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Tamil Nadu (TNBSE)Class 7 Science★ 6-10 marks in the TN Class 7 Term 3 exam through book-back MCQs, fill-ups and short answers

Polymer Chemistry

Samacheer Kalvi (TN State Board) Class 7 Science — Term 3 Chapter 3, Polymer Chemistry. Natural and synthetic fibres (cotton, wool, silk, rayon, nylon, acrylic), the properties and types of plastics (thermoplastic and thermosetting), biodegradable and non-biodegradable materials, and the uses of plastics, with the actual book-back questions, common mistakes and quick revision.

⏱ 15 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Differentiate natural and synthetic fibres
2Identify rayon, nylon and acrylic and their properties
3Describe the properties and types of plastics
4Differentiate thermoplastics and thermosetting plastics
5Explain biodegradable and non-biodegradable materials

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Why this chapter matters

Polymer Chemistry explains the fibres and plastics we use every day and the pollution plastics cause. Natural vs synthetic fibres, types of plastics and biodegradability are directly tested book-back content in the TN Class 7 Term 3 exam.

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A 5-minute refresher here will save you 30 minutes of confusion below.

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Chapter 3 — Matter Around Us

Molecules and materials.

Polymer Chemistry — Class 7 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 7 Science, Term 3 — Chapter 3. Fibres, plastics and polymers.

1. About this chapter

This chapter covers natural and synthetic fibres, plastics and their types and properties, and biodegradable and non-biodegradable materials.

2. Fibres

A polymer is a large molecule made of many small repeating units.
Natural fibres come from plants or animals — cotton (plant), wool and silk (animal). A natural fibre burns when placed in a flame.
Synthetic (man-made) fibres are made by chemical processes — rayon, nylon, acrylic, terylene.
- Rayon is the first man-made fibre; it is similar to silk and is made by the chemical treatment of wood pulp.
- Nylon is the strongest fibre. Acrylic resembles wool. PET stands for Polyethylene terephthalate.

3. Plastics

All plastics are polymers. Plastics are light, strong, durable and waterproof; they are not soluble in water (so being water-soluble is not a property of plastics).
Types of plastics:
- Thermoplastics soften on heating and can be reshaped (polythene, PVC).
- Thermosetting plastics set permanently and cannot be reshaped — e.g. melamine, bakelite.
Use: plastics have many uses, including medical ones such as blood bags.

4. Biodegradable and non-biodegradable

Biodegradable materials are broken down by nature (paper, cotton, food waste).
Non-biodegradable materials are not broken down — plastic is non-biodegradable, which makes it a serious pollutant.

5. Worked examples

Example 1. Which is the first man-made fibre? Rayon.

Example 2. Which fibre is the strongest? Nylon.

Example 3. Is plastic biodegradable? No — it is non-biodegradable.

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

The first man-made fibre is — (a) nylon / (b) rayon. Ans: (b) rayon.
The strongest fibre is — (a) nylon / (b) cotton. Ans: (a) nylon.
A natural fibre among these is — (a) cotton / (b) nylon. Ans: (a) cotton.
A thermosetting plastic is — (a) polythene / (b) melamine. Ans: (b) melamine.
The material that is non-biodegradable is — (a) paper / (b) plastic. Ans: (b) plastic.
The property that is not of plastics is — (a) durable / (b) soluble in water. Ans: (b) soluble in water.

II. Fill in the blanks 7. Rayon is a fibre obtained by the chemical treatment of wood pulp. 8. The fibre similar to silk in appearance is rayon. 9. PET is the acronym for Polyethylene terephthalate.

III. Answer briefly 10. Differentiate thermoplastics and thermosetting plastics. — Thermoplastics soften on heating and can be reshaped; thermosetting plastics set permanently and cannot be reshaped. 11. Give one good use of plastic. — Making blood bags (and many other items).

7. Common mistakes

Mistake: Calling rayon a natural fibre. Fix: Rayon is a man-made (synthetic) fibre — though made from natural wood pulp.
Mistake: Saying plastics dissolve in water. Fix: Plastics are not soluble in water.
Mistake: Thinking all plastics can be remoulded. Fix: Only thermoplastics can; thermosetting plastics (melamine) cannot.

8. Quick revision

Term 3 · Ch 3 · polymer chemistry.
Natural fibres: cotton (plant), wool, silk (animal); burn in a flame. Synthetic: rayon (first, from wood pulp, silk-like), nylon (strongest), acrylic (wool-like).
All plastics are polymers (durable, waterproof, not water-soluble); thermoplastics reshape, thermosetting (melamine) do not.
Plastic is non-biodegradable (a pollutant); used even for blood bags. PET = Polyethylene terephthalate.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Natural fibres

cotton (plant), wool & silk (animal); burn in flame

From living sources.

Synthetic fibres

rayon (first, wood pulp, silk-like), nylon (strongest), acrylic (wool-like)

Man-made.

Plastics

all polymers; durable, waterproof, not water-soluble

Thermoplastic vs thermosetting.

Biodegradability

plastic is non-biodegradable

A pollutant.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Calling rayon a natural fibre

✓ Rayon is a man-made (synthetic) fibre, though made from natural wood pulp.

WATCH OUT

✗ Saying plastics dissolve in water

✓ Plastics are not soluble in water.

WATCH OUT

✗ Thinking all plastics can be remoulded

✓ Only thermoplastics can; thermosetting plastics (melamine) cannot.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on rayon, nylon, cotton, melamine, plastic and properties.

Questions

Fill in the blanks

Wood pulp, silk-like fibre and PET.

Questions

Answer briefly

Thermoplastic vs thermosetting; uses of plastic.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

The first man-made fibre is ____.

▶ Show solution

rayon.

Q2EASY· MCQ

The strongest fibre is ____.

▶ Show solution

nylon.

Q3EASY· MCQ

A thermosetting plastic is ____.

▶ Show solution

melamine.

Q4EASY· MCQ

Which property is NOT a property of plastics?

▶ Show solution

Soluble in water (plastics are not water-soluble).

Q5EASY· Fill in the blanks

PET is the acronym for ____.

▶ Show solution

Polyethylene terephthalate.

Q6MEDIUM· Answer briefly

Differentiate thermoplastics and thermosetting plastics.

▶ Show solution

Thermoplastics soften on heating and can be remoulded (polythene, PVC), while thermosetting plastics set permanently and cannot be reshaped (melamine, bakelite).

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Term 3 Chapter 3 of Samacheer Kalvi Class 7 Science.
•Natural fibres: cotton (plant), wool and silk (animal); they burn in a flame.
•Synthetic fibres: rayon (first, from wood pulp, silk-like), nylon (strongest), acrylic (wool-like).
•All plastics are polymers — durable, waterproof and not soluble in water.
•Thermoplastics can be remoulded; thermosetting plastics (melamine) cannot.
•Plastic is non-biodegradable (a pollutant); PET = Polyethylene terephthalate.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 6-10 marks across book-back MCQ, fill-ups and short answers

Question type	Marks each	Typical count	What it tests
MCQ / Fill	1	5-7	Fibres, plastics, biodegradability
Short Answer	2	1-2	Plastic types and uses

Prep strategy

Separate natural and synthetic fibres
Remember rayon = first, nylon = strongest
Note plastics are not water-soluble
Distinguish thermoplastic and thermosetting

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Clothing

Fibres like cotton, nylon and rayon make our clothes.

Medicine

Plastics are used for blood bags and syringes.

Environment

Understanding biodegradability guides waste management.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Classify each fibre as natural or synthetic
Quote rayon (first) and nylon (strongest)
Note plastics are not water-soluble
Distinguish the two plastic types

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Suggest three ways to reduce plastic pollution.
Compare the properties of cotton and nylon for making clothes.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 7 Term 3 ExamHigh

NMMS / Foundation ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

Although its raw material (wood pulp) is natural, rayon is produced by chemically treating and reforming that material, so the fibre itself is manufactured — making it a man-made (semi-synthetic) fibre.

Plastic is non-biodegradable, so it does not break down naturally and accumulates in the soil and oceans for hundreds of years, harming wildlife and the environment.

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