<span>to isolate and test single variables</span>
Explanation:
Viruses, viroids and prions are included in acellular microorganisms. These organisms when present outside the living host cell are considered non-living, as they behave as inert particles, but inside the host cell they can replicate and behave like living organisms
Answer:
Birds do not have a diaphragm; instead, air is moved in and out of the respiratory system through pressure changes in the air sacs. ... Bird lungs do not expand or contract like the lungs of mammals. In mammalian lungs, the exchange of oxygen and carbon dioxide occurs in microscopic sacs in the lungs, called 'alveoli.
Explanation: