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 electron transport chain releasing energy
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

Name the two products of the light-dependent reaction that are required for the light-independent reaction.

Answer 2

ATP;
Reduced NADP:

Question 3

Proton pumping to form a proton gradient is an example of active transport.
True or False

Answer 3

False:
Active transport requires ATP!
Energy for proton pumping is from high energy electrons.

Question 4

Describe the light independent reaction

Answer 4

Carbon dioxide combines/reacts with RuBP;
2. Produces two glycerate (3- )phosphate/GP using (enzyme)
Rubisco;
3. GP reduced to triose phosphate;
4. Using reduced NADP;
5. Using energy from ATP;
6. Triose phosphate converted to glucose/hexose/RuBP/ribulose bisphosphate/named organic substance;

Question 5

Where precisely is rubisco found in a cell?

Answer 5

Stroma

Question 6

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

Answer 6

Have faster production of ATP and reduced
NADP;
(So) have faster / more light-independent reaction;
(So) produce more sugars that can be used in respiration;
(So) have more energy for growth;
Have faster / more synthesis of new organic materials.

Question 7

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

Answer 7

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 8

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

Answer 8

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
Less reduction of GP to triose phosphate;

Question 9

Describe what happens during photoionisation in the light dependent reaction.

Answer 9

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 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Absorb different/more wavelengths of light for photosynthesis;

Question 13

Explain the relationship between stomatal opening and photosynthesis.

Answer 13

Stomata allow uptake of carbon dioxide;
Carbon dioxide used in / required for photosynthesis;

Question 14

Explain why scientists measure the rate of production of oxygen in this investigation. (Rate of photosynthesis)

Answer 14

Oxygen produced in light-dependent reaction;
The faster (oxygen) is produced, the faster the light-dependent reaction.