The correct option is C Saturation occurs at 10 percent of the full sunlight
There is a linear relationship between incident light and CO2 fixation rates at low light intensities. At higher light intensities, gradually the rate does not show further increase as other factors become limiting and interesting to note is that light saturation occurs at 10 per cent of the full sunlight. Hence, except for plants in shade or in dense forests, light is rarely a limiting factor in nature.
The C4 plants respond to higher temperatures and show higher rate of photosynthesis while C3 plants have much lower temperature optimum.
Water stress causes the stomata to close hence reducing the CO2 availability. Besides, water stress also makes leaves wilt, thus, reducing the surface area of the leaves and their metabolic activity as well.
The C4 plants posses PEPcase as primary carboxylase enzyme which carboxylates CO2 that is absorbed from the stomata. In these plants there is a special mechanism, which was developed because they evolved at a time when the climate had low carbon dioxide levels, that converts carbon dioxide to malic acid which is stored and later used so they can keep their stomata closed during the daytime to prevent transpirational loss of water. Hence the concentration of CO2 is not a limiting factor for them.
Light is an important factor in the process of photosynthesis. As the light intensity increases, the rate of photosynthesis increases. However, at certain intensity, light is no longer the limiting factor for the overall rate of photosynthesis. This is called as saturation point. At the light saturation point, increasing the light no longer causes an increase in photosynthesis. Light saturation occurs at 10% of the fall sunlight.