Final answer:
Viruses are noncellular entities consisting of a nucleic acid core surrounded by a protein capsid. They lack mRNA but can replicate using proteins from a host cell or encoded in their own genome. Viruses have a diverse morphology, and their classification is based on factors like capsid shape, presence of an envelope, and core composition.
Step-by-step explanation:
Viruses are noncellular entities that lack a cellular structure. They do not have organelles, ribosomes, or a plasma membrane. However, they do have a nucleic acid core surrounded by a protein capsid. Additionally, some viruses have an outer envelope made of protein and phospholipid membranes derived from the host cell.
While viruses lack mRNA themselves, they can still replicate. They achieve replication either by using the replication proteins of a host cell or by using proteins encoded in the viral genome. Viruses have a diverse morphology, and their classification is based on factors like capsid shape, presence of an envelope, and core composition.