How do viruses differ from animals to pants?
viruses are a biological puzzule to humans. we still can’t classiy them as plants or animals virus are parasites with a noncellular structure composed mainly of nucleic acid within a protein coat. Viruses usually are too small (100–2,000 Angstrom units) to be seen with the light microscope and thus must be studied by electron microscopes. In one stage of their life cycle, in which they are free and infectious, virus particles do not carry out the functions of living cells, such as respiration and growth; in the other stage, however, viruses enter living plant, animal, or bacterial cells and make use of the host cell’s chemical energy and its protein- and nucleic acid–synthesizing ability to replicate themselves. The existence of submicroscopic infectious agents was suspected by the end of the 19th cent.; in 1892 the Russian botanist Dimitri Iwanowski showed that the sap from tobacco plants infected with mosaic disease, even after being passed through a porcelain filter known to retain
