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

Quick revision notes for Class 9 Science Chapter 2 (Cell: The Building Block of Life). These Class 9 Science Chapter 2 notes are ideal for quick revision just before exams.

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.

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.

Written by Satish

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