Limiting Factors in Photosynthesis
Limiting factors control how fast photosynthesis can happen - think of them as bottlenecks in the system. The main ones are light intensity, temperature, and CO₂ concentration, and whichever is in shortest supply becomes the limiting factor.
Light intensity affects the rate up to a point called light saturation, where the light-dependent reactions can't work any faster. Beyond this point, something else becomes limiting. The light compensation point is where photosynthesis exactly balances respiration.
Temperature affects photosynthesis because it's controlled by enzymes like rubisco. Higher temperatures increase reaction rates (more kinetic energy), but too much heat denatures the enzymes. This is why you see different optimal temperatures for different plants.
CO₂ concentration directly affects the Calvin cycle since it's a raw material. In normal air (about 0.04% CO₂), this is often the limiting factor. Increasing CO₂ boosts photosynthesis until something else becomes limiting.
Pro Tip: Understanding limiting factors helps explain why commercial greenhouses control temperature, light, and CO₂ levels to maximise plant growth!
Mineral nutrition also matters. Plants need magnesium for chlorophyll (deficiency causes yellowing called chlorosis), nitrogen for amino acids and proteins, and phosphate for ATP and NADP.