CBSE Class 10 Answered

The internal structure of leaf is composed of several layers as follows:

• Epidermis – It the protective, outer layer of cells on the surface of a leaf. The guard cells (and stoma) are part of the epidermis. The lower epidermis has more stomata than upper epidermis.

• Cuticle - The surface of many leaves is coated with a waxy cuticle which is secreted by the epidermis. It prevents water loss on leaves, green stems, and fruits. 

• Palisade layer – A tightly packed layer of parenchyma cells located under the upper epidermis and filled with chloroplasts. So these cells contain most of the leaf's chlorophyll, converting sunlight into usable chemical energy for the plant through photosynthesis.

• Vascular bundle – Xylem and phloem tissues, commonly known as leaf veins.

• Spongy mesophyll – It is the layer below the palisade mesophyll; it has irregularly-shaped cells with many air spaces between the cells. These cells contain some chlorophyll. The spongy mesophyll cells communicate with the guard cells (stomata), causing them to open or close, depending on the concentration of gases.

(Stomata are natural openings in leaves and herbaceous stems that allow for gas exchange. Guard cells are specialized kidney-shaped cells that open and close the stomata.)