U3 AOS2 Topic 3: Factors Affecting Rate of Photosynthesis

Factors affecting rate of photosynthesis involves:

·        Light

·        Temperature and pH

·        Carbon dioxide

·        Water

·        Enzyme inhibition

Light:

Light is needed for photosynthesis in light dependent stage. The rate of photosynthesis increases with increase in light intensity until a saturation point after which the rate of photosynthesis remains constant. At saturation point, the enzymes within chlorophyll are functioning at maximum rate and saturated with their substrate.

Temperature and pH:

Different enzymes are present in plant cell which catalyze biochemical pathways in photosynthesis. These enzymes have an optimum temperature and optimum pH at which they are functional. If temperature decreases or increases than the optimum temperature of that enzyme, then enzyme can denature and does not catalyze the respective reaction. If pH is changed for the enzyme, it can no longer catalyze the reaction.

Carbon Dioxide:

Plant cells need CO₂ in light independent stage of photosynthesis. The rate of photosynthesis increases with increased concentration of CO2 until a saturation point where all the enzymes are saturated with their substrate.

Water:

Water is an important factor in photosynthesis. When there is less water in atmosphere or when high temperature causes the water to transpire from leaf surface, the loss of water causes the stomata to close to conserve the water. The closing of stomata does not allow CO2 to enter the plant cells and therefore rate of reaction decreases. The closing of stomata also traps O2 inside plant cells and therefore photorespiration starts occurring instead of photosynthesis.

Enzyme inhibitors:

Competitive and non competitive inhibitors can decrease the rate of photosynthesis. Competitive inhibitors compete with substrate for active site whereas non competitive inhibitors bind to the site other than active site i.e. allosteric site. These inhibitors can block the enzymes which catalyze photosynthesis and therefore decrease the rat of photosynthesis.