Photosynthesis is the main life process of plants, the means by which they manufacture the energy to conduct all other life functions. The sunlight captured by the green cells in the leaves produce plant sugars and energy. Respiration, foliage growth, root development, turgor pressure and reproductive activity all play off this basic process of light capturing and conversion.
Photosynthesis converts the light energy from the sun into a chemical energy that can be stored and dispersed throughout the plant to carry out all of the interdependent life processes. The light energy captured by cells in the leaves mixes with carbon dioxide and water in the cells to make sugar. This process cannot occur if the plant does not receive sunlight, and all of the life processes will be slowed or altered if only minimal light is available.
Water in the plant and taken up by the plant roots is used along with the energy from light to run the photosynthetic process. Plants under drought stress either from lack of soil irrigation or from dessication from sun, high winds, arid climates or high heat will strain to complete photosynthesis. The internal turgor pressure in water-based tissues called phloem holds the plant and leaves in an upright position where they can absorb optimal sunlight. Under drought stress, the plant can wilt and collapse, reducing the surface area the plant has to soak up the sunlight and conduct photosynthesis.
Plants take carbon dioxide in through openings on the underside of the leaves called stomata. The stomata open and close to take in carbon dioxide and release oxygen. Under plant stress from excessive heat and/or drought stress, the stomata do not open, and a secondary, less-efficient survival process kicks in called the Calvin cycle, where the plants' basic processes are turned inward and stomata remain closed until environmental conditions become more favorable and night comes, the weather cools and moisture is more plentiful. This restricts the flow of carbon dioxide, water and light energy to carry out the photosynthesis process, slowing all plant functions over the short term.