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The general structure of a leaf is built to do specific, needed functions.

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Introduction

LEAF SRTUCTURE The general structure of a leaf is built to do specific, needed functions. However the main function for most leaves is ultimately photosynthesis. Other functions include: water storage/regulation; gaseous exchange; protection (for example - spikes on cacti); and trapping food in some cases (for example Venus flytraps). The annotated diagram I have drawn below shows an example of the main structures inside a dicot leaf: This shows the structure of a general dicot leaf. The xylem and phloem are shown - indicating where the vein (vascular bundle - xylem vessels) is in the leaf cross section. Throughout the leaf the veins branch a lot to distribute water and minerals and therefore the minerals (mainly magnesium and iron) needed for chlorophyll are taken directly and easily fast the palisade mesophyll and therefore each chloroplast can receive the necessary minerals without difficulty. Also nitrogen compounds needed for protein synthesis are brought through minerals transferred by the same process of diffusion through the mesophylls. ...read more.

Middle

The advantages of the waxy cuticle are mainly to reduce water loss through transpiration but also to provide a small barrier against water-borne infections/diseases and also to stop damage from rain drops in some 'heavy rain' areas. There are no disadvantages of the waxy cuticle that I can see that affects the plant itself. As the plant must be able to control this water exchange the plant has evolved stomatal pores. There are shown on the diagram as stoma, openings in the leaf controlled by 'doors' called guard cells. The stoma also control gaseous exchange in the leaf. The plant needs CO2 for respiration and it needs a way of getting rid of the waste product from respiration, O2. This is all controlled by the guard cells which open and close at specific times during the day to regulate all effecting factors of the plant. Below is a diagram taken from www.emc.maricopa.edu that shows simple diagram of a stomatal pore. ...read more.

Conclusion

This then creates a very big problem for the plant, as it is not producing enough 'food' for the plant to survive upon. The plant usually gets round this problem by terminating the leaf and only using the fully functional leaves until the plant can grow a replacement. The epidermal cells themselves act as a barrier. They are mainly to defend the inner tissues from, in some cases herbivores, dehydration or pathogens. The layers are both on the top and bottom of every leaf and are usually one cell thick. These cells do not have chloroplasts, which would seem a reasonable idea for the plant to think about. A secondary function of the epidermal cells is to produce and replace the waxy cuticle in areas, which it may wear thin or get destroyed for one reason or another. It can also produce the waxy cuticle to different thicknesses, which would be sensible in hotter, drier climates and therefore, in theory, reduce loss of water by transpiration to a greater extent. However this may not always be possible in the cases of extremely hot climates, such as deserts. ...read more.

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