Parasites are defined as what type of organisms?

Parasites are defined as organisms that live on or in a host organism, deriving their nutrients at the host's expense. They can be classified broadly into two categories: animal parasites and plant parasites. Animal parasites include various types of organisms such as worms, insects, and protozoa, while plant parasites may include certain types of fungi or bacteria that thrive on or within plant tissue. This classification emphasizes that parasites can be of either vegetable (plant-based) or animal (animal-based) origin, making option B the correct choice.

In contrast, the other options don't capture the comprehensive definition of parasites. Single-celled organisms, while potentially parasitic, do not encompass the full range of both plant and animal parasitic forms. Microbial organisms include bacteria and viruses, which, while some can be parasitic, do not exclusively fit the broader definition of parasites. Fungal organisms could be parasites, particularly in the context of plant pathogens, but they do not include the diverse range of animal parasites. Thus, the most accurate classification is by recognizing that parasites can be either vegetable or animal.