Gas Exchange | Biology for GCSE/IGCSE - Year 11 PDF Download

Investigating Gas Exchange

• Plants respire constantly to obtain energy through aerobic respiration, a process vital for their survival and growth. This continuous respiration ensures that plant cells have a constant supply of oxygen while expelling carbon dioxide, which is a byproduct of this metabolic process.
• In daylight, plants engage in photosynthesis, a crucial process where they convert light energy into chemical energy, using carbon dioxide to produce glucose and other organic compounds. Oxygen is released as a byproduct, essential for the sustenance of many life forms on Earth.
• Conversely, during the night, when sunlight is unavailable, photosynthesis halts, but respiration persists. This nighttime respiration maintains the plant's metabolic functions, ensuring the intake of oxygen and the release of carbon dioxide, which are pivotal for cellular processes.

• During the day, especially under bright sunlight, plants photosynthesize faster than they respire, resulting in a net intake of carbon dioxide and a net output of oxygen.
• We can investigate the effect of light on net gas exchange in an aquatic plant using a pH indicator like hydrogencarbonate indicator.
• This is possible because dissolved carbon dioxide forms an acidic solution.
• Hydrogencarbonate indicator reflects the carbon dioxide concentration in solution.
• The table below shows the color changes of the indicator at different carbon dioxide concentration levels:

• Several leaves from the same plant are placed in stoppered boiling tubes containing some hydrogencarbonate indicator.
• The effect of light can then be investigated over a period of a few hours.
• Results from a typical experiment are shown in the table below: