Photosynthesis – Factors Affecting the Rate

Photosynthesis - Factors Affecting the Rate

In most instances it is the strength of growth factors that either decrease or increase photosynthesis. This article will discuss growth factors impacting the photosynthetic process. For information on photosynthesis and the role chloroplast and chlorophyll, light and dark reactions and respiration see: Photosynthesis, Chlorophyll, Reactions and Respiration

Light Intensity

The intensity of light is central to the maximization of the rate of photosynthesis. The most favorable light level for photosynthesis is 10,000 lux. Low light intensity lowers the rate of photosynthesis. However, after reaching an intensity of 10,000 lux, there is no increase in the rate of photosynthesis. With greater light intensity, as chlorophyll is bleached from the chloroplast and the plant’s stomas are closed to slow down water lost through respiration, the rate of photosynthesis may in fact be lowered


There other factors which affect the rate of photosynthesis other than the intensity and wavelength of the light that reaches the plants. Although photosynthesis can be enhanced by maximizing growth factors, genetics plays a major role in the plant’s programmed ability to conduct photosynthesis. The majority of a plant’s photosynthesis abilities are coded in seed genetics.


Scientific experimentation has shown that a relative humidity of 65% to 80% increases the growth rate of most plants. Humidity below this level can result in decreased photosynthesis as plants develop thin leaves and close stomas to try to prevent excess loss of water through respiration and evaporation. Humidity above 80% will result in the plants having trouble disposing of toxic chemicals through evaporation and an increased probability of bud mold


Enzymes stop working if temperatures are too high or too low. Since both the stages of photosynthesis require enzyme activity, temperature has an affect on the rate of photosynthesis.

Carbon Dioxide

Carbon dioxide is essential for the light reactions in all plants that carry on photosynthesis. In the atmosphere, the concentration of carbon dioxide ranges from .03 to .04 %. However, it has been determined that 0.1% of carbon dioxide in the atmosphere increases the rate of photosynthesis significantly.


Although only a small portion of water absorbed by the plant is used in photosynthesis, a shortage of water does affect the rate at which photosynthesis occurs. Lack of water also impacts the quantity of carbon dioxide available for photosynthesis. This is because in response to the drying of leaves plants close their stomata in order to conserve water being lost as water vapor through them.

Chlorophyll Concentration

The concentration of chlorophyll impacts the rate of reaction as the chlorophyll absorbs light energy without which the reactions cannot proceed. Several of the above growth factors can impact the amount of chlorophyll present in the chloroplasts. A deficiency or lack of chlorophyll results in chlorosis, or yellowing of leaves. This can occur due to disease mineral deficiency.


Air pollution can cause stomas to be clogged which will reduce the gas exchange necessary for optimal photosynthesis. Various water pollutants can result in less than optimal plant photosynthesis and plant growth.

This article covered factors affecting the rate of photosynthesis. For information on controlling factors affecting the rate of photosynthesis see: Controlling Factors Affecting the Rate of Photosynthesis Photosynthesis – Controlling Factors Affecting the Rate


Britannica Online Encyclopedia website, accessed August 5, 2010

Photosynthesis UC Clermont College Biology website, accessed August 5, 2010

Estrella Mountain Photosynthesis website, accessed August 5, 2010