Plants create their own food through a process called photosynthesis. In order for sunlight energy to be transformed into carbohydrates, the green pigment chlorophyll is needed to absorb the light before other plant processes can take place. Wherever chlorophyll and other pigments are present, there is photosynthesis, most often in leaves and stems. But without roots supplying water and nutrients from the soil, photosynthesis cannot happen efficiently.
The leaf is perhaps the most recognized part of a plant. Usually filled with green chlorophyll, a leaf can also have other colored pigments or lack of pigment. The main component of the leaf is the blade, which is attached to the stem of the plant by a thin petiole. The leaf has veins in it that allow for the transport of water, nutrients and sugars through the rest of the plant.
The main function of leaves is to produce food through photosynthesis. Sunlight energy is converted into carbohydrates, either starch or sugar. Leaves also are the means by which a plant transpires, where moisture from the roots is evaporated to the air and carbon dioxide is absorbed. Evaporation of water is a means to keep the plant cool in the intense heat and sunlight of summer.
Supporting the leaves and also exposed to sunlight are stems, sturdy support strings of rigid plant tissues that hold the vascular tissues of xylem and phloem. This system allows for water and nutrients to travel upward from the roots to the leaves and sugars manufactured in the leaves travel down to nourish the roots. Plant hormones are also transported via the vascular tissue in the stems.
Plants may have green stems that contribute to photosynthesis. In much bigger plants, the stems may be so large and structurally important that they are protected with specialized cells and materials, such as bark, hairs, spines, and thorns.
Stems may also grow underground, resembling roots. Tubers, rhizomes and bulbs may be regarded as underground stems--they are storage compartments for starches made by the leaves in photosynthesis. These supply the initial energy needed by plants in spring to create new leaves.
Roots serve two primary functions: anchorage and absorption of essential water and nutrients. Although roots do not photosynthesize, their role in sustaining this food-making process elsewhere in the plant is profound. The roots are covered in minute hairs that increase the surface area, allowing for tremendous uptake of water and elements at a molecular level. Roots absorb the water and nutrients, and they flow upward to the stems and leaves, providing the building blocks for photosynthesis. Without them, the plant cannot effectively survive.