Explain in detail the external structure of the leaf.

Leaf:

1. Leaf is the broad flattened structure of the plant containing the green pigment called chlorophyll which helps the plant perform photosynthesis.
2. Leaf acts as the site of photosynthesis where solar energy is converted to chemical energy during photosynthesis.
3. Leaf contains minute pores called stomata where gaseous exchange and transpiration occurs.
4. Lamina, petiole and stipule are the three major parts of the leaf.

Lamina:

1. The lamina is the green flattened structure where both photosynthesis and transpiration occurs.
2. Lamina contains the midrib and veins.
   • Midrib: Midrib is a centrally placed thick vein which runs along the entire leaf.
   • Veins: The structures that originate from the midrib and extend to the leaf blade are veins.
   • Both midribs and veins possess conducting tissues xylem and phloem in them which conducts water, food and minerals around the leaf.

Petiole:

1. The lamina of the leaf and the stem stays connected by a stalk-like structure called the petiole.
2. Petiole helps with transportation of food produced during photosynthesis.

Stipule:

1. In some leaves, there are appendages or stalks formed at the base of the petiole called the stipule.
2. In some cases, the stipules protect the growing leaves or buds.