Questions - Answers
 

Very short Answer Type Questions 

1. Write briefly on the occurrence of micro organisms.

A:  Micro organisms are found everywhere. They are omnipresent in soil, water, air, living organisms, food etc. Some of them are found in extreme conditions like arctic snow, volcanic ash, hot water springs etc.
 

2. Define microbiology.

A: Microbiology is the branch of biology that deals with scientific study of micro organisms that are not visible to the naked eye. It is also concerned with structure, function and classification of microbes and using their activities.
 

3. Name the bacterium which is common inhabitant of human intestine. How is it used in biotechnology?
A: Escherichia coli. The plasmids of E.coli are used as vectors during genetic engineering in biotechnology.
 

4. What are pleomorphic bacteria? Give an example.
A: The bacteria that change their shape depending upon the type of environment and nutrients available are called pleomorphic bacteria.
e.g.: Acetobacter.
 

5. What is sex pilus? What is its function?
A: The elongated tubules with hollow cores on the surface of bacteria which help in conjugation are called sex pili. They act as conjugation tubes and help to bind two conjugant bacteria during conjugation.
 

6. What is genophore?
A: Genophore is the bacterial chromosome.
 

7. What is plasmid? What is its significance?
A: Small circular double stranded DNA molecules in bacterial cells are called plasmids. They contain few genes and confer resistance to drugs. They also produce toxins and enzymes. As they can be readily manipulated and transferred they are used in genetic engineering.
 

8. What is conjugation? Who discovered it and in which organism?
A: Conjugation is the direct transfer of DNA between the living donor and the living recipient bacterial cells through a conjugation tube. It was first discovered by Lederberg and Tatum in Escherichia coli.
 

9. What is transformation? Who discovered it and in which organism?
A: Transformation is the uptake of naked DNA fragments from the surrounding environment and incorporation of DNA into the genome of a bacterial cell and expression of that genetic information in it. It was discovered by Frederick Griffith in Streptococcus pneumoniae.
 

10. What is transduction? Who discovered it and in which organism?
A: Transduction is the transfer of genetic material from one bacterium to another through a bacteriophage virus. It was discovered by Lederberg and Zinder in Salmonella typhimurium.
 

Short Answer Type Questions

1. Explain the importance of Microbiology.
A: Importance of microbiology:
* A large number of micro organisms are useful to man in many ways.
* Saprophytic bacteria and fungi cause decomposition of organic wastes and help in the process of humification and mineralization which are important to the nutrient cycles.
* Many fungi and bacteria are used for production of antibiotics, alcohols, enzymes and hormones on industrial scale.
* Bacterial plasmids are used as tools in genetic engineering and bio technology.
* LAB is used for conversion of milk into curds. Bacteria are also used in sewage treatment.
* Some bacteria like Methano coccus and Methano bacillus are useful in production of bio gas.
* Bacteria are also used as bio control agents in pest and diseases control in agriculture. Bacteria like Rhizobium, Azospirillum, Azotobater are used as bio fertilizers.
* Micro organisms like Nostoc and Anabaena are used as nitrogen fixers in agriculture.
* Microbes are presently used in bio-mining for extraction of metals like uranium.
* Bacterial DNA components are used as Biosensors to detect toxic pollutants.
* They are also used in medical diagnostics, food and fermentation operations.
* Bacteria are the real tools in genetic engineering.
 

2. How are bacteria classified on the basis of morphology?
A: Bacteria are classified into the following types based on the morphology and shapes:
Cocci – spherical
Bacilli – Rod shaped
Spirillum – helical rods (more than one complete twist)
Vibrios – comma shaped (less than one complete twist)
Pleomorphic – bacteria change their shape depending on the type of environment or available nutrients.
Spirochaets – flexible spiral bacteria (slender long an cork-screw shaped)
Filamentous – long thread like or filament like chains
Bacteria cells may be single or in groups like
Monococcus – single spherical cell
Diplococcus – a pair of spherical cells
Tetra coccus – a group of four spherical cells
Streptococcus – linear chain of spherical cells
Staphylococcus – bunches of spherical cells
Sarcinae – eight spherical cells arranged as a cube
Monobacillus – single rod shaped cell
Diplobacillus – a pair of rod shaped cells
Streptobacillus – chains of bacilli appearing like straws
 

3. How are bacteria classified on the basis of number and distribution of flagella?
A: Based on the number and distribution of flagella bacteria may be classified into the following types:
Monotrichous – bacterium with a single polar flagellum
Amphitrichous –bacterium with single flagellum at each end
Lophotrichous – bacterium two or more flagella at one pole
Peritrichous – bacterium with flagella distributed all over the cell.

4. What are the nutritional groups of bacteria based on their source of energy and carbon?
A: According to the source of carbon and energy four nutritional groups of bacteria are recognized:

5. Write briefly about chemo heterotrophs and their significance.
A: Chemo heterotrophs derive both carbon and energy from organic compounds. They are divided into types:
    * Saprophytes
    * Parasites
Saprophytes are free living and feed on dead organic remains. e.g.: Bacillus
Parasites live on the cells or tissues of living organisms like plants, animals Etc.
e.g.: Xanthomonas citri on citrus, Salmonella typhimurium on human beings (causes typhoid).

Ignificance: Saprophytes are responsible for decomposition of organic matter and are most crucial in the processes of humification mineralization and nutrient cycling.
Parasites cause diseases and loss but some of them may be employed as bio pesticides.
Parasitic bacteria like Bdellovibrio bacteriovorus are used for cleaning rivers like Ganges.
 

6. Explain the conjugation in bacteria.
A: * Conjugation is a method of genetic recombination in bacteria.
* It was first observed by Lederberg and Tatum in Escherichia coli.
* In this process two living bacteria designated as F⁺ and F- come into contact and form a conjugation tube with the help of sex pili.
* The F⁺ cell which has a F plasmid acts as donor cell and F^- cell which does not have the plasmid is called recipient cell.

* The pilus shortens between the two bacteria as they come close to each other.
* The F plasmid of the donor cell now replicates and passes the replicated DNA through the onjugation tube into the recipient cell.
* Thus conjugation is completed and the cells move apart.
* This method is a conservative process where the donor cell retains complete copy of the DNA transferred.
 

Long Answer Type Questions
1. Explain different methods of sexual reproduction in bacteria.
A: Sexual reproduction: As there is no true sexual reproduction bacteria reproduce by exchange of genetic material also called genetic recombination in the following three ways: 
1) Conjugation
 2) Transformation
 3) Transduction
 

 Conjugation:
* It is the direct transfer of DNA between the living donor and the living recipient cells.
* It was first observed by Lederberg and Tatum in Escherichia coli.
* Two bacterial cells designated as F⁺ and F- come into contact and a conjugation tube or sex pili connect the two cells.
* The F+ cell contains F plasmid and F^- cell lacks F plasmid.· The pilus or conjugation tube shortens and the F⁺ cell replicates its F plasmid DNA.
* The copy of replicated DNA passes through the bridge formed by the pilus into the recipient cell or F-cell and the conjugation is said to have completed.
* This is a conservative process where the donor cell retains the complete copy of the DNA transferred.
 

Transformation:
* It is the uptake of naked DNA fragments from the surrounding environment and incorporation of it into the genome of live bacterial cell.
* Later on the genetic information of DNA fragments is expressed in the recipient cells.
* It was discovered by Frederick Griffith in Streptococcus pneumoniae.
 

Transduction:
* It is the transfer of genetic material from one bacterium to another through a bacteriophage virus.
* It was discovered by Lederberg and Zinder in Salmonella typhimurium.
 

2. “Bacteria are friends and foes of man”. Discuss.
A: Bacteria are called “friends and foes of man” as they are both beneficial and sometimes causing harm to human beings. Many bacteria cause diseases to human beings like Tetanus – Clostridium tetani, Cholera – Vibrio cholera, Typhoid – Salmonella typhi, Diphtheria – Corynebacterium diphtheria, Tuberculosis – Mycobacterium tuberculosis Pneumonia – Diplococcus pneumoniae, Leprosy – Mycobacterium leprae Gonorrhoea – Neisseria gonorrhea and Syphilis – Treponema pallidum. Clostridium botulinum caused spoilage of food called Botulism. Some of the bacteria cause plant diseases like Blight of rice – Xanthomonas oryzae, Citrus canker – Xanthomonas axonopodis pv. citri and Crown gall of apple and pear – Agrobacterium tumefaciens. 
    At the same time a large number of bacteria are useful to man in many ways. Saprophytic bacteria cause decomposition of organic wastes and help in the process of humification and mineralization which are important to the nutrient cycles. Many bacteria are used for production of antibiotics, alcohols, enzymes and hormones on industrial scale. Bacterial plasmids are used as tools in genetic engineering and bio technology. LAB is used for conversion of milk into curds. Bacteria are also used in sewage treatment. Some bacteria like Methano coccus and Methano bacillus are useful in production of bio gas. Bacteria are also used as bio control agents in pest and diseases control in agriculture. Bacteria like Rhizobium, Azospirillum, Azotobater are used as bio fertilizers. Thus it is rightly said that Bacteria are both friends and foes of man.