Describe the structure and function of the internal parts of a leaf
The internal parts of a leaf can be divided into three main regions: the epidermis, the mesophyll, and the vascular tissues.
1. Epidermis: The epidermis is the outermost layer of cells that covers both the upper and lower surfaces of the leaf. It is usually transparent and consists of a single layer of tightly packed cells. The main function of the epidermis is to protect the leaf from excessive water loss and regulate gas exchange. On the upper surface of the leaf, the epidermis contains specialized cells called guard cells that form openings called stomata. Stomata allow for the exchange of gases, such as carbon dioxide and oxygen, with the atmosphere.
2. Mesophyll: The mesophyll is the middle layer of the leaf and is responsible for photosynthesis. It is composed of two distinct types of cells: the palisade mesophyll and the spongy mesophyll. The palisade mesophyll is found just below the upper epidermis and consists of tightly packed cells that contain a large number of chloroplasts. These chloroplasts capture sunlight and enable photosynthesis. The spongy mesophyll, located beneath the palisade mesophyll, is composed of loosely arranged cells with numerous air spaces. The air spaces in the spongy mesophyll allow for the exchange of gases between the mesophyll cells and the rest of the leaf.
3. Vascular Tissues: The vascular tissues of a leaf consist of xylem and phloem, which are responsible for transporting water, minerals, and sugars throughout the plant. The xylem transports water and minerals from the roots to the leaves, while the phloem transports sugars produced during photosynthesis from the leaves to other parts of the plant. These vascular tissues are organized into veins that run parallel to each other throughout the leaf. The main vein, called the midrib, is usually larger and extends from the stem into the leaf. Smaller veins, called secondary veins, branch off from the midrib and distribute water, minerals, and sugars to all parts of the leaf.