As I know, both protozoa and viruses use host cells. But I want to clear up a couple of doubts about the two.

1. Do protozoa take over the host cells? I know protozoa live in the cells, but I think that only viruses take over the host cells. Is this right?

2. Which of the two injects their DNA and RNA into the host cell? I think that only viruses do this.

1. Protozoa do not take over the host cells in the same way that viruses do. Protozoa are single-celled organisms that can live inside or outside the host cells, depending on the specific type of protozoa. They can invade the cells of their host, but they generally do not take over the cells' machinery to replicate themselves. Instead, they feed on the host cells or use them as a sheltered environment for their own survival and reproduction. Protozoa can cause various diseases in humans and animals, such as malaria or toxoplasmosis.

2. You are correct that it is primarily viruses that inject their DNA or RNA into host cells. Viruses are considered obligate intracellular parasites because they cannot replicate or carry out their life cycle without utilizing the host's cellular machinery. In order to do this, viruses inject their genetic material (DNA or RNA) into the host cell. Once inside the cell, the viral genetic material takes control over the cellular machinery, causing the host cell to produce more viruses. This process allows the virus to multiply and spread throughout the host's body, leading to infection and disease.

Overall, while both protozoa and viruses can interact with host cells, the mechanisms by which they do so differ significantly. Protozoa usually inhabit or invade the host cells without taking over their machinery, while viruses inject their genetic material into cells to manipulate them for their own replication.