Photosynthesis

Question 1

Describe the light dependent reaction of photosynthesis.

Answer 1

• chlorophyll absorbs light energy which excites electrons- photo ionisation
• electron is lost to electron transport chain
  -electron goes down through a series of redox reactions releasing energy
  -energy maintains proton gradient across the thylakoid membrane
  -H+ moves through ATP synthase
  -providing energy for the joining of ADP and Pi forming ATP
• photolysis of water= 2H2O—> 4E- + 4H+ + O2
• H+ and electrons used to reduce NADP forming NADPH

Question 2

Name two of the products of light dependent reaction used in the light independent reaction.

Answer 2

• NADPH
  -ATP

Question 3

Describe the light independent reaction

Answer 3

-RuBP is combined with CO2 to form 2GP
-GP is then reduced to triose phosphate
-using NADPH
-using energy from ATP
-triose phosphate converted to organic compounds such as glucose

Question 4

Where is rubisco found in the cell?

Answer 4

Stroma

Question 5

Explain why scientists measure rate of production of oxygen in this investigation. 2 marks

Answer 5

-oxygen is produced in light dependent reaction of photosynthesis
-faster the rate of production of oxygen the faster the rate of light dependent reaction of photosynthesis

Question 6

Explain why plants that have more chlorophyll will grow faster than plants with less chlorophyll. 5 marks

Answer 6

• faster production of NADPH and ATP
• so faster rate of light dependent reaction
  -so more sugars produced for respiration
• so have more energy for growth
• faster synthesis of organic materials

Question 7

ATP is produced in the light dependent reaction, suggest why this isn’t their only source of ATP. 4 marks

Answer 7

• not all parts of the plant photosynthesise eg roots
• can not photosynthesise in the dark
  -plant requires more ATP than produced in light dependent reaction
  -ATP used in active transport

Question 8

Describe the effect of introducing a herbicide (electron transport inhibitor).

Answer 8

• proton gradient is not maintained across the thylakoid membrane
• less ATP produces
  -less NADPH produced
  -slower rate of light independent reaction

Question 9

Describe what happens during photo ionisation in the light dependent reaction.

Answer 9

-chlorophyll absorbs light energy exciting electrons
- electrons are lost and travel down electron transport chain through a series of redox reactions releasing energy

Question 10

When produces a chromatogram explain why the origin is marked using a pencil rather than ink.

Answer 10

• pencil will not move with the solvent front whereas ink will
  -pencil will not contaminate results whereas ink will mix with leaf pigment

Question 11

While making a chromatogram describe the method used to separate the pigments after the solution of pigment has been apply to the origin. 2 marks

Answer 11

-level of solvent below the origin line
-remove before solvent line reaches the end

Question 12

Suggest and explain the advantage to plants having different colour pigments in leaves.

Answer 12

-wider range of wavelengths of light can be absorbed for photosynthesis

Question 13

Explain the relationship between stomatal opening and photosynthesis. 2 marks

Answer 13

-stomata opening allows co2 to enter
-co2 used in light independent reaction of photosynthesis