Photosynthesis

Question 1

Where does the light-dependent reaction occur in plants?

Answer 1

In the thylakoids of chloroplasts

Question 2

Where does the light-independent reactions occur in plants?

Answer 2

In the stroma of chloroplasts

Question 3

Explain the role of light in photoionisation

Answer 3

• chlorophyll molecules absor energy from photons of light

- excites 2 electrons causing them to be released from the chlorophyll

Question 4

What does exciting an electron mean?

Answer 4

Raising it to a higher energy level

Question 5

What are the 2 main stages involved in ATP production in the light-dependent reaction?

Answer 5

• ETC

- chemiosmosis

Question 6

What happens in the ETC?

Answer 6

Electrons released from chlorophyll moved down a series of carrier proteins embedded in the thylakoid membrane & undergo a series of redox reaction, which releases energy

Question 7

How is a proton concentration gradient established during chemiosmosis?

Answer 7

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

Question 8

How does chemiosmosis produce ATP in the light-dependent stage?

Answer 8

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

Question 9

Explain the role of light in photolysis

Answer 9

Light energy splits molecules of water

Question 10

What are the products of photolysis of water?

Answer 10

• H+ ions
• e-
• O2

Question 11

What happens to H+ ions in photolysis?

Answer 11

Move out of thylakoid space via ATP synthase and are used to reduce the coenzyme NADP

Question 12

What happens to electrons in photolysis?

Answer 12

Replace electrons lost from chlorophyll

Question 13

What happens to oxygen in photolysis?

Answer 13

Used for respiration or diffuses out of leaf as waste gas

Question 14

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

Answer 14

• NADP + 2H + 2e- -> reduced NADP
• catalysed by dehydrogenase enzymes
• stroma of chloroplasts

Question 15

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

Answer 15

• H+ ions: photolysis of water

- Electrons: NADP acts as the final electron acceptor of the ETC

Question 16

Name the 3 main stages in the Calvin cycle

Answer 16

• carbon fixation
• reduction
• regeneration

Question 17

What happens during carbon fixation?

Answer 17

• Reaction between CO2 & RuBP catalysed by rubisco

- Forms unstable 6C intermediate that breaks down into 2x GP

Question 18

What happens during reduction in the Calvin cycle?

Answer 18

• 2x GP are reduced to 2x TP
• requires 2x reduced NADP & 2x ATP
• forms 2x NADP & 2x ADP

Question 19

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

Answer 19

1C leaves the cycles

- some of the TP is converted into useful organic molecules

Question 20

What happens during regeneration in the Calvin cycle?

Answer 20

• after 1C leaves the cycle, the 5C compound RuP forms
• RuBP is regenerated from RuP using an ATP
• forms 1 ADP

Question 21

State the roles of ATP & reduced NADP in the light-independent reaction

Answer 21

• ATP: reduction of GP to TP & provides phosphate group to convert RuP into RuBP
• reduced NADP: coenzyme transports electrons needed for reduction of GP to TP

Question 22

How many carbon atoms in RuBP, GP & TP?

Answer 22

RuBP: 5
GP: 3
TP:3

Question 23

Describe the structure of a chloroplast

Answer 23

• usually disc-shaped
• double membrane
• thylakoids
• integranal lamellae
• stroma

Question 24

What is a thylakoid?

Answer 24

Flattened disc that stacks to form grana

Question 25

What are intergranal lamellae?

Answer 25

Tubular extensions attach thylakoids in adjacent grana

Question 26

What is the stroma?

Answer 26

Fluid filled matrix

Question 27

How does the structure of the chloroplast maximise the rate of the light-dependent reaction?

Answer 27

- ATP synthase channels within granal membrane - large surface area of thylakoid membrane for ETC - photosystems position chlorophyll to enable maximum absorption of light

Question 28

How does the structure of the chloroplast maximise the rate of the light-independent reaction?

Answer 28

- own DNA & ribosomes for synthesis of enzymes like rubisco | - concentration of enzymes & substrates in stroma is high

Question 29

What is a limiting factor?

Answer 29

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

Question 30

Name 4 environmental factors that can limit the rate of photosynthesis

Answer 30

- light intensity - CO2 levels - temperature - mineral/magnesium levels

Question 31

What are some common farming practices used to overcome the limiting factors affecting photosynthesis?

Answer 31

- artificial light especially at night - artificial heating - additon of CO2 to greenhouse atmosphere

Question 32

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

Answer 32

- to increase yield | - additional cost must be balanced with yield to ensure maximum profit

Question 33

How could a student investigate the effect of a named variable on the rate of photosynthesis?

Answer 33

1. Use a potometer 2. Place balls of calcium alginate containing green algae in hydrogencarbonate indicator 3. Colour change orange -> magenta as CO2 is consumed & pH increases

Question 34

State the purpose and principle of paper chromatography

Answer 34

Molecules in a mixture are separated based on their relative attraction to the mobile phase vs the stationary phase

Question 35

Outline a method for extracting photosynthetic pigments

Answer 35

Use a peste and mortar to grind a leaf with an extraction solvent

Question 36

How can paper chromatography be used to separate photosynthetic pigments?

Answer 36

1. Use a capillary tube to spot pigment extract into pencil start line 1cm above bottom of paper 2. Place chromatography paper in solvent 3. Allow solvent to run until it almost touches the end of the paper 4. Pigments move different distances

Question 37

What are Rf values?

Answer 37

- ratios that allow comparison of how far molecules have moved in chromatograms

Question 38

How can Rf values be calculated?

Answer 38

Distance between origin and centre of pigment spot / distance between origin and solvent front