17 - Photosynthesis

Question 1

What are the 3 photopigments found in the group of chlorophyll?

Answer 1

1. Chlorophyll A 2. Chlorophyll B 3. Carotene

Question 2

Which of the 3 photopigments found in the group of chlorophyll is the main one?

Answer 2

Chlorophyll A

Question 3

What colour are Chlorophyll A, Chlorophyll B and Carotene respectively?

Answer 3

Green, blue-green and orange

Question 4

What is a photosystem?

Answer 4

Clusters of photopigments and proteins that capture light energy

Question 5

Where are photosystems found?

Answer 5

In the thylakoid membrane

Question 6

What is found at the centre of a photosystem?

Answer 6

The reaction centre

Question 7

What are organisms which photosynthesise classed as?

Answer 7

Autotrophs

Question 8

What is an advantage of the highly folded structure of thylakoid membranes?

Answer 8

Provides a large surface area for the absorption of photons

Question 9

Apart from the photopigments from the chlorophyll group can you name one other?

Answer 9

Xanthophyll or Carotenoids

Question 10

Where in a photosystem is chlorophyll a located?

Answer 10

The reaction centre

Question 11

What are the two stages of photosynthesis?

Answer 11

Light-dependent and light-independent

Question 12

Summarise what goes on in the light-dependent stage of photosynthesis?

Answer 12

Energy from sunlight is absorbed and used to form ATP, and hydrogen from water is used to reduce coenzyme NADP to NADPH

Question 13

Summarise what goes on in the light-independent stage of photosynthesis?

Answer 13

Hydrogen from NADPH and CO2 are used to build organic molecules such as glucose, with ATP supplying the required energy.

Question 14

At around what wavelength does PSII absorb light?

Answer 14

680nm

Question 15

At around what wavelength does PSI absorb light?

Answer 15

700nm

Question 16

Which of the two photosystems reacts first?

Answer 16

PSII

Question 17

What are the two possible types of photophosphorylation?

Answer 17

Cyclic and non-cyclic

Question 18

Briefly explain what happens in cyclic photophosphorylation?

Answer 18

Instead of the electrons from PSI being used to reduce NADP, they can be returned to PSI to form ATP without the input of electrons from PSII

Question 19

What is not produced during cyclic photophosphorylation?

Answer 19

NADPH

Question 20

What is photolysis?

Answer 20

Where water molecules are broken down using energy supplied by photons

Question 21

How is ATP produced during the light-dependent reactions of photosynthesis?

Answer 21

High-energy electrons leave the photosystems and travel through electron transport chains, which releases energy that can be used to pump protons so that chemiosmosis can occur

Question 22

How are the electrons which leave PSII replaced?

Answer 22

Via the electrons produced by the photolysis of water

Question 23

Do electrons from PSI and PSII pass down the same electron transport chains?

Answer 23

No, different ones

Question 24

How are the electrons lost from PSI replaced during non-cyclic photophosphorylation?

Answer 24

By electrons released from PSII

Question 25

How is NADPH produced by PSI?

Answer 25

Electrons leaving the transport chain of PSI are accepted by the coenzyme NADP, along with H+ ions released via photolysis of water, to form NADPH

Question 26

How does photolysis lead to increased ATP production?

Answer 26

The H+ ions released go through chemiosmosis to power ATP synthase

Question 27

What are the reactions of the light-independent stage of photosynthesis collectively known as?

Answer 27

The Calvin Cycle

Question 28

Where does the Calvin Cycle take place?

Answer 28

In the stroma

Question 29

Briefly, what does the Calvin Cycle do?

Answer 29

Uses NADPH, ATP and CO2 to produce organic molecules such as glucose

Question 30

Briefly summarise the reactions of the Calvin Cycle

Answer 30

1. RuBP combines with CO2 (via the enzyme RuBisCo) to form an unstable hexose intermediate 2. This splits into two GP molecules 3. Each GP molecule reacts with ATP and NADPH to form a TP molecule 4. One TP molecule is used to synthesis organic molecules, the other is used to regenerate RuBP

Question 31

What enzyme is used in the Calvin Cycle?

Answer 31

RuBisCo (Ribulose Bisphosphate Carboxylase)

Question 32

What is a disadvantage of RuBisCo?

Answer 32

It has a high affinity for oxygen, so this can inhibit the Calvin Cycle

Question 33

What are some organic molecules which can be produced from TP?

Answer 33

Glucose, lipids, amino acids

Question 34

What are the 3 stages of the Calvin Cycle?

Answer 34

1. Fixation 2. Reduction 3. Regeneration

Question 35

How many full turns of the Calvin Cycle are required to produce one glucose molecule?

Answer 35

6

Question 36

How many of the 12 TP molecules produced by 6 turns of the Calvin Cycle are removed to make glucose?

Answer 36

2

Question 37

What are the three limiting factors of photosynthesis?

Answer 37

1. Light Intensity 2. CO2 availability 3. Temperature

Question 38

Why is water availability not a limiting factor for photosynthesis?

Answer 38

If water levels were that low then the plant would be in survival mode and not photosynthesising

Question 39

How is light intensity a limiting factor for photosynthesis?

Answer 39

It is needed as an energy source in the light-dependent stage of photosynthesis so that ATP and NADPH can be produced

Question 40

How is CO2 availability a limiting factor for photosynthesis?

Answer 40

It affects how much TP can be produced by the Calvin Cycle

Question 41

How is temperature a limiting factor for photosynthesis?

Answer 41

Higher temperatures increase the rate of reactions catalysed by enzymes such as RuBisCO, but above 25 degrees Celsius photorespiration occurs due to stomatal closure, so the rate of respiration slows