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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 including chemical preservatives, salting, sugaring, oil, vinegar, heat treatment, and proper storage.
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Chapter Information
Subject: Science
Class: 8
Chapter: Microorganisms: Friend and Foe
Question Type: Multiple Choice Questions (MCQs)
Practice Set: 4
Difficulty Level: Moderate
Based On: NCERT Syllabus
Introduction
Microorganisms can grow and multiply in food under favourable conditions. Their growth may cause food to spoil and become unsuitable or unsafe for consumption.
To protect food from microbial growth, different food preservation methods are used. These methods work by creating conditions that make it difficult for microorganisms to grow.
Common preservation methods include chemical preservatives, salting, sugaring, oil and vinegar, heat treatment, drying, and refrigeration.
This Practice Set 4 focuses on important methods of food preservation and helps students understand how these methods reduce or prevent microbial growth.
What You Will Learn
✔ Food spoilage
✔ Food preservation
✔ Chemical preservatives
✔ Salting
✔ Sugaring
✔ Use of oil and vinegar
✔ Heat treatment
✔ Pasteurisation
✔ Refrigeration
✔ Importance of proper food storage
Why This Topic Is Important
Food preservation is closely connected with everyday life. Pickles, jams, sauces, milk, vegetables, and many other food products are preserved using different techniques.
These methods help increase the shelf life of food and reduce spoilage caused by microorganisms.
Understanding the scientific principle behind food preservation helps students understand why different foods require different preservation methods.
5 MCQs with Answers and Useful Details
Q1. Which of the following is commonly used as a chemical preservative in packaged food?
A) Sodium benzoate
B) Sodium chloride only
C) Sand
D) Starch
Answer:
A) Sodium benzoate
Useful Detail
Sodium benzoate is a chemical preservative used in some food products such as jams, squashes, and fruit juices.
Chemical preservatives help prevent or slow the growth of microorganisms and therefore increase the shelf life of certain foods.
The type and amount of preservative used in food products are regulated for safety.
Correct Answer: A) Sodium benzoate
Q2. Why does adding salt help preserve certain foods?
A) It increases the amount of water available to microorganisms.
B) It helps reduce the availability of water for microbial growth.
C) It immediately converts food into sugar.
D) It increases microbial reproduction.
Answer:
B) It helps reduce the availability of water for microbial growth.
Useful Detail
Salting is a traditional method of food preservation.
A high concentration of salt reduces the availability of water that many microorganisms need for growth. This helps slow down or prevent microbial multiplication.
Salt is used to preserve products such as pickles, fish, and certain vegetables.
Correct Answer: B) It helps reduce the availability of water for microbial growth.
Q3. Why is a high concentration of sugar used in jams and jellies?
A) It encourages microbial growth.
B) It reduces the availability of water for microorganisms.
C) It increases the temperature of the food.
D) It removes all nutrients from the food.
Answer:
B) It reduces the availability of water for microorganisms.
Useful Detail
A high concentration of sugar is used in foods such as jams, jellies, and fruit preserves.
The concentrated sugar solution reduces the availability of water required by many microorganisms for growth. This helps prevent spoilage and increases the shelf life of the food.
Thus, sugaring is an important traditional food preservation technique.
Correct Answer: B) It reduces the availability of water for microorganisms.
Q4. Which method is commonly used to preserve pickles?
A) Adding oil and salt
B) Adding only water
C) Keeping them uncovered
D) Increasing moisture
Answer:
A) Adding oil and salt
Useful Detail
Pickles are commonly preserved using salt, oil, and sometimes vinegar, depending on the recipe.
Salt helps reduce the availability of water for microorganisms, while oil can prevent contact with air and create conditions that make microbial growth more difficult.
Properly prepared and stored pickles can therefore remain usable for a longer period.
Correct Answer: A) Adding oil and salt
Q5. What is the purpose of pasteurisation of milk?
A) To increase harmful microorganisms
B) To destroy many harmful microorganisms by controlled heating
C) To turn milk into curd immediately
D) To remove all water from milk
Answer:
B) To destroy many harmful microorganisms by controlled heating
Useful Detail
Pasteurisation is a method used to preserve milk.
In this process, milk is heated to a suitable temperature for a specific period and then cooled rapidly. This treatment destroys many harmful microorganisms and helps increase the shelf life of milk.
Pasteurisation does not mean that milk becomes completely free of all microorganisms.
Correct Answer: B) To destroy many harmful microorganisms by controlled heating
Important Formulas & Concepts
Science Chapter 2 does not contain mathematical formulas. Important scientific concepts are given below.
1. Food Preservation
Food preservation involves methods used to prevent or slow down spoilage and extend the shelf life of food.
2. Chemical Preservatives
Certain chemicals are added to food to prevent microbial growth and increase shelf life.
3. Sodium Benzoate
Sodium benzoate is a commonly used chemical preservative in some food products.
4. Salting
Salt helps preserve food by reducing the availability of water needed by many microorganisms.
5. Sugaring
High concentrations of sugar reduce water availability and help prevent microbial growth.
6. Oil
Oil can help preserve certain foods by limiting contact with air and creating conditions less favourable for many microorganisms.
7. Vinegar
Vinegar creates an acidic environment that helps prevent the growth of many microorganisms and is commonly used in pickling.
8. Pasteurisation
Pasteurisation involves controlled heating followed by rapid cooling to destroy many harmful microorganisms in milk.
9. Refrigeration
Low temperatures slow down the growth and multiplication of many microorganisms.
10. Shelf Life
Shelf life refers to the period during which food remains suitable for consumption when stored under appropriate conditions.
Related Practice Questions
Q1. What is food preservation?
Q2. How does salt help preserve food?
Q3. Why is sugar added to jams and jellies?
Q4. What is pasteurisation?
Q5. How does refrigeration help preserve food?
Mini Quiz Challenge
Try answering these questions within 60 seconds.
Q1. Which chemical is commonly used as a food preservative?
A) Sodium benzoate
B) Calcium carbonate
C) Oxygen
D) Starch
Q2. Which method is commonly used to preserve fish?
A) Salting
B) Adding plain water
C) Increasing moisture
D) Keeping it in sunlight without drying
Q3. High sugar concentration helps preserve:
A) Jams and jellies
B) Fresh drinking water
C) Raw milk only
D) Fresh leaves
Q4. Pasteurisation is commonly associated with:
A) Milk
B) Sand
C) Wood
D) Glass
Q5. Refrigeration generally:
A) Speeds up microbial growth
B) Slows down microbial growth
C) Removes all microorganisms
D) Converts bacteria into fungi
Exam Tips
✔ Learn the meaning of food preservation.
✔ Remember sodium benzoate as an example of a chemical preservative.
✔ Understand how salting reduces microbial growth.
✔ Remember that high sugar concentration helps preserve jams and jellies.
✔ Learn the role of oil and vinegar in pickling.
✔ Remember that pasteurisation is commonly used for milk.
✔ Do not confuse pasteurisation with complete sterilisation.
✔ Refrigeration slows the growth of many microorganisms.
✔ Learn examples of foods preserved by different methods.
✔ Understand that preservation methods mainly create conditions unfavourable for microbial growth.
Quick Revision Notes
✔ Food Preservation: Preventing or slowing food spoilage.
✔ Chemical Preservatives: Chemicals used to inhibit microbial growth.
✔ Sodium Benzoate: A commonly used chemical preservative.
✔ Salting: Uses salt to reduce water availability.
✔ Sugaring: High sugar concentration reduces water availability.
✔ Oil: Helps preserve foods such as pickles.
✔ Vinegar: Creates acidic conditions that help prevent microbial growth.
✔ Pasteurisation: Controlled heating followed by rapid cooling.
✔ Refrigeration: Low temperature slows microbial growth.
✔ Shelf Life: Period for which food remains suitable for use under proper storage conditions.
Common Mistakes Students Make
❌ Thinking preservatives encourage microbial growth.
❌ Thinking adding salt provides more water for microorganisms.
❌ Forgetting why sugar helps preserve jams.
❌ Thinking pasteurisation completely removes every microorganism.
❌ Confusing pasteurisation with boiling milk for an unlimited time.
❌ Thinking refrigeration kills all microorganisms.
❌ Assuming oil alone is the only preservation method used for pickles.
❌ Forgetting that vinegar provides acidic conditions.
Key Takeaways
✔ Food preservation reduces or slows microbial spoilage.
✔ Chemical preservatives can increase the shelf life of certain foods.
✔ Salt helps preserve food by reducing water availability.
✔ Sugar helps preserve jams and jellies.
✔ Oil and vinegar are commonly used in pickling.
✔ Pasteurisation is an important method of milk preservation.
✔ Refrigeration slows the growth of many microorganisms.
✔ Different foods require different preservation methods.
FAQs
Q. What is food preservation?
Answer:
Food preservation is the process of preventing or slowing the growth of microorganisms and other causes of spoilage so that food remains usable for a longer period.
Q. How does salt preserve food?
Answer:
A high concentration of salt reduces the availability of water needed by many microorganisms, thereby slowing their growth.
Q. Why is sugar used in jams and jellies?
Answer:
A high concentration of sugar reduces the availability of water for microorganisms and helps prevent spoilage.
Q. What is pasteurisation?
Answer:
Pasteurisation is a controlled heating process used mainly for milk, followed by rapid cooling, to destroy many harmful microorganisms.
Q. Does refrigeration kill all microorganisms?
Answer:
No. Refrigeration mainly slows down the growth and multiplication of many microorganisms. It does not necessarily kill all microorganisms.
Conclusion
Class 8 Science Chapter 2 – Microorganisms: Friend and Foe Practice Set 4 focuses on the important topic of food preservation.
Students revised chemical preservatives, salting, sugaring, oil, vinegar, pasteurisation, refrigeration, and the role of these methods in controlling microbial growth.
Understanding food preservation methods helps students connect textbook concepts with common foods and practices used in everyday life.
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- Class 8 Science Chapter 2 Microorganisms Friend and Foe part3
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- Class 8 Science Chapter 2 Microorganisms Friend and Foe part-1
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