Surface Area to Volume Ratio

 Let us regard the Amoeba as cube shaped. The surface areas and volumes of cubes of lengths 1,2 and 3 cm.

     We see that as the size of the Amoeba increases, the surface area to volume ratio decreases. The ability of the Amoeba to exchange materials in a given time is related to its surface area, the greater the ability to exchange materials. On the other hand, the needs of the Amoeba, such ad oxygen intake and carbon dioxide excretion, is related to its volume, I.e. the larger the volume the greater the needs of the Amoeba. Thus, as the Amoeba increases in size, it ability to carry out material exchange cannot cope with its needs. Therefore, the S.A/V ratio becomes a limiting factor as an organism increases in size.