Photosynthesis Factors: Temperature, Light, and CO2 Impact

Posted on Mar 6, 2025 in Biology

Photosynthesis: Factors Affecting the Rate

At low temperatures, the rate of photosynthesis is very low.
Photosynthesis requires enzymes. As the temperature increases, the kinetic energy of the reactants increases, thereby increasing the rate of photosynthesis.
This rate increases until an optimum temperature is reached. In plants, this optimum temperature is usually between 25°C and 35°C.
After the optimum temperature is reached, the rate of photosynthesis drops dramatically because the temperature can cause the enzymes to denature (lose their shape and active site).

Light is used to produce ATP and split water by photolysis to form H+ ions and oxygen.
As light intensity increases, the rate of photosynthesis also increases.
At low light intensities, an increase in light causes a drastic increase in the rate of photosynthesis.
As light intensity increases, the rate of photosynthesis begins to level off and becomes constant.
As light intensity increases further, there is no change in the rate of photosynthesis as enzymes are working at their maximum rate.

CO2 is the essential molecule in the formation of organic molecules.
At low CO2 concentrations, an increase in the amount of CO2 will increase the rate of photosynthesis. At very low levels, no photosynthesis will take place.
As the CO2 concentration increases, the rate of photosynthesis begins to plateau.
At high levels of CO2 concentration, the rate of photosynthesis remains constant unless light intensity is increased to create more ATP or temperature is increased to provide more kinetic energy.

Early bacterial life introduced oxygen to the atmosphere about 3.5 billion years ago.
As the first free oxygen was released through photosynthesis by cyanobacteria, it was initially soaked up by iron dissolved in the oceans and formed red-colored iron oxide, which settled to the ocean floor.
Over time, distinctive sedimentary rocks called banded iron formations were created by these iron oxide deposits. Once the iron in the oceans was used up, the iron oxide stopped being deposited, and oxygen was able to start building up in the atmosphere about 2.4 billion years ago.
This was known as the “Great Oxidation Event.”
The oxygen remained at about 2% until about 700 million years ago (mya). Then there was a significant rise in oxygen until it reached about 20%.
This led to a huge increase in species as multicellular organisms evolved.

The electromagnetic spectrum consists of the entire range of electromagnetic radiation.
The part of the spectrum that is involved in photosynthesis is called the visible light spectrum.
An action spectrum is the rate of photosynthesis plotted against the wavelength of light. It shows which wavelengths of light are most effectively used during photosynthesis.
The highest rates of photosynthesis occur at red and blue wavelengths.
The absorption spectrum shows the percentage of light absorbed by the photosynthetic pigments in chloroplasts at each different wavelength.
The graphs are very similar because photosynthesis occurs when light is absorbed by the chlorophyll pigments; therefore, the wavelengths that have the greatest rates of absorption will also have high rates of photosynthesis.
Green wavelengths of light are reflected and therefore have a very low percentage of absorption on the absorption spectra (this is why most leaves are green).