The process by which oxygen and carbon dioxide are exchanged between an organism and its environment. One-celled organisms accomplish gas exchange through simple diffusion across their cell membrane due to their large surface area-to-volume ratio.
Multicellular organisms adapted to carry out gas exchange
As organisms increase in size, their surface area-to-volume ratio decreases, making diffusion less efficient.
Larger organisms have higher metabolic demands and thicker body walls, making direct diffusion insufficient.
Maintenance of concentration gradients
Ventilation (in air): Movement of air in and out of respiratory structures to keep fresh air with high oxygen coming in and stale air with high carbon dioxide going out
Circulatory System: Transporting oxygen away from gas exchange surfaces and bringing in carbon dioxide to maintain a gradient
Counter-current Exchange (in water): Blood flows in the opposite direction to water, maximizing oxygen uptake
Cellular Respiration: Continuous use of oxygen and production of carbon dioxide at the cellular level
Potometer
Device used for measuring the rate of water uptake of a leafy shoot
Causes of water uptake are photosynthesis and transpiration
Using a potometer
1. Leafy shoot loses water vapour to air
2. Water drawn up the stem to replace the water transpired
3. Readings taken of the movement of bubble along a ruler in a given time
