CBSE Class 9 Science Chapter 5: The Fundamental Unit of Life NCERT Solutions

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NCERT Solutions PDF Class 9 PDF

This section provides detailed NCERT Solutions for Class 9 Science, Chapter 5: The Fundamental Unit of Life. It covers essential concepts such as the discovery of cells by Robert Hooke, the reasons why cells are considered the basic structural and functional units of all living organisms, and the mechanisms by which substances like carbon dioxide and water move across the selectively permeable plasma membrane. The solutions explain diffusion and osmosis, highlighting how the cell membrane regulates the passage of materials. These solutions are designed to help students grasp the fundamental principles of cell biology and prepare effectively for their exams.

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Quick info

BoardCBSE
ClassClass 9
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 5: The Fundamental Unit of Life

Chapter summary

Chapter 5, 'The Fundamental Unit of Life,' focuses on the cell as the basic building block of life. These NCERT Solutions explain the historical discovery of cells, the significance of the cell's structure and function, and the processes of diffusion and osmosis governing substance transport across the plasma membrane. The solutions clarify the selective permeability of the cell membrane, aiding students in understanding cellular processes.

Learning outcomes

  • Understand the discovery of cells and the scientist credited with it.
  • Explain why the cell is considered the fundamental structural and functional unit of life.
  • Describe the process of diffusion for gas exchange in cells.
  • Explain the concept of osmosis and its role in water movement across the cell membrane.
  • Define and explain the selective permeability of the plasma membrane.

Topics covered

Paper topics

  • Cell Discovery
  • Robert Hooke
  • Structural Unit of Life
  • Functional Unit of Life
  • Plasma Membrane
  • Selectively Permeable Membrane
  • Diffusion
  • Osmosis
  • Movement of CO2
  • Movement of Water

Important topics

  • Cell as the Fundamental Unit of Life
  • Role of Plasma Membrane
  • Diffusion and Osmosis
  • Selective Permeability

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Questions and Solutions

Question 1

Who discovered cells and how?
Solution: Cells were first discovered in the year 1665 by an English botanist named Robert Hooke. He made this discovery by examining a thin slice of cork under a simple, early version of a microscope that he himself had built.

Question 2

Why is the cell called the structural and functional unit of life?
Solution: The cell is referred to as the fundamental structural and functional unit of life because it serves as the basic building block for all living organisms, much like bricks form a building. Furthermore, each cell is capable of performing all the essential activities necessary for life, such as metabolism, growth, and reproduction. The specific shape and size of a cell are often related to the particular function it performs within the organism.

Question 1

How do substances like CO<sub>2</sub> and water move in and out of the cell? Discuss.
Solution: The movement of substances into and out of the cell is regulated by the plasma membrane, which acts as a selectively permeable barrier.

Movement of CO<sub>2</sub>: Carbon dioxide (CO<sub>2</sub>) is a waste product of cellular respiration and is typically present in a higher concentration inside the cell than outside. CO<sub>2</sub> moves out of the cell from the region of higher concentration to the region of lower concentration, following the principle of diffusion. Conversely, oxygen (O<sub>2</sub>) enters the cell via diffusion when its concentration is lower inside the cell compared to the surroundings.

Movement of Water: Water moves across the plasma membrane from an area where it is in higher concentration to an area where it is in lower concentration. This specific type of water movement through a semi-permeable membrane is known as osmosis. The rate and direction of water movement are influenced by the concentration of dissolved substances in the water.

Question 2

Why is the plasma membrane called a selectively permeable membrane?
Solution: The plasma membrane is termed selectively permeable because it does not allow all substances to pass through it freely. Instead, it controls which substances can enter or leave the cell, allowing some materials to pass while restricting the movement of others. This selective regulation is crucial for maintaining the cell's internal environment and carrying out its functions.

Common mistakes

  • Confusing diffusion and osmosis.
  • Not fully explaining the 'selectively permeable' nature of the plasma membrane.
  • Incomplete understanding of why cells are called structural and functional units.

Revision tips

  • Review Robert Hooke's discovery and the primitive microscope used.
  • Clearly articulate the dual role of cells as structural and functional units.
  • Differentiate between diffusion and osmosis with examples of substance movement.
  • Focus on the selective nature of the plasma membrane and its implications.

Practice MCQs

Q1. Who is credited with the discovery of cells in 1665?

Q2. Why are cells called the 'structural unit of life'?

Q3. Which process allows CO2 to move out of the cell?

Q4. The movement of water across a semi-permeable membrane is called:

Q5. What characteristic of the plasma membrane allows it to control substance movement?

Frequently asked questions

Who discovered cells and when?

Cells were discovered in 1665 by Robert Hooke, an English botanist, who observed them in a slice of cork using a primitive microscope.

Why is the cell considered the basic unit of life?

The cell is considered the basic structural unit because it forms the building blocks of all living organisms, and the basic functional unit because it is capable of carrying out all essential life processes.

How does carbon dioxide move in and out of a cell?

Carbon dioxide moves in and out of the cell through diffusion. It moves from an area of higher concentration (inside the cell) to an area of lower concentration (outside the cell).

What is osmosis?

Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration across a selectively permeable membrane.

What does it mean for the plasma membrane to be selectively permeable?

It means the plasma membrane allows only certain substances to pass through it, while preventing the passage of others, thus controlling the movement of materials into and out of the cell.

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