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

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

Answer 2

• ATP;
• Reduced NADP;

Question 3

Describe the light independent reaction

Answer 3

• 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 4

Where precisely is rubisco found in a cell?

Answer 4

• Stroma

Question 5

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

Answer 5

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

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 dependant 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
  OR
• 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
  OR
• (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;