Photosynthesis

Question 1

What is light compensation point

Answer 1

Amount of CO2 absorbed = amount produced
Rate of respiration = photosynthesis

Question 2

Define photosynthetic pigments

Answer 2

Molecules that absorb light energy

Question 3

Purpose of accessory pigments

Answer 3

Absorb greater range of light wavelengths

Question 4

2 types of Chlorophyll a
Name an accessory pigment

Answer 4

A = P680, PS2
A = P700, PS1
Chlorophyll b or carotenoids

Question 5

How are pigments arranged in thylakoid membrane

Answer 5

Pigments arranged in funnel shapes = photosystems
Primary pigment reaction centre = Chlorophyll a

Question 6

Importance of photosynthetic pigments in photosynthesis

Answer 6

Absorb light energy
Electrons excited
Accessory pigments pass energy to primary pigments
Primary pigments pass electrons to ETC
For LDS

Question 7

Explain LDS

Answer 7

Photon hits PS2
Pass energy down to primary pigment
Electrons excited + leave chlorophyll a
Electrons accepted by ETC
Electrons passed down ETC to PS1

Energy released from electrons being passed down ETC
Used to pump H+ from stroma to thylakoid
ATP synthesised
Proton motive force

Photolysis replaces 2 e- lost from PS2

Cyclic
Electrons from PS1 passed along ETC
Recycle back to PS1
Energy lost during this
Phosphorylates ADP to ATP

Non-cyclic
2 excited e- passed along ETC - release energy for ATP synthesis
2 e- then passed to PS1 (replace lost e-)
Same time - light hit PS1 = loses 2 e-
2e- accepted by ferredoxin
Passes it to NADP
Make reduced NADP (NADP reductase)

Question 8

Compare cyclic + non-cyclic LDS
PS used
Photolysis?
What happens to e- released from chlorophyll
Products

Answer 8

Cyclic
PS1
No
Goes to ETC + back to PS1
ATP

Non-cyclic
PS1 + PS2
Yes
Goes to ETC + to PS1
ATP, reduced NADP + O2

Question 9

Explain LIS (Calvin cycle)
Site of LIS

Answer 9

CO2 + RuBP - catalysed by RuBisCO
= 6C intermediate - immediately broken down
Into 2 GP
GP converted to TP
Use: 2ATP + 2NADPH
TP converted to RuBP
Use: ATP

Stroma

Question 10

Uses of TP

Answer 10

Synthesis of carbohydrates, lipids (from fatty acids) + amino acids
Glucose to make sucrose, starch or cellulose

Question 11

Effects on LIS
Reduced CO2
Reduced GP
Reduced TP
Reduced RuBP
Reduced ATP
Reduced NADPH

Answer 11

CO2
Less GP + TP, more ATP + NADPH + RuBP
GP
Less TP + RuBP + glucose, more ATP + NADPH
TP
Less RuBP + GP, more CO2, ATP + NADPH
RuBP
Less GP + TP, more CO2
ATP
Less TP + RuBP
GP build up
NADPH
Less TP + RuBP, more GP + ATP

Question 12

Explain how light affects LDR

Answer 12

More light absorbed by photosystems
More excited e-
More photophosphorylation + photolysis
More ATP + NADPH

Question 13

Saturation point

Answer 13

Light is limiting factor, increase in light intensity will not increase rate of photosynthesis

Question 14

How does temperature affect the Calvin cycle

Answer 14

Temp above 30 = photorespiration
O2 competes with CO2 for active site of RuBisCO
= reduced CO2 accepted by RuBP
= less GP + TP
Initial rise in RuBP then lack of regeneration