Partitioning

Question 1

Energy balance

Answer 1

Sources - provide assimilates and energy; anything carbon based and anything photosynthetic
Sinks - use up assimilates; non photosynthetic parts; often edible

Question 2

Energy losses due to inefficiencies

Answer 2

50% - out of photosynthetic spectrum
5% - reflected
6% - photochemical inefficiency (no conversion to sugars)
13% - thermodynamic limit
11% - carbohydrate synthesis (making enzymes etc)
6% - photorespiration

<5% of solar energy ends up as biomass

Question 3

Photorespiration

Answer 3

Rubisco fixes oxygen instead of CO2 so wastes energy as useless product (2 phosphoglycoate) formed
Happens when CO2 levels are low

Question 4

C3 vs C4 plants

Answer 4

C3 has more issues w photorespiration - horizontal layers of cells

C4 have reduced photoresp., increased WUE and photosynthetic efficiency
Concentrates carbon around rubsico and decreases oxygen
Spatial separation of processes
Circular cell arrangement

Question 5

Photochemical inefficiency

Answer 5

Energy lost to heat; sometimes result of light: low light = more efficient as less energy lost as heat
Photosynthesis increases linearly w light intensity, then levels off when too high due to other limiting factors
Excess light dissapated as heat
Too much energy = free radical production and leaf damage

Max quantum yield - point where uses light most efficiently
Light compensation point - light required to overcome respiratory processes, but not enough for high photosynth than respiration

Question 6

NPQ

Answer 6

Adaptation to deal w excess energy - photosynthetic proteins absorb excess e- energy and dissipate as heat

Slow to turn on and off to protect plant
Make NPQ more responsive to reduce energy loss - only want on when necessary

Question 7

Xanthophyll cycle

Answer 7

Xanthophyll - pigment in plants; wide peak in blue only; good at stimulating conversion of excess e- energy into heat

Production of zeaxanthin from violaxanthin via antheraxanthin

Zeaxanthin - antioxidant to protect lipid membranes from free radicals

Question 8

Partitioning

Answer 8

Make plant more efficient at putting energy where we want to eat
Products need a sink
Selectively breed plants depending on what we want to eat - different energy partitioning within plant
e.g. wheat - want high grain mass and fewer assimilates to roots and tillers
Sink strength can depend on stress

Question 9

Harvest index

Answer 9

Fraction of crop mass that’s economically viable

Mass of product / Total above ground biomass

Question 10

Transport - passive and active movement

Answer 10

Passive - e.g. osmosis: moving sugars along conc gradient; moves from high to low conc

Active - movement from low to high; want more sugar in sinks; requires energy for sugar transporters

Question 11

Transportome

Answer 11

Move sugars and starch out of chloroplast and into cell and then other cell
Correct crossing of membranes via sugar transporters
High energy production
Control this pathway to control where sugars go for yields