3.5 Photosynthesis

Question 1

Where in the chloroplast does the light dependant stage take place ?

Answer 1

In the thylakoids

Question 2

Where in the chloroplast does the light independent stage take place ?

Answer 2

The stroma

Question 3

What is the Stroma?

Answer 3

Fluid centre which contains enzymes involved in the LIR

Question 4

What are the thylakoid membranes?

Answer 4

Folded membranes which contain photosynthetic proteins such as chlorophyll and electron carrier proteins involved in the LDR.

Question 5

Give an example of a photosynthetic protein

Answer 5

Chlorophyll

Question 6

What is essential for the LDR to take place ?

Answer 6

Light

Question 7

What is the first stage of the LDR ?

Answer 7

Photolysis

Question 8

What happens during photolysis ?

Answer 8

Light energy is absorbed by chlorophyll and splits water into oxygen, H+ and e-.

Question 9

Write an equation to show what happens during photolysis

Answer 9

H20 –> 1/2 02 + 2e- + 2H+

Question 10

Where does the H+ go that is formed during photolysis ?

Answer 10

It is picked up by NADP to form NADPH to be used in the LIR

Question 11

What is the 02 produced during photolysis used for ?

Answer 11

Either used in respiration or if not needed diffuses out of leaf through stomata

Question 12

What is the second stage of the LDR ?

Answer 12

Photoionisation of chlorophyll

Question 13

What happens during photoionisation of chlorophyll ?

Answer 13

Light energy is absorbed by the chlorophyll and the energy excites the electrons and raises them up an energy level to leave the chlorophyll

Question 14

What is the third stage of the LDR?

Answer 14

Chemiosmosis

Question 15

What happens during chemiosmosis ? ( 7 steps)

Answer 15

1- electrons move through electron transfer chain
2- electrons release energy when they move
3- that energy is used to pump H+ ions across the membrane
4- H+ use active transport to get from stroma to the thylakoid lumen
5- High conc of H+ in thylakoid lumen creates an electrochemical gradient
6- H+ diffuse through ATP synthase
7- Causes energy to make ATP and combine to make NADPH

Question 16

What is ATP synthase ?

Answer 16

An enzyme which catalyses the reaction of ADP + Pi –> ATP

Question 17

What produces energy to catalyse the production of ATP ?

Answer 17

Change in shape of ATP synthase when H+ pass through.

Question 18

What is another name for the LIR ?

Answer 18

The Calvin cycle

Question 19

What enzyme catalyses the Calvin cycle ?

Answer 19

RuBisCo

Question 20

What 3 things are essential for the Calvin cycle to take place ?

Answer 20

Carbon dioxide, Reduced NADP, ATP

Question 21

Where does the CO2 come from to be used in the Calvin cycle ?

Answer 21

The atmosphere

Question 22

CO2 and RuBisCo combine to make what ? How many Carbons ?

Answer 22

2 molecules of GP (3 carbons each)
6 Carbon atoms in total

Question 23

The Formation of GP is catalysed by which enzyme ?

Answer 23

RuBisCo

Question 24

What is GP reduced to and how ?

Answer 24

GP is reduced to TP by using energy from ATP and by accepting a H from NADPH

Question 25

How many times does the Calvin cycle have to take place for a hexose sugar to be made?

Answer 25

6

Question 26

What is needed to catalyse TP turning into RuBisCo?

Answer 26

ATP

Question 27

How many carbons does a molecule of RuBisCo have ?

Answer 27

5 Carbons

Question 28

1 Molecule of Carbon leaves TP to be made into other product such as…?

Answer 28

Starch, Sucrose, Cellulose

Question 29

What are the three limiting factors of photosynthesis ?

Answer 29

Light intensity, Temperature, Carbon dioxide concentration

Question 30

Suggest three things agriculturalists can do to maximise photosynthesis

Answer 30

1- Use artificial lighting
2- Heating a greenhouse to increase temperature
3- Burning fuel such as paraffin burners to increase carbon dioxide

Question 31

What is the problem agriculturalists may occur when maximising photosynthesis ?

Answer 31

Very costly, Have to make sure it is worth it for profit gained

Question 32

When doing chromatography of photosynthetic pigments why should you mark the origin with pencil ?

Answer 32

Otherwise ink and leaf pigments would mix and alter results

Question 33

Suggest and explain the advantage of having different coloured pigments in leaves

Answer 33

Absorb different wavelengths of light for photosynthesis