spindle and the alignment and polarization of chromosomes (figure 2-4). Each cell
receives a copy of the parent chromosomes. Amitosis is rare in the higher forms of life,
but it may occur in the lower forms.
Figure 2-4. Types of cell reproduction-binary fission.
e. Binary Fission (Transverse Fission). Binary fission is the simplest form of
cell division and that most frequently seen in the study of microbiology. Binary fission
normally occurs when a cell reaches an optimum size and environmental conditions are
favorable. The center of the cell constricts, a new cell membrane (or cell wall) forms
between the two portions of the cell, and cleavage occurs, forming two new cells. A
copy of the chromosome is produced so that each new cell has the same genetic
information. Figure 2-4 is a graphical representation of binary fission.
CLASSIFICATION OF ORGANISMS
a. General. Classification is an orderly arrangement of organisms with similar
physical, biochemical, and genetic characteristics into groups. Taxonomy, the science
of classification, is subject to change as new and more precise information becomes
b. Five Kingdom System. The five-kingdom system is based on the difference
among eucaryotic and prokaryotic forms of life, including their cellular organization
(unicellular, unicellular-colonial, or multicellular) and their nutrition (absorptive, ingestive,
photosynthetic, or combination of these). The characteristics of the kingdoms are
shown in Table 2-1. You will notice that viruses are not included in any kingdom, that is
because they are not cells nor are they living organisms.
c. Scientific Names of Organisms. Every living organism is assigned
a scientific name (usually in Latin) by which it is identified uniformly by scientists
worldwide. The scientific name of an organism, which is always italicized, consists of
two identifiers-the genus and the species. The first letter of the genus is capitalized.
For example, bos taurus denotes a member of the genus Bas (cattle), and taurus
indicates the species taurus (common European cattle). It is customary, when
discussing additional species of a genus previously mentioned, to indicate the genus by
the first letter of the genus name. For example, B. indicus refers to Indian, or Zebu
(Brahman) cattle. When referring collectively to a number of species within the same
genus, a writer frequently uses the genus name, followed by the abbreviation "spp" in
lower case letters. For example, Salmonella spp refers collectively to species of
bacteria within the genus Salmonella.