Photosynthesis

Question 1

Describe the light dependent reaction

Answer 1

• Chlorophyll absorbs light energy & Excites electrons
• electrons removed (Oxidation of chlorophyll) via photoionisation;
• Electrons move along carriers/electron transport chain releasing energy (Series of REDOX reactions)
• Energy released (by electrons) used to form proton gradient;
• H+ ions move through ATP synthase;
• providing energy to join ADP and Pi to form ATP;
• Photolysis of water produces 2 protons, 2 electrons and ½ oxygen;
• NADP reduced by electrons / electrons and protons / hydrogen;

Question 2

Describe the light independent reaction

Answer 2

• Carbon dioxide combines with ribulose bisphosphate/RuBP;
• Produces two glycerate (3-)phosphate/GP;
• GP reduced to triose phosphate;
• Using reduced NADP;
• Using energy from ATP;
• Triose phosphate converted to glucose/hexose/RuBP/ named organic substance;

Question 3

ATP is produced in the light dependant reaction, suggest why this is not their (plants) only source of ATP.

Answer 3

• Plants don’t photosynthesis in the dark;
• Not all the parts of the plants photosynthesise;
• Plants require more ATP than is produced in the light dependant reaction;
• ATP used in Active Transport (accept other named processes)

Question 4

Describe the effect of introducing a herbicide/inhibitor on the electron transport chain (4)

Answer 4

• Reduced transfer of protons across thylakoid membrane
OR
• Reduced chemiosmotic gradient/proton gradient across thylakoid membrane;
• (So) less ATP produced;
• (So) less reduced NADP produced;
• (So) light-independent reaction slows/stops
OR
• Less reduction of GP to triose phosphate;

Question 5

Describe what happens during photoionisation in the light dependent reaction.

Answer 5

• Chlorophyll absorbs light
OR
Light excites/moves electrons in chlorophyll;
• Electron/s are lost
OR
(Chlorophyll) becomes positively charged;
Accept electrons go to electron transport/carrier chain for ‘electrons lost’.

Question 6

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

Answer 6

• Ink and (leaf) pigments would mix
OR
• (With ink) origin/line in different position
OR
• (With pencil) origin/line in same position
OR
(With pencil) origin/line still visible;

Question 7

While making a chromatogram, describe the method used to separate the pigments after the solution of pigment had been applied to the origin.

Answer 7

• Level of solvent below origin/line;
• Remove/stop before (solvent) reaches top/end;

Question 8

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

Answer 8

• Absorb different/more wavelengths of light for photosynthesis;

Question 9

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 9

1.High concentration of carbon dioxide at night

2.No photosynthesis in dark

3.(In dark) plants (and other organisms) respire;

4.In light, net uptake of carbon dioxide by plants/ plants use more carbon dioxide than they produce/ rate of photosynthesis greater than rate of (aerobic) respiration;

5.Decrease in carbon dioxide concentration with height;

6. At ground level fewer leaves/less photosynthesising
   tissue/more animals/less light; (e.g. roots do not
   photosynthesise)

Question 10

Describe and explain the importance of
Photolysis (3 marks)

Answer 10

Replaces electrons lost from chlorophyll
Maintains a higher proton concentration within the thylakoid space (compared to stroma)

Question 11

Contrast Nuclear and Chloroplast
DNA (3marks)

Answer 11

DNA
[3 marks]
1. (Associated with) histones/proteins
no histones/proteins;
2.Linear v circular;
3.Introns v no introns;
4.Long(er) v short(er);

Question 12

explain the relationship between stomatal opening and photosynthesis

Answer 12

1.stomata allows uptake of co2
2. co2 required in photosynthesis

Question 13

name two products of the light dependent reaction that are required for the light independent reaction

Answer 13

1. ATP
2. reduced NADP

Question 14

where precisely is rubisco found in a cell?

Answer 14

stroma

Question 15

explain why the scientists measured the rate of production of oxygen in this investigation (rate of photosynthesis)

Answer 15

1. oxygen produced in the light dependent reaction
2. the faster oxygen is produced the faster the light dependent reaction

Question 16

explain why plants that have more chlorophyll will grow faster than plants with less chlorophyll[5]

Answer 16

1.have faster production of ATP and reduced NADP

2. so have fast light independent reaction
3. so produced more sugars that can be used in respiration
4. so have more energy for growth
5. so more synthesis of new organic materials