barm - a commercial leavening agent containing yeast cells; used to raise the dough in making bread and for fermenting beer or whiskey. yeast. yeast cake - small cake of compressed moist yeast. brewer's yeast - yeast used in fermenting beer. leaven, leavening - a substance used to produce fermentation in dough or a liquid. mother - a stringy slimy substance consisting of yeast cells and bacteria; forms during fermentation and is added to cider or wine to produce vinegar.
1 Viruses, on the other hand, do not have any cells. 2  Viruses are made up of a protein structure called a capsid. 3  Though this capsid contains the virus's genetic material, it lacks the features of a true cell, such as cell walls, transport proteins, cytoplasm, organelles, and so on. Viruses, on the other hand, do not have any cells. 2  Viruses are made up of a protein structure called a capsid. 3  Though this capsid contains the virus's genetic material, it lacks the features of a true cell, such as cell walls, transport proteins, cytoplasm, organelles, and so on.
All viruses of a type are identical and their particles have a cubical, helical or complex structure. A virus is a biological agent that reproduces inside the cells of living hosts. When infected by a virus, a host cell is forced to produce thousands of identical copies of the original virus at an extraordinary rate. Unlike most living things, viruses do not have cells that divide; new viruses are assembled in the infected host cell.