The Effect of Temperature on the Rate of Photosynthesis

By Michael Parker
In some instances, temperature has the greatest influence on the rate of photosynthesis.
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Photosynthesis is the process in which light, water and carbon dioxide are converted into oxygen and sugar. Most plants rely on photosynthesis to provide the sugar they need for growth and energy. The rate of photosynthesis is greatly affected by temperature. Most plants are known to grow well within a certain temperature range, and if the temperature is too far outside this range, photosynthesis may completely stop.

Photosynthesis Process

Since plants cannot travel after food sources to obtain energy, they must be able to absorb what they need from a stationary position. Plants do so with their roots, chlorophyll and stomata. Stomata are pores that absorb carbon dioxide, located on the underside of leaves. Chlorophyll is the green pigment seen on plants and is what allows the plant to absorb light energy. The roots of a plant absorb water from the soil. Photosynthesis happens in two phases: The first phase is called the light-dependent phase. In this phase, oxygen is produced and light energy is stored as chemical energy with the help of enzymes. The second phase of photosynthesis is called the light-independent phase. Enzymes convert carbon dioxide and the chemical energy produced in phase one into sugar.

Temperature and Photosynthesis

Enzymes are proteins that speed up the rate of a chemical reaction. For an enzyme to work, it must collide with a molecule. Warmer temperatures cause molecules to move faster and with more energy. This increased movement and energy causes more of the molecules to collide with the enzymes, which increases the rate of reaction. Similarly, cooler temperatures cause molecules to move slower. This decreases the chance of a collision and slows the rate of reaction. Since photosynthesis relies on several enzymes, warmer temperatures will increase the rate of photosynthesis. The optimum temperature for photosynthesis is between 77 and 95 degrees Fahrenheit (25 to 35 degrees Celsius). Temperatures that are too high will cause an enzyme to become denatured. A denatured enzyme is one that has lost its chemical structure, and will no longer work.

Other Factors

Light intensity, temperature and carbon dioxide concentration are all major factors that may become limiting factors. A limiting factor is an environmental variable that controls the growth or activity of an organism. If any one of these major factors are not available in sufficient amounts, they become limiting factors and decrease the rate of photosynthesis. How much the rate of photosynthesis is reduced will depend on how limited the access to any one of these factors is, and the conditions the plant is adapted for. For example, a temperature of 55 degrees Fahrenheit will be a limiting factor for many citrus trees, since they prefer a temperature of 80 degrees. Alternatively, 55 degrees Fahrenheit is an ideal temperature for a cool-weather plant like broccoli. For broccoli in this case, carbon dioxide or light are what become potential limiting factors.

Temperature Tolerance

Heat stress is a function of temperature, the duration that temperature persists and the rate of increase in temperature. High temperatures are associated with causing high heat stress in plants. The American Horticulture Society has created a heat zone map that characterizes 12 different zones and the plants suitable for those zones. For cold temperatures, the U.S. Department of Agriculture created a hardiness map showing the minimum temperature a plant can survive across 10 zones. A plant's survival in these various temperatures depends on its ability to moderate the impact exposure to weather will have on photosynthesis and other processes. For example, an adaptation some desert plants have is smaller or less broad leaves. This helps the leaves exchange heat with the air, keeping the plant's temperature from rising to fatal levels.

About the Author

Based in Los Angeles, Michael Parker is a science writer who specializes in environmental issues. He received a Bachelor of Science in environmental engineering from Humboldt State University and holds a Master of Science in civil engineering from California State University Los Angeles.