What do organisms called parasites obtain from their living host?

Parasites are organisms that live on or inside a host and derive their sustenance at the host's expense. The primary objective of a parasite is to exploit the host’s resources for their own growth and reproduction. Therefore, they obtain energy and nutrients from their living host, which are essential for their survival and development.

These nutrients can include sugars, amino acids, and fats, which are crucial components necessary for cellular processes. By tapping into the host’s biological systems, parasites ensure they can thrive despite the often detrimental effects their presence may have on the host’s health.

In contrast, other options do not accurately represent what parasites seek from a host. Water and oxygen, for instance, are basic elements that many living organisms, including parasites, need, but they are not the primary focus of parasitic relationships. Light and heat are types of energy but are not resources that parasites obtain from their hosts in the same manner. Similarly, carbon dioxide and waste products are byproducts of metabolic processes that parasites do not seek to obtain; indeed, those are typically expelled from the body. Thus, the most accurate representation of what parasites harvest from their hosts is energy and nutrients.