5.1 Photosynthesis

Question 1

How are chloroplasts structured?

Answer 1

• Membrane-bound organelle
• Stroma containing thylakoids, circular DNA, 70s ribosomes, starch granules

Question 2

What happens during the light-dependent reaction?

Answer 2

• Chlorophyll absorbs light energy which excites its electrons
• So electrons are released from chlorophyll
• Electrons move along the electron transport chain, releasing energy
• This energy is used to actively transport protons into thylakoid
• Protons diffuse down their electrochemical gradient into stroma via ATP synthase
• Releasing energy which is used to join ADP + Pi to form ATP
• NADP accepts a proton and electron to become reduced NADP
• Water splits to produce proteins, electrons and oxygen

Question 3

What happens during the light-independent reaction?

Answer 3

• CO2 reacts with RuBP to form 2 molecules of GP
• Catalysed by the enzyme rubisco
• GP is reduced to triose phosphate using reduced NADP and energy from ATP
• Some triose phosphate is converted into useful organic substances
• Some triose phosphate used to regenerate RuBP using energy from ATP

Question 4

What factors affect rate of photosynthesis?

Answer 4

• Temperature
• Light intensity
• Carbon dioxide concentration