Why does the curve flatten out at high light intensity?

At very high light, light is no longer the bottleneck. Another factor, such as CO₂ concentration or the number of available chloroplasts, becomes the limiting factor.

What happens if the temperature is too high?

Since the light-independent reactions are catalyzed by enzymes (like Rubisco), excessive heat will cause these proteins to denature, leading to a sharp drop in photosynthetic rate.

Photosynthesis Limiting Factors Lab (AP & IB Bio)

Key Concepts

Limiting Factors

The rate of a physiological process is limited by the factor that is at its least favorable value.

Saturation Point

The value of a factor beyond which further increases no longer increase the rate of photosynthesis.

Temperature Sensitivity

Photosynthesis involves enzymes; rates increase with temperature up to an optimum, then decline as enzymes denature.

The Multi-Factor Dynamics

Photosynthesis is not governed by a single variable. Instead, the rate is determined by a complex interplay of light, carbon dioxide, and temperature.

In this simulator, you can plot curves and see how 'lifting' one limitation often reveals another hidden bottleneck in the system.

Adjust the knobs on the left to see how the curve topography changes and identify the threshold where each factor becomes limiting.

Limiting Factors Summary

Factor	Mechanism Path	Typical Phenomenon	Teaching Conclusion
Light Intensity	Controls ATP/NADPH production in light reactions.	At low light, dark reaction cannot sustain high throughput.	With low light, increasing CO₂ gives little net gain.
CO₂ Concentration	Controls substrate supply for carbon fixation.	At high light but low CO₂, net rate remains low.	Under bright light, CO₂ often becomes the bottleneck.
Temperature	Modulates Calvin-cycle enzyme activity and denaturation risk.	Too high temperature causes rapid efficiency drop.	There is an optimum range; both cold and heat can limit.

Factors Affecting Photosynthesis

About this simulation