Cell: The Building Block of Life
NCERT Class 9 Science • Chapter 2
Quick Answer
This Class 9 chapter explores the cell as the basic structural and functional unit of life. It covers the cell theory, prokaryotic and eukaryotic cells, the plasma membrane, cell wall, nucleus, and key organelles such as mitochondria, chloroplasts, and the endoplasmic reticulum, plus diffusion and osmosis across membranes.
↓ Free PDF, NCERT solutions, summary, key terms, FAQs below.
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Key Terms
- Cell
- The smallest structural and functional unit of all living organisms. Every living thing is made of one or more cells.
- Cell Theory
- The principle that all living things are made of cells, cells are the basic unit of life, and all cells arise from pre-existing cells.
- Plasma Membrane
- The thin, selectively permeable boundary surrounding the cell that controls the movement of substances into and out of it.
- Nucleus
- The membrane-bound organelle that contains the cell's genetic material (DNA) and controls cell activities and reproduction.
- Prokaryotic Cell
- A simple cell lacking a true membrane-bound nucleus and organelles, as found in bacteria.
- Osmosis
- The movement of water molecules across a selectively permeable membrane from a region of higher water concentration to one of lower water concentration.
- Mitochondria
- The organelles known as the powerhouse of the cell because they release energy through respiration in the form of ATP.
Frequently Asked Questions
Why is the cell called the building block of life?▾
The cell is the smallest unit that can carry out all the activities of life. All living organisms, from bacteria to humans, are built from one or many cells, which is why it is called the basic building block of life.
What is the difference between prokaryotic and eukaryotic cells?▾
Prokaryotic cells, such as bacteria, lack a true membrane-bound nucleus and organelles. Eukaryotic cells, found in plants, animals, and fungi, have a defined nucleus and membrane-bound organelles.
What is the difference between diffusion and osmosis?▾
Diffusion is the movement of any particles from a region of higher concentration to lower concentration. Osmosis is specifically the movement of water across a selectively permeable membrane from higher to lower water concentration.
What are the main differences between plant and animal cells?▾
Plant cells have a rigid cell wall, a large central vacuole, and chloroplasts for photosynthesis. Animal cells lack a cell wall and chloroplasts and usually have smaller, temporary vacuoles.
What is the function of the nucleus?▾
The nucleus stores the cell's genetic material (DNA) and acts as the control centre, directing cell growth, metabolism, and reproduction.
Why are mitochondria called the powerhouse of the cell?▾
Mitochondria release energy from food molecules through cellular respiration, producing ATP. This energy powers the cell's activities, which is why they are called its powerhouse.
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