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: OCR Biology A (H020), AS-level, 3.1.1 Exchange surfaces. Topic: Exchange Surfaces and Breathing.
Key terms in this lesson
- prokaryotic cell
- A cell with no nucleus or membrane-bound organelles, found in bacteria.
- diffusion
- The net 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 outer surface area to its volume; it decreases as size increases, which limits the rate of exchange achievable by diffusion alone.
More in Exchange Surfaces and Breathing
- The First Breath
- Measuring Lung Capacity
- Lung Volume
- Breathing Rate and Ventilation Rate
- Gas Exchange in Insects
- Diffusion Gradient
- Mass Transport
- Increasing the Rate of Diffusion
All 24 lessons in Exchange Surfaces and Breathing · All OCR AS-level Biology topics