Photosynthesis

Question 1

Where do the light-dependent & light-dependent reactions occur in plants?

Answer 1

Light-dependent: in the thylakoids of chloroplast

Light-independent: stroma of chloroplast

Question 2

Explain the role of light in photoionisation.

Answer 2

Chlorophyll molecules absorb energy from photons of light

This ’excites’ 2 electrons (raises them to higher energy level), causing them to be released from the chlorophyll

Question 3

Name the 2 main stages involved in ATP production in the light-dependent reaction.

Answer 3

1 - electron transfer chain

2 - chemiosmosis

Question 4

What happens in the electron transfer chain (ETC)?

Answer 4

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

Question 5

How is a proton concentration gradient established during chemiosmosis?

Answer 5

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

Question 6

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

Answer 6

H+ ions (protons) move down their concentration gradient down from the thylakoid space into the stroma via the channel protein ATP synthase.

ATP synthases catalyses ADP + Pi -> ATP

Question 7

Explain the role of light in photolysis.

Answer 7

Light energy splits molecules of water

2H2O -> 4H+ +4e- + O2

Question 8

What happens to the products of photolysis of water?

Answer 8

. H+ ions: move out of thylakoid space via ATP synthase & 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 9

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

Answer 9

. NADP + 2H+. + 2e- —> reduced NADP

. Catalysed by dehydrogenase enzymes

. Stroma of chloroplasts

Question 10

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

Question 11

What are the 2 stages of photosynthesis

Answer 11

Light independent reaction

And

Light dependent reaction

Question 12

Where does LDR occur

Answer 12

Thylakoid membrane or grana

Question 13

Where does LIR occur

Answer 13

In storms of chloroplasts

Question 14

Does LDR need light

Answer 14

LDR requires light

Light energy + water used to create ATP and reduced NADP - needed for LIR

Question 15

What are the 4 stages that occur in LDR

Answer 15

1. Photoionisation of chlorophyll
2. Production of ATP and reduced NADP
3. Chemiomosis
4. Photolysis

Question 16

What happens in photolysis of water

Answer 16

Photo (light) Lysis (splitting)

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

H20 → ½ 02 + 2e + 2H+

The H+ is picked up by NADP to form NADPH and is used in the LIR.

The e- are passed along a chain of electron carrier proteins.

The oxygen is either used for respiration or diffuses out of the leaf through the stomata.

Question 17

Equation for the photolysis of water

Answer 17

H,0 → ½ 02 + 2e + 2H+

Question 18

What happens in the photoionisation of chlorophyll

Answer 18

Light energy is absorbed by the chlorophyll and the energy results in electrons becoming excited and raising up an energy level to leave chlorophyll.

Therefore the chlorophyll has been ionised by light.

Some of the energy from the released electrons is used to make ATP and reduced NAPD in chemiosmosis.

Question 19

What happens in chemiosmosis in photosynthesis

Answer 19

The electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane.

As they move along they release energy and some of the energy from electrons is used to pump the protons across chloroplast membranes.

An electrochemical gradient is created.
The protons pass through the enzyme ATP synthase, which results in the production of ATP.

The protons combine with the co-enzyme NADP to become reduced NADP. Because the protons move from a high to low concentration gradient this is known as chemiosmosis.

Question 20

What happens when chlorophyll absorbs light

Answer 20

Leads to Photoionisation of chlorophyll

Question 21

What is the LIR

Answer 21

Calvin cycle

Question 22

What enzyme catalyses the Calvin cycle

Answer 22

Enzyme rubisco which is found in fluid in stroma

Question 23

Why is the Calvin cycle temp sensitive

Answer 23

It involves enzymes

Question 24

What does the Calvin cycle use to forma hexose sugar

Answer 24

CO2

Reduced NADP

ATP

Question 25

What are ATP and reduced NADP used for in the calving cycle

Answer 25

Atp is hydrolysed to provide energy from this reaction

Reduced NADP donates H to reduce molecules GP in cycle

Question 26

What are the limiting factors of photosynthesis

Answer 26

Temp

CO2 conc

Light intensity

Question 27

Process of LIR (Calvin cycle)

Answer 27

Carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate
(GP) a 3 carbon compound.

This reaction is catalysed by the enzyme Rubisco.

GP is reduced to triose phosphate (P) using energy from ATP and by accepting a H from reduced NADP

Some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances.

The rest of the molecule is used to regenerate RuBP, with the energy from ATP.

Whilst glucose is the product, this monosaccharide can join to form disaccharides such as sucrose, and polysaccharides such as cellulose and starch.

It can also be converted into glycerot and therefore combine with fatty acids to make lipids for the plant.

Question 28

Why is it important to remove limiting factors of photosynthesis

Answer 28

Maximise photosynthesis

Maximise plant growth

Question 29

What are some techniques used in agricultural practices to remove limiting factors

Answer 29

These range from growing plants under artificial lighting to maximum the light intensity, heating a greenhouse to increase the temperature and burning fuel, such as paraffin burners, to release more carbon dioxide.

Question 30

What is the extent that needs to be considered of the techniques used in removing limiting factors

Answer 30

The extent that each technique is used needs to be consider in terms of profit. If the extra growth from photosynthesis is minimal, it will not be cost effective to pay for heating/lighting/fuel.