Unit 2 AQA Biology - Gas Exchange, Plant Leaf

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Gas exchange in the leaf of a plant
The leaf is an organ to maximise photosynthesis. As photosynthesis requires carbon dioxide
requires carbon dioxide and produces oxygen, the leaf must be an efficient gas exchange
The palisade cells carry out most of the photosynthesis, and so the structure of the leaf
centres around giving the palisade leaves exactly what they need (light, carbon dioxide and
water) and taking away what they produce (sugar and oxygen).
Some adaptions in its structure for
gas exchange are as follows:
Loosely packed mesophyll
cells. This means there are air spaces
between cells, providing a large
surface area for gas exchange.
Stomata open to allow
gases to diffuse in and out of the
internal air spaces along their
concentration gradients (stomata
close to prevent water loss)
A thin, flat shape that provides a large surface area.
NB: the syllabus specifies a dicotyledonous plant, or dicot, which generally means a
`standard' flowering plant.


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