Topic 5 - Photosynthesis

Question 1

What are the two stages of photosynthesis?

Answer 1

The light dependent reaction
The light independent reaction.

Question 2

Where does the LDR occur?

Answer 2

In the thylakoid membrane

Question 3

What happens in the LDR ?

Answer 3

Light energy and water are used to create ATP and reduced NADP, which are needed for the LIR.

Question 4

What are the 4 key processes of the LDR?

Answer 4

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

Question 5

What happens during the photolysis of water?

Answer 5

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

Question 6

What is the oxygen from photolysis used for?

Answer 6

Either used for respiration o diffuses out of the leaf.

Question 7

What are the electrons from photolysis used for?

Answer 7

They are passed along a chain of election carrier proteins.

Question 8

What is the H+ from photolysis used for?

Answer 8

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

Question 9

What happens during the photoionisation of chlorophyll?

Answer 9

Chlorophyll absorbs light energy in the form of photons and the energy results in elections becoming excited and raising up an energy level to leave chlorophyll.

Question 10

How are H+ ions moved across the thylakoid membrane?

Answer 10

The excited electrons from photoionisation lose energy as they move down the ETC. The energy released is used to actively transport H+ across the chloroplast membrane and into the thylakoid space.

Question 11

How are H+ ions involved in the synthesis of ATP in chloroplasts?

Answer 11

H+ move down their concentration gradient into the stroma via ATP synthase in the thylakoid membrane, resulting in the production of ATP.

Question 12

What is chemiosmosis?

Answer 12

Elections move down the ETC which creates a proton gradient that drives ATP synthesis

Question 13

Describe the process of chemiosmosis?

Answer 13

1. Elections more along embedded proteins in the thylakoid membrane.
2. As they move along energy is released and some energy is used to pump protons across chloroplast membranes.
3. An electrochemical gradient is created. Protons pass through ATP synthase resulting in the production of ATP.
4. The protons combine with the co-enzyme NADP to become NADPH.

Question 14

Which molecules from the LDR are needed in the LIR?

Answer 14

ATP
NADPH

Question 15

Where does the LIR occur?

Answer 15

Stroma

Question 16

What enzyme catalyses the LIR?

Answer 16

RuBisCo

Question 17

What are the 3 stages of the LIR?

Answer 17

1. Formation of glycerate-3-phosphate (GP)
2. Formation of triose phosphate (TP)
3. Regeneration of ribose bisphosphate (RuBP)

Question 18

How is GP formed in the LIR?

Answer 18

• CO2 reacts with RuBP (5C)
• Catalysed by RuBisCo
• Creates 2x glycerate-3-phosphate (GP)

Question 19

How is TP produced from GP in the LIR?

Answer 19

GP is reduced by NADPH to form TP using H+ ions.

Question 20

How many TP molecules are used to form glucose?

Answer 20

01-Jun

Question 21

How many TP molecules are used to form RuBP?

Answer 21

05-Jun

Question 22

Which 3 factors can limit the rate of photosynthesis?

Answer 22

Light intensity
Temperature
CO2 concentration

Question 23

What is a coenzyme?

Answer 23

A molecule that aids the function of an enzyme

Question 24

What is a limiting factor?

Answer 24

A factor which can slow down the rate of a reaction e.g photosynthesis