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SCIPAD - BIG IDEAS - BOOK 2
LIFE OF MICROBES
Bacteria
Bacteria are unicellular (‘uni’ means one) organisms. They are thought to be the most widely
distributed organisms on Earth. They are present in soil, the air, on mountain tops, the bottom of
the deepest oceans, in the food we eat, in the water we drink and on the surface of and within
our bodies.
There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre
of fresh water. In all, it has been estimated that there are about five million trillion trillion, or 5 × 1030
bacteria on Earth. Some researchers believe the total biomass of bacteria exceeds that of all
plants and animals.
Classification of Bacteria
Bacteria were traditionally classified according to their shape and were placed into four major
groups.
Cocci
Spherical
Bacilli
Rod-shaped
Vibrio
Comma shaped
Spirillum
Spiral shaped
Coccus
Bacillus Streptobacilli
Diplobacilli
Diplococci Streptococci Staphylococci
1. Define the term 'unicellular':
2. Outline how bacteria were traditionally classified:
3. State the generalised shape of the following bacteria:
(a) Bacilli:
(b) Spirillum:
(c) Vibrio:
(d) Cocci:
4. Using the diagram above, define the following prefixes:
(a) Diplo:
(b) Strepto:
(c) Staphylo:
5. ‘Strep throat’ is a bacterial infection caused by Streptococcus. Describe the shape of
these bacteria.
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