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L3 Plant Sciences > Week 14 L7: C3 and C4 Photosynthesis > Flashcards

Week 14 L7: C3 and C4 Photosynthesis Flashcards

1
Q

What is the photosynthesis reaction?

A

6CO2 + 6H2O –> C6H12O6 + 6O2

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2
Q

Where do the light dependent reaction occur?

A

thylakoids

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3
Q

Where does the light independent reaction occur?

A

stroma

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4
Q

What is RuBisCo?

A

enzyme in the calvin cycle responsible for fixing CO2.

Binds CO2 and converts it to 2 molecules of 3-phospho-glycerate.

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5
Q

Why is RubisCo bad?

A

Cant differentiate between O2 and CO2

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6
Q

When does RuBiso become even less efficient due to climate change?

A

elevated temps, its affinity for O2 becomes even higher. (Carboxylase decrease vs oxygenase increase, CO2 solubility decreases.)
reduced pp CO2 vs O2.
not adapt well to climate change.

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7
Q

What does the plant produce when guard cells close?

A

increase O2
more futile Rubico reactions
lose energy even though they are photosynthesising
photorespiration reaction.

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8
Q

What happens in hot environments to C3 plants?

A

Water available but limited
Transpiration or water loss rates high
RuBisCo inefficient at high temps
Photorespiration increases

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9
Q

What happens in arid/dry environments to C3 plants?

A

Low water potential and/or availability
Shut stomata
Reduce water loss
But CO2 falls and O2 increases

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10
Q

What C3 plants can grow in dry enviroments?

A

cacti
pineapple
epiphytic orchids

rice wheat potato

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11
Q

What plants can grow in dry environments?

A

cacti
pineapple
epiphytic orchids

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12
Q

How did evolution mitigate photorespiration?

A

CO2 concentrating mechanism (CCM)
-help promote carboxylase activity
O2 exclusion or insensitivity - cant be poisoned, no futile reaction.

Adaptations present in C4 and CAM photosynthesis

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13
Q

Why did rubusco have oxygenase activity?

A

As CO2 levels were high billions of years ago andthere were no consequences to it oxygenase ability.

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14
Q

Why did C4 and CAM arise?

A

Increasing O2 levels.
Historical climate change
Falling CO2 levels
Increasing O2 levels

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15
Q

What is CAM?

A

Crassulacean Acid Metabolism (CAM)

survival adaptationgather sunlight during the day and fix carbon dioxide molecules at night.

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16
Q

When does CAM occur?

A

Take up CO2 during low temps (night)
Need to store CO2 until light is available (day)
Good for arid or low water availability areas

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17
Q

What plants use CAM?

A

vanilla

cacti

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18
Q

What limits CAM?

A

The size of its CO2 battery

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19
Q

When is CAM useful?

A

Really an adaptation to surviving drought rather than biomass accumulation

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20
Q

Why do not many crops use CAM?

A

Vacuole acidity unpalatable

Other adaptations make them less appealing

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21
Q

How can CAM be useful?

A

Open up new areas for farming?

Introduce facultative CAM to existing crops to improve drought survival.

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22
Q

How can CAM be useful?

A

Open up new areas for farming?

Introduce facultative CAM to existing crops to improve drought survival.

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23
Q

What does C4 plants separate?

A

separate chemical reaction

separate RuBisCo and O2

24
Q

When would CAM be useful?

A

Achieves CO2 levels 25-50 higher than atmospheric
Good for areas with sufficient water and temps >20°C
At 25°C C4 plants can produce double the biomass of C3
Grow with high yield. very effective.

25
Q

What is the difference between C3 rice and C4 maize?

A

location of mesophyll

26
Q

Where does light dependent and light independent occur?

A

in all cells

27
Q

Why does rubisco poison C3 plants?

A

Both light reactions happen in the same cells

28
Q

What is the difference between mesophyll and bundle sheath cell?

A

sheath has no PS2 COMPLEX, no oxygen. Can fuel the rubico in the Calvin cycle. and is CO2 is refixed by rubisco

29
Q

What is the difference between mesophyll and bundle sheath cell?

A

sheath has no PS2 COMPLEX, no oxygen. Can fuel the rubisco in the Calvin cycle. and is CO2 is refixed by rubisco

30
Q

What do the thylakoids permit?

A

chlorophyll
light reactions
generate ATP and NADPH
Oxygen generating

31
Q

Where and what uses ATP and NADPH?

A

stroma

used by RuBisCo

32
Q

Where is CO2 fixed?

A

Stroma, where it can be fixed into these complex carbon skeletons. used for growth metabolism

33
Q

What is the basis of C3 photosynthesis?

A

Rubisco binding CO2 and fixing it

34
Q

Why are 25% of RuBisCo reactions wasted?

A

Due to a process called photorespiration. cant differentiate between CO2 and O2.
Plant wastes energy

35
Q

When RuBisCo binds O2 instead of CO2, what is produced?

A

2-phosphoglycerate

36
Q

How does RuBisCo waste energy generated from photosystems 1 and 2?

A

futile reaction.

To convert 2-phosphoglycerate to 3-phosphoglycerate, ATP and NADPH are needed.

37
Q

How does RuB cost the plant even more?

A

in the conversion to 3-phospho-glycerate, the cell releases CO2, H2O2 and NH3, which are toxic.

The plant needs waste energy converting these to detoxify them.

38
Q

Where are the adaptation to mitigate photosynthesis?

A

C4 and CAM photosynthesis

39
Q

What is CAM photosynthesis?

A

gather sunlight during the day and fix carbon dioxide molecules at night.

40
Q

What is the mesophyll?

A

the inner tissue (parenchyma) of a leaf, containing many chloroplasts

41
Q

What is temporal separation?

A

CAM,

Separates photosynthesis into 2 stages,

42
Q

Where is CO2 stored in the plant?

A

vacuole - malate acid

43
Q

What is the carbon fixing enzyme in CAM?

A

PEPC - phosphoenolpyruvate carboxylase

44
Q

What does PEPC convert CO2 to?

A

Malate acid

45
Q

What are the disadvantages of CAM?

A

Yield penalty
CO2 fixation limited by [PEP]
Uses 3 more ATP than C3 per CO2 fixed

46
Q

Where are the C4 biochemical reactions happening?

A

Separate parts of the plant. Rubisci and O2 are in different parts of the plant so dont get the futile photorespiration

47
Q

What are the C4 plants?

A

maize

sugar cane

48
Q

What is kranz anatomy?

A

The chloroplasts concentrated in the sheath cells

49
Q

Why does C4 photosynthesis not poison Rub?

A

No phII, the O2 producing photosystem part

50
Q

What enzyme fixes CO2 in the mesophyll of C4 photosynthesis?

A

PEPC

Is O2 insensitive

51
Q

What happens to malate when it enters the sheath?

A

decarboxylated by malic acid

52
Q

How does C4 increase WUE?

A

For a given CO2 conc you have, the stomata are more shut - less water loss. keep CO2 conc higher but have less water loss

53
Q

How does C4 increase NUE?

A

Reducing rubisco reduces the demand for proteins, many proteins contain N

54
Q

Where is NADP found?

A

chloroplast

55
Q

Where is NAD found?

A

mitochondria

56
Q

Why do you need extra light for C4?

A

It needs more energy to convert CO2 to glucose

needs more light per molecule of glucose fixed

57
Q

What is the increased WUE likely a bi-preoduct of?

A

trying to increase rub efficiency. It works well in dry enviro - CAM

L3 Plant Sciences (17 decks)

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