Question

Single celled animals are said to be Immortal because
A. They grow in definitely in size
B. They can tolerate any degree of change in temperature
C. They can reproduce throughout their lifespan
D. They continue to live as their daughter cells.

Answer 1

No individual is Immortal but, unicellular organisms are considered biologically immortal. A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell. Examples include such bacteria as Salmonella and protozoa like Entamoeba coli.

Complete answer:
The correct option is D. they continue to live as their daughter cell
In this question, we have asked why single celled organisms are said to be immortal. As we know, no individual is Immortal but unicellular organisms are said to be biologically immortal. It is because they do not grow old and die instead. They reproduce asexually and make offspring and they themselves become daughter cells. Usually, prokaryotes like Amoeba undergo only binary division, which is an asexual form of reproduction. Asexual reproduction will not bring any variation in the new daughter cell formed from the mother cell which is totally opposite to what happened in sexual reproduction hence all the cellular components are as such transmitted or in other words they are simply the replica of their parent. So, logically, there is no difference within the parent and daughter cell and mother calls live as daughter calls.
Our first option is they grow indefinitely in size, which is wrong, they do not grow indefinitely in size. Second option is they can tolerate any degree of change in temperature, which is also wrong. Single celled organisms also die due to huge changes in temperature. Option c is they can reproduce throughout their lifespan. It is not true because some organisms go in dormancy in harsh conditions and do not reproduce in unfavourable conditions. Option D is they continue to live as their daughter cell. As we already mentioned, the daughter cell is exactly the same as the mother cell so we can say that the mother cell is not living as a daughter cell. So, this option is true.

Note: This statement is not actually true, single celled organisms are only biological Immortal or only theoretically immortal because each and every organism undergoes some or the other changes during the course of evolution. So, the daughter cells are not always the same as the parent cell.