photosynthesis

Question 1

During photosynthesis, oil-palm trees convert carbon dioxide into organic substances. Describe how (6)

Answer 1

1.      Carbon dioxide combines with ribulose bisphosphate

2.      Produces two molecules of glycerate (3-)phosphate

3.      Reduced to triose phosphate

4.      Using reduced NADP;

5.      Using energy from ATP;

6.      Triose phosphate converted to other organic substances

7.      In light independent reaction / Calvin cycle;

Question 2

The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur (5)

Answer 2

1.      High concentration of carbon dioxide at night

2.      No photosynthesis in night

3.    In night plants  respire;

4.      In light, net uptake of carbon dioxide by plants / plants use more carbon dioxide than they produce

5.      Decrease in carbon dioxide concentration with height;

6.      At ground level fewer leaves / less photosynthesis/ less light

Question 3

In the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. Describe how (5)

Answer 3

1.      Carbon dioxide combines with ribulose bisphosphate

2.      To produce two molecules of glycerate 3-phosphate / GP;

3.      Reduced to triose phosphate / TP;

4.      Requires reduced NADP;

5.      Energy from ATP;

Question 4

In the light-dependent reaction of photosynthesis, light energy generates ATP.

Describe how (5)

Answer 4

1.      Light excites electrons in chlorophyll;

2.      Electrons pass down electron transfer chain;

3.   passage involves redox reactions;

4.      Electron transfer chain associated with chloroplast membranes e.g. chemiosmosis

5.      Energy released

6.      ATP generated from ADP and phosphate

Question 5

  Describe the light-independent reactions of photosynthesis and explain how they allow the continued synthesis of hexose sugars (6)

Answer 5

1.       RuBP combines with CO2;

2 .      to form 3C compound / TP / GP;

3 .     using ATP;

4.       and reduced NADP /

5.       2 molecules of 3C compound / TP / GP form hexose;

6 .      all RuBP is regenerated;

Question 6

     Describe the role of electron transport chains in the light-dependent reactions of photosynthesis (6)

Answer 6

  1.       electron transport chain accepts excited electrons;

2.       from chlorophyll

3.       electrons lose energy along chain;

4.       ATP produced;

5.       from ADP and Pi;

6.       reduced NADP formed;

Question 7

Explain why the increase in the dry mass of a plant over twelve months is less than the mass of hexose produced over the same period (3)

Answer 7

   1.       some hexose / biomass used in respiration;

2.       CO2 produced (is lost to air);

3.       some parts of the plant are eaten / some lost to decomposers / in leaf fall;