Biological Chemistry - Photosynthesis (Factors and Rate)

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. In plants, photosynthesis generally involves the green pigment chlorophyll and generates oxygen as a byproduct.

The overall balanced chemical equation for photosynthesis is: $6CO_{2} + 6H_{2}O \xrightarrow{light/chlorophyll} C_{6}H_{12}O_{6} + 6O_{2}$

Limiting Factors: These are environmental conditions that, when in short supply, prevent the rate of photosynthesis from increasing. The three main limiting factors are light intensity, carbon dioxide concentration, and temperature.

Light Intensity: As light intensity increases, the rate of photosynthesis increases proportionally until another factor (like $CO_{2}$ concentration) becomes limiting. The relationship between light intensity ($I$) and distance ($d$) from the source follows the inverse square law: $I \propto \frac{1}{d^{2}}$.

Carbon Dioxide Concentration: $CO_{2}$ is a raw material. Increasing its concentration increases the rate of reaction until the enzymes involved in the process are saturated or another factor becomes limiting.

Temperature: Since photosynthesis relies on enzymes (such as RuBisCO), the rate increases as temperature rises towards an optimum point (usually between $25^{\circ}C$ and $35^{\circ}C$). Above the optimum temperature, enzymes begin to denature, causing the rate to decrease sharply.

Chlorophyll: The amount of chlorophyll is also a factor. Diseases (like tobacco mosaic virus) or lack of minerals (like magnesium for the chlorophyll molecule) can reduce the rate of photosynthesis.