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Tuesday, August 16, 2011

Answers of CBSE Based Class 8 Science Test -1 From Microorganisms

Answers Of Science Class 8 Test From Chapter 2 - MicroOrganisms -15082011.docx

M.M: 73 marks                                                     Date: 16/08/2011
Time: 1 hour
Q 1: Fill in the blanks (1 mark each per question x 31 = 31 marks)

A 1:
  1. Those organisms which are too small to be seen without a microscope are called micro-organisms.
  2. As a result of nitrogen cycle, the percentage of nitrogen in the atmosphere remains more or less constant.
  3. Our Earth’s atmosphere has 78 percent of nitrogen gas.
  4. The process of converting nitrogen gas of atmosphere into compounds of nitrogen, which can be used by plants is called nitrogen fixation.
  5. Two examples of leguminous plants are peas and beans.
  6. The circulation of nitrogen element through living things and non living environment such as air, soil and water is called nitrogen cycle in nature.
  7. Rhizobium bacteria can convert nitrogen gas or air into nitrogen compounds.
  8. The food material which is preserved by pasteurisation is milk.
  9. Common salt has been used to preserve meat and fish for ages.
  10. Deep freezing method is nowadays used for preservation of foods like meat, fish and their products – food and vegetables.
  11. Pasteurisation method is based on the name of French scientist Louis Pasteur.
  12. Mustard oil and Sirka are still widely used as preservatives for the preservation of fruits and vegetables in the form of pickles.
  13. The three special chemicals which are used for preservation of food are sodium metabisulphite, sodium benzoate and citric acid.
  14. The process in which the food materials are given suitable physical or chemical treatment to prevent them from getting spoilt is called food preservation.
  15. Cholera is caused by bacteria.
  16. The most common disease that spreads by mosquitoes is malaria.
  17. Plasmodium or Malarial Parasite causes malaria disease.
  18. Female Anopheles mosquito carries the parasite of malaria.
  19. Another disease that spreads by mosquitoes is dengue.
  20. Two dangerous diseases caused by housefly are cholera and tuberculosis. (Others: Typhoid, Diarrhoea).
  21. Two plant diseases caused by micro-organisms are Rust Of Wheat and Citrus Canker. (more than one word can come in a single blank).
  22. Alcohol is produced with the help of yeast.
  23. Edward Jenner discovered the vaccine for smallpox in 1798.
  24. Two materials that cannot be decomposed by micro-organisms are glass and plastic. (others: metals)
  25. Lactobacilli bacteria promote the formation of curd from milk.
  26. Alexander Fleming discovered Penicillin.
  27. The process of conversion of sugar into alcohol by the action of yeast is called fermentation.
  28. Yeast is the micro-organism used in making bread, cakes and pastries.
  29. Viruses are the micro-organisms which reproduce only inside the living cells of other organisms.
  30. Full form of HIV is Human Immunodeficiency Virus.
  31. AIDS stand for Acquired Immune Deficiency Syndrome.
Q 2: Complete the following table showing some common human diseases by filling the causative micro-organism, mode of transmission and one general preventive measure. (3 marks x 4 = 12 marks).

A 2: 
Human disease
Causative micro-organism
Mode of transmission
General Preventive Measure
Vaccination should be done at proper age.
- Drink clean and boiled drinking water
- Vaccination should be done.
Maintain personal hygiene and good sanitary habits.
Hepatitis B
- Drink clean and boiled drinking water.
- Vaccination should be done.
Q 3: In brief, write about pasteurisation.                            (2 marks)
A 3: Pasteurisation is the method used for preservation of milk. In pasteurisation, following is done:
  1. Milk is heated to about 70 degree Celsius for 15 to 30 seconds to kill most of the bacteria in it.
  2. This hot milk is cooled very quickly to a low temperature to prevent any of the remaining bacteria from growing further.
  3. This cold milk is stored in cold in refrigerators.
Q 4: What do you understand by food poisoning? What are its two major symptoms?                                                                 (3 marks)
A 4: Food poisoning is a disease caused by the presence of toxic substances in food formed by the action of micro-organisms Or, due to large number of micro-organisms like bacteria and fungi in the food.
Two major symptoms of food poisoning are:
  1. Vomiting
  2. Diarrhoea (loose motions)
Other symptoms:
  1. Pain in abdomen
  2. Headache
  3. Fever
Q 5: Write one reason behind sugar being used as a preservative?             (1 mark)
A 5: Sugar reduces the moisture content from the fruit which reduces/slows the growth of micro-organisms like bacteria which spoil the fruits etc.
Q 6: Write names of two diseases that are caused in animals by micro-organisms. Also write the type of micro-organism that causes the respective disease.                                                         (4 marks)
A 6: The names of two diseases caused by micro-organisms in animals are:
  1. Foot and mouth disease
  2. Anthrax
Other disease caused by micro-organism in animals is Aspergillus.
Causes of diseases caused by microorganisms in animals are:
  1. Foot and mouth disease is caused by a virus.
  2. Anthrax is caused in cattles by bacteria called Bacillus Anthracis.
  3. Aspergillus disease is caused by fungus.
Q 7: Which type of micro-organism causes Dengue? Write the  carrier of dengue disease.                                                    (2 marks)
A 7: Dengue is caused by a virus. The female Aedes mosquito acts as a carrier of dengue.
Q 8: What do you understand by communicable diseases? Write names of two such diseases.                                                (3 marks)
A 8: Communicable diseases are those diseases caused by micro-organisms which can spread from an infected person to a healthy person through air, water, food or physical contact etc. Two examples of communicable diseases are Common cold and Cholera. Other examples are Chickenpox, Tuberculosis (TB), Malaria and AIDS.
Q 9: Explain in brief, how micro-organisms helps in keeping the environment clean?                                                             (2 marks)
A 9:  Certain bacteria and fungi decompose (break down into smaller parts) the organic matter present in dead plants, dead animals and animals wastes and convert them into simple substances which mix up with soil. These simple substances have plant nutrients that are used by new plants again for their growth. Thus, micro-organisms convert harmful or useless material into useful material and keep the environment clean.
Q 10: What do you understand by a vaccine? Write names of four diseases that can be prevented by vaccination at the right time.                                                                                                     (3 marks)
A 10: A vaccine is a special kind of medicine or preparation which provides immunity or protection against a particular disease. Four diseases which can be prevented by vaccination children at right age are: Cholera, smallpox, typhoid and polio. (Others are: TB, Tetanus, Measles, Rabies, Diphtheria and Pertussis – Whooping cough).
Q 11: Define antibiotic. Write two examples of the same. (3 marks)
A 11: A medicine that either kills the disease causing micro-organisms or stops their growth is called antibiotic. The names of two antibiotics are Penicillin, Streptomycin. Other antibiotics are Erythromycin and Tetracycline.
Q 12: Why is curd added to idlis and bhaturas?                    (1 mark)
A 12: Curd is added to idlis and bhaturas to make them soft and spongy.
Q 13: Write short note on Protozoa and Fungi. Give two examples of each. Make diagram of one type of protozoa and one type of fungi.                                                                                   (6 marks)

A 13: Protozoa are a group of single-celled organisms which are classified as animals.Protozoa are found in lakes, ponds, rivers, sea water and damp soil. Two common examples of protozoa are: Amoeba, Paramecium. Others are: Entamoeba and Plasmodium. The diagram at left shows Amoeba.

Fungi are a large group of organisms which do not have chlorophyll and do not photosynthesise. Some examples of fungi are: Yeast, Moulds, Puffballs. The diagram at left shows bread mould.