BRAINCAKEGas Exchange in Small Organisms
All organisms need to take in oxygen for aerobic respiration and get rid of carbon dioxide. This exchange of gases between an organism and its environment is called gas exchange.
In very small organisms, such as single-celled organisms like Amoeba, gas exchange happens by diffusion across the cell surface membrane. Oxygen diffuses in because it is used up in respiration, keeping its concentration inside low. Carbon dioxide diffuses out because respiration keeps producing it, so its concentration inside stays high.
Diffusion alone is enough for small organisms because:
• they have a large surface area to volume ratio, so there is plenty of surface to supply each unit of volume;
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Key terms in this lesson
- surface area to volume ratio
- The surface area of an organism divided by its volume; it decreases as size increases, limiting exchange by diffusion.
More in Gas Exchange
- Surface Area to Volume Ratio
- Gas Exchange in Large Organisms
- Factors Affecting the Rate of Diffusion
- Effective Gas Exchange Systems
- The Human Gas Exchange System
- Gas Exchange in the Alveoli
- Adaptations of the Human Gas Exchange System
- Breathing
All 23 lessons in Gas Exchange · All Edexcel AS-level Biology topics