by hydrolysing a molecule of ATP to gain energy. GO also accepts a hydrogen form NADPH to become triose phosphate (TP)
3. Some carbon from the triose phosphate (TP) leaves the cycle to be converted into useful organic substances like glucose. Once the cycle has occurred six times a hexose sugar is formed.
4. Once some of the carbon has left, it leaves 5 carbon molecules remaining. This is used to regenerate the RuBP, with the energy from ATP

Question 10

What happens between RuBP, Carbon dioxide and Rubisco to form GP?

Answer 10

Carbon dioxide diffuses through the stromata to react with RuBP
Rubisco catalyses this reaction and forms two molecules of GP

Question 11

What happens between RuBP, Carbon dioxide and Rubisco to form GP?

Answer 11

Carbon dioxide diffuses through the stromata to react with RuBP
Rubisco catalyses this reaction and forms two molecules of GP

Question 12

How does GP become triose phosphate (TP)?

Answer 12

GP gains energy by hydrolysing an ATP molecule to become reduced by taking a hydrogen molecule from NADPH to become triose phosphate.

Question 13

What are the factors that could be limiting for photosynthesis?

Answer 13

Carbon dioxide concentration
Temperature
Light intensity

Question 14

How does temperature act as a limiting factor?

Answer 14

The light independent reaction is enzyme controlled so if the temperature is too cold there will be insufficient kinetic energy. However if it’s too hot the enzymes will denature.

Question 15

How is the chloroplast adapted to carry out the light independent reaction of photosynthesis?

Answer 15

1. The fluid of the stroma contains the enzymes to carry out the reaction, like Rubisco. The stroma fluid is membrane bound in the chloroplast which allows for a chemical environment which has a high concentration of enzymes and substrates to be maintained within it - distinct environment from the cytoplasm
2. The stroma fluid surrounds the grana allowing for NADPH and ATP to be steadily diffused into the stroma
3. Both DNA and ribosomes are present allowing quick and easy manafacturing of proteins involved in the light independent reaction