AQA Biology - Stomata

For Biology Paper 1 in the Combined Science, I understand most things well.

However, no matter how much revision on Stomata and transpiration, I just never get it.

Can someone help me - simplify as much as possible.

Thanks :smile:

Reply 1

ShylaB14

Stomata are small holes on the underside of a leaf. They allow gases and water to escape.
Around these holes, there are guard cells and these shrink or widen the stomata. If a plant has a lot of water, some of it fills up the guard cells and cause them to become turgid (hard and rigid) and this widens the stomata so that water an escape. If there is too little water, the guard cells become flaccid (flat and deflated) and ends up covering the stomata. This stops water from leaving.

I'm not so confident about transpiration, I'm afraid but I hope that explanation helped. If not, you could tell me where it's a bit confusing and I'll try to explain that better.

Good luck with your exams :smile:

Reply 2

medzie

Cheers, I'm starting to understand it a lot better!

One question, why are the stomata on the underside of the leaf?

Reply 3

josh20019

Transpiration is the movement of water in the plant. Usually from the roots to xylem to leaves into the air

It is affected by limiting factors
Humidity
Temperature
Air flow
Light intensity

Reply 4

Perfection Ace

Original post by medzie

Cheers, I'm starting to understand it a lot better!

One question, why are the stomata on the underside of the leaf?

The underside is more shaded/cooler. This means less humid and thus more water molecules surrounding the stomata. This establishes/maintains a water potential gradient resulting in less water lost.

Reply 5

prettysmart

Original post by medzie

Cheers, I'm starting to understand it a lot better!

One question, why are the stomata on the underside of the leaf?

i think its because it reduces the rate of transpiration, if there’re on the top part of the plant, water can easily be evaporated from the plant by the sun

Reply 6

euphrosynay

@medzie having more stomata on the underside of the leaf helps reduce water loss through transpiration. the top part of the leaf would be more exposed to sunlight, and so it would lose much more water. they are on the underside so that gases can still enter and leave, but less water escapes from the leaves.

Reply 7

ShylaB14

I know someone has already said it, but since it is more shaded and cooler under the leaf, less evaporation happens. This, as Perfection Ace said, reduces the amount of water lost.

I'm glad I can help :smile:

Reply 8

MissUnicorn

Stomata are also adapted to move by their shape, meaning where it is light and there is high carbon dioxide, the stomata open up in order to photosynthesise as carbon dioxide is needed for photosynthesis