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Bio II > Lecture 17: Photosynthesis (Part 3) > Flashcards

Lecture 17: Photosynthesis (Part 3) Flashcards

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1
Q

What function does the Calvin cycle have?

A

It fixes (incorporates) and reduce carbon atoms from CO2 into carbohydrates

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2
Q

Where is the machinery of the Calvin Cycle found? (Where does it occur)

A

in the stroma of chloroplasts

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3
Q

What type of organisms does the calvin cycle makes an organism into?

A

an autotroph

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4
Q

What is another name for the Calvin Cycle?

A

the reductive pentose phosphate cycle

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5
Q

Are the reactions in the Calvin Cycle light-dependant?

A

No, they are light-independent but require ATP and NADPH produced by light-dependent reactions

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6
Q

What are the three phases of the Calvin Cycle?

A
  1. Fixation
  2. Reduction
  3. Regeneration
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7
Q

Is energy used in the fixation phase of the calvin cycle?

A

no

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8
Q

What is the enzyme responsible for fixation?

A

rubisco

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9
Q

What is the balanced equation of fixation in the calvin cycle?

A
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10
Q

What is the full name of 3-PGA?

A

3-phosphoglycerate

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11
Q

What does the suffix -ate signify?

A

it is the name of an organic acid

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12
Q

What is the balanced equation of reduction in the calvin cycle?

A
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13
Q

What is the full name of G3P?

A

Glyceraldehyde-3-Phosphate

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14
Q

One turn of the calvin cycle fixes how many molecules of CO2 and produces how many molecules of G3P?

A

fixes one molecule of CO2 and produces two Glyceraldehyde-3- Phosphate (G3P).

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15
Q

How come can one carbon in CO2 become 6 carbons total in the two G3P molecules?

A

5 carbons were already in the cycle (as RuBP)

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16
Q

How many turns of the calvin cycle is required to fix enough carbon (3) for the NET production of one molecule of one G3P (3-carbon sugar)?

A

3

one turn fixes one carbon into two G3P (3carbons x2) so there is already 5 carbons involved in the process

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17
Q

What is the balanced equation of regeneration

A
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18
Q

In which phases of the calvin cycle is ATP used?

A

Reduction on regeneration

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19
Q

In which phases of the calvin cycle is NADPH used?

A

reduction

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20
Q

Can you sketch the structures of 1,3-Bisphosphoglycerate and ribulose-5-phosphate?

A
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21
Q

What are the sugars produced by photosynthesis?

A

fructose and glucose

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22
Q

What are the two molecules that can be made of fructose and glucose?

A

Sucrose and starch

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23
Q

Where is sucrose produced?

A

cytosol

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24
Q

What is the function of sucrose?

A

for transport

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25
Q

Where is starch produced?

A

in chloroplasts

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26
Q

What is the function of starch?

A

for energy storage

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27
Q

What is rubisco?

A

The CO2-fixing enzyme

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28
Q

What is the full name of rubisco?

A

ribulose 1,5- bisphosphate carboxylase/oxygenase

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29
Q

Where is rubisco used?

A

Rubisco is found in all organisms that use the Calvin cycle to fix carbon.

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30
Q

In which part of the cell is rubisco found?

A

It is packed in chloroplasts

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31
Q

How abundant is rubisco in the environement?

A

is thought to be the most abundant enzyme on Earth.

32
Q

How efficient is rubisco?

A

It is an inefficient enzyme: It is slow and lacks specificity.

33
Q

What is the structure of rubisco?

A

Composed of eight large chain subunits and eight small chain subunits in cyanobacteria, algae, and plants.

34
Q

Do the subunits in rubisco act together?

A

no, active site in the large chain and each active site acts independently.

35
Q

By which genome are the large chain subunits and the small chain subunits encoded by?

A

Large chain subunits encoded by chloroplast genome while the small chain subunits encoded by the nuclear genome.

36
Q

What leads to photorespiration?

A

When O2 reacts with RuBP on rubisco’s active site, one of the products undergoes photorespiration

37
Q

What competes with CO2 for rubisco’s active site?

A

O2

38
Q

What happens to photosynthesis when photorespiration occurs?

A

the rate of photosynthesis declines drastically

39
Q

What is the reaction formula for photorespiration?

A
40
Q

Why does photorespiration decrease the efficiency of photosynthesis?

A
  • Photorespiration “undoes” photosynthesis because it consumes energy and releases fixed CO2. (what photosynthesis tries to produce)
41
Q

What is the glycolate pathway?

A

a salvage pathway that returns reduced carbon from phosphoglycolate to the Calvin cycle in the form of 3PG.

The pathway:
A. Releases CO2 (unfixes carbon fixed by the Calvin cycle).
B. Uses energy carriers produced in the light reactions: ATP and NADH.

42
Q

Why do we call the glycolate pathway a “salvage pathway”?

A

definition salvage (save): partially fixes what’s done by photorespiration

return some reduced carbon back from phosphoglycolate to the Calvin cycle in the form of 3- phosphoglycerate.

43
Q

In which organelle(s) does glycolate pathway’s reactions occur?

A

three:

44
Q

How much percent is “saved” by the glycolate pathway as fixed carbon return back in the form of 3PG?

A

75%

45
Q

How much percent of carbon is lost despite the efforts of glycolate pathway? In what form?

A

25%, in the form of carbon

46
Q

Which enzyme in peroxisomes will breakdown the H2O2 produced?

A

GP-C (catalase)

47
Q

Why does photorespiration exist in plants? (If photorespiration is harmful to plants, natural selection should select against it!)

A

Photorespiration may be a molecular relic because Rubisco first evolved at a time when the atmosphere had far less O2 and more CO2.

Not enough time for change or cost of photorespiration is low.

Photorespiration might play a protective role in plants that outweighs the cost.

48
Q

How does photorespiration play a protective role in plants?

A

plants that live in hot and dry conditions may close their stomata to prevent water loss and this causes the gas exchange to stop (O2 concentration will rise)

photorespiration is favored as O2 concentration rise (O2 wins over CO2 on rubisco active site) to bring CO2 levels back to normal

49
Q

What are stomata?

A

leaf structures where gas exchange occurs

50
Q

What are the function of guard cells in stomata?

A

regulate the pore size

51
Q

What permits the guard cells of the stomata to close?

A

evaporation

52
Q

Are stomata usually closed or opened during the day?

A

Normally opened during the day and closed at night.

53
Q

Why do stomata close at night?

A

because synthesis require light and stomata need to be open to allow gas exchange in photosynthesis

54
Q

Where are stomata located?

A

on leaf surfaces

55
Q

What would happen to plants if they did not halt photosynthesis by closing their stomata in dry and hot environements?

A

they risk to die from dehydration

56
Q

Are C3 or C4 plants more abundant?

A

C3

57
Q

What are C4 pathways?

A

Carbon fixation pathway used by C4 plants

are adaptations that allow a plant to minimize photorespiration.

58
Q

What type of plants use C4 pathways?

A

some plants that live in hot/dry climates that must close their stomata during the day to prevent dehydration.

59
Q

What are the functions of C4 pathways?

A

A. Limit photorespiration by increasing the ratio of
CO2:O2 where carbon fixation occurs.
B. Involve fixing carbon into 4-carbon organic acids.

60
Q

What is the enzyme that catalyzes C4 pathways?

A

PEP carboxylase

61
Q

What are 4-carbon organic acids used for?

A
  1. transport CO2
  2. store CO2
62
Q

What is the function of Carbon Concentrating Mechanisms?

A

Mechanisms for increasing the CO2:O2 ratio around Rubisco.

63
Q

What are the two Carbon Concentrating Mechanisms?

A

A. C4 Pathway: Spatial separation of steps.
B. CAM Pathway: Temporal separation of steps.

64
Q

What differs between C4 Pathway and CAM Pathway?

A

One is a Spatial separation of steps and the other is a Temporal separation of steps.

65
Q

Which pathway do C4 plants use to prevent photorespiration?

A

spatial separation of steps in C4 pathway

66
Q

Are stomata of C4 plants completely closed during the day?

A

no. only partially

just enough to prevent dehydration

67
Q

What is the structure of C4 plants?

A
68
Q

What is the work done by C4 acids in C4 plants?

A

transport CO2 to the bundle-sheath cells.

69
Q

How do C4 and CAM plants differ?

A

C4 plants’ stomata only partially close during the day whereas CAM’s completely close

Use the temporal separation of steps in CAM pathway to prevent photorespiration

70
Q

“How” does PEP carboxylase fix CO2 in C4 plants?

A

in mesophyll cells

71
Q

“How” does PEP carboxylase fix CO2 in CAM plants?

A

at night

72
Q

What is the work done by 4-carbon organic acids in CAM plants?

A

they get stored
in the mesophyll cells.

73
Q

How is the release of CO2 in C4 plants?

A

they are released in bundle-sheath cells

74
Q

How is the release of CO2 in CAM plants?

A

The four-carbon organic acids release CO2 around Rubisco during the day.

75
Q

Why can’t CAM plants just carry out photosynthesis at night?

A

Bio II (21 decks)

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