Photosynthesis is the biological process by which plants, algae, and some bacteria convert light energy into chemical energy. This process involves reactions that transform carbon dioxide and water into glucose and oxygen. While various environmental factors can influence the speed at which photosynthesis occurs, their impact can differ significantly. This article explores these influences to identify the factor with the least variable effect on photosynthesis in natural environments.
The Major Factors Influencing Photosynthesis
The rate of photosynthesis is governed by environmental factors that can limit the process. Light intensity fuels the light-dependent reactions of photosynthesis. As light intensity increases, the rate of photosynthesis rises proportionally until the photosynthetic machinery becomes saturated, and further increases in light no longer boost the rate.
Carbon dioxide concentration is another determinant, serving as a primary raw material for the Calvin cycle, where sugars are synthesized. An increase in atmospheric carbon dioxide levels generally leads to a higher rate of photosynthesis. This continues until other factors, such as light or enzyme availability, become limiting, causing the rate to plateau.
Temperature also impacts photosynthetic rates because it affects the activity of enzymes. Each enzyme has an optimal temperature range. Photosynthesis rates increase with temperature up to a certain point, but if temperatures become too low, enzyme activity slows, and if they become too high, enzymes can denature, leading to a decline or cessation of the process.
The Factor with the Smallest Effect
Oxygen concentration typically has the smallest variable effect on the rate of photosynthesis. This is due to photorespiration. The enzyme RuBisCO, central to carbon fixation, can mistakenly bind with oxygen instead of carbon dioxide.
When RuBisCO binds with oxygen, it initiates photorespiration. This wasteful pathway consumes energy and results in the loss of fixed carbon as carbon dioxide, reducing photosynthetic efficiency. The concentration of oxygen in Earth’s atmosphere remains stable, consistently around 20.946% (approximately 21%) by volume. Because this level does not fluctuate dramatically, oxygen’s inhibitory effect on RuBisCO is relatively constant and predictable. This makes it less of a variable limiting factor compared to light, carbon dioxide, or temperature.
Why Isn’t Water the Answer?
Many might assume water has a minor effect on photosynthesis, perhaps because plants appear to be surrounded by it. Water is a reactant consumed in the light-dependent reactions. Its role extends beyond being a reactant.
The impact of water scarcity on photosynthesis is indirect. When a plant experiences water stress, it closes its stomata, tiny pores on the leaf surface. This stomatal closure prevents excessive water loss through transpiration. While conserving water, this action restricts carbon dioxide uptake from the atmosphere, effectively starving the plant of a crucial ingredient. Consequently, a lack of water can cause the rate of photosynthesis to plummet or even cease, demonstrating its catastrophic effect.