Photosynthesis- Dark reactions

Question 1

where do dark reactions occur

Answer 1

chloroplast stroma

Question 2

what is the purpose of dark reactions

Answer 2

to fix atmospheric CO2 into carbohydrates

Question 3

what is the calvin cylce

Answer 3

the assimilation of CO2 into sugars

Question 4

how many molecules of CO2 required for 1 molecule of glyceraldehyde 3-phosphate

Answer 4

3

Question 5

TRUE or FALSE: the calvin cycle uses 9 ATP and 6NADPH produced by light reactions

Answer 5

TRUE

Question 6

the calvin cycle produces 6 triosphosphates. Of these, how many are used to regenerate the needed 3x ribulose 1,5 bisphosphate?

Answer 6

5

Question 7

what are C3 plants?

Answer 7

plants in which the 3 carbon compound, ribulose 1,5 bisphosphate is the first intermediate used

Question 8

what enzyme catalyses the first step of CO2 fixation?

Answer 8

RuBiSCO. i.e. ribulose 1,5-bisphosphate carboxylase/oxygenase

Question 9

RuBiSCO is the ??? in hexose synthesis

Answer 9

rate limiting step

Question 10

how many CO2 molecules are fixed by 1 RuBiSCO per second?

Answer 10

3 –> low efficiency

Question 11

“Dark reactions” are the fixation of CO2 into organic carbon which is catalysed by ??? and driven by ATP and NADPH

Answer 11

aqueous enzymes

Question 12

NADPH and ATP from the light reactions feed into the “???”
(Carbon-assimilation) Reactions

Answer 12

Dark

Question 13

TRUE or FALSE: dark reactions can occur in the absence of light, but accelerated by light

Answer 13

TRUE

Question 14

The most abundant protein in the biosphere, making up 35-50% of soluble chloroplast protein is which enzyme ???

Answer 14

RuBisCO

Question 15

RuBisCO is activated by ??? which carbamoylates it

Answer 15

RuBisCO activase

Question 16

Rubisco must be carbamoylated by CO2 to be active BUT over time, rubisco binds to ??? which prevents rubisco activation. Rubisco activase overcomes this using energy from ATP hydrolysis to displace the ???

Answer 16

ribulose 1,5-bisphosphate
ribulose 1,5-bisphosphate.

Question 17

Stage 2: Conversion of 3-Phosphoglycerate to ??? uses ATP and NADPH

Answer 17

Glyceraldehyde 3-Phosphate

Question 18

6 carbons get attached to 6 ribulose 1,5 bisphosphate to produce 12 G3P chains = 36 carbons. Of 12 G3P, 2 are used for glucose, the rest are used to recreate ???

Answer 18

Ribulose 1,5 bisphosphate

Question 19

Stage 3: Regeneration of Ribulose 1,5-Bisphosphate from ??? (more specifically, glyceraldehyde 3-phosphate)

Answer 19

Triose Phosphates

Question 20

RuBisCO as an oxygenase: Rubisco is not just specific for CO2 but can also fix ???

Answer 20

O2

Question 21

Why doesn’t RuBisCO discriminate between O2 and CO2?

Answer 21

Before photosynthetic organisms raised the O2 content of the
atmosphere, there was no selection pressure for rubisco to discriminate between CO2 and O2

Question 22

Significant amounts of O2 are fixed with a ratio of about 1 O2 per 4 CO2
incorporated into the cycle by ???

Answer 22

RuBisCO

Question 23

Oxygenase activity results in a significant loss of ??? and waste of energy (photorespiration)

Answer 23

carbon

Question 24

2-phosphoglycolate is a product of CO2 fixation or O2 fixation?

Answer 24

O2 fixation

Question 25

salvage of 2-phosphoglycolate involves it travelling through the
- Chloroplast stroma
- Peroxisomes
- Mitochondra
requiring the use of energy and consuming ??? at 2 points

Answer 25

Consumes O2 at two points

Question 26

Why is the salvage of 2-phosphoglycolate wasteful? because a carbon is lost as ??? without production of energy

Answer 26

CO2

Question 27

TRUE or FALSE: in the salvage of 2-phosphoglycolate, the process of carbon fixation is reversed

Answer 27

TRUE

Question 28

what is rate limiting in photosynthesis?

Answer 28

RuBisCO

Question 29

Improved efficiency of ??? would have a large impact on CO2 reduction in the atmosphere, and
food and biofuel production

Answer 29

RuBisCO

Question 30

Ways of Improving RuBisCO:
- Improve specificity: Replace crop gene with RuBisCO from red algae or purple photosynthetic bacteria
- Increase catalytic activity: Introduction of altered RuBisCO with higher activity
- Increase levels of ???

Answer 30

expression

Question 31

C3 plants use the conventional pathway of CO2 uptake in which the first intermediate produced is a C3 compound. i.e. ???

Answer 31

3-phosphoglycerate

Question 32

C4 plants use an alternative pathway of CO2 uptake in which the first intermediate produced is a C4 compound i.e. ???

Answer 32

oxaloacetate

Question 33

characteristics of C4 plants:
- HIGH or LOW (?) photosynthetic rates
- High growth rates
- Low photorespiration rates (better efficiency)
- Low rates of water loss
- Specialised leaf structure

Answer 33

HIGH

Question 34

Phosphoenolpyruvate (PEP)
carboxylase incorporates atmospheric CO2 via ???

Answer 34

HCO3-

Question 35

TRUE or FALSE: PEP carboxylase has no affinity for O2

Answer 35

TRUE. this makes it more efficient

Question 36

C4 plants have a different anatomy
which allows them to concentrate CO2 and overcome ???

Answer 36

photorespiration

Question 37

pros/cons of C4 Photosynthesis:
- It concentrates CO2 for Rubisco in the ??? Cycle but requires additional energy and so is used when the gains in efficiency outweigh the increased energy requirement

Answer 37

Calvin cycle

Question 38

photosynthesis in C4 or C3 (?) plants is more efficient in hot, arid or tropical climates

Answer 38

C4

Question 39

Rubisco’s affinity for CO2 decreases with increased temperature; above 30°C the C4 or C3 (?) pathway provides a significant gain in the efficiency of CO2 fixation

Answer 39

C4

Question 40

Concentration of CO2 in C4 pathway
allows stomata to partially close during the day, conserving ???

Answer 40

water