Question

We can demarcate a facultative parasite is one which
A. Inevitably requires a living host
B. Only requires dead organic matter to live
C. Is a parasite but can also become saprophyte
D. Is a saprophyte but can also become a parasite

Answer 1

Hint: Fungi are the facultative parasites example Armillaria, the parasite on living trees. They are important ecological agents which do microbial decomposition. They are scavengers feeding on the dead. They can use the host for survival.

Complete answer:
A microbe can either live on its own, that is, they can feed themselves, a shelter for themselves. But there are some microbes which need others for their nutrition and shelter. They can either provide their host with something or can only take their advantage.
What are facultative parasites? The organisms which do not completely depend on the host for their survival but can become parasitic in the absence of favourable conditions. They are called facultative parasites.

Let us match the options with this definition.
> Option A. Inevitably requires a living host: They need a host but are not dependent on them. They can survive in their favourable conditions.
> Option B. Only requires dead organic matter to live: Organisms feeding on dead are saprophytic. They can feed on the dead but also can feed on the organic microbes.
> Option C. Is actually a parasite but can also become saprophyte: they become parasites only when they do not have favourable conditions.
> Option D. Is actually a saprophyte but can also become a parasite: It is right as they are saprophyte and only when bad conditions are there they become a parasite.

Hence, The correct answer is option (D).

Note: This is the rare form of parasitism. They can survive with/without a host. Facultative parasites seek out any host. An example is- roundworms, amoeba etc. Host-parasite has interdependent relations. They need to provide each other support.