Photosynthesis

Question 1

Describe the light-dependent reaction.

Answer 1

• chlorophyll absorbs light energy and excites electrons via photoionisation
• electrons move along electron transport chain releasing energy in a series of redox reactions
• forms proton gradient
• protons move through ATP synthase
• provides energy for ADP + Pi = ATP
• photolysis of water produces 2 protons, 2 electrons and 1/2 oxygen = PHOTOLYSIS
• NADPH by electrons

Question 2

Products of light-dependent reaction.

Answer 2

• ATP
• NADPH

Question 3

Describe the light independent reaction.

Answer 3

• carbon dioxide fixates with RuBP
• produces two GP molecules
• GP reduced to two triose phosphate molecules
• using reduced NADPH
• using energy from ATP
• TP converted to glucose/ RuBP and other organic substances

Question 4

Where does the light dependent reaction occur?

Answer 4

• thylakoid membrane

Question 5

Where does the light independent reaction occur?

Answer 5

• stroma

Question 6

Why do plants with more chlorophyll grow faster than those with less?

Answer 6

• faster production of ATP and reduced NADP
• more LIR
• produce more sugars that can be used in respiration
• more energy for growth
• faster synthesis of new organic materials

Question 7

Suggest why ATP isn’t just produced in the LDR.

Answer 7

• plants don’t photosynthesise in the dark
• not all parts photosynthesise
  plants require more than is produced in the LDR
• ATP used in active transport

Question 8

Describe the effect of introducing an inhibitor on the ETC.

Answer 8

• reduced transfer of protons across thylakoid membrane
• so less ATP
• so less NADPH
• so LIR slows/stops

Question 9

Describe what happens during photoionisation in the LDR.

Answer 9

• light excites electrons
• electrons lost

Question 10

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

Answer 10

• ink and leaf pigments would mix

Question 11

Describe the method used to separate the pigments after the solution of pigment had been applied to origin.

Answer 11

• level of solvent below origin
• stop before top is reached

Question 12

Suggest and explain the advantage to plants having different colour leaf pigments.

Answer 12

• absorb different/ more wavelengths of light for photosynthesis

Question 13

Explain relationship between stomatal opening and photosynthesis.

Answer 13

• stomata allow uptake of carbon dioxide
• carbon dioxide required for photosynthesis