Photosynthesis

Question 1

Describe the light dependent reaction

Answer 1

• Chlorophyll absorbs light energy & Excites electrons
• Chlorophyll loses electrons (Oxidation of chlorophyll) via photoionisation;
• Electrons move along 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 (occurs in thylakoid space) of water produces 2 protons, 2 electrons and ½ oxygen (replace e- lost during photoionisation)
• NADP reduced by electrons and protons

Question 2

Describe the light independent reaction (Calvin Cycle)

Answer 2

• Carbon dioxide combines with ribulose bisphosphate/RuBP (5C)
• Produces two glycerate (3-)phosphate/GP;
• GP reduced to triose phosphate;
• Using reduced NADP;
• Using energy from ATP;
• Triose phosphate converted to glucose/RuBP/ other 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 (e.g. roots) 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

Answer 4

• Reduced transfer of protons across thylakoid membrane
• (So) less ATP produced;
• (So) less reduced NADP produced;
• (So) light-independent reaction rate decreases
• Less reduction of GP to triose phosphate;

Question 5

Describe what happens during PHOTOIONISATION in the light dependent reaction.

Answer 5

• Chlorophyll absorbs light, excites electrons
• Electrons are lost

Question 6

Role of ATP

Answer 6

• provides energy for active transport/ muscle contraction
• releases energy in small amounts
• one step
• makes energy available rapidly
• phosphorylates
• reformed

Question 7

Where does photolysis occur

Answer 7

thylakoid space

Question 8

Fluorescence

Answer 8

excited e- cannot lose energy via the ETC so releases the energy as light or heat

Question 9

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

Answer 9

• 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 10

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

Answer 10

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

Question 11

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

Answer 11

• Absorb different/more wavelengths of light for faster rates of photosynthesis;

Question 12

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

Answer 12

1. ATP;
2. Reduced NADP;

Question 13

Where precisely is rubisco found in a cell?

Answer 13

Stroma

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Explain the relationship between stomatal opening and photosynthesis.

Answer 16

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

Question 17

Where does LDR/ LIR occur?

Answer 17

LDR= thylakoid
LIR= stroma