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

Answer 5

• 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 6

Describe what happens during photoionisation in the light dependent reaction.

Answer 6

• 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 7

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

Answer 7

• 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 8

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

Answer 8

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

Question 9

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

Answer 9

• Absorb different/more wavelengths of light for photosynthesis;