Photosynthesis

Question 1

What does a chloroplast contain?

Answer 1

Outer membrane, inner membrane, thylakoids, grana, stroma, 70s ribosomes, circular DNA, starch grains

Question 2

Where in a chloroplast does the light dependent reaction take place?

Answer 2

Thylakoid membrane

Question 3

Where in a chloroplast does the light independent reaction (Calvin cycle) take place?

Answer 3

Stroma

Question 4

How do plants use light energy during the light dependent reaction? (6)

Answer 4

1. Chlorophyll absorbs lights which excites electrons so they leave the chlorophyll (photoionisation)
2. Light splits H2O into H+, O2, and electrons (photolysis) and the chlorophyll regains its lost electrons
3. Electrons lost from chlorophyll are transferred down the thylakoid membrane by electron carriers via redox reactions - electrons lose energy (electron transfer chain)
4. Energy released is used to pump H+ across the thylakoid membrane which creates a H+ gradient
5. H+ diffuse back over the thylakoid membrane via ATP synthase which releases energy used to produce ATP from ADP + Pi
6. H reduces NADP to NADPH

Question 5

How is CO2 coverted into organic substances (light independent reaction)? (6)

Answer 5

1. CO2 reacts with RuBP, catalysed by the Rubisco enzyme, to produce 2 molecules of GP
2. GP is reduced by NADPH using the energy released from the hydrolysis of ATP to produce 2 molecules of triose phosphate
3. 1 carbon from triose phosphate is used to produce organic substances
4. Remaining 5 carbons are used to regenerate RuBP using energy released from the hydrolysis of ATP

Question 6

What are the 3 limiting factors of photosynthesis?

Answer 6

1. Light intensity
2. Temperature
3. CO2 concentration

Question 7

How does increased light intensity increase the rate of photosynthesis?

Answer 7

More light dependent reaction so more ATP and NADPH produced so more GP reduced to triose phosphate in light independent reaction

Question 8

How does increased temperature increase the rate of photosynthesis?

Answer 8

Light independent reaction happens faster as enzymes (Rubisco) have more kinetic energy so more enzyme-substrate complexes form

Question 9

How does increased CO2 concentration increase the rate of photosynthesis?

Answer 9

More CO2 reacts with RuBP so more GP produced and reduced to triose phosphate so more organic substances produced and RuBP regenerated

Question 10

Which is the limiting factor when a graph first starts to increase?

Answer 10

Whichever is on the x-axis

Question 11

How do you explain why light intensity is a limiting factor?

Answer 11

As you increase light intensity, rate of photosynthesis increases