5.8—Core Practical 10 - factors affecting photosynthesis rate

To investigate how light intensity, wavelength, temperature or carbon-dioxide availability affects photosynthesis rate, vary one independent variable and measure a response such as oxygen production or a colour change.

Use a controlled distance or filter for light, keep temperature stable, standardise plant material and CO2 concentration, repeat measurements and use a rate over a defined interval rather than a final amount alone.

Moving a lamp closer may increase oxygen bubbles at first, but heat from the lamp can become a second variable. A water bath or heat shield helps separate light intensity from temperature.

A plateau does not mean photosynthesis has stopped; another factor may have become limiting. Bubble counts are a proxy and need consistent bubble size, timing and calibration.