Photosynthesis and Limiting Factors Simulator
Equations in this simulation
| O₂ | oxygen | the gas in the bubbles; light splits water to release it, and the carbon dioxide is built into sugar |
|---|
| I | light intensity at the plant (µmol of photons per m² per second) | the inverse square law: twice as far, a quarter of the light | |
|---|---|---|---|
| I₁₀ | intensity at 10 cm | 800 µmol m⁻² s⁻¹ for this lamp; full sunlight is about 2,000 | |
| d | Lamp distance d (cm) |
With the current values:
| J | rate the light alone could support (bubbles per minute) | ||
|---|---|---|---|
| α | bubbles per minute per unit of light, when light is the only limit | 0.1 | |
| e | how well the plant uses this color | red 1, white 0.75, blue 0.75, green 0.3: chlorophyll absorbs red and blue and reflects green |
With the current values:
| P_max | rate the enzymes could reach with unlimited light (bubbles per minute) | ||
|---|---|---|---|
| C | dissolved carbon dioxide and hydrogencarbonate (mM) | 0.5 mM from the tap water plus what Sodium hydrogencarbonate added (grams per liter) gives, at 84 g per mole | |
| f(T) | temperature factor | doubles every 10 °C (Q₁₀ = 2) until the enzymes start to be damaged above about 35 °C |
With the current values:
| P | gross rate of photosynthesis | the smaller of J and P_max, with a smooth bend between them (θ = 0.9) | |
|---|---|---|---|
| R | respiration | the plant uses oxygen all the time: 3 bubbles a minute at 25 °C, doubling every 10 °C | |
| net | bubbles per minute given off | zero below the compensation point, where photosynthesis only just covers respiration |
With the current values:
How to use the photosynthesis simulator
- Set the lamp distance, the light color, the sodium hydrogencarbonate added to the water and the water temperature. The pondweed gives off bubbles of oxygen from its cut stem, faster when it photosynthesizes faster. The results give the bubbles per minute, the light reaching the plant and the factor that limits the rate now.
- Choose what to plot the rate against and press Count the bubbles for a minute: the minute is sped up to six seconds, and the count lands on the chart as a yellow mark, a little above or below the model curve as real counts are. Change the variable step by step and count again to build the curve, then find where it levels off.
- Watch the limiting factor change: at a distance light limits the rate, close up carbon dioxide or temperature does, and above about 35 °C the enzymes start to be damaged. Green light barely works. The Molarity Calculator turns grams of sodium hydrogencarbonate into a concentration, and the Enzyme Kinetics Simulator shows why temperature matters.
Frequently asked questions
What are the limiting factors of photosynthesis?
Light intensity, carbon dioxide concentration and temperature. At any moment the rate is held back mostly by the one in shortest supply: more light does nothing if the plant is short of carbon dioxide. Raise the limiting factor and the rate climbs until another factor takes over, which is why the rate curves rise and then level off.
Why does moving the lamp change the light so much?
Light from a small lamp spreads out over a sphere, so its intensity falls with the square of the distance: twice as far gives a quarter of the light, three times as far a ninth. That is why the rate is often plotted against 1 ÷ d², which is proportional to the light intensity.
Why does the plant give off no bubbles in dim light?
Plants respire all the time, using oxygen. In dim light photosynthesis only makes as much oxygen as respiration uses, or less, so none is left over to form bubbles. The light level where the two balance is the compensation point.
Is counting bubbles an accurate way to measure photosynthesis?
It is quick but rough. Bubbles differ in size, some oxygen dissolves in the water, and the gas is not pure oxygen. Collecting the gas in an upturned measuring cylinder or a syringe, or measuring dissolved oxygen with a probe, gives better numbers.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.