BRAINCAKEGas Exchange in Large Organisms
Large multicellular organisms cannot rely on diffusion across their body surface for gas exchange, for three main reasons:
• They have a low surface area to volume ratio, so their outer surface is too small to supply all their cells.
• Many cells are far from the surface. Diffusion is only fast over very short distances, so it is far too slow across the long distances inside a large body.
• Many large animals, especially mammals and birds, are active and keep a constant body temperature. They have a high metabolic rate, so they need a lot of oxygen per unit mass.
Large organisms solve this in two ways.
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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.
- metabolic rate
- The rate at which an organism uses energy through the chemical reactions in its cells.
More in Gas Exchange
- Gas Exchange in Small Organisms
- Surface Area to Volume Ratio
- 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