Photosynthesis

Question 1

Equation for photosynthesis

Answer 1

6CO2 + 6H2O + energy from photons –> C6H12O6 + 6O2

Question 2

How is the glucose produced used?

Answer 2

Converted to disaccharide for transport and then to starch for storage

Question 3

What is carbon fixation?

Answer 3

The process by which carbon dioxide is converted to sugars. It is endothermic so requires energy. It also needs electrons so it is a reduction reaction. Photosynthesis is an example of carbon fixation.

Question 4

What is the compensation point?

Answer 4

When photosynthesis and respiration occur at the same rate so that there is no net gain or loss of carbohydrate.

Question 5

What is the compensation period?

Answer 5

The time taken to reach the compensation point

Question 6

Why do grana have large surface areas?

Answer 6

• distributions of photosystems that contain photosynthetic pigments that trap light energy
• for electron carriers and ATP synthase

Question 7

What does the stroma contain?

Answer 7

Enzymes needed to catalyse LIR, starch grains, oil droplets, small ribosomes and a loop of DNA

Question 8

Chlorophyll a

Answer 8

• P680 found in photosystem II, peak of absorption is light at wavelength at 680nm
• P700 in photosysyem I
  Both absorb red light

Question 9

Chlorophyll b

Answer 9

absorbs light that appears yellow green

Question 10

Photolysis

Answer 10

The splitting of water by an enzyme in the presence of light
2H2O –> 4H+ + 4e- + O2

Question 11

Non-cyclic photophosphorylation

Answer 11

1. Photon of light strikes PSII and its energy is channelled to the primary pigment P680
2. Light energy excites a pair of electrons which escape from the chlorophyll molecule and are captured by an electron carrier
3. These electrons replaced by electrons from photolysis
4. The iron ion in the electron carrier becomes reduced to Fe3+, then donates an electron to the next carrier to become reoxidised to Fe2+
5. As electrons are passed down ETC energy is released and is used to pump protons across the thylakoid membrane into the thylakoid space
6. Electrons captured by PSI which has lost electrons due to excitation by light energy
7. Electrochemical gradient forms so protons diffuse down gradient through ATP synthase causing ATP to form.
8. As protons pass through channel they are accepted, along with electrons, by NADP which becomes reduced, catalysed by NADP reductase

Question 12

Cyclic photophosphorylation

Answer 12

• uses only PSI
• light strikes PSI so electrons escape, pass to electron carrier system and back to PSI
• small amount of ATP produced
• no photolysis of water, no protons or oxygen produced so no NADPH is generated