Class 8 Science – Chapter 3
Synthetic Fibres and Plastics
Step 4: Plastics and the Environment

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Why are Plastics Harmful to the Environment?

• Plastics are non-biodegradable.
• They do not decompose easily.
• They remain in soil and water for many years.
• Burning plastics releases poisonous gases.

Effects of Plastics on Living Beings

• Animals eat plastic waste and get sick.
• Plastic blocks drainage systems.
• Water bodies get polluted.
• Soil fertility decreases.

The 4R Principle

• Refuse – Say no to plastic bags.
• Reduce – Use less plastic.
• Reuse – Use plastic items again.
• Recycle – Convert waste plastic into new products.

Safer Alternatives to Plastics

• Cloth bags
• Paper bags
• Steel and glass containers
• Earthen pots

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🌱 Save Environment – Reduce Plastic Use

 

Class 8 Science – Chapter 3
Synthetic Fibres and Plastics
Step 3: Plastics – Types & Properties

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What are Plastics?

Plastics are synthetic materials made from polymers. They can be moulded into different shapes when heated.

Types of Plastics

1. Thermoplastics

Thermoplastics can be softened on heating and hardened on cooling. This process can be repeated many times.

• Examples: Polythene, PVC
• Used in toys, containers, bottles

2. Thermosetting Plastics

Thermosetting plastics do not soften on heating. Once moulded, they cannot be reshaped.

• Examples: Bakelite, Melamine
• Used in switches, handles, kitchenware

Properties of Plastics

• Lightweight
• Strong and durable
• Resistant to water and chemicals
• Bad conductor of heat and electricity

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⭐ Plastics are useful but harmful to the environment if misused

 

Class 8 Science – Chapter 3
Synthetic Fibres and Plastics
Step 2: Types of Synthetic Fibres

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1. Nylon

Nylon was the first fully synthetic fibre made by humans. It is very strong, elastic and lightweight.

• Used to make ropes, parachutes, fishing nets
• Used in socks, toothbrush bristles and seat belts

2. Polyester

Polyester fibres are strong, wrinkle-resistant and easy to wash. Terylene is a popular type of polyester.

• Used in dress materials
• Used to make bottles, curtains and carpets

3. Acrylic

Acrylic fibre looks like wool and is used as a substitute for wool.

• Used to make sweaters, blankets and shawls
• Cheaper than wool

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⭐ Different synthetic fibres are used for different purposes

 

Class 8 Science – Chapter 3
Synthetic Fibres and Plastics
Step 1: Introduction & Basic Concepts

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What are Fibres?

Fibres are thin, hair-like strands that are used to make fabrics. Examples: cotton, wool, silk, nylon.

Types of Fibres

• Natural Fibres – Obtained from plants or animals (cotton, wool, silk)
• Synthetic Fibres – Man-made fibres prepared from chemicals

What are Synthetic Fibres?

Synthetic fibres are fibres made by humans using chemical substances. These fibres are prepared from petrochemicals.

Examples of Synthetic Fibres

• Nylon
• Polyester
• Acrylic

Why Synthetic Fibres are Popular?

• Strong and durable
• Easy to wash and dry
• Wrinkle-resistant
• Less expensive

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⭐ Synthetic fibres are widely used in our daily life

 

Class 8 Science – Chapter 2
Microorganisms: Friend and Foe
Important Exam Questions (VSA / SA / LA)

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A. Very Short Answer Questions (1 Mark)

1. What are microorganisms?
2. Name one nitrogen-fixing bacterium.
3. Which microorganism is used in making curd?
4. What is vaccination?
5. Name one disease caused by virus.

B. Short Answer Questions (2–3 Marks)

1. How do microorganisms help in agriculture?
2. What is pasteurisation? Why is it important?
3. Why should antibiotics not be taken without medical advice?
4. How do microorganisms spoil food?
5. What are vaccines? How do they work?

C. Long Answer Questions (5 Marks)

1. Explain the useful roles of microorganisms in our daily life.
2. Describe different methods of food preservation with examples.
3. How do microorganisms cause diseases? Write preventive measures.
4. Explain nitrogen fixation and its importance for plants.

D. Case-Based / Application Questions

1. Ravi fell ill after drinking unboiled milk. (a) Which microorganisms may be responsible? (b) How could this have been prevented?
2. Why are vaccines given at an early age?

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⭐ These questions are HIGHLY IMPORTANT for exams

 

Class 8 Science – Chapter 2
Microorganisms: Friend and Foe
Worksheet – FULL Answers (Step-by-Step)

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Section A – Fill in the Blanks (Answers)

1. Microorganisms that fix nitrogen in soil are called Rhizobium.
2. The process of heating milk to kill germs is called pasteurisation.
3. Yeast is used in the production of bread and alcohol.
4. Cholera is caused by bacteria.
5. Vaccines help our body to develop immunity against diseases.

Section B – True or False (Answers)

1. All microorganisms are harmful – False
2. Viruses can reproduce only inside a living cell – True
3. Antibiotics are effective against viral diseases – False
4. Microorganisms help in making curd – True
5. Food preservation prevents the growth of microorganisms – True

Section C – Very Short Answer (Answers)

1. Typhoid is a disease caused by bacteria.
2. Yeast is used in bread making.
3. Vaccination is the process of giving vaccines to protect the body from diseases.
4. Rhizobium is a nitrogen-fixing bacterium.

Section D – Short Answer (Answers)

1. Uses of microorganisms:
   • Help in making curd, bread and alcohol.
   • Used in medicines like antibiotics.
2. Antibiotics should not be taken without a doctor’s advice because improper use can make bacteria resistant and reduce the medicine’s effectiveness.
3. Microorganisms spoil food by growing on it and releasing harmful substances, causing bad smell, taste and food poisoning.

Section E – Long Answer (Answers)

1. Role of microorganisms in agriculture:
   • Fix nitrogen in soil and increase fertility.
   • Used to make biofertilisers.
   • Help in decomposition of organic matter.
2. Methods of food preservation:
   • Refrigeration
   • Drying
   • Salting and sugaring
   • Pasteurisation
   • Use of preservatives

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✅ Practice Answers = Strong Exam Preparation

 

Class 8 Science – Chapter 2
Microorganisms: Friend and Foe
Worksheet – Practice Questions

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Section A – Fill in the Blanks

1. Microorganisms that fix nitrogen in soil are called __________.
2. The process of heating milk to kill germs is called __________.
3. Yeast is used in the production of __________.
4. Cholera is caused by __________.
5. Vaccines help our body to develop __________ against diseases.

Section B – True or False

1. All microorganisms are harmful. ( )
2. Viruses can reproduce only inside a living cell. ( )
3. Antibiotics are effective against viral diseases. ( )
4. Microorganisms help in making curd. ( )
5. Food preservation prevents the growth of microorganisms. ( )

Section C – Very Short Answer

1. Name any one disease caused by bacteria.
2. Which microorganism is used in bread making?
3. What is vaccination?
4. Name one nitrogen-fixing bacterium.

Section D – Short Answer

1. Write two uses of microorganisms in our daily life.
2. Why should antibiotics not be taken without a doctor’s advice?
3. How do microorganisms spoil food?

Section E – Long Answer

1. Explain the role of microorganisms in agriculture.
2. Describe different methods of food preservation.

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📝 Practice Regularly for Exam Success