TOPIC 5 - photosynthesis

Question 1

where do LDR and LIR take place?

Answer 1

LDR - thylakoids of chloroplasts
LIR - stroma of chloroplasts

Question 2

what are the stages of the LDR?

Answer 2

1. photoionisation fo PSII
2. Photolysis of water
3. Photoionisation of PSI
4. Active transport of H+ ions
5. Oxidative phosphorylation
6. Reducing NADP

Question 3

Describe what happens during photoionisation of PSII

Answer 3

Chlorophyll absorbs light
Electrons excited and move to higher energy level
Electrons move down electron transport chain to PSI

Question 4

what happens in the electron transfer chain?

Answer 4

electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane and undergo a series of redox reactions, which releases energy.

Question 5

Describe what happens during photolysis of water

Answer 5

Light energy splits water molecules into H+, e- and oxygen
The electrons replace those lost from PSII during photoionisation

Question 6

what happens to the products of the photolysis of water?

Answer 6

H+ ions = move out of the thylakoid space via ATP synthase and used to reduce co enzyme NADP

e- = replace electrons lost from chlorophyll
O2 = used for respiration or leaves the leaf as waste gas

Question 7

What is chemiosmosis ?

Answer 7

Electrons move down the electron transport chain and creating a proton gradient
This drives ATP synthesis

Question 8

Explain how H+ ions are moved across the thylakoid membrane

Answer 8

The excited electrons from photoionisation lose energy as they move down the electron transport chain
The energy is used to actively transport H+ into the chloroplast

Question 9

Explain how H+ are involved in the synthesis of ATP in chloroplasts

Answer 9

H+ move down their concentration gradient into the stroma
This is via ATP synthase in the thylakoid membrane
The energy synthesises ATP from ADP and Pi

Question 10

Explain why the photoionisation of PSI is important

Answer 10

The excited electrons are transferred to NADP with H+ to form reduced NADP
This is needed for the light-independent reaction

Question 11

Which molecules from the light-dependent reaction are needed in the light-independent reaction?

Answer 11

ATP
reduced NADP

Question 12

Where does the light dependent reaction take place?

Answer 12

thylakoid membranes of chloroplasts

Question 13

where does light independent reaction take place?

Answer 13

stroma of chloroplast

Question 14

What are the 3 stages of the light-independent reaction?

Answer 14

1. Formation of glycerate 3-phosphate
2. Formation of triose phosphate
3. Regeneration of ribulose bisphosphate

Question 15

Explain how glycerate 3-phosphate (GP) is formed?

Answer 15

Ribulose bisphosphate (RuBP) combines with CO2
Forms unstable 6 carbon compound which breaks down to give 2 molecules of glycerate 3-phosphate
Catalysed by Rubisco

Question 16

How does CO2 enter the stroma from the atmosphere?

Answer 16

Diffusion through the stomata
Difussion into the stroma

Question 17

Which enzyme catalyses the reaction of CO2 with ribulose bisphosphate (RuBP) ?

Answer 17

Rubisco

Question 18

How many molecules of glycerate 3-phosphate (GP) are produced from 1 molecule of CO2 and 1 molecule of ribulose bisphosphate (RuBP) ?

Answer 18

2

Question 19

How many carbon atoms are in ribulose bisphosphate ?

Answer 19

5

Question 20

How many carbon atoms are in glycerate 3-phosphate (GP) ?

Answer 20

3

Question 21

Explain how triose phosphate (TP) is formed from glycerate 3-phosphate (GP)

Answer 21

Glycerate 3-phosphate (GP) is reduced to triose phosphate (TP) using H+ ions

Question 22

How is glycerate 3-phosphate (GP) reduced to triose phosphate (TP) ?

Answer 22

GP is reduced to TP using redcued NADP using energy from ATP

Question 23

What two things can triose phosphate (TP) be used for?

Answer 23

1. regenerating ribulose bisphosphate (RuBP)
2. Converted to useful organic substances

Question 24

How many of the carbon atoms in 2 molecules of triose phosphate (TP) are used to regenerate ribulose bisphosphate (RuBP) ?

Answer 24

5/6 carbon atoms

Question 25

Which two stages in the light independent reaction is ATP hydrolysed ?

Answer 25

Reduction of glycerate 3-phosphate (GP) to triose phosphate (TP)
Regeneration of ribulose bisphosphate (RuBP)

Question 26

describe the structure of the chloroplast?

Answer 26

• disc shape
• double membrane
  -thylakoids stacked to form grana
• lamellae attach adjacent grana
• stroma = fluid filled matrix

Question 27

how does the structure of the chloroplast maximise the rate of LDR?

Answer 27

• large SA of thylakoid membrane for ETC
• photosystem position chlorophyl to enable maximum absorption of light

Question 28

how does the strucutre of the chloroplast maximise the rate of LIR?

Answer 28

• own DNA and enzymes for synthesis of enzymes such as rubisco
• conc of enzymes and substrates is high in stroma

Question 29

what are 4 factors that can limit the rate of photosynthesis?

Answer 29

-light intensity (LDR)
-CO2 levels(LIR)
temperature (enzyme controlled steps)
-mineral/ Mg levels (maintain normal functioning of chlorophyll)

Question 30

outline common agricultural practices used to overcome the effect of limiting factors in photosynthesis.

Answer 30

• artificial light, especially at night
• artificial heating
• addition of co2 in greenhouse using paraffin burners

Question 31

why do farmers overcome limiting factors?

Answer 31

to increase yield
to ensure maximum profit