Lakhmir Singh & Manjit Kaur: Microorganisms Friends and Foe- 3 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.61. Which disease is spread by:
(a) female Anopheles mosquito?
(b) female Aedes mosquito? 

(a) Female Anopheles mosquito carries the parasite of malaria.
(b) Female Aedes mosquito acts as carrier of dengue virus.

Q.62. Name two fruits which are preserved:
(a) In the form of pickles
(b) In the form of jams. 

(a) The fruits which are preserved in the form of pickles by using oil and vinegar as preservative are raw mango and lemon.
(b) The fruits which are preserved in the form of jams by using sugar as preservative are mango and orange.

Q.63. What is the mode of transmission of the following diseases?
(a) Rust of wheat
(b) Citrus canker
(c) Yellow vein mosaic of bhindi (Okra)

Q.64. Name any two animal diseases and two plant diseases caused by micro-organisms.

The following diseases are caused by the micro-organisms:

Q.65. State the causative micro-organisms and modes of transmission of the following human diseases:
(i) Tuberculosis
(ii) Measles
(iii) Chickenpox
(iv) Polio
(v) Cholera
(vi) Typhoid
(vii) Hepatitis B
(viii) Malaria
(ix) Dengue

Q.66.
(A) What is meant by communicable diseases? Name any two communicable diseases. 

Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Cholera and tuberculosis are examples of communicable diseases.

(B) What are the various ways in which communicable diseases can occur and spread?

The communicable diseases can occur and spread in the following ways:

• Through air we breathe
• Through water we drink
• Through food we eat, and
• Through carriers such as mosquito.

Q.67. 
(A) Name any five human diseases caused by micro-organisms. Also name the causative micro-organisms and mode of transmission for each of these diseases.

(B) State the various ways of preventing the occurrence and spreading of communicable diseases.

There are various ways of preventing the occurrence and spreading of communicable diseases. These are as follows: 

• Maintain personal hygiene and good sanitary habits. 
• Drink boiled drinking water. 
• Spray insecticides and control breeding of mosquitoes by not allowing water to collect in the surroundings. 
• Keep the infected person separated from others & advise him/ her to keep a handkerchief on the nose and mouth while sneezing. 
• Timely vaccination against diseases should also be taken. 
• Food must be kept covered.

Q.68.
(A) What is a vaccine? How does a vaccine work?

A vaccine is a special kind of preparation which provides immunity against a particular disease. Vaccine consists dead and weakened microbes which are harmless and do not cause any disease. Vaccine works as follows: 

• When the vaccine containing dead or weakened microbes is introduced into the body of a healthy person, the body fights and kills the microbes by producing some substance called antibodies. 
• Some of the antibodies remain in the body for a long time and protect it from any future attack of disease germs. Thus, a vaccine develops the immunity from a disease.

(B) Why are children given vaccination?

Vaccination is the process of giving a vaccine orally or by injection which gives protection against a particular disease. Vaccination protect the children from number of diseases. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination.
Since the immune system of children is not strong and they are more likely to catch any disease very easily, so all the children should be vaccinated at the proper ages to provide them immunity from certain diseases.

Q.69. What is meant by 'nitrogen fixation'? State two ways in which nitrogen gas of the atmosphere can be 'fixed' in nature to get nitrogen compounds in the soil.

The process of converting atmospheric nitrogen into compounds of nitrogen is called nitrogen fixation. The two ways in which in which nitrogen gas of the atmosphere can be 'fixed' in nature to get nitrogen compounds in the soil are:
(i) Nitrogen fixation by lightning: Lightning also helps in fixing atmospheric nitrogen into the soil. The temperature and pressure during lightning convert atmospheric nitrogen into oxides of nitrogen. These nitrogen compounds combine with rainwater to form nitric and nitrous acid which mix with the soil.
(ii) Nitrogen fixation by certain bacteria and blue-green algae: Certain bacteria and blue-green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen.

Q.70. Draw a neat, labelled diagram of nitrogen cycle in nature. Which natural phenomenon occurring in the sky is responsible for nitrogen fixation?

A neat, labelled diagram of the nitrogen cycle in nature is shown below:

Lightning is a natural phenomenon which occurs in the sky and responsible for nitrogen fixation. The temperature and pressure during lightning convert atmospheric nitrogen into oxides of nitrogen. These nitrogen compounds combine with rain water to form nitric and nitrous acid which mix with the soil. These acids are utilized by various organisms.

Q.71. The bread dough rises because of:
(a) Heat
(b) Grinding
(c) Growth of yeast cells
(d) Kneading 

Correct Answer is Option (c)

Growth of yeast cells Yeast is used in baking industry for making bread. It increases 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.

Q.72. Yeast is used in the production of:
(a) Sugar
(b) Alcohol
(c) Hydrochloric acid
(d) Oxygen 

Correct Answer is Option (b)
Yeast is used for commercial production of alcohol and wine.

Q.73. The process of conversion of sugar into alcohol is called:
(a) Nitrogen fixation
(b) Moulding
(c) Fermentation
(d) Infection 

Correct Answer is Option (c)
Fermentation The process of conversion of sugar into alcohol is known as fermentation. Louis Pasteur Discovered fermentation in 1857.

Q.74. Which of the following is an antibiotic?
(a) Sodium bicarbonate
(b) Streptomycin
(c) Alcohol
(d) Yeast

Correct Answer is Option (b) 
Streptomycin, tetracycline, and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.

Q.75. The most common carrier of communicable diseases is: 
(a) Ant
(b) Housefly
(c) Dragonfly
(d) Spider

Correct Answer is Option (b) 
The housefly is the most common carrier of communicable diseases. The houseflies feed on garbage, animal excreta, and dead organic matter. Diseases cholera and tuberculosis are spread by houseflies.

Q.76. The carrier of malaria-causing protozoan is:
(a) Female anopheles
(b) Cockroach
(c) Housefly
(d) Female anopheles mosquito

Correct Answer is Option (d) 
The carrier of a malaria-causing protozoan called plasmodium is the female anopheles mosquito.

Q.77. The vaccine for smallpox was discovered by:
(a) Alexander Fleming
(b) Edward Jenner
(c) Louis Pasteur
(d) Rober coch

Correct Answer is Option (b) 
Edward Jenner discovered the vaccine for smallpox in 1978.

Q.78. Alcohol can be converted into vinegar by the action of micro-organisms called:
(a) Viruses
(b) Yeast
(c) Protozoa
(d) Bacteria

Correct Answer is Option (b) 
The dilute solution of acetic acid is called vinegar. Alcohol can be converted into vinegar by the action of micro-organisms called bacteria. In this process, first alcohol is produce by using yeast. The acetobacter bacteria is then added to alcohol. Acetobacter bacteria convert alcohol into acetic acid (or vinegar).

Q.79. The first antibiotic called penicillin was extracted from:
(a) A bacterium
(b) A protozoan
(c) A fungus
(d) An alga

Correct Answer is Option (c) 
An antibiotic Penicillin was extracted from fungus (mould) by Alexander Fleming in 1929. This antibiotic was made from the fungus called penicillium.

Q.80. Which of the following is not a communicable disease?
(a) Cholera
(b) Cancer
(c) Chickenpox
(d) Malaria

Correct Answer is Option (b) 
Cholera, chickenpox, and malaria are communicable diseases while cancer is not a communicable disease.

Q.81. Which of the following increases the fertility of the soil
(A) Lactobacillus bacteria
(B) Rhizobium bacteria
(C) Spirogyra algae
(D) Blue-green algae
(a) A and B
(b) B and C
(c) A and D
(d) B and D

Correct Answer is Option (d)
B and D as these two organisms are able to fix nitrogen gas from atmosphere to enrich soil with nitrogen compounds hence increasing fertility of soil.

Q.82. Which of the following cannot be used as a food preservative?
(a) Sodium metabisulphite
(b) Sodium hydroxide
(c) Sodium benzoate
(d) Citric acid

Correct Answer is Option (b)
Sodium metabisulphite, sodium benzoate, and citric acid are used as food preservatives whereas sodium hydroxide is not used as a food preservative.

Q.83. Which of the following disease is not caused by bacteria?
(a) Cholera
(b) Typhoid
(c) Tuberculosis
(d) Measles

Correct Answer is Option (d)
Cholera, typhoid, and tuberculosis are caused by bacteria whereas measles is caused by a virus.

Q.84. The micro-organisms which can reproduce and multiply only cells of other organisms are:
(a) Protozoa
(b) Fungi
(c) Bacteria
(d) Viruses

Correct Answer is Option (d)
Viruses are too much smaller in comparison to other micro-organisms. They do not show most of the characteristics of 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.

Q.85. The dengue disease spread by the Aedes mosquito is caused by:
(a) Bacteria
(b) Virus
(c) Protozoan
(d) Fungus

Correct Answer is Option (b)
Dengue disease is caused by a virus. The Female Aedes mosquito acts as carrier of dengue virus.

Q.86. Which of the following disease is not caused by viruses?
(a) Measles
(b) Smallpox
(c) Cholera
(d) Polio

Correct Answer is Option (c)
Measles, smallpox, and polio are caused by viruses while cholera is caused by a bacterium.

Q.87. The micro-organism which is capable of converting sugar into alcohol and carbon dioxide is:
(a) Bacterium
(b) Fungus
(c) Alga
(d) Protozoan

Correct Answer is Option (b)
Yeast, a fungus is capable of converting sugar into alcohol and carbon dioxide.

Q.88. Which of the following is not a use of micro-organisms?
(a) Preparation of medicines (or drugs)
(b) Preparation of food by photosynthesis
(c) Recycling of materials in nature
(d) Increasing the fertility of the soil

Correct Answer is Option (d)
Some of the micro-organisms are used to preparation of medicines. Some of micro-organisms are used recycling of materials in nature and increasing the fertility of soil. The synthesis of food by photosynthesis takes place in leaves with the help of inorganic material like carbon-dioxide and water in the presence of sunlight and chlorophyll.

Q.89. Malaria disease is caused by a:
(a) Virus
(b) Protozoan
(c) Bacterium
(d) Fungus

Correct Answer is Option (b)
Malaria disease is caused by a protozoan called plasmodium.

Q.90. The parasite called Plasmodium causes a disease known as:
(a) Measles
(b) Polio
(c) Malaria
(d) Dengue

Correct Answer is Option (c)
The parasite called Plasmodium causes a disease known as malaria. The female Anopheles mosquito carries the parasite of malaria.

Q.91. After consuming a dish of mutton, a person complained of nausea, vomiting, diarrhoea, and pain in the abdomen.
(a) What type of disease is he suffering from?
(b) What causes this disease?

(a) He is suffering from food poisoning.
(b) Micro-organisms like bacteria and fungi present in the spoilt dish of mutton cause the disease, and food poisoning.

Q.92. Match the micro-organism in column A with their action on Column B:

(i) e;
(ii) a ;
(iii) b;
(iv) c ;
(v) d ;
(vi) f ;
(vii) g

Q.93. To which category of micro-organisms do the following belong?
Amoeba, Lactobacillus, Chlamydomonas, Penicillium, Yeast, HIV

Amoeba – Protozoa ;
Lactobacillus – Bacteria;
Chlamydomonas – Algae;
Penicillium – Fungi;
Yeast – Fungi;
HIV – Virus

Q.94. Name the causative micro-organisms do the following belong?
(a) Rust of wheat
(b) Citrus canker
(c) Yellow vein mosaic of bindi (Okra) 

(a) Rust of wheat – Fungi
(b) Citrus canker – Bacteria
(c) Yellow vein mosaic of bindi (Okra) – Virus

Q.95. The mosquito P is a carrier of the virus and spreads a disease Question Another mosquito R is the carrier of protozoan S and spreads s disease called T.
(a) Name (i) mosquito P, and (ii) disease Question
(b) Name (i) mosquito R (ii) protozoan S, and (iii) disease T.
(c) What is the sex of mosquito P?
(d) What is the sex of mosquito r?

(a) (i) Female Aedes mosquito (ii) Dengue
(b) (i) Female Anopheles mosquito (ii) Plasmodium (iii) Malaria
(c) Female
(d) Female