Which type of organism typically relies on a host for nourishment and growth?

The type of organism that typically relies on a host for nourishment and growth is a pathogen. Pathogens are microorganisms, such as bacteria, viruses, fungi, or parasites, that invade host organisms and derive nutrients from them. This relationship is often detrimental to the host, as the pathogen can cause disease or disrupt normal bodily functions while consuming the host's resources.

In contrast, hygiene and infection are not types of organisms. Hygiene refers to practices that promote health and cleanliness, while an infection is the result of pathogens entering and multiplying within a host, leading to illness. Fungal cells are a specific type of pathogen, but they do not encompass all organisms that rely on hosts. Therefore, the most comprehensive answer that captures the fundamental idea of organisms relying on hosts is pathogen.