3.3.1 Surface Area to volume ratio Flashcards
Tissue Fluid
The environment around the cells of multicellular organisms
Relationship between SA:vol. ratio and metabolic rate
- Organisms with a high metabolic rate exchange more materials and so require larger S.A.
Important factors for exchange of substances
- Surface Area
- Volume
Surface Area
Total area of organism exposed to external environment
Volume
Total internal volume of the organism
What impacts Surface Area:Volume Ratio
Size
Volume increases much more rapidly than surface area as size increases -> low S.A. : vol. ratio
Surface Area: Volume Ratio in small organisms
- High SA: vol. ratio
- Simple diffusion of substances across the outer surface of small, inactive organisms
Why don’t large multicellular organisms rely on diffusion from the outer surface?
Too slow, would take too long for the substances to reach the middle of the organism
Organisms adaptations for exchange of substances
- A flattened shape
- Specialised exchange surfaces with large areas
Organisms adaptations: Flattened shape
No cell is ever far from the surface
Organisms adaptations: Specialised exchange surfaces with large areas
Increases surface area:volume ratio
Features of specialised exchange surfaces
- Large SA:vol. ratio
- Very thin
- Selectively permeable
- Movement of the environmental medium
- Transport system
Features of specialised exchange surfaces: Large Surface Area: Volume Ratio
Increases rate of exchange
Features of specialised exchange surfaces: Very thin
Short diffusion distance -> materials cross the exchange surface rapidly
Features of specialised exchange surfaces: selectively permeable
to allow selected materials to cross
