Light, carbon dioxide, and temperature all affect how fast a plant photosynthesizes — but not by averaging together. This simulator lets you isolate each factor yourself and watch which one is actually holding the reaction back.
Photosynthesis converts light energy into the chemical energy of glucose, using carbon dioxide and water as raw materials and releasing oxygen as a byproduct. Its rate depends on three environmental inputs: light intensity, CO2 concentration, and temperature. A classic real experiment measures this rate directly by counting the O2 bubbles released by aquatic pondweed (Elodea) under different conditions — exactly what the simulator above visualizes, with each bubble representing one unit of O2 output.
A common misconception is that rate depends on some average or sum of all three inputs. In reality, biologists describe this with Blackman’s law of limiting factors: the rate is set by whichever single input is scarcest at that moment, and improving an input that isn’t currently the bottleneck does nothing until it becomes the new one. This is why the simulator computes its rate as the minimum of the three factors rather than their average — and why the Limiting Factor readout is worth watching as you experiment. Try maximizing two sliders and slowly raising the third: the rate won’t move at all until that third factor actually becomes the scarcest one.
Light and CO2 each show diminishing returns as you raise them — the reaction rate rises quickly from zero, then flattens out. This happens because once an input is abundant, it stops being the reaction’s bottleneck, and something else (ultimately, the speed of the enzymes carrying out the reaction) takes over as the limit. Temperature behaves differently: it isn’t just abundant or scarce, but has its own optimum. Below the optimum, more heat speeds up molecular motion and enzyme activity; past it, that same heat begins to denature rubisco, the enzyme that fixes CO2 during the light-independent reactions, causing the rate to collapse rather than plateau. This is the identical temperature-activity relationship you’d see in any enzyme-catalyzed reaction, because at its core, photosynthesis’s rate-limiting step is exactly that.