Class 9 Science Chapter 2 Cell: The Building Block of Life – Revision Notes

Cell: The Building Block of Life draws out the differences between plant and animal cells and catalogues what each organelle does, and this page turns that comparison into a compact set of notes.

Last Updated: September 23, 2026

Common Mistakes Students Make in This Chapter

Types of Cells

• Prokaryotic: no membrane-bound nucleus (e.g. bacteria).
• Eukaryotic: true, membrane-bound nucleus (plants, animals, fungi).

Plant vs Animal Cell

• Plant cell only: cell wall, large central vacuole, chloroplasts.
• Shared: plasma membrane, cytoplasm, nucleus, mitochondria, ER.

Organelles and Functions

• Nucleus — genetic material, control centre.
• Mitochondria — respiration, energy (ATP) production.
• Chloroplast — photosynthesis (plants).
• Rough ER — protein synthesis; Smooth ER — lipid synthesis.
• Vacuole — storage, turgor pressure (large in plants).
• Plasma membrane — selectively permeable boundary.
• Cell wall — rigid support (plants).

Cell Division

• Mitosis: 1 cell → 2 identical cells (growth/repair).
• Meiosis: 1 cell → 4 genetically different cells, half chromosome number (gametes).
• Uncontrolled division → linked to cancer.

Quick visual: a worked diagram from the full Solutions page, for reference.

One-Line Summary

The cell is the basic unit of life, built from organelles like the nucleus, mitochondria, and membrane, and divides by mitosis (growth) or meiosis (reproduction), with plant cells adding a wall, vacuole, and chloroplasts that animal cells lack.

Frequently Asked Questions

This chapter is about the cell as the basic building block of life. What are the two main types of cells covered?
The chapter covers prokaryotic cells, which lack a defined nucleus and membrane-bound organelles, and eukaryotic cells, which have a true nucleus enclosed by a nuclear membrane along with other membrane-bound organelles.

Why is the cell called the structural and functional unit of life?
Every living organism, whether unicellular or multicellular, is made up of cells, and all life processes such as respiration, nutrition, and reproduction ultimately take place at the cellular level.

What to Revise First (and Last) in This Chapter

Written by Satish

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