CH11 Photosynthesis

Question 1

Where does light-dependant reaction occur

Answer 1

Thylakoids of chloroplasts

Question 2

Where does the light-independent reaction take place

Answer 2

Stroma of chloroplasts

Question 3

Role of light in photoionisation

Answer 3

Chlorophyll absorb energy from photons of light
This excited 2 electrons (raises them to a higher energy level)
Causing them to be released from the chlorophyll

Question 4

2 main stages in ATP production in LDR

Answer 4

Electron transfer chain

Chemiosmosis

Question 5

What happens in electron transfer chain (ETC)

Answer 5

Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane and undergo a series of redox reactions, releasing energy

Question 6

How is a proton concentration gradient established during chemiosmosis

Answer 6

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

Question 7

How does chemiosmosis produce ATP in the LDR

Answer 7

H+ ions move down their concentration gradient from the thylakoid space into the stroma via the channel protein ATP synthase
ATP synthase catalyses:
ADP + Pi –> ATP

Question 8

What is photolysis

Answer 8

The splitting of water into 2 electrons 2 protons and oxygen gas

Question 9

What happens to products of photolysis

Answer 9

H+ = Move out of thylakoid space via ATP synthase and are used to reduce coenzyme NADP
e- = Replace electrons lost from chlorophyll
O2 = Used for respiration or diffuses out of leaf as waste gas

Question 10

How and where is reduced NADP produced in LDR

Answer 10

NADP + 2H+ + 2e- –> reduced NADP
Catalysed by dehydrogenase enzymes
Stroma of chloroplasts

Question 11

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

Answer 11

H+ = photolysis of water
e- = NADP is final electron acceptor in ETC

Question 12

3 main stages of Calvin Cycle

Answer 12

Carbon fixation
Reduction
Regeneration

Question 13

What occurs during carbon fixation

Answer 13

Reaction between CO2 and (RuBP) catalysed by rubisco

Forms unstable 6C intermediate which breaks down into 2x GP

Question 14

What happens during reduction

Answer 14

2x GP reduced to 2x TP
Requires 2 reduced NADP and 2 ATP
Forms 2 NADP and 2 ADP

Question 15

How does LDR result in production of useful organic substances

Answer 15

1C leaves the cycle

Some TP converted into useful organic molecules

Question 16

What happens during regeneration

Answer 16

After 1C leaves the cycle, the 5C compound RuP forms
RuBP is regenerated from RuP using 1 ATP
Forms 1 ADP

Question 17

Roles of ATP and reduced NADP in LiR

Answer 17

ATP - Reduction of GP to TP and provides phosphate to convert RuP to RuBP

NADP - coenzyme transports electrons needed for reduction of GP to TP

Question 18

State number of carbons in RuBP
GP
TP

Answer 18

RuBP - 5
GP - 3
TP - 3

Question 19

Describe. structure of chloroplast

Answer 19

Disc-shaped
Double membrane
Thylakoids - flattened discs stack to form grana
Intergranal lamellae - tubular extensions attach thylakoids to in adjacent grana
Stroma - fluid-filled matrix

Question 20

How does structure of chloroplast maximise rate of LDR

Answer 20

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

Question 21

How does structure of chloroplast maximise rate of LiR

Answer 21

Own DNA and ribosomes for synthesis of enzymes - rubisco

Concentration of enzymes and substrates in stroma is high

Question 22

Define limiting factor

Answer 22

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 rate of photosynthesis

Answer 23

Light intensity - LDR
CO2 levels - LiR
Temperature - Enzymes
Mineral levels - maintain normal functioning of chlorophyll

Question 24

Common agricultural practices to overcome limiting factors

Answer 24

Artificial light
Artificial heating
Addition of CO2 to greenhouses

Question 25

Why to farmers try to overcome limiting factors

Answer 25

Increase yield

Additional cost must be balanced to ensure profit

Question 26

Method for extracting photosynthetic pigment

Answer 26

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

Question 27

How paper chromatography can be used to separate photosynthetic pigment

Answer 27

Use capillary tube to spot pigment extract onto pencil line 1cm above bottom of paper
Place chromatography paper in solvent
Allow solvent to run until it almost touches the other end of paper

Question 28

What are Rf values - how are they calculated

Answer 28

Ratios that allow comparison of how far molecules move in chromatograms - Distance between origin and centre of pigment spot / distance between origin and solvent front