photosynthesis, limiting factors

we started photosynthesis just before we broke up for summer but she never explained this and it's doing my head in. i know we don't really need to know it at gcse but it's annoying me
so the limiting factors of photosynthesis are light, temperature and carbon dioxide, but why is water not one?
if carbon dioxide is then why not water?
the only thing i can think of is that plants can store water, or that it might use water for things other than photosynthesis, but it should still be a limiting factor right, because if a plant doesn't have enough water it won't be able to photosynthesise.

Reply 1

QuentinM

Universities Forum Helper

17

Great question! Theoretically, water should be a limiting one-you are spot on. HOWEVER one detail they dont mention with water absorption/transpiration in plants is just how damn inefficient the process is. Based on studies looking at whatever the plants can be using water for, plants absorb massively more water (some estimates have ti at 10x too much water) than they need. So in practice, plants should never have water as a rate limiting factor. Unless its like a xerophyte, or plant that struggles to access water (e.g. a cactus)-then its more likely to be one, but not "directly" if you see what i mean (as in, the plants have other adaptions to stop them losing water, like spines, which also reduce carbon dioxide uptake)

Hope this helps

Reply 2

alotofonetoknow

OP

4

Original post by QuentinM

Great question! Theoretically, water should be a limiting one-you are spot on. HOWEVER one detail they dont mention with water absorption/transpiration in plants is just how damn inefficient the process is. Based on studies looking at whatever the plants can be using water for, plants absorb massively more water (some estimates have ti at 10x too much water) than they need. So in practice, plants should never have water as a rate limiting factor. Unless its like a xerophyte, or plant that struggles to access water (e.g. a cactus)-then its more likely to be one, but not "directly" if you see what i mean (as in, the plants have other adaptions to stop them losing water, like spines, which also reduce carbon dioxide uptake)

Hope this helps

ah that makes sense, thank you, so if a plant gets less water it won't really affect the rate of photosynthesis because it has a large store

Reply 3

QuentinM

Universities Forum Helper

17

Original post by alotofonetoknow

ah that makes sense, thank you, so if a plant gets less water it won't really affect the rate of photosynthesis because it has a large store

Its not just that it has a store-Its that plants absorb far more water than they actually need, so unless you reduce a plants water by a huge amount (like more than half i'd guess) photosynthesis shouldnt be affected. And to be honest, something else would likely become a limiting factor before that

photosynthesis, limiting factors

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