Leaves are the primary organs for photosynthesis in most plants (not cactuses).

Basically a system of cells specialized for photosynthesis by packing themselves with chloroplasts.

Leaf structure is arranged to maximize the effectiveness of these chloroplasts.

Leaves are: positioned to maximize CO2 uptake and O2 disposal, and maximize light absorption; made to minimize water loss, regulate water use, and to readily transport nutrients to and from the leaf cells, with the objective to keep the chloroplasts running smoothly.

The Organ of Chloroplasts