A leaf is composed of three important components: lamina, petiole, and leaf base. The lamina is also known as leaf blade whereas the petiole is termed as leaf stalk. The leaf base is the component through which the leaf gets attached with the plant’s stem. We can clearly see the veins on a given leaf blade. The regular pattern exhibiting the arrangement of veins is termed as venation of leaf.
Indentations and clefts are clearly visible on the leaf blades of certain plants. These indentations will conveniently reach upto the midrib of the leaf. In this way, the leaf blade can be clearly bifurcated into numerous leaflets. These leaflets are termed as small pinnae and we call this leaf as compound leaf. The leaf is termed as simple leaf if there are no leaflets present on the leaf blade.
The cuticle is a thin waxy covering that is present on the outer surface of the leaf. The main function of the cuticle is prevention of water loss through the leaf. However, plants growing in an aquatic habitat will never have a cuticle. The layer of cells present below the cuticle is termed as epidermis. The veins of the leaf contain the conducting channels, namely, the vascular tissue, xylem, and phloem. Veins are nothing but extensions that run through the tips, roots, and edges present in the leaves.
The upper layer of the vein is composed of cells that are known as bundle sheath cells. These cells would be creating a circle around the conducting channels, that is, xylem and phloem. Xylem is the upper layer of cells whereas phloem is the lower layer of cells. Xylem is the conducting tissue that is used to transport water whereas phloem is the conducting tissue that would be used to transport food.
The middle layer of cells present on the leaf is termed as mesophyll. Mesophyll would be then bifurcated into two layers, namely, the palisade and spongy. The cells present in the palisade layer would resemble that of columns and would be present just below the epidermis. On the other hand, the spongy cells are packed very loosely, lying between the palisade layer and the lower epidermis. The air spaces that are present between the spongy cells can be easily used for the purpose of gas exchange. Chloroplasts are present within the mesophyll cells. The process of photosynthesis would occur in these chloroplasts.
The lower area of the leaf consists of epidermis. Tiny holes termed as stomata are present within the epidermis of the leaf. A special kind of cells termed as guard cells would surround the stomata. They resemble the shape of two cupped hands. The stoma would either open or close by responding to changes in water pressure. When the guard cells are swollen with water, they would bend. When the period is dry, the guard cells would close.
Thanks to evolution, we now come across leaves of different sizes and shapes. However, the basic function of leaves is to conduct the process of photosynthesis. In this case, sunlight and CO2 would be used to synthesize carbohydrates. Leaves also minimize the loss of water through their surface.