3.5.1 Photosynthesis

Question 1

Where do the LDR and LIR take place

Answer 1

LDR - thylakoid
LIR - stroma

Question 2

Explain the role of light in photoionisation

Answer 2

Pigment absorbs energy from light
Excites 2 electrons and they are released and go down electron transfer chain

Question 3

What happens in the electron transfer chain (ETC)

Answer 3

Electrons released from pigment move down a series of carrier proteins in thylakoid membrane, undergo a series of redox reactions which releases energy

Question 4

How is a H+ gradient established

Answer 4

Some energy from ETC is used to actively transport H+ from stroma into thylakoid space

Question 5

How is ATP produced in LDR

Answer 5

H+ moves down conc gradient from thylakoid space into stroma via ATP synthase. ATP synthase catalyses ADP+Pi -> ATP

Question 6

Explain the role of light in photolysis

Answer 6

Light energy splits molecules of water
2H2O –> 4H+ + 4e- + O2

Question 7

What happens to products of photolysis of water

Answer 7

H+ moves out thylakoid by ATP synthase to LIR
e- replaces electrons lost from pigment
O2 - respiration or diffuses out as waste

Question 8

How and where is NADP produced in LDR

Answer 8

NADP + H+ + 2e- –> NADPH
Stroma

Question 9

Describe what happen between RuBP and CO2

Answer 9

Reaction between RuBP and CO2 is catalysed by rubisco
Forms 2x GP

Question 10

Describe what happens to GP

Answer 10

Using energy released from ATP and H+ from NADPH, GP is reduced into 2x triose phosphate

Question 11

How does the LIR result in growth

Answer 11

1 carbon leaves the cycle each time
eg some of the TP is converted into useful organic molecules eg hexose sugar

Question 12

What happens to TP in LIR

Answer 12

After 1C leaves the cycle, RuBP reforms using phosphate from ATP

Question 13

Describe the structure of a chloroplast

Answer 13

Disc shaped
Double membrane
Thylakoids - flattened discs stack to form grana
Lamellae
Stroma

Question 14

How does the structure of the chloroplast maximise the rate of LDR

Answer 14

Large SA of thylakoid membrane for ETC
Photosystems position chlorophyll to enable maximum absorption of light
ATP synthase channels within granal membrane

Question 15

How does the structure of the chloroplast maximise the rate of the LIR

Answer 15

Own DNA and ribosomes for synthesis of enzymes eg rubisco
Conc of enzymes and substrates in stroma is high

Question 16

Define limiting factor

Answer 16

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

Question 17

3 environmental factors that can limit the rate of photosynthesis

Answer 17

Light intensity
Co2 levels
Temperature

Question 18

Common agricultural processes used to overcome limiting factors

Answer 18

Artificial light
Artificial heating
Addition of CO2 to greenhouse atmosphere

Question 19

Why do farmers try to overcome the effect of limiting factors

Answer 19

To increase yield
Additional cost must be balanced with yield to ensure maximum profit

Question 20

Outline a method for extracting photosynthetic pigments

Answer 20

Use a pestle and mortar to grind a leaf with an extraction solvent eg propanone

Question 21

Outline how paper chromatography can be used to separate photosynthetic pigments

Answer 21

Use a capillary tube to spot pigment extract onto pencil origin line
Place chromatography paper in solvent
Allow solvent to run until it nearly reaches end of paper

Question 22

State the number of carbon atoms in RuBP, GP, TP

Answer 22

RuBP = 5
GP = 3
TP =3