Photosynthesis

Question 1

Where does the light dependent reaction take place?

Answer 1

In the thylakoids of the chloroplasts

Question 2

Where does the light independent reaction take place?

Answer 2

Stroma of the chloroplasts

Question 3

Explain the role of photoionisation

Answer 3

Chlorophyll molecules absorb energy from photons of light

This ‘excites’ 2 electrons causing them to be released from the chlorophyll

Question 4

Name the two main stages involved in ATP production in the light dependent reaction

Answer 4

Electron transfer chain

Chemiosmosis

Question 5

What happen in the electron transport chain?

Answer 5

Electrons are released from chlorophyll move down a series of carrier proteins in the thylakoid membrane and undergo a series f redox reactions which releases energy

Question 6

How is a proton concentration gradient established during chemiosmosis?

Answer 6

Some energy released from the ETC is coupled to the active transport of protons from the stroma into the thylakoid space

Question 7

How does chemiosmosis produce ATP in the light dependent stage?

Answer 7

Protons move down their concentration gradient from the thylakoid space into the stroma via ATP synthase

Question 8

Explain the role of light in photolysis

Answer 8

Light energy splits molecules of water

2 H20 = 4H+ + 4e- + O2

Question 9

What happens to the products of the photolysis of water?

Answer 9

H+ ions: move out of the thylakoid space via ATP synthase and are used to reduce the coenzyme NADP

e-: replace electrons lost from chlorophyll

O2: used to respiration or diffuses out of leaf as waste gas

Question 10

How and where is reduced NADP produced in the light dependent reaction?

Answer 10

NADP + 2H+ + 2e- = reduced NADP

Catalysed by dehydrogenase enzymes

Stroma of chloroplasts

Question 11

Where do the H+ ions and electrons used to reduce NADP come from?

Answer 11

H+ ions: photolysis of water

Electrons: NADP acts as the final electron acceptor of the electrons transport chain

Question 12

Name the 3 stages in the Calvin cycle

Answer 12

1. Carbon fixation
2. Reduction
3. Regeneration

Question 13

What happens during carbon fixation?

Answer 13

Reaction between CO2 and ribulose bisphosphate catalysed by rubisco

Forms unstable 6C intermediate that breaks down into 2x glycerate 3 phosphate

Question 14

What happens during reduction?

Answer 14

2x glycerate-3-phosphate are reduced to 2x triose phosphate

Requires 2 x reduced NADP and 2 x ATP

Question 15

How does the light independent reaction result in the production of useful organic substances?

Answer 15

1C leaves the cycle

Question 16

What happens during regeneration?

Answer 16

After 1C leaves the cycle the 5C compound Rup forms

RuBP is regenerated from RuP using 1x ATP

Forms 1x ADP

Question 17

State the roles of ATP and reduced NADP in the light independent reaction

Answer 17

ATP: reduction of glycerate 3 phosphate to triose phosphate and provides a phosphate group to convert RuP into RuBP

Reduced NADP: coenzyme transports electrons needed for reduction of glycerate 3 phosphate to trios phosphate

Question 18

State the number of carbon atoms in RuBP, glycerate 3 phosphate and triose phosphate

Answer 18

RuBP: 5
Glycerate-3-phosphate: 3
Triose phosphate: 3

Question 19

Describe the structure of a chloroplast

Answer 19

Disc shaped

Double membrane

Thylakoids: flattened discs stack to form grana

Intergranal lamellae

Stroma

Question 20

How does the structure of chloroplasts maximise the rate of the light dependent reaction?

Answer 20

ATP synthase channels with granal membrane

Large surface area of thylakoid membrane for ETC

Photosystems position chlorophyll to enable maximum absorption of light

Question 21

How does the structure of the chloroplasts maximise the rate of the light independent reaction?

Answer 21

Own DNA and ribosomes for synthesis of enzymes

Concentration of enzymes and substrates in stroma is high

Question 22

What is a limiting factor?

Answer 22

A factor that determines maximum rate of a reaction even if other factors change to become more favourable

Question 23

Name 4 environmental factors that can limit the rate of photosynthesis

Answer 23

Light intensity
CO2 levels
Temperature
Mineral levels

Question 24

Outline some agricultural practices used to overcome the effect of limiting factors in photosynthesis

Answer 24

Artificial light
Artificial heating
Addition of CO2 to greenhouse atmosphere

Question 25

Why do farmers try to overcome the effect of limiting factors?

Answer 25

To increase yield

Additional cost must be balanced with yield to ensure maximum profit