Class 8 Science Practice Question Answers - Microorganisms: Friend or Foe

Q1: Name the groups in which microorganisms are broadly classified.
Ans: Microorganisms are broadly classified in four groups:

1. bacteria
2. fungi
3. protozoa
4.  algae

Q2: Name the type of microorganism that is smaller than bacteria.
Ans: Virus

• A virus is a type of microorganism that is smaller than bacteria.
• Unlike bacteria, viruses cannot reproduce on their own; they need a host cell.
• Viruses can infect various organisms, including plants, animals, and bacteria.
• Common illnesses caused by viruses include colds, influenza, and chickenpox.

Q3: Write the name of a bacterium that helps in the formation of curd.
Ans: Lactobacillus is a type of bacterium that plays a crucial role in the formation of curd. 
Here are some key points about it:

• Lactobacillus is essential for converting milk into curd.
• This bacterium thrives in warm milk, multiplying and fermenting it.
• It is also involved in making other dairy products like cheese.
• Curd is a key ingredient in various dishes, such as idlis and bhaturas.

Q4: Write a use of yeast.
Ans: Yeast is primarily used in the production of:

• Alcohol - including beer and spirits.
• Wine - fermented from crushed fruits.
• Bread - where it helps dough rise by producing carbon dioxide.
• Other beverages - contributing to various fermentation processes.

Q5: What does yeast produce during respiration?
Ans: Yeast produces carbon dioxide during respiration. This process is essential for various applications:

• In baking, the gas creates bubbles that make dough rise.
• Yeast is also used in the production of alcohol and wine.
• It ferments sugars found in grains and fruits.

Q6: Tiny organisms which cannot be seen with the naked eyes are called
(a) microorganisms
(b) animals
(c) fungi
(d) bacteria
Ans: (a)
Explanation: Microorganisms are organisms that are too small to be seen with the naked eye. They include bacteria, viruses, fungi, protozoa, and other microscopic life forms.

Q7: Microorganisms are also known as
(a) yeast
(b) microbes
(c) viruses
(d) Amoeba
Ans: (b)
Explanation: "Microbes" is a common term used to refer to microorganisms. It's a shorter way of saying "microscopic organisms."

Q8: Fungus can be seen with a
(a) microscope
(b) telescope
(c) magnifying glass
(d) both (a) and (c)
Ans: (a)
Explanation: Fungi are microscopic organisms and cannot be seen clearly without the aid of a microscope. They include molds, yeasts, and mushrooms.

Q9: Microorganisms that causes disease are also kn
(a) pathogens
(b) fungi
(c) antigen
(d) microbes
Ans: (a)
Explanation: Pathogens are microorganisms, such as bacteria, viruses, and fungi, that can cause diseases in their hosts. They are responsible for various infectious diseases.

Q10: Pathogens are also called
(a) germs
(b) antigen
(c) antibody
(d) carrier
Ans: (a)
Explanation: "Germs" is a colloquial term often used to refer to disease-causing microorganisms or pathogens. It's a simple way to describe the microorganisms that can make people sick.

Q11: Bacteria, fungi, protozoa and _______ are the major four groups in which microorganisms are classified.
Ans: algae

Q12: Two microorganisms which live in symbiotic association in lichens are _______ and _______.
Ans: algae, fungus
Lichens are formed by the symbiotic relationship between algae and fungi, where algae provide food through photosynthesis while fungi offer protection and moisture.

Q13: We use a _______ to see the microorganisms.
Ans: microscope
A microscope is an essential tool that allows us to view small organisms that are not visible to the naked eye.

Q14: _______ are considered different from other microorganisms because they can multiply only by entering the host organisms.
Ans: Viruses
Viruses are unique as they cannot reproduce independently; they require a host cell to replicate.

Q15: The gas released during the preparation of bread is _______.
Ans: carbon dioxide
During the fermentation process, yeast converts sugars into alcohol and carbon dioxide, which causes the bread to rise.

Q16: Who discovered the vaccine for small pox?
Ans: Edward Jenner
Edward Jenner is credited with developing the first successful smallpox vaccine, which laid the foundation for immunology.

Q17: What is fermentation?
Ans: Fermentation is the process of conversion of food into alcohol.
Fermentation is a metabolic process that converts sugars into acids, gases, or alcohol, commonly used in food production.

Q18: Define refrigeration.
Ans: The storing of food products at the temperature of 0°C to 5°C is known as refrigeration.
Refrigeration slows down the growth of bacteria and preserves food by maintaining a low temperature.

Value-Based Questions

Q19: Seema got cough and cold badly. Her teacher asked her to take rest at home and use handkerchief while sneezing and coughing. She obeyed her teacher.

1. Why should we keep a handkerchief on nose and mouth while sneezing or coughing?
2. What are the modes of transfer of diseases from infected to healthy person?
3. Do you think Seema’s teacher decision was right? Why?
4. What value of Seema is shown here?

Ans:

1. We should keep a handkerchief on nose and mouth while sneezing or coughing because fine drop-lets carrying thousands of viruses or bacteria spread in the air.
2. Air, water, food, carriers and physical contact.
3. Yes, because cough and cold spreads through air and there are chances that other students may also get infected.
4. Seema is an obedient girl.

Q20: On Rahul’s birthday, his mother prepared many dishes for him. After having their meal, they found that many food items were left over. Rahul’s mother kept these leftovers in a air-tight container and refrigerate them.

1. What is food preservation?
2. What will happen to the food if it is not refrigerated?
3. What is the role of refrigeration in food preservation method?
4. What value of Rahul’s mother is shown here?

Ans:

1. The methods used for prevention of spoiling of food by the action of microbes is called food preservation.
2. The food will get spoil and emit bad smell with changed colour or taste.
3. Refrigeration retards or slow down the growth of microorganisms and enzyme activity on food. Thus, it prevents spoilage of food.
4. Rahul’s mother is intelligent, economical, have scientific aptitude towards preservation of food.