The Class 9 Science Chapter 2 Cell The Building Block of Life explores the discovery of cells, their structure, types, and functions. It also explains how cells grow, divide, and contribute to the functioning of living organisms.
All living organisms – from tiny bacteria to large plants and animals – are made up of cells. The cell is the smallest unit capable of carrying out life processes. From observing onion cells under a microscope to understanding organelles like mitochondria and nucleus, this chapter builds a strong foundation in biology.
Cell The Building Block Worksheet
Our Class 9 Science worksheets are thoughtfully designed to strengthen conceptual understanding, improve problem-solving skills, and help students prepare confidently for exams. Designed according to the latest curriculum 2026-27, our worksheets offer a variety of questions to practice.
What Students Will Learn
- Structure and function of cells
- Differences between plant and animal cells
- Role of organelles
- Concept of osmosis and diffusion
- Types of cell division
Chapter 2 Cell The Building Block of Life Study Notes
Introduction to Cells
- All living organisms are made up of cells.
- A cell is the basic structural and functional unit of life.
- Cells perform all vital functions like respiration, digestion, and reproduction.
- Some organisms are unicellular (e.g., bacteria), while others are multicellular (e.g., humans).
Discovery of Cell
- Robert Hooke (1665) observed cork cells under a microscope.
- He named them “cells” because they looked like small rooms.
- Later scientists studied living cells and their functions.
Cell Theory
The cell theory states:
- All living organisms are made of one or more cells
- The cell is the basic unit of structure and function
- All cells arise from pre-existing cells
- This theory explains growth, reproduction, and continuity of life.
Size and Shape of Cells
- Cells vary greatly in size:
- Smallest: Bacteria
- Largest: Ostrich egg
- Cells have different shapes depending on function:
- Nerve cell → long and branched
- Red blood cell → round
- Muscle cell → elongated
Tools to Study Cells
Microscope
- Cells are studied using microscopes.
- Types:
- Light microscope (school labs)
- Electron microscope (high magnification)
- Key Terms
- Magnification = Enlargement of image
- Resolution = Ability to distinguish two points
Structure of a Cell
All cells have three basic parts:
- Cell membrane (plasma membrane)
- Cytoplasm
- Nucleus
Cell Membrane (Plasma Membrane)
- Thin, flexible boundary
- Made of lipids and proteins (fluid mosaic model)
Functions:
Protects cell
Controls entry and exit of substances
Transport Processes:
Diffusion – Movement from high to low concentration
Osmosis – Movement of water across membrane
Cell Wall
- Present only in plant cells
- Made of cellulose
Functions:
Provides shape and rigidity
Protects cell
Prevents bursting
Cell Organelles and Their Functions
1. Endoplasmic Reticulum (ER)
Transport system of cell
Types:
RER → Protein synthesis
SER → Lipid synthesis
2.Ribosomes
Protein factories
Found on ER or free in cytoplasm
3.Golgi Apparatus
Packaging and transport
Modifies proteins
4.Lysosomes
“Suicide bags”
Break down waste materials
5.Mitochondria
Powerhouse of cell
Produces ATP (energy)
Has its own DNA
Cell Division
- Importance:
- Growth
- Repair
- Reproduction
Types:
(i) Mitosis
Produces identical cells
For growth and repair
(ii) Meiosis
Produces gametes
Half chromosome number
Class 9 Science Chapter 2 Question Answers
Q1. What is a cell?
Answer: A cell is the smallest unit of life capable of performing all vital functions.
Q2. Who discovered the cell?
Answer: Robert Hooke discovered the cell in 1665.
Q3. Define prokaryotic cells.
Answer: Cells without a true nucleus and membrane-bound organelles.
Q4. Describe structure of a cell.
Answer:
A cell has:
- Cell membrane (outer covering)
- Cytoplasm (fluid)
- Nucleus (control center)
- Organelles (mitochondria, ER, Golgi, etc.)
- Each part performs specific functions.
Q5. Differentiate between plant and animal cells.
Answer:
Plant cells have cell wall, plastids, large vacuole.
Animal cells lack cell wall and plastids but have centrioles.
Q6. Explain osmosis with example.
Answer:
Osmosis is movement of water across membrane.
Example: Potato placed in salt solution shrinks (page 4 experiment).