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Leaf Structure

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Leaf Structure
As we all know, leaves are the green part of plants. What most people do not know is the actual function of the leaves. Leaves have several different functions. The first function is photosynthesis, which we have described in an earlier lesson. The larger the leaf, the more area there is for photosynthesis. This is why small-leaved plants have many leaves and large-leaved plants only have a few. The second function of leaves is gas exchange. Plants need carbon dioxide during photosynthesis and release oxygen into the atmosphere, so it is important that the leaves are able to exchange gas easily. The third function of leaves is that they are the site of transpiration, which is the evaporation of water that helps pull dissolved nutrients up from roots.
blade

Leaf Blade: Wide flattened area of leaf for concentrating sunlight on photosynthetic cells.
Petiole: Short stem that attaches leaf to main stem or branch.
Veins: Vascular bundles within leaf for transport.
Node: Growth region of stem where leaves or new branches arise.
Auxiliary bud: Baby leaf or stem (next year’s growth).


Leaves are also commonly adapted for other functions such as food and water storage, support and defense.

Examples:

A bulb onion has a very short stem with thick fleshy scale leaves

Cacti have evolved their leaves in to woody non-photosynthesis spines. The small surface area of the spine reduces water loss and protects the plant. Because of their lack of large leaves, cacti have most of their photosynthesis in their stems.

Some plants have evolved their leaves in to the role of petals to help in attracting pollinators.

Carnivorous plants have evolved their leaves in to a form of insect trap. The most common being the Venus Fly Trap.





Sources:
http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/extleaf.htm