Q 1) What are microorganisms?

Answer: Living organisms which are so small in size that they cannot be seen with unaided eye are called microorganisms or microbes.

Q 2) What are the major groups of microorganisms?

Answer: Microorganisms are classified into four major groups, bacteria, fungi, protozoa and algae. Viruses are also microscopic but are different from other microorganisms.

Q 3) Where do microorganisms live?

Answer: Microorganisms live in all types of environment, ranging from ice cold climate to hot springs; and deserts to marshy lands. They are also found inside the bodies of animals including humans. Some microorganisms grow on other organisms while others exist freely.

Q 4) Explain the uses/benefits of microorganisms.

Answer:

1. Making of Curd and Bread: Bacterium Lactobacillus is used to prepare curd. It multiplies in milk and converts it into curd. Yeast is used in the preparation of Bread. Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of this gas fill the dough and increase its volume to form the bread.
2. Commercial Use: Microorganisms like yeast are used for the large scale production of alcohol and wine. For this purpose yeast is grown on natural sugars present in grains like wheat, rice and barley and also in crushed fruit juices like grape juice. Yeast converts the sugar into alcohol.
3. Medicinal Use: Antibiotics, which are used to kill or stop the growth of disease-causing microorganisms, are produced from bacteria and fungi.
4. Vaccine: When dead/weakened microbes in the form of vaccine are introduced into a healthy body, the body fights and kills the invading bacteria by producing suitable antibodies. These antibodies remain in the body and provide protection from the disease-causing microbes forever.
5. Increasing Soil Fertility: Some bacteria are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility. These microbes are commonly called biological nitrogen fixers.
6. Cleaning the Environment: Microorganisms decompose dead organic waste of plants and animals converting them into simple substances. These are used again by other plants and animals. Thus, microorganisms can be used to degrade harmful substances and thereby clean up the environment.

Q 5) Explain in detail how diseases are caused by microorganisms.

Answer:

1. Disease causing microorganisms known as pathogens can enter our body through air we breathe, the water we drink or the food we eat.
2. Diseases can also get transmitted by direct contact with an infected person. Such diseases are called communicable diseases.
3. There are some insects and animals which act as carriers of disease causing microbes. House fly carries pathogens stuck to its body from garbage and animal excreta to uncovered food items by sitting on it. Similarly, female Anopheles mosquito carries the parasite of malaria and female Aedes mosquito acts as carrier of dengue virus.
4. Details of some of the common diseases are given below.

Disease	Causative Microorganism	Mode of Transmission
Tuberculosis	Bacteria	Air
Measles	Virus	Air
Chicken Pox	Virus	Air / Contact
Polio	Virus	Air / Water
Cholera	Bacteria	Water / Food
Typhoid	Bacteria	Water
Hepatitis A	Virus	Water

5. Similarly, diseases are also caused by microorganisms in animals and plants. For example, anthrax in cattle caused by bacterium.
6. Details of some plant diseases are as below.

Disease	Causative Microorganism	Mode of Transmission
Citrus canker	Bacteria	Air
Rust of wheat	Fungi	Air / Seeds
Yellow vein mosaic of bhindi	Virus	Insect

 Q 6) What is fermentation?

Answer: The process of conversion of sugar into alcohol is known as fermentation.

Q 7) What is food poisoning?

Answer: Microorganisms that grow on our food, sometimes produce toxic substances. These make food poisonous causing serious illness and even death. This is known as food poisoning.

Q 8) Explain methods of food preservation.

Answer:

1. Chemical Method: Chemicals that are used to preserve food items are called preservatives. Sodium benzoate and sodium metabisulphite are common preservatives. They are used in jams and squashes to prevent them from spoiling.
2. Preservation by Common Salt: Common salt has been used to preserve food items like meat, fish, amla, raw mangoes, tamarind etc. for ages. Salting food items prevents the growth of bacteria.
3. Preservation by Sugar: Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of bacteria.
4. Preservation by Oil and Vinegar: Use of oil and vinegar prevents spoiling of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.
5. Heat and Cold Treatments: Boiling kills many microorganisms and freezing inhibits the growth of microbes. These properties are used in pasteurization in which milk is heated and instantly chilled and stored. This process prevents the growth of microbes.
6. Storage and Packing: Food items like dry fruits and vegetables are sold in sealed air tight packets to prevent the attack of microbes.

Q 9) Explain nitrogen fixation.

Answer:

1. Crops absorb a lot of nitrogen from soil and soil becomes deficient in nitrogen after a certain period.
2. Nitrogen gas is available in plenty in the air, but plants cannot use it in the manner they can use carbon dioxide. They need nitrogen in a soluble form.
3. The bacterium called ‘Rhizobium’ can take atmospheric nitrogen and convert it into a usable form. This is called nitrogen fixation.
4. But Rhizobium cannot make its own food, so it often lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen. Thus, nitrogen in the soil can be replenished by cultivating these crops.

Q 10) Explain nitrogen cycle.

Answer:

1. Our atmosphere has 78% nitrogen gas. Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins.
2. The atmospheric nitrogen cannot be taken directly by plants and animals. Certain bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen.
3. Once nitrogen is converted into these usable compounds, it can be utilized by plants from the soil through their root system. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds.
4. When plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again.
5. Certain other bacteria convert some part of them to nitrogen gas which goes back into the atmosphere. As a result, the percentage of nitrogen in the atmosphere remains more or less constant. This is called ‘Nitrogen Cycle’.