NCERT Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life
NCERT Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life covers cell structure, cell discovery, plasma membrane, cell wall, nucleus, cytoplasm, cellular organelles (endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria, plastids, vacuoles), and cell division.
Overview of Topics & Subtopics (Click to Jump)
1. Discovery of Cell & Cell Theory
Short Note:
• Discovery of Cell: Robert Hooke (1665) first discovered cells in cork slices using a primitive microscope and called them "little rooms".
• Free Living Cells: Leeuwenhoek (1674) observed living cells in pond water.
• Nucleus Discovery: Robert Brown (1831) discovered the nucleus in the cell.
• Protoplasm: Purkinje (1839) coined the term 'Protoplasm' for the fluid substance of the cell.
• Cell Theory: Proposed by Schleiden (1838) and Schwann (1839), later expanded by Virchow (1855) — "All cells arise from pre-existing cells" (Omnis cellula-e-cellula).
2. Plasma Membrane, Osmosis & Cell Wall
Short Note:
• Plasma Membrane: Flexible, selectively permeable membrane made up of lipids and proteins that regulates entry and exit of substances.
• Diffusion & Osmosis: Movement of gases (CO2, O2) occurs by diffusion. Movement of water across a semi-permeable membrane from higher to lower water concentration is Osmosis.
- Hypotonic Solution: Water enters cell → Cell swells.
- Hypertonic Solution: Water leaves cell → Cell shrinks (Plasmolysis in plant cells).
- Isotonic Solution: No net movement → Cell size stays same.
• Cell Wall: Rigid outer covering present outside plasma membrane in plant, fungal, and bacterial cells, made mainly of cellulose in plants.
3. Nucleus, Cytoplasm & Cell Organelles
Short Note:
• Nucleus: Controls cellular activities. Contains double-layered nuclear membrane, nucleolus, and chromatin network (DNA & proteins).
• Prokaryotes vs. Eukaryotes: Prokaryotes lack a membrane-bound nucleus and organelles; Eukaryotes have well-defined nucleus and membrane-bound organelles.
• Key Organelles:
- Endoplasmic Reticulum (ER): Rough ER (synthesizes proteins with ribosomes); Smooth ER (synthesizes lipids and detoxifies poisons).
- Golgi Apparatus: Packaging and dispatching of cellular materials.
- Lysosomes: "Suicide bags" of cell; contain digestive enzymes to destroy waste/foreign materials.
- Mitochondria: "Powerhouse of the cell"; generates ATP energy through cellular respiration.
- Plastids: Present in plant cells. Chloroplasts (photosynthesis), Chromoplasts (colored), Leucoplasts (storage).
- Vacuoles: Storage sacs for solids/liquids (very large in plant cells, providing turgidity).
4. Plant Cell vs. Animal Cell & Cell Division
Short Note:
• Plant Cell vs. Animal Cell: Plant cells have cell walls, plastids, and large central vacuoles, but lack centrosomes. Animal cells lack cell walls and plastids, but have small vacuoles and centrosomes.
• Cell Division: Process by which new cells are formed for growth, repair, or reproduction.
- Mitosis: Process of cell division for growth and repair, producing two identical daughter cells with the same number of chromosomes as the parent cell.
- Meiosis: Process of cell division for gamete formation, producing four non-identical cells with half the number of chromosomes (haploid).
Intext Questions - Page Number: 59
Intext Questions - Page Number: 61
• CO2: Moves in and out of the cell across the plasma membrane by the process of diffusion (movement from a region of higher concentration to lower concentration).
• Water: Moves in and out of the cell across the selectively permeable plasma membrane by osmosis, following the water concentration gradient.
Textbook Chapter End Exercise Questions
1. Cell Wall: Plant cells have a rigid cellulose cell wall outside the plasma membrane, whereas animal cells lack a cell wall.
2. Plastids: Plant cells contain plastids (like chloroplasts for photosynthesis), whereas animal cells do not contain plastids.
3. Vacuoles: Plant cells have a single large central vacuole occupying most cell volume, whereas animal cells have multiple small, temporary vacuoles.
Read More & Chapter Resources
These short notes are designed for quick revision. Read the main points once, then use the related material below to practise the same chapter. Revising a concept and checking it with questions can make your preparation more focused.