Question

As an animal’s body size increases, the number of cells in the organism also increases. Why must the number of cells increase in order to increase body size? Why can’t there simply be the same number of cells, each with larger volume?

All animals begin life as a single-celled zygote, but become multicellular through development. The increase in number of cells must come from an increased number of mitotic divisions and this in turn may increase the risk of developing cancer. However, when looking at animals of varying body size, scientists find no correlation between body size and cancer incidence. In fact, some large bodied animals such as elephants (Loxodonta africana and Elephas maxima) have very low rates of cancer. It has recently been reported that elephants have at least 20 copies of the TP53 gene that makes the protein p53, whereas humans only have one copy (2 alleles).

Describe the process whereby elephants probably acquired so many copies of the TP53 gene? Hint: it also may have been responsible for so many copies of CYP, RAS and BRC1 genes.

How is the possession of extra TP53 genes and adaptation for large, long-lived organisms? In your answer, identify which cancer hallmark this may be an adaptation against.

Answer 1

(1)

Mathematically, surface area is a squared dimension while volume is cubed. This means as the volume of a cell increases, the increase in surface area varies with the square of the increased dimension whereas the increase in volume varies with the cube of the increased dimension.

the surface area to the volume ratio gets smaller as the cell gets larger. Smaller cells are much more efficient in absorbing nutrients since they have larger surface area to the volume ratio. Thus, if the cell grows beyond a certain limit, its surface area is too small to supply its raw materials to its volume

Hence larger number of Small size cells are more efficient compared to small number of large size cells