Science B4 Revision

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.

Osmosis is the diffusion of water from high concentration of water to low concentration of water  through a partially-permeable membrane.

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.