5.6.5 factors affecting photosynthesis Flashcards
examples of limiting factors for photosynthesis
- carbon dioxide
- water (water stress)
- light intensity (energy source)
- temperature
describe how light intensity is a limiting factor of photosynthesis
light intensity is necessary:
- provides energy for light-dependent stage, which produces ATP & NADPH for calvin cycle
- also causes stomata to open for gaseous exchange & transpiration to allow uptake of water
limiting factor:
- if constant suitable carbon dioxide concentration & favourable temperature
- light intensity low = rate of photosynthesis is low
- light intensity increases = rate of photosynthesis increases
- if light intensity increases but photosynthesis rate doesn’t, then another factor is limiting
what happens if there is little or no light to the calvin cycle
- GP cannot be reduced to TP as not hydrogen available from NADPH
- TP levels fall & GP accumulates
- TP levels fall = RuBP cannot be regenerated
effect of carbon dioxide concentration as a limiting factor on the calvin cycle
- RuBP cannot accept carbon dioxide, so it accumulates
- GP cannot be made
- thus, TP cannot be made
why is the calvin cycle sensitive to temperature
involves many enzyme-catalysed reactions
effect of changing temperature of the calvin cycle: from low temperature to 25-30 degrees
if plants have sufficient water, carbon dioxide & light intensity = the rate of photosynthesis increases as temperature increases
effect of changing temperature of the calvin cycle: above 30 degrees
- (most plants) growth rates may reduce due to photorespiration = oxygen competes with carbon dioxide for RuBisCO’s active site
- reduces amount of carbon dioxide being accepted by RuBP = reduces quantity of GP & TP being produced, whilst initially caused accumulation of RuBP
- due to lack of TP, RuBP cannot be regenerated
effect of changing temperature of the calvin cycle: above 45 degrees
- enzymes may denature
- reduce concentrations of GP & TP
- eventually reduce concentration of RuBP as cannot be regenerated due to lack of TP
why is water necessary
- transpiration stream has cooling effect on plant
- water passing from xylem to leaves keeps plant cells turgid
- turgid guard cells keep stomata open for gaseous exchange
effect of water stress (not enough available water) on plant
- roots unable to take up enough water to replace water lost through transpiration
- cells lose water & become plasmolysed
- plant roots produce abscisic acid & if translocated to leaves, causes stomata to close = reduces gaseous exchange
- tissues become flaccid & leaves wilt
- rate of photosynthesis greatly reduces
