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the green planet 2 > photosynthesis and plant physiology > Flashcards

photosynthesis and plant physiology Flashcards

1
Q

what events have contributed to changes in our atmosphere over evolutionary history?

A
  1. evolution of oxygenic photosynthesis.
  2. evolution of multi-cellular life
  3. formation of eukaryotes
  4. formation of algae
  5. formation of land plants
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2
Q

the great oxygenation event.

A
  1. 2.5 billion years ago there was no photosynthesis.
  2. cyanobacteria evolved and oxygen came out of this organism.
  3. this changed the amount of oxygen in the atmosphere.
  4. oxygen rose so dramatically that it caused a major extinction event.
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3
Q

what are the light and dark reactions?

A

light - energy harvesting.

dark - CO2 fixation.

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4
Q

where does the light reaction take place?

A

leaf – spongy mesophyll – chloroplast – thylakoid membranes – granal stacks.

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5
Q

where do the dark reactions take place?

A

leaf – spongy mesophyll – chloroplast – granal space.

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6
Q

how are the light and dark reactions connected?

A
  1. water is split into oxygen in the light reactions
  2. energy from this reaction generates ATP and NADPH
  3. these are used to power the dark reactions
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7
Q

what are the four main complexes found in the thylakoid membranes in the light reactions?

A
  1. photosystem II (in granal stacks)
  2. ATP synthase complex
  3. photosystem I (ON granal stacks)
  4. cytochrome b6f complex - throughout and ties them all together.
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8
Q

Emerson enhancement effect

A

shining far-red and red light together had a larger impact on photosynthesis than both kinds of light combined.

showed that two different kinds of complexes were working.

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9
Q

stages in Z scheme

A
  1. PSII splits water into oxygen, protons and electrons.
  2. red light energy is used to energise electrons to a negative state.
  3. these electrons go through b6f complex then onto PSI.
  4. in PSI, far red excites the electron even higher and it is then passed on to NADP+ to generate NADPH
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10
Q

in what complexes are the following lights used?

  1. red light
  2. far-red light
A
  1. PSII
  2. PSI
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11
Q

cyclic electron flow

A

instead of giving electron to NADP+ after PSI, it is sent back to cyt b6f. this creates more proton motor force.

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12
Q
  1. linear electron flow products
  2. cyclic electron flow products
A
  1. NADPH and protons
  2. protons only
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13
Q

ATP synthase

A

uses protons produced in Z scheme to drive synthesis of ATP.

this ATP is needed for the dark reactions.

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14
Q

what is the minimum amount of photons required for photosynthesis?

A

8 photons

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15
Q

how can activities of PSI and PSII be co-ordinated?

A
  1. maintain efficiency of light utilisation.
  2. avoid photo-inhibition due to over-excitation of PSII.
  3. vary the proportions of NADPH and ATP produced.
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16
Q

what is an example of post translational control?

(this will balance the photosystems)

A
  1. plants sense the build up of electrons in the plastoquinone pool as a result of too much light.
  2. plants produce STN7 enzyme which phosphorylates light harvesting complexes in PSII.
  3. this moves them to PSI which reduces the capacity for PSII to capture light.
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17
Q

what four processes are involved in the Calvin cycle?

A
  1. fixation
  2. reduction
  3. rearrangement
  4. regeneration
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18
Q

fixation

A

CO2 is captured.

CO2 combines with Rbu-1, 5-P2 to make a 3-PGA molecule.

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19
Q

reduction

A

3-PGA is turned into GA-3-P.

20
Q

rearrangement

A

Rbu-5-P is made here.

21
Q

regeneration

A

Rbu-5-P is phosphorylated and turns into Rbu-1,5-P2

22
Q

for every one cycle of the Calvin cycle what happens to each of these three molecules?

  • CO2
  • 3-PGA
  • Rbu1,5-P2
A
  • CO2 is added
  • 2 3-PGA are being made.
  • 1 Rbu1,5-P2 is being regenerated.
23
Q

how many times do you have to go round the Calvin cycle to take out one 3 carbon molecule?

A

3 times.

24
Q

how many times do you have to go round the Calvin cycle to take out glucose?

A

6 times.

25
Q

how many ATP are used in one Calvin cycle?

how many NADPH are used in one Calvin cycle?

A

ATP = 3

NADPH = 2

26
Q

how many photons are needed to produce one glucose molecule?

A

48

27
Q

what mistake does rubisco make?

A

captures oxygen instead of CO2.

therefore instead of making 3-PGA it makes 2-phosphoglycolate which is toxic to plants.

28
Q

what is rubiscos purpose?

A

captures CO2 and converts it into 3-PGA.

29
Q

at what three levels does rubisco need to be regulated?

A
  1. transcription (small and large sub-units are made in different places)
  2. assembly (controlled by chaperone proteins)
  3. reversible inhibition
30
Q

photorespiratory pathway and its two downsides

A

pathway plants need to go through when rubisco makes its mistake.

  1. lose CO2
  2. energy expensive
31
Q

specificity factor

A

tells us how well rubisco will pick out a CO2 in the atmosphere compared to an oxygen when both are present.

32
Q

what happens to rubisco at higher temperatures?

A

it is faster but less specific for CO2 (makes more mistakes)

33
Q

what three sub cellular compartments is the photo respiratory salvage pathway shared over?

A
  1. chloroplast
  2. peroxisome
  3. mitochondrion
34
Q

what is kranz anatomy and how does it benefit C4 plants?

A

mesophyll organised around veins with bundle sheath cells sitting on the inside. (circular shape)

C4 plants suppress photorespiration and concentrate CO2 in the bundle sheath cells meaning thy can keep rubisco out of the spongy mesophyll.

35
Q

photosynthesis of C4 plants. brief overview and its advantages.

A
  1. CO2 pumped into bundle sheath cell where rubisco is strictly localised.
  2. CO2 levels in BS chloroplasts are increased.
  3. rubisco O2 reaction is outcompeted by high CO2 levels.
  4. rubisco can then perform close to its Vcmax (max rate that it can capture CO2)
36
Q

cost of C4 photosynthesis

A
  1. higher energetic demand
  2. low coverage of C4 plants globally
37
Q

CAM photosynthesis

A

NIGHT - CO2 enters through open stomata pores and kept as malate in the vacuole.

DAY - stomata closed. malate converted to CO2 for fixation by rubisco.

38
Q

biophysical carbon concentrating mechanisms in algae and cyanobacteria

A

algae = pyrenoid (rubisco is requested and CO2 is drawn here)

cyanobacteria = carboxysomes (draw in CO2 to get captured by rubisco)

39
Q

infrared gas analyser

A

clamp leaf with equipment - leaf is held in a chamber.

measures CO2 going in and out of the plant and water going in and out of the plant.

conditions in the chamber like light, temperature and air flow rate can be controlled and changed to look at plants efficiency in photosynthesis.

40
Q

leaf chlorophyll fluorescens

A

measures light reactions, specifically PSII and can be done at a larger scale.

provides pulse of light which either gets reflected, dissipated (vanishes as heat) or is used in the Z scheme.

measures how many electrons are coming from PSII and are being delivered to NADP+ to make NADPH.

41
Q

use of bacteriorhodopsin to improve the light reactions

A
  1. introduce bacteriorhodopsin to plants which absorbs light in the green spectrum.
  2. it is a proton pump and increases the proton motor force meaning more protons are sent to produce ATP.
42
Q

engineering of light harvesting complexes to improve light reactions.

A
  1. replace chlorophyll a with d+f (these have a better absorption spectrum).
  2. add NDH-1 complex after PSII because this makes NDPH directly.
  3. in order to make protons after this however, PSI replaced by type 2 reaction centre.
  4. type 2 reaction centre absorbs in much farther red spectrum.
  5. the reaction centre combines with cyt b6f to create a cyclic electron flow
43
Q

why is rubisco difficult to improve?

A
  1. assembly of rubisco requires chaperone enzymes which are unknown to us.
  2. rubisco is specific to certain plant species.
  3. it is only either fast and not specific or sow and specific.
44
Q

how can the dark reactions be improved?

A
  1. improve rubisco
  2. introduce C4 photosynthetic pathway into C3 plant (introduce kranz anatomy and single cell C4 changes)
  3. engineering non-plant CCMs into crops
  4. engineer a bypass of photorespiration
  5. engineer rubisco and other enzyme activity in Calvin cycle to enhance it.
45
Q

3 things needed to get non-plant CCMs working in crop species.

A
  1. aggregate rubisco
  2. increase CO2 at site of rubisco
  3. reduce leakage of CO2.

the green planet 2 (10 decks)

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