DAV Class 8 Science Chapter 2 Question Answer – Microorganisms: Friends or Foes

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 2 Question Answer – Microorganisms: Friends or Foes are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 2 Question Answer – Microorganisms: Friends or Foes

DAV Class 8 Science Ch 2 Solutions – Microorganisms: Friends or Foes

Something To Know

A. Fill in the blanks:

Question 1.
The study of microorganisms is known as ________ .
Answer:
microbiology

Question 2.
The bread dough rises because of the production of ________ .
Answer:
carbon dioxide

Question 3.
________ are the microorganisms that cause diseases.
Answer:
pathogens

Question 4.
________ and ________ are two chemical preservatives.
Answer:
sodium benzoate and potassium metabisulphite

Question 5.
________is a fungus that causes food poisoning.
Answer:
Aspergillus

B. Match the following:

Column I	Column II
(1) Ringworm	(a) Food poisoning
(2) Clostridium	(b) Biogas reactor
(3) Anthrax	(c) Fungus
(4) Lactobacillus	(d) Column I
(5) Methane	(e) Curd

Answer:

Column I	Column II
(1) Ringworm	(c) Fungus
(2) Clostridium	(a) Food poisoning
(3) Anthrax	(d) Column I
(4) Lactobacillus	(e) Curd
(5) Methane	(b) Biogas reactor

C. Tick (✓) the correct option:

Question 1.
The process, that helps milk to last longer but does not kill all microbes in it, is known as—
(a) Vaccination
(b) Pasteurization
(c) Bioaugmentation
(d) Fermentation
Answer:
(b) Pasteurization (✓)

Question 2.
Rust of wheat is caused by-
(a) Fungus
(b) Virus
(c) Bacteria
(d) Protozoa
Answer:
(a) Fungus (✓)

Question 3.
Medicines, containing killed or weakened pathogens, and used to prevent infectious diseases, are called-
(a) Disinfectants
(b) Antibodies
(c) Antibiotics
(d) Vaccines
Answer:
(d) Vaccines (✓)

Question 4.
Which of the following reproduces only inside a host cell?
(a) Virus
(b) Alga
(c) Protozoan
(d) Bacteria
Answer:
(a) Virus (✓)

Question 5.
A disease, caused by a virus, and spread by an insect, is-
(a) Polio
(b) Dengue
(c) Rabies
(d) Mumps
Answer:
(b) Dengue (✓)

D. Answer the following questions in brief:

Question 1.
Why are viruses considered as being at the ‘borderline’ between living and non-living things?
Answer:
A virus behaves like a non-living when it is outside a host cell. Once a virus enters a host cell, it starts to behave like a living being. Due to this, viruses are considered as the borderline between living and non-living.

Question 2.
What is fermentation? How is this process useful in the food and beverage industries?
Answer:
An anaerobic process through which sugars are converted into alcohol or acids and carbon dioxide by the action of microbes is called fermentation. Fermentation is useful in the food and beverages industries in various ways. Some examples are as follows:

Fermentation in batter helps in making tasty dosa.
Fermentation in dough helps in raising the dough while making bread and cake.
Fermentation of fruit juice helps in making wine.

Question 3.
‘In the absence of microorganisms the earth would become a heap of dead plants and animals.’ Justify this statement.
Answer:
When a plant or animal dies, its remains are decomposed by microorganisms. Decomposition is the process through which all constituent materials of a living being are sent back to the environment. Had there been no microorganisms, dead remains of plants and animals would be keeping on accumulating all around us. So, it can be said that in the absence of microorganisms the earth would become a heap of dead plants and animals.

Question 4.
Munna observes that the yield of wheat, growing in his field, has reduced in the current year. He gets the soil tested and the report confirms the deficiency of one particular nutrient. Accordingly, he is advised to grow peas after harvesting wheat.

(a) Name the nutrient found insufficient.
Answer:
Nitrogen

(b) How do you think growing peas will help in replenishing the soil?
Answer:
Pea plants give shelter to Rhizobium bacteria. These bacteria carry out nitrogen fixation in soil. Thus, pea plants help in replenishing nitrogen in soil.

Question 5.
Why does it take less time to prepare curd in summers as compared to preparing it in winters?
Answer:
Microorganisms reproduce at a faster rate between 20 to 40°C. They reproduce at a much slower rate when temperature is below this range. Milk is converted into curd by multiplication of lactobacillus. This is why it takes less time to prepare curd in summers as compared to preparing it in winters.

Question 6.
How are the following diseases transmitted?
(a) Malaria
Answer:
By female Anopheles mosquito

(b) Common cold
Answer:
Through cough droplets in air

(d) Typhoid
Answer:
Through contaminated food and water

Question 7.
What are antibiotics? How are they produced? Give two examples of these.
Answer:
A substance which prevents the multiplication of bacteria or kills the bacteria is called antibiotic. Antibiotics are prepared from microorganisms. Examples: Penicillin, Streptomycin.

E. Answer the following questions:

Question 1.
‘Microorganisms are very useful in manufacturing different food items.’ Explain the above statement.
Answer:
Fermentation is useful in the food and beverages industries in various ways. Some examples are as follows:

Fermentation in batter helps in making tasty dosa.
Fermentation in dough helps in raising the dough while making bread and cake.
Fermentation of fruit juice helps in making wine.

These examples show that microorganisms are very useful in manufacturing different food items.

Question 2.
Give reasons for the following:

(a) Yeast is added to the batter used to make ‘dosas’.
Answer:
Yeast is added to the batter so that fermentation can take place. Fermented batter is good for making tasty dosa.

(b) It is important to brush one’s teeth before going to bed.
Answer:
Food particles remain stuck between teeth. Bacteria in out mouth eat these food particles. In the process, bacteria damage our teeth. Brushing of teeth helps in reducing the chances of bacteria damaging out teeth. Hence, it is important to brush one’s teeth before going to bed.

(c) Reducing the quantity of salt in pickle can cause it to go bad soon.
Answer:
Salt helps in removing water from pickle. This helps in preservation of pickle over a longer duration. Less salt would mean some water would be left in the pickle.
This may result in pickle getting bad sooner.

(d) Food, from puffed or enlarged cans, should not be consumed.
Answer:
Puffed or enlarged cans mean that air has leaked inside the can. Presence of air inside the can may help microbes to proliferate. This would spoil the food items. Hence, food from puffed or enlarged cans should not be consumed.

(e) When using frozen food items one should take out only the required quantities; thawed food should never be frozen.
Answer:
We know that microorganisms do no multiply below zero degrees Celsius. Once the food is thawed, its temperature becomes same as room temperature. This gives the microbes a chance to multiply which can spoil the food. Hence, while using frozen food items one should take out only the required quantity. Thawed food should not be consumed.

Question 3.
How do communicable diseases spread? Suggest ways to prevent the following diseases:
(a) Tuberculosis
(b) Athlete’s foot
(c) Cholera
Answer:
Communicable diseases spread through various means like air, vectors, person to person contact, and contaminated food and water.
(a) Tuberculosis can be prevented by living in well ventilated and well lit places.
(b) Cleaning your feet, shoes and socks; at a regular basis helps in preventing athlete’s foot.
(c) Avoid eating or drinking contaminated food and water helps in preventing cholera.

Question 4.
What are pathogens? Name two pathogens each that cause diseases in (i) plants and (u) animals.
Answer:
Microorganisms which can cause diseases are called pathogens, (i) Bacteria and (ii) Fungi are the examples of pathogens which cause diseases in plants and animals.

Question 5.
Mohan bought samosas from a roadside vendor and ate it. After some time, he felt nausea and started vomiting. He had severe pain in the abdominal region and suffered from diarrhoea. What could be the reason for his condition? What is it called? How could it be prevented?
Answer:
This could have happened due to food poisoning. Food poisoning can be prevented by avoiding eating food from roadside vendors.

Question 6.
Which diseases the following children are most likely to suffer from?
(a) Ramu drinks water from a nearby lake. This water is neither boiled nor disinfected.
Answer:
Cholera

(b) Ashu does not take bath every day. He maintains poor personal hygiene.
Answer:
Ringworm

(d) Sohan is living in an area where the population is very high. He does not use a mosquito net (while sleeping), or insect-repellant creams (while playing in the open).
Answer:
Malaria

(e) Mohan was with two of his friends who were coughing and sneezing (they were suffering from common cold). One of these friends did not keep a handkerchief in front of his mouth while coughing and sneezing.
Answer:
Common cold

Value Based Questions

Soham and his wife were overjoyed after the birth of their daughter. They share their1 joy with their relatives and friends. Soham’s wife decides to take their daughter for her first round of vaccinations. However, Soham’s mother does not like the idea of putting the child through the discomfort of ‘injections’. Soham explains to his mother in a polite and patient way, that this slight discomfort and pain is necessary as it shall ensure that the child lives a long and healthy life.

Question 1.
Was Soham right in supporting his wife’s decision? List any two values that are demonstrated by his behaviour.
Answer:
Soham is right in supporting his wife’s decision. Mohan cares for his family and have respect for women.

Question 2.
How does vaccination help in providing immunity?
Answer:
Vaccination introduces weak or dead pathogen in the body. The body prepares antibody against these pathogens. Thus, the body learns to fight that disease even in future. That is how vaccination helps in providing immunity.

Question 3.
Find out the names of any five diseases that can be prevented by timely vaccination of children.
Answer:
Tuberculosis, Diptheria, Mumps, Pertussis, Tetanus

Something To Do

Question 1.
Visit a nearby health centre, or contact a doctor. Find out the names of diseases for which vaccinations are available and the age at which they have to be given to the child.
Answer:
Do it yourself

Question 2.
Genetic engineering is a branch of science in which microorganisms are being extensively used. Try to find out the role of microorganisms in genetic engineering.
Answer:
Useful genes from bacteria can be transferred to a crop or a useful animal. For example; BT cotton has a beneficial gene from a bacteria.

Question 3.
Visit an animal health centre or a veterinarian (a physician for animals). Collect information about various vaccinations that are available for domestic animals (like cows) and pets (like dogs).
Answer:
Do it yourself

Question 4.
Write how the following methods of preservation work. Also, add two examples of foods that can be preserved by each of these methods.

Method	How it works	Examples (of food preserved)
Pickling	Removes moisture from food.	Raw mango, lemon pickles
Ozone treatment	Kills microbes	Fruits, vegetables
Drying	Removes moisture	Rice, wheat, maize
Adding preservatives	Inhibit the growth of microbes	Jams, jelly
Canning	Kills microbes	Tomato, beans, mushroom
Vacuum packing	Removes air from packet	Fried food
Freezing	Prevents proliferation microbes of microbes	Fruits, vegetables
Radiation	Kill microbes	Fruits, vegetables
Salting	Removes moisture	Fish, pickles

Question 5.
Find out about the temperature at which the following occur/exist/work:
DAV Class 8 Science Chapter 2 Question Answer - 1
(a) Decomposition
Answer
20 to 40°C

(b) Pasteurization
Answer:
80 to 100°C

(d) Refrigerator
Answer:
0 to 20°C

(e) Deep freezer
-20°C

(f) Human body
Answer:
20 to 40°C
Based on the information provided in the picture, predict the chances of growth and survival of microbes in each of the above.
Answer:
Microbes will survive and grow in case of a and f.

DAV Class 8 Science Chapter 2 Solutions – Microorganisms: Friends or Foes Important Questions and Answers

I. Fill in the blanks:

1. Malaria is spread by ________ .
Answer:
Mosquito

2. Flu is spread through ________ .
Answer:
Air

3. Diarrhoea is spread by contaminated ________ .
Answer:
Water

4. Adding salt in food helps in removal of ________ from food item.
Answer:
Water

5. Sodium benzoate is a ________ .
Answer:
Food preservative

II. Tick the correct answer:

Question 1.
Malaria is caused by which of these?
(a) Bacteria
(b) Virus
(c) Fungi
(d) Protozoa
Answer:
(d) Protozoa

Question 2.
Ringworm is caused by which of these?
(a) Bacteria
(b) Virus
(c) Fungi
(d) Protozoa
Answer:
(c) Fungi

Question 3.
Which of these diseases can be spread by a dog’s bite?
(a) Tetanus
(b) Rabies
(c) Dengue
(d) Chikungunya
Answer:
(b) Rabies

Question 4.
Pasteurization is used for which of these food items?
(a) Milk
(b) Vegetables
(c) Fruits
(d) Pickles
Answer:
(a) Milk

Question 5.
Smut is a disease of which plant?
(a) Lemon
(b) Rice
(c) Tobacco
(d) Potato
Answer:
(b) Rice

Question 6.
Ranikhet is a disease of which of these animals?
(a) Cattle
(b) Poultry
(c) Dog
(d) Cat
Answer:
(b) Poultry

III. Answer the following questions:

Question 1.
Define microorganisms.
Answer:
Organisms which are invisible to the naked eye but visible under the microscope are called microorganisms. Examples: bacteria, yeast, protozoans and algae.

Question 2.
Explain the beneficial role of microorganisms in agriculture.
Answer:
Some bacteria and blue-green algae (cyanobacteria) help in nitrogen fixation. This is important as this is the only way through which a plant can get nitrogenous nutrients. Rhizobium bacteria live in the root nodules of leguminous plants. They help in nitrogen fixation in soil.

Question 3.
How do bacteria cause tooth decay?
Answer:
Many bacteria live in our mouth. They eat the food particles which remain stuck between the teeth. During eating the food particles, bacteria produce acids which corrode the tooth enamel and results in tooth cavities in the long run.

Question 4.
What do you understand by food poisoning?
Answer:
Food poisoning happens because of consumption of contaminated food. Vomiting, nausea, severe pain in abdomen, diarrhoea and dehydration are the symptoms of food poisoning. Clostridium and Staphylococci are the bacteria which cause food poisoning and Aspergillus is a fungus which causes food poisoning.

Question 5.
What are the main goals of food preservation?
Answer:
Prevention of growth of microorganism and retarding the oxidaton of fats are the main goals of food preservation.

IV. Projects:

Question 1.
Make a list of food items which can be preserved by drying in the sun.
Answer:
Do it yourself.

Question 2.
Make a list of food items which are preserved by using salt or sugar.
Answer:
Do it yourself.

Question 3.
How does your family ensure that you get clean and safe drinking water? What are its benefits?
Answer:
Do it yourself.