Class 9 Science MCQ Questions with Answers | Cotton Fibre, Plasma Membrane, Linear Motion, Density & SI Unit of Temperature

Chapter Information

Subject: Science

Class: 9

Chapters Covered:

• Improvement in Food Resources
• The Fundamental Unit of Life
• Motion
• Matter in Our Surroundings
• Force and Laws of Motion

Question Type: Multiple Choice Questions (MCQs)

Difficulty Level: Easy to Moderate

Based On: Latest NCERT Syllabus

Introduction

Class 9 Science introduces students to important concepts from Biology, Physics, and Chemistry that explain everyday phenomena and natural processes. Topics such as plant fibres, cell structure, motion, density, and temperature measurement help build a strong scientific foundation. This practice set provides original, NCERT-aligned explanations to improve conceptual understanding and exam readiness.

What You Will Learn

✔ Source of cotton fibre

✔ Properties of the plasma membrane

✔ Linear motion

✔ Density and its formula

✔ SI unit of temperature

Why This Topic Is Important?

These concepts are frequently asked in school examinations, CBSE and State Board assessments, Olympiads, and scholarship exams. Understanding these fundamentals also prepares students for advanced Science topics in higher classes.

Exam Relevance

These questions are useful for:

✔ CBSE Exams

✔ State Board Exams

✔ School Tests

✔ Unit Tests

✔ Half-Yearly Exams

✔ Annual Exams

✔ Olympiad Preparation

✔ Scholarship Examinations

Q1. Cotton comes from:

1. A) Fruit
2. B) Leaf
3. C) Root
4. D) Stem

Answer

Fruit

Concept

Cotton is a natural plant fibre obtained from the fruit of the cotton plant.

Explanation

Cotton fibres develop around the seeds inside the cotton fruit (boll). When the fruit matures, it bursts open, exposing the soft white fibres that are collected and processed to make yarn and fabric.

Exam Focus

Remember: Cotton fibre is obtained from the fruit (boll) of the cotton plant.

Q2. Plasma membrane is:

1. A) Rigid
2. B) Permeable
3. C) Selectively permeable
4. D) Impermeable

Answer

Selectively permeable

Concept

The plasma membrane controls the movement of substances into and out of the cell.

Explanation

The plasma membrane is selectively permeable, meaning it allows only certain substances to pass while restricting others. This selective transport helps maintain the internal environment of the cell.

Exam Focus

Remember: Plasma membrane = Selectively permeable membrane.

Q3. Motion in straight line:

1. A) Circular
2. B) Linear
3. C) Random
4. D) Oscillatory

Answer

Linear

Concept

Motion can be classified according to the path followed by an object.

Explanation

When an object moves along a straight path, the motion is called linear motion or rectilinear motion. Examples include a train moving on a straight track or a person walking along a straight road.

Exam Focus

Remember: Straight-line motion = Linear (Rectilinear) Motion.

Q4. Density =

1. A) Mass × Volume
2. B) Volume / Mass
3. C) Mass / Volume
4. D) None

Answer

$$\mathrm{\frac{Mass}{Volume}}$$

Concept

Density describes how much mass is contained in a given volume.

Explanation

Density is defined as the mass per unit volume of a substance. It is an important physical property used to compare materials and determine whether an object will float or sink in a liquid.

Formula

$$\rho=\frac{m}{V}$$

Where:

• $$\rho$$ = Density
• $$m$$ = Mass
• $$V$$ = Volume

Exam Focus

Remember:

$$\mathrm{Density=\frac{Mass}{Volume}}$$

Q5. SI unit of temperature:

1. A) Fahrenheit
2. B) Kelvin
3. C) Celsius
4. D) Joule

Answer

Kelvin

Concept

Temperature is an SI base quantity.

Explanation

The SI unit of temperature is Kelvin (K). Scientists use the Kelvin scale because it begins at absolute zero, the lowest possible temperature. Celsius and Fahrenheit are commonly used in daily life, but Kelvin is the standard SI unit.

Exam Focus

Remember: SI Unit of Temperature = Kelvin (K)

Important Formulas & Concepts

1. Cotton Fibre

• Natural plant fibre.
• Obtained from the fruit (boll) of the cotton plant.
• Widely used in the textile industry.

2. Plasma Membrane

Functions:

• Protects the cell.
• Controls the movement of substances.
• Is selectively permeable.

3. Linear Motion

• Motion along a straight line.
• Also called rectilinear motion.

Examples:

• Moving train on a straight track.
• A person walking in a straight path.

4. Density

Formula:

$$\rho=\frac{m}{V}$$

SI Unit:

$$\mathrm{kg/m^3}$$

5. SI Unit of Temperature

• Kelvin (K)
• SI base unit for temperature.

Related Practice Questions

1. From which part of the cotton plant is cotton fibre obtained?
2. Why is the plasma membrane called selectively permeable?
3. Define linear motion with one example.
4. Write the formula and SI unit of density.
5. Why is Kelvin used as the SI unit of temperature?

Mini Quiz Challenge

True or False

1. Cotton fibres are obtained from the fruit of the cotton plant.
2. The plasma membrane is completely impermeable.
3. Motion along a straight path is called linear motion.
4. Density is equal to mass divided by volume.
5. Kelvin is the SI unit of temperature.

Exam Tips

✔ Remember the source of natural fibres such as cotton.

✔ Revise the functions of the plasma membrane.

✔ Learn the difference between linear, circular, and oscillatory motion.

✔ Memorize the density formula and its SI unit.

✔ Do not confuse Celsius with the SI unit of temperature.

Quick Revision Notes

✔ Cotton fibre is obtained from the fruit (boll) of the cotton plant.

✔ Plasma membrane is selectively permeable.

✔ Straight-line motion is called linear motion.

✔ Density =

$$\rho=\frac{m}{V}$$

✔ SI Unit of Density =

$$\mathrm{kg/m^3}$$

✔ SI Unit of Temperature = Kelvin (K).

Common Mistakes Students Make

❌ Thinking cotton is obtained from the stem or leaves.

❌ Confusing permeable and selectively permeable membranes.

❌ Mixing up linear and circular motion.

❌ Writing density as volume divided by mass.

❌ Choosing Celsius instead of Kelvin as the SI unit.

Key Takeaways

• Cotton fibre is obtained from the fruit (boll) of the cotton plant.
• The plasma membrane is selectively permeable and regulates the movement of substances.
• Motion along a straight path is called linear motion.
• Density is the mass per unit volume of a substance.
• Kelvin (K) is the SI unit of temperature.

FAQs

1. From which part of the plant is cotton obtained?

Cotton fibre is obtained from the fruit (boll) of the cotton plant.

2. Why is the plasma membrane called selectively permeable?

Because it allows only specific substances to enter or leave the cell while restricting others.

3. What is linear motion?

Linear motion is the movement of an object along a straight line.

4. What is the formula for density?

$$\rho=\frac{m}{V}$$

where m is mass and V is volume.

5. What is the SI unit of temperature?

The SI unit of temperature is Kelvin (K).

NCERT Reference

Book: NCERT Science Class 9

Chapters Covered:

• Chapter 1 – Matter in Our Surroundings
• Chapter 5 – The Fundamental Unit of Life
• Chapter 8 – Motion
• Chapter 3 – Atoms and Molecules (Density concept used in measurements)
• Chapter 15 – Improvement in Food Resources (Cotton as a crop and fibre source)

Based On: Latest NCERT Curriculum (CBSE)