Unit 10: The simplest living beings                                       1   2   3   4  

3. Bacteria

Bacteria are the oldest and simplest form of life. Bacteria appeared more than 3,500 million years ago. All the other living beings have evolved from creatures similar to bacteria.

They are among the smallest living beings. Their size goes from 1 μm to 10 μm. It means that they can only be seen through microscope.

Bacteria belong to the Monera Kingdom and they all are unicellular and prokaryotes.

This is the most successful group of living beings. Bacteria are everywhere.

The reasons are: 

-     They have a great diversity of nutrition.

-     They reproduce very fast.

-     They are adapted to all the environments.

-     They are very resistant. Many of them live in extreme conditions,

    like acidic or extremely salty water and sulfur hot springs.

They usually band together in groups (colonies), although they can be found in singles or forming pairs, chains or clusters of varying number.

Today it is more usual to classify them following other criteria such as their type of nutrition or the structure of their cellular wall.

b) Vital functions:

Nutrition:

       Bacteria can be:

- Autotrophs. They make up organic matter from inorganic matter.

       - Some bacteria do photosynthesis and use solar energy.

       - Other ones do chemosynthesis and use energy

          from chemical reactions.

- Heterotrophs. They must consume elaborated organic matter.

  They can be:

       - Parasites: They live in the body of other organisms,

         harming them.These bacteria produce diseases.

       - Symbiotic: They live with other organisms too, but both provide

          mutual benefit. Very often they cannot live separated.

       - Saprophytes. They feed on the wastes of other organisms

          or the decaying matter.

       - Decomposers. They transform the organic matter into inorganic

          matter that can come back to the ground and can be used

          by autotrophic organisms.

Interaction:

      Bacteria have a simple interaction with their environment.

      They can feel changes of temperature, salts concentration, light, etc.

      Their responses can be movement, secretion of substances or reproduction.

Reproduction:

       They reproduce asexually. Cell makes a copy of its DNA and then divides

 into two separate cells. This type of cellular division is know as binary fission.

3.1. Classify the following bacteria.

a. What criterion have you used to do it?

b. How is more common finding them?

 c. Can we classify them in another way? Indicate how we can do it.

3.2. Indicate the main difference between:

   a. Symbiotic bacteria - Parasite bacteria

   b. Decomposer bacteria - Saprophyte bacteria.

   c. Photosynthetic bacteria - Chemosynthetic bacteria

3.3. Why have bacteria had so much evolutionary success?

3.4. Listen to the description of the Monera Kingdom

and indicate if the sentences are true or false.