Bacteria are of immense
importance because of
their rapid growth,
mutation rates, as well as,
their ability to exist under
The oldest fossils known,
nearly 3.5 billion years
old, are fossils of bacterialike organisms.
• Those that are classified as autotrophs are either photosynthetic, obtaining energy from
sunlight or chemosynthetic, breaking down inorganic substances for energy .
• Bacteria classified as heterotrophs derive energy from breaking down complex organic
compounds in the environment.
• This includes saprobes, bacteria that feed on decaying material and organic
• Bacteria are often maligned as the causes of
human and animal disease. However, certain
bacteria, the actinomycetes, produce antibiotics
such as streptomycin and nocardicin.
• Bacteria live on the roots of certain
plants, converting nitrogen into a usable form.
• Bacteria make up the base of the food web in
be useful as
GENERAL CHARACTERISTICS OF VIRUS
Viruses are infectious agents with both living and nonliving characteristics.
1. Living characteristics of viruses
a. They reproduce at a fantastic rate, but only in living host cells.
b. They can mutate.
2. Nonliving characteristics of viruses
• They are a cellular, that is, they contain no cytoplasm or cellular organelles.
• They carry out no metabolism on their own and must replicate using the host cell's metabolic
CHARACTERISTICS OF VIRUS
Virion (Virus particles)
size range is ~10-400
All virions contain a
nucleocapsid which is
composed of nucleic
acid (DNA or RNA) and
a protein coat (capsid)
Some viruses consist
only of a
• virions having envelopes =
• virions lacking envelopes =
Many viruses that infect humans
and other animals are enveloped.
Envelopes form when viral
glycoproteins and oligosaccharides
associate with the plasma
membrane of the host cell.
All envelopes have a phospholipid