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posted Jan 27, 2015, 10:03 PM by   [ updated Sep 9, 2017, 3:58 PM by Upali Salpadoru ]


A bacterium is about 4-8 μm.

(1 meter = 10-6 μm.       μ-One millionth part.)

Biggest bacteria is Thiomargarita namibiensis, up to 0.75mm.

Fig.1 Structure of a Bacterium.

Capsule. - A rigid cell wall made of polysaccharides and amino acids. This provides protection although absent in some species.
Cell wall- This contains a unique substance called peptidoglycan 

  Cytoplasm -  A fluid consisting of  water, enzymes, nutrients,  wastes,  The structures such as ribosomes, a    chromosome, and plasmids are embedded in this.
   Nucleoid- .This contains the genetic material without a a covering membrane.
   Pilli - These are protoplasmic protuberences which are sensitive and helps to adhere to a surface.
   Flagella -  These help the cell to move usually in water.


We see a section of a bacteria. As it  has a cell wall it cannot be an animal. Can it be a plant?

       What can it be then?



 It does not have chloroplast.  Even the most essential nucleus is also absent.

That cell wall is not cellulose

They belong to another kingdom called MONERA.


The beneficial acts of bacteria, are almost entirely eclipsed by the malevolent manifestations of a few notorious specimens.

Bacteria are the smallest independent living cells; probably made their first appearance long before any other living creature, 

These tiny specks of cytoplasm and DNA, wrapped up in a membrane, are capable of extremely complicated bio-chemical reactions, derive energy from the most unbelievable sources and tolerate extremely harsh  conditions as in volcanic vents, hot springs and Arctic ice. 

Types of Bacteria

Fig.2 Types of bacteria

According to shape bacteria are divided into three groups.






Escherichia coli



Helicobacter pylori

syphilis, yaws,

Staphylococcus aureus





   Good !




1.   They are the greatest de-composers of organic matter that accumulate due to the death of plants and animals.

2.    Harmless bacteria inhabit the mouth, nose guts and the skin so that pathogenic bacteria cannot find a place.

3.   Bacteria helps to make yogurt, cheese and vinegar.

4.    Lactobacillus acidophilus present in yogurt is claimed to maintain a healthy gut, provide immunity and reduce bad cholesterol and even prevent cancer.

5.    Streptomycin is used to produce certain antibiotics. Actinomycetes, produce antibiotics such as streptomycin and nocardicin

6.    Vitamin B12 is produced by bacteria, such as  Pseudomonas

7.    Rhizobia dwelling in certain plant roots  are also responsible for the changing of nitrogen gas to nitrates.

8.    Vitamin K which is an essential factor for the clotting of blood is synthesised by bacteria.

9.    Fibre consuming animals, like the grazing mammals and insects like termites get the help of bacteria to digest the cellulose.

10.  Some bacteria are used to breakdown the oil  in the case of oil spills from cargo vessels.

10. Some bacteria are used to breakdown the oil  in the case of oil spills from cargo ships.

1.    The cocci, , produce pus and cause pustules and boils in the body,

2.    Bacilli are responsible for tuberculosis.­­­

3. Spirilla cause  diseases, includingsyphilis.

4.    Clostridium botulinum,  causes botulism; it can be found in food and can cause death even invery small amounts.

5.    Clstridium tetani causes deadly tetanus.

6.    Campylobacter is responsible for most cases of food poisoning, causing severe aches, discomfort and vomiting.

7.   Streptococcus that are responsible for strep throat and pneumonia.

Who has won?

A few good bacteria.


Name of Bacteria


Benefit to man.

1.Lactobacillus acidophilus

Our intestines.

Helps in the digestion of food. Prevents the growth of harmful bacteria.

2. Bifidobacterium bifidum.


help to repair stomach ulcers

3. Streptococcus thermophilus


A culture used in the manufacture of yogurt, mozzarella cheese and some other dairy products.

4. Bacteroides thetaiotamicron

Alimentary canal.

Allows humans to digest  some vegetarian food.

5. Rhizobium leguminosarum .

Root nodules of leguminous plants.

Makes Nitrogen available for plants.

6. Streptomycetes


Decomposes organic matter supplying humus.

A few Pathogenic Bacteria





Bacillus anthrasis

From animals



Borditella pertussis

Contact with patients

Whooping cough


Clostridium botulium

Bad food


Better preservation

Clostridium tetani

Animal dung



Helicobacter pylori


Peptic ulcer


Micobacterium tuberculosis



BCG vaccine

Salmonella typhi

Contaminated food


Better personal hygine

Chlamydia  pneumoniae

By inhaling


Aftercare of flu

Treponema    pallidium

Sexual contact


Healthy sex

Vibrio cholorae

Water contamination.


Boiled water

Yersinia pestis

Fleas in rats


Exterminate pests

Comparing Microbes





Some can crawl using sensitive pili  and swim using rotating flagella.


Most fungi exhibit growth movements.

They grow towards an area rich in nutrients and moisture.

They only possess the ability to push their DNA into a living cell.



Pili and flagella are sensitive.

Grow towards moisture and food.

They identify a specific host.

3. Nutrition.

Excrete enzymes into the food and absorb the nutrients selected by the cell membrane. (extra cellular digestion)

Saprophytes or parasites. Rarely symbiotic.

They generally live inside the food.

Extracellular digestion.



A Viruses get energy from the host cell for reproduction.

(There is no growth as such)



4. Respiration-

Aerobic (using O2)    or anaerobic(without O2) .

Some derive energy  using other chemicals such as sulphur and iron

Fermentation is the general mode.

( Sugar is broken down to to produce alcohol and carbon dioxide giving energy.)


There is no respiration outside a host cell.

5. Growth.

Grow in size inside the cell.

The thallus makes body matter and elongates by cell division  producing buds or branches.

They increase in size when inside a host.


Cells are surrounded by a cell wall and a cell membrane.

DNA is not enclosed by a membrane

(Prokaryotic cell)


The mycelium is surrounded by a cell wall made of chitin.


In some species they are divided into units by septa.


The genetic material is covered with a protein coat called a capsid.


7. Reproduction.

Matured bacteria reproduce by binary fission.(Asexual)

Some undergo conjugation.(Sexual)


Fragmentation is the norm.


A virus has to enter a living cell to make copies of itself.



By diffusion into the surrounding.

Mainly by osmosis.

They pass any waste produced into the host cell.

More about bacteria.
  •  One acre of land may contain about a  ton of  bacteria.  
  • A gram of soil typically contains about 40 million bacteria.
  • Hans Christian Joechim Gram identified two types of bacteria. Gram-positive bacteria that retains a particular dye and Gram-negative bacteria which do not retain the violet dye . Gram-negative bacteria are more resistant against antibodies . They are used in medicine, in industry and making cheese.

If you wish to know about the natural enemies of bacteria click: Bacteriophages


1. 0     Name any 5 of the numbered parts.

2 x 5 = 10
1.Why do the scientists consider bacteria as living things?
a. They show movement.
b. They absorb inorganic substances and synthesize their cytoplasm.
c. They multiply by a process called cell division..
d. Using oxygen and giving out carbon dioxide.
2.       This is a reason for not considering bacteria as a plant.
         a.       Lack of cellulose.  b.  Locomotion.   C. Extra cellular digestion.  d. Lack of chloroplast.
3.       What is the normal way of nutrition in bacteria ?
         a.       Photo synthesis.  b.  Respiration.   c. Engulfing  the food.  d.   Extra cellular digestion.
4.       Why are the bacteria grouped as procaryotes?
         a.  Lack of organelles     .    b. Presence of cell wall.   c. Presence of DNA.   d. Uni cellular.

   5 x 4 = 20 marks.

    2.0 Answers-          1.  c,   2.  d,   3. d.   4. a,

3.0    Complete this chart.



1.       Capsule


2.       Cell wall



Controls intake and exit of materials.

4.       Nucleoid



Helps locomotion.

                                                                                                                   4x5= 20 marks

4.0   Give your verdict on the following statements.                      

1 Bacteria are used in making cheese and yogurt.       U.

2 Some bacteria spoils food.                                           B

3 Some Bacteria can live in hot springs.                        T

4 Bacteria produce eggs.                                                 F

5 Some bacteria cause disease.                                       H

6 Bacteria cause cold and flu.                                         F

7 Bacteria decays dead plants and animals.                   U

8 Bacteria undergo binary fission.                                 T

9 Actions of bacteria are controlled by a nucleus.         F

10. Some bacteria can convert gaseous Nitrogen to Nitrates.  U.


                    Give a suitable classification based on this

1.    Useful to man.       Useful- U.

2.     Harmful to man.   Harmful  - H.

3.     Hardly any effect to man but true.   True - T.

4.     False.      False- F..

 5 x 10 = 50

        For answers Click: Answer page.