Biology Chapter 13 - Exchange Between Organisms And Their Environment

Front 1

How does the size of an organism and its structure relate to its surface area to volume ratio?

Back 1

Small organisms have a surface area that is large enough compared with their volume to allow efficient exchange across their body surface. As organisms become larger, their volume increases faster than their surface area and therefore they have a small surface area to volume ratio.

Front 2

How do larger organisms increase their surface area to volume ratio?

Back 2

Organisms have evolved one or more of the following features:
- a flattened shape so that no cell is ever far from the surface (e.g- a flat worm)
-specialised exchange surfaces with large areas to increase the surface area to volume ratio (e.g lungs in mammals and gills in fish)

Front 3

How are surfaces specially adapted to facilitate exchange?

Back 3

- a large surface area to volume ratio to increase the rate of exchange
- very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly
- partially permeable to allow selected materials to cross without obstruction
-movement of the environmental medium e.g air, to maintain a diffusion gradient
-movement of an internal medium e.g blood, to maintain a diffusion gradient.