2

Q1. Who discovered the process of fermentation?

Solution

Fermentation was discovered by Louis Pasteur in 1857.

Q2. In pasteurisation, milk is boiled at

• 1) 70°C for 15-30 minutes
• 2) 70°C for 10-20 minutes
• 3) 70°C for 15-30 seconds
• 4) 70°C for 10-20 seconds

Solution

In pasteurisation, milk is boiled at 70°C for 15-30 seconds to kill all the bacteria.

Q3. Helminths are a type of pathogens. 

• 1) False
• 2) True

Solution

True

Q4. Which of the following are used as agents for food preservation in pickles?

• 1) Vinegar
• 2) All of the above
• 3) Oil
• 4) Salt

Solution

In pickles, oil, salt and vinegar serve as preserving agents and prevent spoilage by microorganisms.

Q5. Heating to a temperature of about 60°C for 30 minutes and then chilling is the process of dehydration.

• 1) True
• 2) False

Solution

Heating to a temperature of about 60°C for 30 minutes and then chilling is the process of pasteurisation.

Q6. Killing microorganisms is one of the principles of food preservation.

• 1) True
• 2) False

Solution

True

Q7. Give terms for the following: Conversion of ammonia to nitrates Process of ammonia formation Conversion of nitrates to ammonia 

Solution

Nitrification Ammonification  Denitrification 

Q8. The percentage of nitrogen in air is

• 1) 75%
• 2) 81%
• 3) 78%
• 4) 79%

Solution

Nitrogen makes up for about 78% of the total gas in the atmosphere.

Q9. Plagueaffects humans and rats only.

• 1) True
• 2) False

Solution

Plague affects rats, squirrels, rabbits, guinea pigs and humans.  

Q10. (i) Name the following:(a) The percentage of nitrogen gas in atmosphere(b) The cyclic movement of nitrogen in different chemical forms from the environment, to organisms, and then back to the environment.(c) The bacterium involved in nitrogen fixation in leguminous plants(ii) Give two examples of leguminous plants.

Solution

(i) (a) 78%(b) Nitrogen cycle(c) Rhizobium(ii) Peas and beans

Q11. Killing microorganisms is one of the principles of food preservation.

• 1) True
• 2) False

Solution

True

Q12. Bacteria living in the root nodules of the plant obtain only shelter from the plant in return for the nitrogen they fix.

• 1) False
• 2) True

Solution

Bacteria living in the root nodules of the plant obtain food and shelter from the plant in return for the nitrogen they fix.

Q13. Insecticides are used to control houseflies.

• 1) True
• 2) False

Solution

True

Q14. Alkaligenes is a species of denitrifying bacteria.

• 1) False
• 2) True

Solution

True

Q15. Nitrosomonas converts ammonia to nitrates.

• 1) True
• 2) False

Solution

True

Q16. Louis Pasteur discovered fermentation in 1857.

• 1) False
• 2) True

Solution

True

Q17. Algae and fungi live a saprophytic or parasitic life.

• 1) True
• 2) False

Solution

Only fungi live a saprophytic or parasitic life.

Q18. Pathogens possess the ability to destroy tissues of the body, making certain organs non-functional.

• 1) True
• 2) False

Solution

True

Q19. Pathogens possess the ability to destroy tissues of the body, making certain organs non-functional.

• 1) False
• 2) True

Solution

True

Q20. Who discovered penicillin mould?

Solution

Alexander Fleming discovered penicillin in 1929, while working on a culture of disease-causing bacteria.

Q21. Tears can contain pathogens.

• 1) False
• 2) True

Solution

True

Q22. How is atmospheric inert nitrogen gas converted to the usable nitrogenous form for various life forms?

Solution

Biological processes: The atmospheric inert nitrogen gas is converted to the usable nitrogenous form with the help of free living nitrogen-fixing bacteria found in the roots of legumes. Physical process: During lightning, the high temperatures and pressures created in the air convert nitrogen to oxides of nitrogen. 

Q23. Boiling water kills the Hepatitis A virus.

• 1) True
• 2) False

Solution

True

Q24. Toxins are produced by certain pathogens.

• 1) True
• 2) False

Solution

True

Q25. TMV is an animal virus.

• 1) True
• 2) False

Solution

TMV is a plant virus.

Q26. Bacteria range in size from 0.2 to 10 μ.

• 1) True
• 2) False

Solution

True

Q27. Paramoecium is a fungus.

• 1) True
• 2) False

Solution

Paramoecium is a protozoan.

Q28. Which of the following is not a characteristic of spoiled food?

• 1) Bad taste
• 2) Bad smell
• 3) Changed colour
• 4) Good aroma

Solution

Spoiled food has bad taste, changed colour and a foul smell.

Q29. Vaccination is not given against

• 1) Chicken pox
• 2) Measles
• 3) Malaria
• 4) Cholera

Solution

There is no vaccination against malaria. However, it is a treatable disease.

Q30. Name a common chemical used to preserve dried fish for a long time.

Solution

Salt is used to preserve dried fish for a prolonged time.

Q31. Spores are killed at 98°C.

• 1) True
• 2) False

Solution

Spores are killed at 110°C.

Q32. Which of the following contains nitrogen?

• 1) All of these
• 2) Proteins
• 3) Nucleic acids
• 4) Vitamins

Solution

Nitrogen forms an important component of most of the essential molecules and compounds for life, such as proteins, chlorophyll, nucleic acids and vitamins.

Q33. Anthrax bacillus helps in nitrogen fixation.

• 1) False
• 2) True

Solution

Rhizobium helps in nitrogen fixation.

Q34. Which of the following diseases spread through physical contact?

• 1) Cholera
• 2) AIDS
• 3) Tuberculosis
• 4) Chicken pox

Solution

Chicken pox is a viral disease and can spread from person to person through contact.

Q35. Bacteria living in the root nodules of the plant obtain only shelter from the plant in return for the nitrogen they fix.

• 1) False
• 2) True

Solution

Bacteria living in the root nodules of the plant obtain food and shelter from the plant in return for the nitrogen they fix.

Q36. Which of the following serves as an indirect source of nitrogen in the soil?

• 1) All of these
• 2) Dead remains of plants
• 3) Animal droppings
• 4) Human faeces

Solution

Dead plants and animals and their organic waste serve as a source of nutrition for microbes which decompose these materials and release nitrogenous compounds into the soil.

Q37. (i) What is meant by 'food poisoning'? What is its cause?(ii) Write the symptoms of food poisoning.(iii) Name two examples of bacteria which cause food poisoning.

Solution

(i) The disease caused due to the presence of a large number of micro-organisms (like bacteria and fungi) in the food, or due to the presence of toxic substances in food, formed by the action of micro-organisms, is called food poisoning. Food poisoning occurs due to the consumption of food spoilt by some micro-organisms. (ii) The major symptoms of food poisoning are: Vomiting, Diarrhoea (Loose motions), Pain in abdomen, headache and fever. (iii) The two most common examples of bacteria which cause food poisoning are bacteria Salmonella and bacteria Clostridium botulinum.

Q38. Using mosquito nets can help prevent which diseases?

Solution

Malaria and dengue spread through mosquitoes, and hence, the use of mosquito nets can help prevent the incidence of malaria and dengue.

Q39. Pickles are preserved by salting.

• 1) False
• 2) True

Solution

True

Q40. How do microorganisms help to keep the environment clean?

Solution

The microorganisms decompose dead organic wastes of plants and animals converting them into simple substances. These substances are again used by other plants and animals. Thus, microorganisms can be used to degrade the harmful and smelly substances and thereby cleans up the environment.

Q41. Louis Pasteur discovered fermentation in 1857.

• 1) False
• 2) True

Solution

True

Q42. Carriers are a type of disease-causing pathogens.

• 1) False
• 2) True

Solution

Carriers transmit disease-causing pathogens from a diseased individual to a healthy individual.

Q43. List four communicable diseases.

Solution

Communicable diseases: Cholera Common cold Chicken pox Tuberculosis 

Q44. Boiling water kills the Hepatitis A virus.

• 1) True
• 2) False

Solution

True

Q45. Gram is a leguminous plant.

• 1) False
• 2) True

Solution

True

Q46. Spores are killed at 98°C.

• 1) False
• 2) True

Solution

Spores are killed at 110°C.

Q47. Nitrosomonas converts ammonia to nitrates.

• 1) False
• 2) True

Solution

True

Q48. Which of the following plant diseases is transmitted by seeds?

• 1) All of the above
• 2) Rust of wheat
• 3) Yellow vein mosaic of Okra
• 4) Citrus canker

Solution

Rust of wheat is a fungal disease in plants and is transmitted by air and seeds.

Q49. Why does the number of mosquitoes increase during the monsoon season?

Solution

Mosquitoes breed in stagnant water. During the monsoon season, water collects in many places and serves as a breeding ground for them, and hence, their number increases.

Q50. (i) Write the symptoms of an animal suffering from disease?(ii) Which is the common factor in the following diseases? Tuberculosis, Measles, Citrus canker

Solution

(i) An animal suffering from any disease shows the following symptoms:a. Becomes inactive and stops taking food.b. Watering in eyes and excessive secretion of saliva. c. Its milk yield, egg-laying and working capacity get drastically reduced.(ii) They are all transmitted through air.

Q51. Briefly explain the main steps in nitrogen cycle.

Solution

The main steps in the nitrogen cycle are: (i) The atmosphere (or air) contains nitrogen gas. The nitrogen-fixing bacteria (present in the soil and in the root nodules of leguminous plants), blue-green algae and lightning in the sky fix nitrogen gas from the atmosphere and convert it into compounds of nitrogen which go into soil. (ii) The plants take compounds of nitrogen from the soil for their growth. The plants absorb the nitrogen compounds from the soil through their roots and convert them into plant proteins and other organic compounds which make up the body of plants. (iii) The plants are eaten up by animals as food. Animals convert plant proteins into animal proteins and other organic compounds which make up their body. Some animals also eat other animals to obtain nitrogen compounds. Thus, animals obtain nitrogen compounds by eating plants as well as other animals. (iv) When plants and animals die, the complex nitrogen compounds (like proteins, etc.) present in their dead bodies are decomposed and converted into simple compounds of nitrogen by certain bacteria and fungi present in the soil. Animal excretions (urine, etc.) are also converted into simple compounds of nitrogen. All the simple compounds of nitrogen formed in this way go into the soil. (v) Some of the compounds of nitrogen (formed from the decay of dead plants and animals) are decomposed by denitrifying bacteria present in the soil to form nitrogen gas. This nitrogen gas goes back into the atmosphere. In this way, the nitrogen gas which was removed from the atmosphere during fixation, is put back into the atmosphere.

Q52. How is atmospheric nitrogen utilized by plants?

Solution

First atmospheric nitrogen is fixed either by lightning or by living organisms like certain bacteria and blue green algae. As a result, nitrogen is converted into usable compounds of nitrogen. These can be utilised by plants from the soil through their root system for producing plant proteins and other compounds.

Q53. Pickles are preserved by salting.

• 1) True
• 2) False

Solution

True

Q54. Cauliflower is preserved by

• 1) Heating
• 2) Dehydration
• 3) Using oil
• 4) Salting

Solution

Vegetables such as cauliflower, peas and spinach are preserved by dehydration or sun-drying.

Q55. Refrigeration kills most microbes.

• 1) True
• 2) False

Solution

Refrigeration inhibits the growth and multiplication of most microbes.

Q56. In a deep freezer, the temperature is maintained at

• 1) Below 4°C
• 2) 4°C
• 3) 0°C
• 4) Below 0°C

Solution

The temperature is usually maintained well below 0°C in a deep freezer.

Q57. Alkaligenes is a species of denitrifying bacteria.

• 1) False
• 2) True

Solution

True

Q58. (i) What are antibiotics? (ii) Name the first antibiotic discovered and who discovered it? (iii) Give example of any two well known antibiotics.

Solution

(i) Antibiotics are the chemical compounds produced by microorganisms which inhibit the growth of some other microorganisms. (ii) The first antibiotic penicillin was discovered by Alexander Flemming. (iii) Streptomycin and Tetracycline.

Q59. TMV is an animal virus.

• 1) True
• 2) False

Solution

TMV is a plant virus.

Q60. Algae and fungi live a saprophytic or parasitic life.

• 1) True
• 2) False

Solution

Only fungi live a saprophytic or parasitic life.

Q61. (i) Discuss the importance of any three preservatives that can be used in pickles?(ii) Name any two common preservatives.

Solution

(i)a. Salt is added to pickles to prevent the attack of microbes.b. Vinegar prevents spoilage of pickles because bacteria cannot live in such an environment.c. Use of oil prevents the spoilage of pickles by not permitting bacteria to grow in this environment.(ii) Sodium benzoate and sodium metabisulphite.

Q62. How does sugar prevent the growth of harmful bacteria?

Solution

Sugar absorbs most of the water and reduces the moisture content, thus preventing the growth of spoilage bacteria.

Q63. What role is played by leguminous plants in enriching soil fertility?

Solution

Leguminous plants have nitrogen fixing bacteria in their root nodules, which can fix atmospheric nitrogen and provide it to the plant and soil. These bacteria therefore increases the soil fertility by enriching the soil with nitrogen.

Q64. Why do our parents advice us to avoid eating the uncovered food sold in stalls?

Solution

Pathogens stick to the bodies of carriers like houseflies when they sit on the garbage and animal excreta. The flies sit on uncovered food and may transfer the pathogens and thus contaminates the food. When a person eats contaminated food, he is likely to get sick. So, it is advisable to always keep food covered and avoid eating uncovered food.

Q65. Name a bacterial disease which can be caused by consumption of contaminated food.

Solution

Cholera spreads through contaminated food and water.

Q66. Insecticides are used to control houseflies.

• 1) False
• 2) True

Solution

True

Q67. Paramoeciumis a fungus.

• 1) False
• 2) True

Solution

Paramoecium is a protozoan. 

Q68. Which technique does not kill microbes?

• 1) All of the above
• 2) Refrigeration
• 3) Deep freezing
• 4) Salting

Solution

Salting, freezing and refrigeration prevent the growth of microbes and do not kill existing microbes.

Q69. Tears can contain pathogens.

• 1) False
• 2) True

Solution

True

Q70. How do high-salt and high-sugar mixtures preserve food?

Solution

High-salt and high-sugar mixtures absorb the internal fluid or water of microorganisms, causing them to shrivel up and eventually die. Thus, they keep the food safe from microorganisms and preserve the food for a long time.

Q71. Tuberculosis is an airborne disease.

• 1) True
• 2) False

Solution

True

Q72. A person is suffering from chickenpox. Write any two ways of preventing the spread of this disease to others.

Solution

The following preventive measures need to be taken in this case:a. Keep the patient in complete isolation.b. Keep the personal belongings of the patient away from those of the others.

Q73. Helminths are a type of pathogens.  

• 1) True
• 2) False

Solution

True

Q74. Nitrates can also be converted to free molecular nitrogen by denitrifying bacteria.

• 1) True
• 2) False

Solution

True

Q75. Heating to a temperature of about 60°C for 30 minutes and then chilling is the process of dehydration.

• 1) False
• 2) True

Solution

Heating to a temperature of about 60°C for 30 minutes and then chilling is the process of pasteurisation.

Q76. Give examples of  Nitrifying bacteria  Denitrifying bacteria 

Solution

Nitrifying bacteria: Nitrosomonas Denitrifying bacteria: Pseudomonas 

Q77. Write any three advantages of food preservation.

Solution

Advantages of food preservation: It decreases the food wastage. It increases the storage period of perishable food materials. It ensures the all year availability of seasonal food materials.

Q78. Tuberculosis is an airborne disease.

• 1) True
• 2) False

Solution

True

Q79. Plague affects humans and rats only. 

• 1) False
• 2) True

Solution

Plague affects rats, squirrels, rabbits, guinea pigs and humans. 

Q80. Boiling of water can help prevent against which diseases?

Solution

The hepatitis B virus is transmitted by water, and boiling water kills it. Thus, consumption of boiled water can help prevent hepatitis B.

Q81. Nitrates can also be converted to free molecular nitrogen by denitrifying bacteria.

• 1) False
• 2) True

Solution

True

Q82. Describe in brief the role of nitrogen-fixing bacteria and lightning in atmospheric nitrogen fixation.

Solution

Nitrogen-fixing bacteria (free-living or symbiotic) mostly found in the roots of leguminous plants convert atmospheric nitrogen to ammonia. During lightning, the high temperature and pressure created in the air convert nitrogen to oxides of nitrogen. These oxides dissolve in water to give nitrous and nitric acids which fall to the land along with rain.

Q83. Bacteria range in size from 0.2 to 10 µ.

• 1) True
• 2) False

Solution

True

Q84. How is milk pasteurised?

Solution

During pasteurisation, milk is first heated at 70°C for 15-30 seconds and then cooled rapidly.

Q85. Anthrax bacillus helps in nitrogen fixation.

• 1) True
• 2) False

Solution

Rhizobium helps in nitrogen fixation.

Q86. What is the vegetable Okra commonly called in India?

Solution

Okra is commonly known as bhindi in India.

Q87. Carriers are a type of disease-causing pathogens.

• 1) False
• 2) True

Solution

Carriers transmit disease-causing pathogens from a diseased individual to a healthy individual.

Q88. Gram is a leguminous plant.

• 1) True
• 2) False

Solution

True

Q89. Name the following: (i) A preparation of dead or weakened microbes that is introduced into a healthy person to protect them from a particular disease in future. (ii) The medicines obtained from microorganisms that are used to kill or stop the growth of the disease-causing microorganisms. (iii) The process of conversion of sugar into alcohol by yeasts. (iv) The product obtained by decomposition of plant and animal wastes by microorganisms.

Solution

(i) Vaccine(ii) Antibiotics(iii) Fermentation(iv) Manure

Q90. Mention the important uses of microorganisms in agriculture and medicine.

Solution

In agriculture, microorganisms help in manure formation and increasing soil fertility. In medicine, microorganisms are used to prepare antibiotics and vaccines.

Q91. Toxins are produced by certain pathogens.

• 1) False
• 2) True

Solution

True

Q92. How can one preserve a liquid in the natural state without affecting its nutritional value?

Solution

Pasteurisation helps preserve liquids in the natural state without affecting the nutritional value.

Q93. A person having common cold sneezes. How is a person standing nearby likely to be affected?

Solution

When a person suffering from common cold sneezes, fine droplets of moisture carrying thousands of viruses are spread in the air. The virus may enter the body of a healthy person standing nearby while breathing and can cause common cold.

Q94. Name three materials which can be preserved by salting.

Solution

Food materials which can be preserved by salting: Meat Fish Vegetables Amla Raw mangoes Pickles Tamarind  (Any three)

Q95. List two disease-causing viruses which are transmitted by air.

Solution

Measles, chicken pox and polio are viral diseases transmitted by air. (Any Two)

Q96. Refrigeration kills most microbes.

• 1) True
• 2) False

Solution

Refrigeration inhibits the growth and multiplication of most microbes.

Q97. Name the carrier organisms for malaria and dengue viruses.

Solution

Carrier for Malaria - Female Anopheles mosquito Dengue - Female Aedes mosquito

Q98. A child is given a shot of chicken pox vaccine. How does this vaccine help in the prevention of chicken pox?

Solution

When the child is given chicken pox vaccine, the dead or weakened microbes of chicken pox are introduced into the child's healthy body. The body fights and kills the microbes in vaccine by producing suitable antibodies. The antibodies against chicken pox remain in the body and recognizes the pathogen when it enters the body another time. Thus, the child is protected from all future attacks of the chicken pox microbe.

Q99. For creating a fluffy dough of maida, we add warm water and yeast to the mixture. What is the importance of the warm water in this case?

Solution

In the mixture, yeast multiplies and releases carbon dioxide, which makes the dough fluffy. In this mixture, the warm water provides adequate moisture for the yeast to grow and also raises the temperature of the mixture, which favours the rapid growth of the yeast.

Q100. Why does maida dough containing yeast powder rise after a few hours?

Solution

Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume.