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Practice Class 8 Science Chapter 2 Microorganisms: Friend and Foe MCQ Questions with Answers and Useful Details based on the NCERT syllabus. Revise food preservation methods, pasteurisation, chemical preservatives, salting, sugaring, and oil and vinegar preservation.
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chapter Information
Subject: Science
Class: 8
Chapter: Microorganisms: Friend and Foe
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 9
Difficulty Level: Moderate to Difficult
Based On: NCERT Syllabus
Introduction
Microorganisms can multiply rapidly under favourable conditions and may cause food spoilage. To protect food from harmful microorganisms and increase its storage life, different methods of food preservation are used.
Common preservation methods include chemical preservation, salting, sugaring, oil and vinegar, refrigeration, and pasteurisation. These methods create conditions that slow down or prevent the growth of microorganisms.
Understanding food preservation is an important part of the chapter because it connects the activity of microorganisms with everyday practices used at home and in the food industry.
This Practice Set 9 focuses on different methods of food preservation and their scientific basis.
What You Will Learn
✔ Food preservation
✔ Chemical preservatives
✔ Sodium benzoate
✔ Salting
✔ Sugaring
✔ Oil and vinegar
✔ Pasteurisation
✔ Refrigeration
✔ Prevention of microbial growth
✔ Food storage
Why This Topic Is Important
Food provides nutrients that can also support the growth of microorganisms. If food is stored under favourable conditions, microorganisms can multiply and cause spoilage.
Food preservation helps delay spoilage and extend shelf life.
Many preservation methods are based on controlling conditions such as moisture, temperature, acidity, or the availability of nutrients. Understanding these methods helps students connect textbook concepts with everyday examples such as pickles, jams, milk, and packaged foods.
5 MCQs with Answers and Useful Details
Q1. Which chemical is commonly used as a chemical preservative for certain foods?
A) Sodium benzoate
B) Sodium chloride only
C) Calcium carbonate
D) Copper sulphate
Answer:
A) Sodium benzoate
Useful Detail
Sodium benzoate is a chemical preservative used in certain food products such as sauces, squashes, and jams.
It helps prevent or slow the growth of microorganisms and therefore increases the shelf life of food.
Chemical preservatives must be used in appropriate quantities according to food-safety regulations.
Correct Answer: A) Sodium benzoate
Q2. Why is salt used in preserving certain foods?
A) It encourages rapid microbial growth.
B) It helps prevent microbial growth by reducing the availability of water.
C) It increases the temperature of food.
D) It converts food directly into protein.
Answer:
B) It helps prevent microbial growth by reducing the availability of water.
Useful Detail
Salting is a traditional method of food preservation.
High concentrations of salt make the environment less favourable for the growth of many microorganisms by reducing the availability of water.
Salt is used for preserving foods such as fish, meat, and some vegetables.
Correct Answer: B) It helps prevent microbial growth by reducing the availability of water.
Q3. Why is a high concentration of sugar used in making jams and jellies?
A) It promotes microbial multiplication.
B) It helps prevent microbial growth by reducing available water.
C) It increases the number of bacteria.
D) It converts sugar into salt.
Answer:
B) It helps prevent microbial growth by reducing available water.
Useful Detail
A high concentration of sugar helps preserve jams and jellies.
Sugar reduces the amount of water available for microorganisms, making it difficult for many microorganisms to grow.
This is why properly prepared jams and jellies can remain usable for a relatively long time when stored appropriately.
Correct Answer: B) It helps prevent microbial growth by reducing available water.
Q4. Which method is commonly used to preserve milk for a longer period by heating it and then rapidly cooling it?
A) Pasteurisation
B) Salting
C) Sugaring
D) Drying
Answer:
A) Pasteurisation
Useful Detail
Pasteurisation is a method used to make milk safer and extend its shelf life.
Milk is heated to a suitable temperature for a specific period and then rapidly cooled. This process reduces harmful microorganisms without completely sterilising the milk.
The method is named after Louis Pasteur, whose work contributed greatly to the development of this technique.
Correct Answer: A) Pasteurisation
Q5. Which combination is commonly used for preserving pickles?
A) Oil and vinegar
B) Water and fresh milk
C) Only plain water
D) Fresh fruit juice without any treatment
Answer:
A) Oil and vinegar
Useful Detail
Oil and vinegar are commonly used in the preservation of pickles.
Oil can prevent exposure to air, while the acidic nature of vinegar creates conditions that are less favourable for many microorganisms.
Salt and spices are also commonly used in traditional pickle preparation.
These methods help delay microbial spoilage and increase the storage life of pickles.
Correct Answer: A) Oil and vinegar
Important Formulas & Concepts
Science Chapter 2 does not contain mathematical formulas. Important scientific concepts are given below.
1. Food Preservation
Food preservation refers to methods used to prevent or slow food spoilage caused by microorganisms.
2. Chemical Preservatives
Certain chemicals are added to foods to inhibit microbial growth and increase shelf life.
3. Sodium Benzoate
Sodium benzoate is a commonly used chemical preservative in certain food products.
4. Salting
Salt helps preserve food by making conditions less favourable for microbial growth.
5. Sugaring
High concentrations of sugar reduce the availability of water for microorganisms and help preserve foods such as jams.
6. Oil and Vinegar
Oil and vinegar are commonly used in pickling to create conditions that inhibit the growth of many microorganisms.
7. Pasteurisation
Pasteurisation involves controlled heating followed by rapid cooling, commonly used for milk.
8. Refrigeration
Low temperature slows the growth and multiplication of many microorganisms.
9. Shelf Life
Shelf life is the period during which food remains suitable for consumption when stored under recommended conditions.
10. Microbial Spoilage
Microbial spoilage occurs when microorganisms grow in food and cause undesirable changes in its quality, taste, smell, or safety.
Related Practice Questions
Q1. What is food preservation?
Q2. Why is sodium benzoate added to some foods?
Q3. How does salting help preserve food?
Q4. What is pasteurisation?
Q5. Why are oil and vinegar used in pickles?
Mini Quiz Challenge
Try answering these questions within 60 seconds.
Q1. Which is a chemical preservative?
A) Sodium benzoate
B) Sugar
C) Salt
D) Oil
Q2. Which method is commonly used for preserving jams?
A) Sugaring
B) Freezing only
C) Washing with water
D) Keeping them uncovered
Q3. Pasteurisation is commonly associated with:
A) Milk
B) Rocks
C) Soil
D) Metals
Q4. Which method is commonly used in pickle preservation?
A) Oil and vinegar
B) Plain water
C) Fresh milk
D) Uncovered storage
Q5. What is the main purpose of food preservation?
A) To encourage spoilage
B) To delay microbial spoilage
C) To increase harmful bacteria
D) To remove all nutrients
Exam Tips
✔ Remember sodium benzoate as a chemical preservative.
✔ Learn that salt helps preserve food by reducing water availability.
✔ Remember the role of high sugar concentration in preserving jams and jellies.
✔ Learn the basic steps of pasteurisation.
✔ Remember that pasteurisation is commonly used for milk.
✔ Revise the role of oil and vinegar in pickles.
✔ Understand that preservation usually slows microbial growth rather than removing every microorganism.
✔ Learn examples associated with each preservation method.
✔ Do not confuse pasteurisation with complete sterilisation.
✔ Connect food preservation methods with the conditions required for microbial growth.
Quick Revision Notes
✔ Food Preservation: Preventing or delaying food spoilage.
✔ Sodium Benzoate: Chemical preservative used in certain food products.
✔ Salting: Uses salt to create conditions less favourable for microbial growth.
✔ Sugaring: High sugar concentration reduces water availability for microorganisms.
✔ Pickling: Often uses oil, vinegar, salt, and spices.
✔ Pasteurisation: Controlled heating followed by rapid cooling.
✔ Milk: Commonly preserved using pasteurisation.
✔ Refrigeration: Low temperature slows microbial growth.
✔ Shelf Life: Period for which food remains suitable under recommended storage conditions.
✔ Microbial Spoilage: Food deterioration caused by microbial growth.
Common Mistakes Students Make
❌ Thinking preservation means killing every microorganism.
❌ Confusing sodium benzoate with common salt.
❌ Forgetting why high concentrations of salt or sugar help preserve food.
❌ Thinking pasteurisation completely sterilises milk.
❌ Confusing pasteurisation with refrigeration.
❌ Forgetting that vinegar provides an acidic environment.
❌ Thinking oil itself is a chemical preservative.
❌ Assuming preserved food can never spoil.
Key Takeaways
✔ Food preservation delays microbial spoilage.
✔ Sodium benzoate is a chemical preservative used in certain foods.
✔ Salt helps preserve food by reducing water availability.
✔ High concentrations of sugar help preserve jams and jellies.
✔ Oil and vinegar are commonly used in pickle preservation.
✔ Pasteurisation is commonly used to preserve milk.
✔ Refrigeration slows the growth of many microorganisms.
✔ Proper storage is important even after preservation.
FAQs
Q. What is food preservation?
Answer:
Food preservation is the process of preventing or slowing the growth of microorganisms and other causes of food spoilage so that food remains usable for a longer period.
Q. Why is sodium benzoate used in food?
Answer:
Sodium benzoate is used as a chemical preservative in certain foods because it helps inhibit the growth of microorganisms.
Q. How does salt preserve food?
Answer:
High concentrations of salt make less water available to microorganisms, making their growth more difficult.
Q. What is pasteurisation?
Answer:
Pasteurisation is a method in which milk is heated to a suitable temperature for a specific time and then rapidly cooled to reduce harmful microorganisms and improve shelf life.
Q. Why are jams preserved with sugar?
Answer:
A high concentration of sugar reduces the availability of water needed by many microorganisms, thereby helping prevent microbial growth.
Conclusion
Class 8 Science Chapter 2 – Microorganisms: Friend and Foe focuses on important methods used to prevent food spoilage.
Students revised chemical preservatives, sodium benzoate, salting, sugaring, oil and vinegar, pasteurisation, refrigeration, and microbial spoilage.
These concepts explain how scientific knowledge about microorganisms is applied in everyday food storage and preservation.
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