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Flashcards in Lecture 3 Deck (24)
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1
Q

What is the main part of the light independent reactions?

A

The Calvin-Benson-Bassham cycle.

2
Q

Where do the products for the light independent reactions come from?

A

The light dependent reactions.

3
Q

What is the main aim of the Calvin cycle?

A

Assimilate CO2 into organic molecules to produce 3-carbon sugar phosphate molecules. (Adding CO2 to existing sugars).

4
Q

Where does the Calvin cycle take place and what does it use?

A

In the stroma using RuBisCO.

5
Q

What is RuBisCO?

A

Ribulose 1,5 bisphosphate carboxylase oxygenase. The worlds most abundant protein which adds CO2 to RuBP to (a 5 carbon molecule) to create two 3 carbon molcules (3-phosphoglycerate).

6
Q

What is the general order of the Calvin Cycle?

A
  1. Fixation of CO2 into an organic molecule.
  2. Reduction of that organic molecule (twice).
  3. Regeneration or RuBP.
7
Q

1st stage of Calvin cycle.

A

RuBP + CO2 -> 2 x 3-phosphoglycerate.

8
Q

2nd stage of Calvin cycle.

A

Reduction of 3-phosphoglycerate into 2 sugars:
one to leave and make sugars
one to regenerate RuBP.

9
Q

3rd stage of Calvin cycle.

A

RuBP regenerated using ATP, ready to collect another Carbon molecule.

10
Q

Why does the Calvin cycle require multiple cycles?

A

To generate and regenerate its components.

11
Q

What does the Calvin cycle require overall?

A

3ATP + 2NADPH.

12
Q

What is the issue with RuBisCO?

A

Uses oxygen molecule on CO2 to fix CO2 which can lead to photorespiration.

13
Q

What is photorespiration?

A

Fixation of Oxygen instead of CO2. Happens 25% of the time and can be toxic to plants.

14
Q

How is it a wasteful process?

A

2-phosphoglycerate can be converted to 3-phosphoglyerate (carbon molecule made during fixation of CO2) but it results in a loss of carbon overall.

15
Q

How did it evolve?

A

RuBisCO evolved before there was oxygen in the atmosphere so it wasn’t an issue back then.

16
Q

Describe a light response curve.

A

Shows rate of photosynthesis increases with light until other factors become limiting. Photosyn. is most efficient at maximum quantum yield (before light is in excess).

17
Q

What are some adaptations to a sunny environment?

A

Smaller, thicker leaves with multiple cell layers that light can penetrate. Paler leaves due to less chlorophyll.
More PS2, less LHCII. Less vulnerable to excess light.

18
Q

What are some adaptations to a shady environment?

A

Larger, thinner leaves. Darker due to more chlorophyll. Able to photosynthesise in less light.
Less PS2, more LHCII.

19
Q

How do plants acclimatise to changing light?

A

Adjust components of the ETC (phenotype plasticity).

20
Q

What effect does too much light have on plants?

A

Sunburn as light energy is harvested by the light harvesting complexes but has nowhere to go. Excited chlorophyll molecules are passed on to O2 creating free radicals within the chloroplast - oxidants that grab electrons from other molecules, damaging proteins, lipids and DNA.

21
Q

What is a short term (seconds-hours) acclimatory response to excess light?

A

Non-photochemical quenching (photosynthetic proteins dissipate excess energy as heat).
Stimulate the Xantophyll cycle.

22
Q

What is the Xantophyll cycle?

A

Xantophyll are pigments in plants.
When under light stress: Violaxanthin -> zeaxanthin.
When under no stress: zeaxanthin -> violaxanthin.

23
Q

What is a middle term (hours-days) acclimatory response to excess light?

A

Changing gene & protein expression to increase production of photosynthetic components and increase photosynthetic capacity.
Ability varies between species.

24
Q

What is a long term (days-weeks) acclimatory response to excess light?

A

Phenotype plasticity leads to morphological changes.