Parasites are defined as what type of organisms?

Parasites are specifically defined as organisms that depend on a host for their survival and reproduction. This relationship is often detrimental to the host, as parasites typically derive their nutrients at the expense of the host's health. The organisms classified as parasites could be of either plant (vegetable) or animal origin, highlighting the broad nature of this category.

In contrast, independent organisms that do not require a host would not fit the definition of a parasite, as they can thrive on their own. Single-celled organisms found in soil, while they might have their own ecological roles, do not necessarily involve a parasitic relationship with a host. Similarly, bacteria that thrive in harsh conditions are a different classification and do not pertain to the parasitic nature outlined in the question.

Thus, the correct answer accurately reflects the essence of what parasites are and underscores their dependency on a living host for survival.