The relation of the three points above can be summed up by Fick’s Law:
However, the amount of gas which an organism needs to exchange is greatly proportional to its volume, nevertheless, the amount of gaseous exchange which takes place is proportional to the surface area over which the exchange happens.
For single celled/unicellular organisms the surface area to volume ratio is large, however, for larger organisms the surface area to volume ratio decreases. The larger the object gets the more complicated it gets.
1cm
1cm 2cm
1cm 3cm
2cm
2cm
3cm 3cm
Surface Area= 6cm2 24cm2 54cm2
Volume= 1cm3 8cm3 27cm3
SA:V= 6:1 3:1 2:1
As this diagram illustrates that the smaller the object the larger the surface area to volume ratio. This is where single celled organism have an advantage. Organisms like Amoeba can exchange gases with environment quickly and easily. However exchange surfaces need to attain certain properties to maximise gaseous exchange. They are:
- Need to have a good blood supply- high concentration gradient
- Moist- Dissolve gases
- Large Surface Area
- Thin walls
- Permeable
As single celled organisms are small so they do not have to have specialised systems like much larger organisms like mammals. Single celled organisms like amoeba do not have to have transport systems or specialised systems because they are so small so substances do not have to travel far to get to their desired destination.
The contractile vacuole in this amoeba is used for water regulation. The excess water, which is collected in the cell, is expelled to the outside environment that is very costly in terms of energy.
The food vacuole contains ingested food. Pseudopods are flowing projections of cytoplasm allow movement, and enable food to be engulfed by phagocytes.
Most single celled organisms are similar to amoeba in the sense that they are found in moist areas. They also have similar structures which consist of a or two nuclei, food vacuoles and contractile vacuoles.
