Plant Physiology: Photosynthesis, Transpiration, and Respiration

 Plant Physiology: Photosynthesis, Transpiration, and Respiration

• The three major functions that are basic to plant growth and development are: • Photosynthesis – The process of using chlorophyll to capture light energy and convert it to energy stored in sugars. Photosynthesis uses light energy, carbon dioxide (CO2), and water (H2O) to generate glucose with a byproduct of oxygen. • Transpiration – The loss of water vapor through the stomates of leaves. • Respiration – The process of metabolizing (burning) sugars to yield energy for growth, reproduction, and other life processes. Respiration uses glucose and oxygen to generate kinetic energy, with a byproduct of carbon dioxide and water. Photosynthesis A primary difference between plants and animals is the plant’s ability to manufacture its own food. In photosynthesis, plants use carbon dioxide from air and water in the soil with the sun’s energy to generate photosynthates (sugar) releasing oxygen as a byproduct.
•  Photosynthesis literally means to put together with light. It occurs only in the chloroplasts, organelles contained in the cells of leaves and green stems. The chemical equation for photosynthesis is This process is directly dependent on the supply of water, light, and carbon dioxide. Limiting any one of the factors on the left side of the equation (carbon dioxide, water, or light) can limit photosynthesis regardless of the availability of the other factors. An implication of drought or severe landscape irrigation restrictions result in reduction of photosynthesis and thus a decrease in plant vigor and growth. Figure 1. Photosynthesis 141-2 In a tightly closed greenhouse, there may be very little fresh air infiltration and carbon dioxide levels can become limiting during the day while photosynthesis is actively occurring, thus limiting plant growth. Large commercial greenhouses may provide supplemental carbon dioxide to stimulate plant growth. The rate of photosynthesis is temperature dependent. In general, warmer temperatures increase the rates of photosynthesis, but only up to a point. At high temperatures, enzymes used in photosynthesis become less efficient. Furthermore, respiration increases with temperature as well. For example, when temperatures rise above 96 degrees Fahrenheit in tomatoes, the rate of food used by respiration rises above the rate of food manufacture through photosynthesis. Plant growth comes to a stop. Most other plants react similarly