Photosynthesis

Question 1

what are the two reactions called and where do they occur

Answer 1

• light dependant - thylakoid
• light independant - stroma

Question 2

describe the light dependant reaction (LDR)

Answer 2

• photoionisation. light energy is absorbed by chlorophyll which excites an electron
• the electron moves through carriers in the electron transfer chain via a series of redox reactions, releasing energy
• this energy pumps protons accross the thyalkoid membrane, establishing an electrochemical gradient
• protons move down the gradient through ATP synthase, providing energy to join ADP + Pi to form ATP
• NADP acts as an electron acceptor and is reduced
• photolysis of water produces protons, electrons and oxygen
• NADPH and ATP produced

Question 3

what are the products of the LDR

Answer 3

NADPH and ATP produced

Question 4

describe the light independant reaction (LIR)

Answer 4

• CO2 combines with RuBP to form two molecules of gp, catalysed by the rubisco enzyme
• each GP molecule is reduced using NADPH and energy from ATP hydrolysis into two molecules of triose phosphate
• carbon is removed from triose phosphate to produce a hexose sugar

Question 5

Which chemicals are needed for the light-dependent reaction

Answer 5

NADP, ADP, Pi and water

Question 6

Which chemicals are needed for the light-dependent reaction?

Answer 6

NADP, ADP, Pi and water

Question 7

What happens during photoionisation?

Answer 7

• Chlorophyll absorbs light energy.
• Electrons go to the electron transport chain.

Question 8

What is the role of chlorophyll in photolysis?

Answer 8

Absorbs light energy;
Loses electrons;
Accepts electrons from water;

Question 9

What is the function of ATP in the light-independent reaction?

Answer 9

Provides energy for the reduction of GP to triose phosphate.

Question 10

Describe the light-independent reaction of photosynthesis (6 marks).

Answer 10

• Carbon dioxide combines/reacts with ribulose bisphosphate/RuBP
• Produces two GP molecules using (enzyme) Rubisco
• GP reduced to triose phosphate
  Using reduced NADP / NADPH
• Using energy from ATP hydrolysis
• Triose phosphate converted to glucose / RuBP / named organic substance

Question 11

What products of the light-dependent reaction are used in the light-independent reaction?

Answer 11

• ATP and reduced NADP / NADPH
• GP is reduced to triose phosphate
• ATP provides energy

Question 12

Environmental factors that should be controlled when measuring the rate of photosynthesis

Answer 12

Light intensity
Carbon dioxide concentration
Temperature
Water OR humidity
Wavelength of light

Question 13

Limiting factors for photosynthesis

Answer 13

Temperature
Carbon dioxide concentration
Light intensity
Wavelength of light

Question 14

Iron deficiency reduces electron transport. Use this information and your knowledge of photosynthesis to explain the decrease in production of triose phosphate in the iron-deficient plants (4 marks).

Answer 14

ATP and reduced NADP produced during light-dependent reaction;

(In the case of iron deficiency)

Less ATP produced;
Less reduced NADP produced;
Less GP to triose phosphate;