Lakhmir Singh & Manjit Kaur: Microorganisms Friends and Foe- 2 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.31. Name two food materials which are usually preserved by deep freezing.

Preservation by deep freezing means preservation of food material in the extreme cold. Low temperature inhibits the growth of micro-organisms completely. Food materials such meat and fish are usually preserved by deep freezing.

Q.32. Name some of the preservatives which are used in the preservation of fruits as jams arid jellies.

Sodium benzoate and sodium meta bisulphite are common preservatives which are used in the preservation of fruits as jams and jellies.

Q.33. Name some of the preservatives which are used in the preservation of fruits and vegetables as pickles. 

Salt, oil and vinegar are some of the preservatives which are used in the preservation of fruits and vegetables as pickles.

Q.34. Name two food materials which can be preserved by using oil or vinegar. 

Fish and meat are often preserved by using oil or vinegar.

Q.35. Name any two special chemicals which are used as food preservatives. 

Sodium benzoate and sodium meta bisulphite are common preservatives.

Q.36. Name the micro-organisms which can fix atmospheric nitrogen in the soil. 

Certain bacteria and blue green algae present in the soil fix atmospheric nitrogen and convert it into compounds of nitrogen.

Q.37. What type of plants can fix nitrogen gas of the air into compounds of nitrogen? 

Leguminous plants can fix atmospheric nitrogen into nitrogen compounds.

Q.38. Name the micro-organisms present in the soil and in the root nodules of leguminous plants which can fix atmospheric nitrogen. 

Some bacteria and blue green algae present in the soil and rhizobium present in the root nodules of leguminous plants can fix atmospheric nitrogen.

Q.39. Name two leguminous plants which can fix nitrogen. 

Leguminous plants such as beans and peas can fix nitrogen.

Q.40. Fill in the following blanks with suitable words:
(a) Alcohol is produced with the help of _________
(b) Blue-green algae fix _________ directly from air to enhance fertility of soil.
(c) Micro-organisms can be seen with help of a _________
(d) Cholera is caused by _________
(e) Common salt has been used to preserve _________ and _________ for ages.
(f) The food material which is preserved by pasteurization is _________
(g) As a result of nitrogen cycle, the percentage of nitrogen in the atmosphere remains more or less _________

(a) yeast
(b) nitrogen
(c) microscope
(d) bacteria
(e) meat; fish
(f) milk
(g) constant

Q.41. How do viruses differ from other micro-organisms such as bacteria? 

Viruses differ from other micro-organisms because they are too much smaller in comparison to other micro-organisms. They do not show most of the characteristics of the living organisms like respiration. They just reproduce. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal. Hence, viruses differ from other micro-organisms.

Q.42. What are micro-organisms? Give any two examples of micro-organisms. 

The organisms which are too small to be seen by the naked eyes and can be seen only though a microscope are called micro-organisms or microbes. Bacteria and viruses are examples of micro-organisms.

Q.43. Can micro-organisms be seen with the naked eye? If not, how can they be seen?

Micro-organisms are too much smaller that they cannot be seen with naked eye. They can be seen with a magnifying glass called microscope.

Q.44. 
(A) How do houseflies carry disease-causing microbes-(or pathogens)? 

The houseflies feed on garbage, animal excreta and dead organic matter. When the housefly sits on garbage and animal excreta for feeding, then the millions of disease-causing micro-organisms present in them sticking to the body of housefly. And when this housefly sits on uncovered food, they may transfer the pathogens and food gets contaminated. When this contaminated food is consumed by a person, pathogens enter into his body and causes various diseases.

(B) State any two ways of preventing diseases spread by houseflies.

The spreading of diseases by houseflies can be prevented by following ways:
(i) Food should always be kept covered.
(ii) Proper sanitation should be maintained in the kitchen.

Q.45.
(A) How do mosquitoes carry disease-causing micro-organisms and spread diseases?

Mosquito acts a carrier of disease causing micro-organism and spreads diseases from one person to another. They carry disease-causing micro-organisms (microbes) inside its body. Female Anopheles mosquito is a carrier of malarial parasite. When it bits a person suffering from malaria, it sucks the blood of that person which contains the malarial parasite microbes. When this infected mosquito bites a healthy person, it transfers the microbes into his blood stream, hence the healthy person also gets malarial disease.

(B) Mention any three ways of preventing diseases spread by mosquitoes.

The spreading of diseases by mosquitoes can be prevented by following ways:
(i) We should not let water collect anywhere in the neighborhood.
(ii) We should keep our surrounding clean and dry.
(iii) Mosquito repellant creams should be applied on the exposed parts of the body.

Q.46.
(A) What is meant by fermentation? Name the scientist who discovered fermentation. 

The process of conversation of sugar into alcohol is known as fermentation. Louis Pasteur discovered fermentation in 1857.

(B) Which micro-organism converts sugar into alcohol during fermentation? 

Yeast converts sugar into alcohol during fermentation. Yeast is used for commercial production of alcohol and wine.

Q.47. 
(A) How do micro-organisms help in increasing soil fertility? 

Some bacteria like rhizobium and blue green algae like Nostoc and Anabaena present in the soil are able to fix nitrogen gas from the atmosphere to enrich soil with nitrogen and increase its fertility. These micro-organisms are commonly called biological nitrogen fixers.

(B) How do micro-organisms help in cleaning the environment?

Some micro-organisms decompose the organic matter of dead plants and animals and convert them into simple substances which mix up with the soil. These substances are again used by other plants and animals. Thus, micro-organisms decompose the harmful and smelly dead remains of plants and animals into harmless materials and thereby clean up the environment.

Q.48. What are antibiotics? What precautions must be taken while taking antibiotics?

Medicines which kill or stop the growth of the disease-causing micro-organisms are called antibiotics. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.
Some of the precautions should be taken while taking antibiotics which are as follows:

• Antibiotics should be taken only on the advice of a qualified doctor.
• A person must finish the full course of antibiotics prescribed by the doctor.
• Antibiotics should not be taken unnecessarily.

Q.49. Why are antibiotics not effective against 'common cold' and 'flu'? 

Antibiotics are not effective against 'common cold' and 'flu' as these are caused by viruses. And the viruses do not have cells but live in the cells of living beings. And the working mechanism of the antibiotics is to break the cell wall and attack on the bacteria.

Q.50. What is the full form of HIV? Name the disease caused by HIV.

The full form of HIV is Human Immunodeficiency Virus. HIV causes AIDS disease.

Q.51. Describe how, curd is made from milk. Name the bacterium which converts milk into curd:

Milk is turned into curd by bacteria. Milk contains many microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd.
When a small amount of pre-made curd is added into warm milk, then lactobacillus bacterium present in curd multiplies in milk and converts it into curd. During this process, lactobacillus bacterium acts on lactose sugar present in milk and converts it into lactic acid. This lactic acid then converts milk into curd.

Q.52. Name the micro-organism used in bread-making which makes the bread-dough rise. How does it make the dough rise?

Yeast is used in baking industry for making bread. It increase the volume of dough. When yeast is mixed in dough for making bread, the yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This makes the dough rise. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.

Q.53. What is food poisoning? How is food poisoning caused?

Microorganisms such bacteria and fungi that grow on our food items sometimes produce toxic substances. These make the food unfit for consumption. Consuming such food can cause a serious illness called food poisoning.
Food hygiene is essential for preventing food poisoning.

Q.54. 
(A) What is meant by food preservation? Name any five methods of preserving food.

Food preservation: Processing of food to prevent their spoilage and to retain their nutritive value for period is called food preservation.
Food can be preserved using following methods:

• Preservation by Salt
• Preservation by Sugar
• Preservation by oil and vinegar
• Heat and cold treatment
• Storage and packing

(B) How do you preserve cooked food at home?

We preserve cooked food in the refrigerator at home. Low temperature inhibits the growth of micro-organisms. When cooked food is kept in a cold place, then the food does not get spoiled easily.

Q.55. 
(A) Why should we not let water collect anywhere in the neighbourhood?

All mosquitoes breed in water . Hence, one should not let water collect anywhere, in coolers, tyres, flower pot etc.

(B) Name one animal disease each caused:
(i) by virus
(ii) by bacteria
(iii) by fungus.

(i) Yellow vein mosaic of bhindi (Okra)
(ii) Citrus canker
(iii) Rust of wheat

Q.56. Where do Rhizobium bacteria live? What is their function?

Rhizobium bacterium is found in the soil. It lives in the root nodules of leguminous plants such as beans and peas, with which it has a symbiotic relationship. It is involved in the fixation of nitrogen in leguminous plants (pulses).

Q.57. Name any two
(a) bacteria
(b) viruses
(c) protozoa
(d) algae, and
(e) fungi.

(a) Bacteria – (I) Lactobacillus bacteria (II) Rhizobium bacteria
(b) Viruses – (I) HIV (II) Tobacco Mosaic virus (TMV)
(c) Protozoa – (I) Amoeba (II) Paramecium
(d) Algae – (I) Spirogyra (II) Chlamydomonas
(e) Fungi – (I) Penicillium (II) Aspergillus

Q.58. State the beneficial effects (or usefulness) of micro-organisms in our lives.

Microorganisms are used for various purposes such as:

• They are used in the preparation of curd, bread and cake.
• They are used in the preparation of alcohol, wine and acetic acid (vinegar).
• They are also used in cleaning up of the environment.
• In agriculture, they are used to increase soil fertility by fixing nitrogen.
• The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Penicillin is an antibiotic made from Penicillium.
• Certain microbes are also used in the biological treatment of sewage and industrial effluents.
• Yeast is used in making idlis, bhaturas, bread, pastries and cakes.

Q.59. Describe the method of pasteurization for the preservation of milk.

The process of pasteurization for the preservation of milk is discovered by Louis Pasteur. In this process, milk is heated to about 70^oC for 15 to 30 seconds to kill bacteria. Next it is chilled very fast to prevent bacteria from growing. It is finally stored at low temperature. This Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Q.60. Name one plant disease each caused:
(a) by fungi
(b) by virus
(c) by bacteria

(a) The plant disease, Rust of wheat is caused by fungi.
(b) Yellow vein Virus Insect mosaic of bhindi (Okra), a plant disease, is caused by virus.
(c) Citrus canker is caused by bacteria.