The leaves of plants come in a variety of shapes and sizes, but they share one common feature: the vast majority of leaves are flattened and thin. What is the biological significance of this shape for plant leaves?
We know that leaves are the main organs for photosynthesis in plants. Under sunlight, they use water and carbon dioxide to synthesize carbohydrates and release oxygen. To carry out photosynthesis effectively, two essential factors are indispensable. First, the chlorophyll in the leaves, which is like a living machine, carries out a series of biochemical reactions to produce carbohydrates and oxygen. Second, the indispensable raw materials for this process are sunlight, water, and carbon dioxide. To enable leaves to obtain sufficient raw materials, or to absorb as much light and carbon dioxide as possible, the surface area of the leaves needs to be as large as possible. As we all know, the surface area of a sphere is the smallest when the volume is the same, while the surface area of a flattened sheet is many times larger. Therefore, on the premise that the necessary tissues can be accommodated, the flatter the leaves are, the more conducive they are to photosynthesis in plants. Therefore, most plant leaves choose a flattened shape.
Of course, to adapt to various specific living environments, the shapes of leaves can also have various peculiar changes. For example, many plants growing in arid regions often become very small or even needle-like to reduce water evaporation from the leaf surface, with the cactus being the most typical representative species. Even more surprisingly, the leaves of some plants have completely degenerated and disappeared, and the chlorophyll is distributed on the surface of the stem, such as the "naked tree" in the desert environment.