GED Science Practice

Which of the following is described as an animal or plant that lives in or on a host?

1. Pathogen

2. Parasite

3. Oxygen

4. Ozone

The correct answer is: Parasite

A parasite is defined as an organism, either animal or plant, that lives on or inside a host organism and benefits at the host's expense. This relationship typically involves the parasite deriving nutrients and energy from the host, which can lead to harm or disease in the host over time. Parasites can take various forms, including worms, protozoa, and certain types of insects, and their dependence on the host is a crucial aspect of their life cycle. In contrast, a pathogen specifically refers to microorganisms, such as bacteria, viruses, fungi, or parasites, that can cause disease. While all parasites can be pathogens, not all pathogens are classified as parasites. Oxygen and ozone are both gases essential for life on Earth, but they do not fit the definition of an organism living in or on a host. Therefore, the definition of a parasite accurately reflects the characteristic of living in or on a host, making it the correct choice.