Photosynthesis

Question 1

Describe the light dependent reaction.

Answer 1

• Chlorophyll absorbs light energy and 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/RuBP/ named organic substance;

Question 3

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

Answer 3

• Plants don’t photosynthesise in the dark
• Not all the parts of the plants photosynthesise
• Plants require more ATP than is produced in the light dependent 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 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

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
• (With ink) origin/line in different position
• (With pencil) origin/line in same position
• (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