Factors affecting photosynthesis

Three factors can limit the rate of photosynthesis: light intensity, carbon dioxide concentration and temperature.

Light intensity

Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the rate of photosynthesis.

A graph with rate of photosynthesis on the y axis and light intensity on the x axis.  The plotted line rises steeply and then levels off to horizontal.

Carbon dioxide concentration

Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.

A graph with rate of photosynthesis on the y axis and light intensity on the x axis.  The plotted line rise steeply and then levels off to horizonal.  During the steep part light is the limiting factor.  During the horizontal part another factor has become limiting.

Temperature

If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.

A graph with rate of photosynthesis on the y axis and carbon dioxide concentration on the x axis.  The plotted line rise steeply and then levels off to horizonal.  During the steep part carobn dioxide is the limiting factor.  During the horizontal part another factor has become limiting.

If you plot the rate of photosynthesis against the levels of these three limiting factors, you get graphs like the ones shown above.

In practice, any one of these factors could limit the rate of photosynthesis.