Photosynthesis

Question 1

Photosynthetic pigments can be divided into 2 classes, namely:

Answer 1

1) Chlorophylls

2) Carotenoids

Question 2

Photosynthetic Pigments

1) CHLOROPHYLLS

Answer 2

• absorb mainly red and blue-violet light; refect green light
• flat, light-absorbing head end containing Mg atom; deficiency reduces chlorophyll production, yellowing leaves
• long hydrocarbon tail, hydrophobic; project into thylakoid membrane, anchor chlorophyll
• different side chains on head; modifies absorptio spectra & increase range of wavelengths of light absorbed

Question 3

Photosynthetic Pigments

2) CAROTENOIDS

Answer 3

• yellow, orange, red, brown pigments
• absorb mainly blue-violet light
• accessory pigments; pass light energy they absorb to chlorophylls
• protect chlorophylls from excess light and oxygen produced in photophosphorylation
• carotenes & xanthophylls

Question 4

Light-dependent reactions (ALT NAME)

Answer 4

Photophosphorylation

Question 5

Product(s) of Light-dependent reactions

Answer 5

ATP & NADPH

Question 6

Light-independent reactions (ALT NAME)

Answer 6

Calvin Cycle

Question 7

Outline of Photophosphorylation

Answer 7

• involves flow of electrons from P680 (PSII) & P700 (PSI); cyclic or non-cyclic
• electrons boosted to higher energy level and become excited through transfer of light energy from light harvesting complex to reaction centre
• excited electrons accepted by primary electron acceptors; photosystems oxidised, primary electron acceptors reduced
• electrons transferred from one e carrier to another in a series of oxidation-reduction rections through ETC
• at the same time, pump H+ (protons) into thylakoid space; results in proton gradient across thylakoid membrane, used to drive ATP production by ATP synthetase in stalked particles through chemiosmosis

Question 8

Location of Photophosphorylation

Answer 8

Thylakoid membrane & Grana (plural)

Question 9

Details of NON-CYCLIC photophosphorylation

Answer 9

• electrons boosted to higher energy level and become excited through transfer of light energy from light harvesting complex to reaction centre
• excited electrons accepted by primary electron acceptors; photosystems oxidised, primary electron acceptors reduced
• electrons lost in PSII replaced by e from photolysis of water (produces H+ and O2)
• electrons transferred from one e carrier to another in a series of oxidation-reduction rections through ETC
• at the same time, pump H+ (protons) into thylakoid space; results in proton gradient across thylakoid membrane, used to drive ATP production by ATP synthetase in stalked particles through chemiosmosis
• these electrons replace those lost in PSI
• e from PSI and protons from hydrolysis of water accepted by NADP, reducing it to NADPH

Question 10

Details of CYCLIC photophosphorylation

Answer 10

• excited electrons accepted by primary electron acceptor in PSI are recycled back to PSI through another ETC involving ferredoxin
• produces ATP (similar to non-cyclic)

Question 11

When does CYCLIC phosphorylation occur?

Answer 11

• lack of water to supply high energy e that replace e lost in PSII
• lack of CO2 in L-IR to reoxidise NADPH to NADP+

Question 12

Purpose of CYCLIC photophosphorylation

Answer 12

• produce more ATP for L-IR

Question 13

Non-cyclic vs cyclic photophosphorylation

Answer 13

1) Products
2) Photosystems involved
3) Operates when plant requires
4) First electron donor
5) Final electron acceptor
6) Pathway of electrons
7) High concentration of H+ in thylakoid space

Question 14

Location of Calvin cycle

Answer 14

Stroma

Question 15

Phases of the Calvin cycle

Answer 15

1) CO2 fixation / carboxylation
2) Reduction
3) Regeneration of CO2 acceptor, RuBP

Question 16

CALVIN CYCLE

A) CO2 fixation / carboxylation

Answer 16

• ribulose bisphosphate (RuBP) accepts CO2 in the process of carboxylation, catalysed by RuBP carboxylase (Rubisco)
• intermediate 6-carbon product is unstable; broken down into 2 molecules of glycerate 3-phosphate (GP)/ 3-phosphoglycerate

Question 17

CALVIN CYCLE

B) Reduction

Answer 17

• glycerate 3-phosphate (GP) / 3-phosphoglycerate phosphorylated by ATP to form 1,3-bisphosphoglycerate
• 1,3-bisphosphoglycerate reduced by NADPH to form glyceraldehyde 3-phosphate (G3P) / triose phosphate (TP)

Question 18

CALVIN CYCLE

C) Regeneration of CO2 acceptor, RuBP

Answer 18

• 5 molecules of 3C glyceraldehyde 3-phosphate (G3P) used to regenerate 3 molecules of 5C RuBP; 3 ATPs used
• 1 molecules of G3P enters biosynthesis of glucose
• 2G3Ps to form 1 glucose molecule; 2 rounds of Calvin cycle required

Question 19

Principle of limiting factors

Answer 19

• the rate of biochemical processes, which involve a series of reactions, is limited by the slowest reaction in the series

OR

• when biochemical processes are affected by several factors, rate is limited by the factor that is nearest its minimum value

Question 20

Main limiting factors affecting rate of photosynthesis

Answer 20

1) Light intensity
2 Quality / wavelength of light
3) Temperature
4) CO2 concentration

Question 21

Definition: absorption spectrum

&

Explanation

Answer 21

• graph of relative amounts of light absorbed at different wavelengths by a pigment
• amount of light absorbed on vertical y-axis; wavelength of light on horizontal x-axis

Question 22

Definition: action spectrum

&

Explanation

Answer 22

• graph showing effectiveness of different wavelengths of light in stimulating photosynthesis
• rate of photosynthesis on vertical y-axis; wavelength of light on horizontal x-axis
• peaks broader than those in absorption spectrum; accessory pigments such as chlorophyll b and carotenoids that broaden range of wavelengths of light absorbed

Question 23

Definition: Compensation point

Answer 23

• light intensity at which rate of photosynthesis = rate of respiration