Asked Sep 10, 2019

What are the most common shapes and arrangements of bacteria and provide a specific example for each.


Expert Answer

Step 1

Bacteria are single-celled prokaryotic organisms. They lack the nucleus and membrane-bound organelles and hence are categorized as simple organisms. Their genetic material is circular in shape. Bacteria can be classified based on their shapes and colonial arrangements after examining them under the microscopes. Another property of bacteria is that they grow in colonies, that is, from one mother bacterium all the other bacteria are produced by simple cell division.

Step 2

The three important shapes of bacteria are:

  1. Cocci- They are the round or spherical shaped bacteria.
  2. Bacilli- They are rod-shaped bacteria.
  3. Spirilla- They are curved or spiral-shaped bacteria. Most of these bacteria are rigid and motile.

Arrangements of these different types of bacteria-

  1. Arrangement of Cocci bacteria: Cocci can be found single, in pairs, in groups of four cocci, in chains, and in clusters. They can be elongated, flattened, or oval.
  2. Diplococci- Such bacteria are round and are found in pairs. Example of this is Streptococcus pneumoniae.
  3. Streptococci- Streptococcus bacteria arrange themselves in chains. Example of this is Streptococcus pyogenes.
  4. Tetrads- In this, the cocci are arranged in a group of four cells. These four cells are arranged in such a manner, that two cells lie in one plane and other two cells lie in another cells. Hence, such arrangement divides these four cells into two planes. Example of this is Aerococcus.
  5. Sarcinae- In this, the cocci are arranged in cuboidal shape. So, it is the three-dimensional shape of the cocci cluster. Example of this is Sarcina ventriculi.
  6. Staphylococci- Here, cocci are arranged in an irregular pattern making the cells look like the grape-like clusters. Example of this is Staphylococcus aureus.


Arrangements of Bacilli:

  1. Diplobacilli – Such type of bacillus is found in pairs after they had ...

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