Which of the following defines the term 'obligate intracellular parasite'?

The term 'obligate intracellular parasite' specifically refers to an organism that cannot reproduce outside of a host cell. These parasites are entirely dependent on the host's cellular machinery for their replication and life cycle, meaning they must enter a host organism to thrive and multiply. This characteristic is crucial because it distinguishes obligate intracellular parasites from other microorganisms that can live and reproduce independently in their environments.

In contrast, the other options do not accurately describe obligate intracellular parasites. The notion that such an organism can survive independently contradicts its obligate nature. Similarly, describing it as a form of yeast does not pertain to the definition since not all yeasts are obligate intracellular parasites, nor does it specify the dependency on a host. Lastly, the ability to produce its own nutrients would mean that the organism is autotrophic and does not require a host, which directly opposes the definition of being obligate. Thus, the accurate description emphasizes the need for a host cell for reproduction, underlining the relationship between the parasite and its host.