The smallest type of pathogens that grow in living cells areparasites.fungi.viruses.bacteria.

To determine the smallest type of pathogens that grow in living cells, we need to understand the characteristics of the options provided:

1. Parasites: These are larger organisms that live on or in a host and can include various forms, ranging from single-celled organisms to multicellular ones. They are not the smallest pathogens.

2. Fungi: Fungi, such as molds and yeasts, are eukaryotic organisms that range in size and are generally larger than bacteria and viruses. Thus, they are not the smallest type of pathogen.

3. Viruses: Viruses are indeed considered the smallest type of pathogens, as they cannot reproduce on their own and require a living host cell to replicate. Their size typically ranges from about 20 nanometers to several hundred nanometers.

4. Bacteria: Bacteria are single-celled prokaryotic organisms, and while they can be quite small, they are generally larger than viruses. Their sizes typically range from about 0.5 to 5 micrometers.

Conclusion

Among the options given, viruses are the smallest type of pathogens that grow in living cells. They are significantly smaller than both bacteria and fungi and rely on host cells for their replication and survival.