Science B4 Revision

Important info on B4 

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  • Created by: Shak
  • Created on: 25-05-11 21:29

Plant leaves:

Photosynthesis occurs mainly in the leaves of plants. Leavers are specially efficiency.

During Photosynthesis - Carbon dioxide diffuses in through the stomata. Oxygen diffuses out through the stomata. And water is absorbed through the root hair cell.

A leaf has four distinct layers:

  • The upper epidermis - is transparent to allow the sunlight through to the layer below.
  • The palisade layer
  • The spongy mesophyll - contains a lots of air spaces connected to the stomata to allow the optimum exchange of gases.
  • The lower epidermis.
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Osmosis is the diffusion of water from high concentration of water to low concentration of water  through a partially-permeable membrane.


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Water in Plants:

Plants use water to...

  • keep their leaves cool
  • transport minerals
  • photosynthesise
  • keep cell firm and the plant supported.

Two adaptation reduces the rate of water from the leaves:

  • A waxy cuticle on the surface of the leaf.
  • Having the majority of the stomata on the lower surface of the leaf.

Stomata open and close  to allow the diffusion of gases and also to control the water loss.

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