Single-celled organisms have a large surface area to volume ratio because they are small. They can therefore exchange substances with their environment by simple diffusion.Oxygen is needed for respiration and carbon dioxide, the product of respiration, is excreted through the cell surface membrane. Diffusion is fast enough to supply materials to the cell and to remove waste products.Prokaryotes have a peptidoglycan cell wall. The cell wall is fully permeable to water and gases. The cell wall does not form a barrier to diffusion.
Gas Exchange in Unicellular Organisms
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Specification: AQA Biology (7401), AS-level, 3.3.2 Gas exchange. Topic: Exchange of Gases.
Key terms in this lesson
- prokaryotic cell
- A cell, such as a bacterium, that lacks a nucleus and membrane-bound organelles and has a single loop of circular DNA.
- diffusion
- The net passive movement of molecules or ions from a region of higher concentration to a region of lower concentration, down a concentration gradient.
- surface area to volume ratio
- The ratio of an organism's or structure's external surface area to its total volume, which decreases as size increases.
More in Exchange of Gases
- The Need for Specialised Exchange Surfaces
- Surface Area to Volume Ratio
- The Rate of Diffusion
- Features of A Specialised Exchange Surface
- Gas Exchange in Insects
- Diffusion Gradient
- Mass Transport
- Increasing the Rate of Diffusion
All 28 lessons in Exchange of Gases · All AQA AS-level Biology topics