Photosynthesis exam questions

• In photosynthesis, which chemicals are needed for the light-dependent reaction?

  NADP, ADP, Pi and water
• Describe what happens during photoionisation in the light-dependent reaction

  1.Chlorophyll absorbs light

  OR

  Light excites/moves electrons in chlorophyll; Ignore photosystems.

  2. Electron/s are lost

  OR

  (Chlorophyll) becomes positively charged
• Explain why the student marked the origin using a pencil rather than using ink.


  1.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;
• Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin

  1.Level of solvent below origin/line;

  Reject water or any named aqueous solution. Accept named organic solvent.

  2. Remove/stop before (solvent) reaches top/end
• The pigments in leaves are different colours.

  Suggest and explain the advantage of having different coloured pigments in leaves

  (Absorb) different/more wavelengths (of light) for photosynthesis;See an expert-written answer!We have an expert-written solution to this problem!
• Heat stress decreases the light-dependent reaction of photosynthesis.

  Explain why this leads to a decrease in the light-independent reaction

  1.(Less/no) ATP;

  2. (Less/no) reduced NADP;
• A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.

  Explain why

  1.(Less/no) carbon dioxide (reacts) with RuBP; 2. (Less/no) GP
• Where precisely is rubisco found in a cell?

  1.troma (of/in chloroplast);
• In natural ecosystems, most of the light falling on producers is not used in photosynthesis.

  Suggest two reasons why

  1.(Light is) reflected; Light is not absorbed on its own is not enough.

  2. (Light is) wrong wavelength;

  Accept frequency for wavelength. Accept reference to absorbing specified wavelengths/frequencies.

  3. (Light) misses chlorophyll/ chloroplasts/photosynthetic tissue;

  4. CO2 concentration or temperature is a limiting factor;
• Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.

  Explain how this reduces the rate of photosynthesis in weeds


  1.Reduced transfer of protons across thylakoid membrane

  OR

  Reduced chemiosomotic gradient / proton gradient across thylakoid membrane;

  2. (So) less ATP produced;

  3. (So) less reduced NADP produced;

  Accept NADPH / NADPH2 / NADPH+

  Reject reduced NAD

  4. (So) light-independent reaction slows / stops;

  OR

  Less reduction of GP to triose phosphate