Calvin Cycle Flashcards
What two abilities does rubisco have
Carboxylating and oxygenating
What are the three processes of the CBB cycle
- Fixation of carbon into organic molecule
- Reduction of that organic molecule
- Regeneration of ribulose bisphosphate
What is the equation for the fixation of carbon into an organic molecule
RuBP + CO2 —> 2 x 3-phosphglycerate
What two molecules are required for the reduction of 3-phosphoglycerate
ATP and NADPH
Which stage occurs twice per CBB cycle
Reduction of 3-phosphoglycerate
Glyceraldehyde 3-phosphste is recycled into what first before RuBP
Ribulose 5-phosphate
What is required to recycle ribulose 5-phosphate into RuBP
ATP (phosphate group added)
Why does photrespirstion sometimes occur
Rubisco has some affinity for oxygen - imperfect shape
Why was photrespirstion not a big problem when oxygenic photosynthesis evolved
Not much oxygen in the atmosphere
Where does 2-phosphoglycate need to be transferred to in order to be converted back to 3-phosphglycerste
Mitochondria before back to chloroplast
Why is photrespirstion wasteful
Requires ATP and prices waste CO2
Above what point on a light response curve does excess light intensity occur
P max
What is the effect of excess light energy in a plant
If not dissipated as heat then can knock electrons off molecules to produce free radical which can damage DNA
In which field on a light response curve is photosynthesis most effective
Maximum quantum yield
What process means photosynthesis does not occur below a certain light intensity
Respiration
At what point on a light response curve does photosynthesis begin
Light compensation point
How are shade leaves adapted to lower light intensities and fewer wavelengths (5 marks)
Larger leaves - absorb more light Thinner leaves More chlorophyll to increase absorption so darker leaves Less PSII as there is less sunlight More LHCII to maximise absorption
How are sun leaves (top of canopy) adapted to higher light inntensites (5 marks)
Smaller leaves - expensive to make leaves
Thicker leaves - cells stacked as sunlight can penetrate
Less chlorophyll so paler leaves
More PSII to use extra sunlight
Less LHCII as light harvesting achieved easily
Why do sun leaves have a higher light compensation point than shade leaves
Not worth photosynthesising in low intensities of light
How do plants acclimatise to their changing environment
Adjust components of the electron transport chain
How do free radicals damage proteins lipids and DNA
By readily accepting electrons
What condition do free radicals within plants lead to
Bleaching
What two short term acclimation processes do plants use in high light intensites
Dissipate excess energy as heat - non-photochemical quenching (NPQ)
Stimulate the Xanthophyll cycle
What medium term process do plants use in high light intensities
Increase photosynthetic capacity
What long term, irriversible, acclimation process do plants use in high light intensities
Change morphology
What is NPQ
Dissipation of heat energy
What does the Xanthophyll cycle convert into what
Violaxanthin into zeaxanthin
What functions as antioxidant to protect lipid membranes whilst stimulating NPQ
Zeaxanthin
Why does increasing photosynthetic capacity take some time
Requires changes in gene expression
