Leaf

A leaf is a plant organ, typically growing from a stem or branch. Leaves are generally flat and lightweight structures that maximize exposure to sunlight. The primary function of a leaf is photosynthesis—the process by which plants convert light, water, and carbon dioxide into sugars for food.

Leaves also participate in the plant's respiration and the release of water vapor into the atmosphere (transpiration). Their form, size, and texture vary widely: some plants have broad leaves suited to wet climates, while others have small leaf-like structures similar to those of desert shrubs, where minimizing water loss is critical.

Structure

A typical leaf consists of a blade (lamina)—the flat part—and a petiole, which attaches it to the stem. Both the upper and lower surfaces are covered by a protective waxy layer called the cuticle, which prevents rapid water loss. Within the leaf are cells containing chlorophyll, the green pigment responsible for capturing light.

Stomata

Leaves contain tiny pores called stomata, concentrated mostly on the undersurface. Through these openings, carbon dioxide enters the leaf while oxygen and water vapor are released. Specialized cells surrounding the stomata open or close them in response to water availability and light conditions.

Leaf Veins

The visible lines on a leaf are vascular tissues that transport water and minerals (xylem) and manufactured food (phloem). These patterns vary: some leaves show a net-like arrangement, while others have parallel veins like those of grasses.

Seasonal Changes

Some plants shed their leaves at specific times, such as during drought or dry seasons. Before dropping, the plant reabsorbs some of the nutrients from the leaf into the stem, and chlorophyll production decreases, causing the color to shift to yellow or red.