Factors affecting the rate of photosynthesis

Affected by : 
Light intensity
Concentration of carbon dioxide
Temperature

Light intensity 

Light is essential during light reaction of photosynthesis.

When concentration of carbon dioxide & temperature are controlled at constant levels,

the rate of photosynthesis is directly proportional to light intensity up to a certain point.

As the light intensity increases, the rate of photosynthesis increases up to a saturated point

(point P).

Beyond the saturation point (point P), further increase in light intensity does not increase

the rate of photosynthesis because of concentration of carbon dioxide & temperature

become the limiting factors.
Both the concentration of carbon dioxide & temperature stop the rate of reaction from
increasing further along PQ.
The rate of photosynthesis will not increase although the light intensity is increases.        
When CO₂ concentration is raised to 0.13%, the rate of photosynthesis is higher. (graph II)
At very high light intensity, the rate of photosynthesis slows down because the chlorophyll
pigment is damaged by UV rays.

 

CO₂ is required in dark reaction as raw material used in the synthesis of glucose.
If there is no other limiting factors that limit the photosynthesis process, as the
concentration of carbon dioxide increases, the rate of photosynthesis increases.
Although the concentration of carbon dioxide keeps increasing, the rate of photosynthesis
will not increase further because light intensity acts as limiting factor.

 

Dark reaction is catalysed by enzymes; thus changes in temperature affects the rate of 
photosynthesis.
An increase in 10⁰C in the surrounding temperature will decrease the rate of photosynthesis
The optimum temperature of varies for each species.
But most plants : between 25⁰C to 30⁰. 
If temperature is too high, photosynthetic enzymes are destroyed by denaturation.
Photosynthesis stops.