Life Sciences, Metabolism, Plant Physiology / Principles and Exploration
Limiting factors in photosynthesis — principles and investigation
The rate of photosynthesis does not always increase with increasing light alone. Adjust the light intensity, carbon dioxide supply index, and water temperature one by one to find out which condition limits the speed. This is an experiment to examine the meaning of limiting factors in which the effect of one factor varies depending on the status of other factors.
How does it work?
Light and CO₂ are each saturated. The speed can only be increased by increasing the insufficient supply. The temperature coefficient is largest around 30 °C.
Speed = min (light limitation, CO₂ limitation) × temperature coefficient × 3
Try this investigation
- Count virtual oxygen bubbles in a myelinated black horse for 60 s. Change the light intensity, CO₂ supply index, and water temperature and check which supply is limited.
- Maintain CO₂ supply of 0.1 g/L·30 °C and record the number of bubbles at relative luminosity of 40 and 100.
- Change one condition at a time. Try increasing only the CO₂ in sufficient light, lowering the temperature from the standard, and lowering only the light at high CO₂.
Interpreting your results
Why is the speed from luminosity 40 → 100 the same at low CO₂?
Use the smaller of the light limit and CO₂ limit. If the light intensity is already sufficient at low CO₂, increasing the CO₂ will increase the speed.
Assumptions and limitations
It is a virtual model based on a black horse. Light intensity and sodium bicarbonate concentration are inputs to the relative light and CO₂ supply function and are not converted to actual dissolved CO₂ concentration. Use light intensity/(30+light intensity), supply concentration/(0.3+supply concentration), exp(−((T−30)/12)²). Assume that one bubble has the same amount of virtual oxygen. Respiration, bubble size, dissolution, biomass, and actual optimal temperature for each species are omitted.