Class IX – Science

Chapter 2: Cell – The Building Block of Life

Doodle PowerPoint Presentation | 66 Slides | Session 2026-27

Unique Study Point (USP) | Sumeet Sahu | Indore | uniquestudyonline.com

This presentation covers the complete Chapter 2 – Cell: The Building Block of Life in an engaging doodle style with detailed diagrams, activities, scientist profiles, exam-focused points, and practice questions after every topic.

Topic 1 – Cell: The Basic Unit of Life

• Where did life begin? – Origin of life in water; thermophiles; first cell membrane
• What is a cell? – Basic structural and functional unit of life
• Unicellular vs Multicellular organisms – examples and comparison
• Levels of organisation: Cell → Tissue → Organ → Organ System → Organism

Topic 2 – How to Study Cells (Microscopy)

• Limit of resolution of the human eye – 0.1 mm; near point = 25 cm
• Size scale: from atoms (0.1 nm) to humans (1 m)
• Robert Hooke (1665) – first to observe a cell; used cork; named cells (from Latin: cellula = little rooms)
• Light Microscope – parts (eyepiece, objective lens, stage, mirror); magnification 10X–40X; total magnification = eyepiece × objective
• How a microscope magnifies – convex lens combination
• Activity 2.1 – Estimate the size of a cell using field diameter formula
• Electron Microscope – uses beam of electrons; nanometre scale; reveals stomata and fine cell details

Topic 3 – Structure of a Cell

• Cell Membrane (Plasma Membrane): Thin, selectively permeable boundary; defines individuality of cell; present in ALL cells
• Osmosis vs Diffusion – key differences; water moves from higher to lower concentration in osmosis
• Effect of solutions on a cell: Isotonic (stays same), Hypotonic (swells), Hypertonic (shrinks)
• Activity 2.2 – Potato experiment to demonstrate osmosis
• Fluid-Mosaic Model – membrane made of lipids + proteins; 7–10 nm thick; fluid and mosaic
• Cell Wall: Extra rigid covering outside membrane in plants, fungi, bacteria; made of cellulose; gives shape and rigidity; permeable
• Activity 2.3 – Plant cells (onion/Rhoeo) vs cheek cells comparison
• Three Basic Parts of a Cell: Plasma Membrane, Cytoplasm, Nucleus
• Three Types of Cells: Bacterial cell, Plant cell, Animal cell – comparison table
• Prokaryotic vs Eukaryotic cells – nucleus, size, organelles comparison
• Acellular agents: Virus (genetic material + protein coat), Viroid (only genetic material), Prion (misfolded protein only)
• Cell Organelles – The Cell Interior:
  • Nucleus – House of Coded Instructions; double membrane; nuclear pore; nucleolus; chromatin; chromosomes; DNA → genes
  • Ribosomes – Protein Factories; found free in cytoplasm or on RER; sites of protein synthesis
  • Endoplasmic Reticulum (ER) – Rough ER (ribosomes, makes proteins); Smooth ER (makes fats/lipids and hormones)
  • Golgi Apparatus – Packaging and Shipping Centre; modifies, sorts and packages proteins; discovered by Camillo Golgi (1898)
  • Lysosomes – Clean-Up System; single membrane; filled with enzymes; breaks down waste; Did You Know: sperm lysosomes help break egg\'s outer layer
  • Mitochondria – Powerhouse of the Cell; double membrane; cristae; own DNA and ribosomes; cellular respiration; ATP = energy currency
  • Plastids – Food Factories of Plant Cells: Chloroplast (green, photosynthesis), Chromoplast (yellow/orange/red, colour pigments), Leucoplast (colourless, starch/oil/protein storage)
  • Vacuoles – Storage and Support; large in plant cells (turgor pressure); small in animal cells
  • Cytoskeleton – network of fine fibres; gives shape and movement
  • Cell Inclusions – stored substances (starch crystals, calcium oxalate)
• Synthetic Biology – Landmark Experiment (2010): First synthetic cell created from computer-designed DNA

Topic 4 – Cell Growth and Division

• Why do cells divide? – replace old/dead cells; growth; ~1% of body cells replaced daily
• Two types of cell division: Mitosis and Meiosis
• Mitosis – produces 2 identical daughter cells; same chromosome number; for growth and repair; stages: Prophase, Metaphase, Anaphase, Telophase/Cytokinesis
• Activity 2.5 – Onion root tip to observe mitosis stages
• Meiosis – produces 4 daughter cells with half chromosomes; occurs in reproductive organs; forms gametes; creates variation
• When division goes wrong: Faulty Mitosis → tumours; Faulty Meiosis → genetic disorders, developmental problems
• Cell Culture – growing plant/animal cells outside body; used for biochemicals, vaccines, medicines
• Meet the Scientists: Arun Kumar Sharma (chromosomes, plant taxonomy); Gottlieb Haberlandt (totipotency, plant tissue culture, 1902)

Topic 5 – Cell Theory

• Three postulates of Cell Theory: (1) All living organisms are made of one or more cells; (2) Cell is the basic unit of structure and function; (3) All cells arise from pre-existing cells
• Scientists: Matthias Schleiden (1838, plants), Theodor Schwann (1839, animals), Rudolf Virchow (1855, new cells from pre-existing cells)
• Contact Inhibition – normal cells stop dividing when they touch neighbours
• Cancer cells lose contact inhibition → uncontrolled division → tumours (benign or malignant)
• Programmed Cell Death (PCD) – controlled self-destruction of cells; example: fingers in embryo
• Plant cells (rigid wall) do NOT show contact inhibition

Quick Revision and NCERT Questions

• At a Glance – complete chapter mega revision slide
• NCERT Questions (Q1–Q16) – all questions from the textbook with detailed answers across 7 slides
• Practice Time slides after every topic

Key Exam Facts

• Cell = basic structural AND functional unit of life
• Robert Hooke discovered cell in 1665 using cork
• Limit of resolution of human eye = 0.1 mm
• Total magnification = eyepiece magnification × objective magnification
• Cell membrane = selectively permeable (allows some substances, blocks others)
• Osmosis = diffusion of water across selectively permeable membrane
• Isotonic: cell stays same; Hypotonic: cell swells; Hypertonic: cell shrinks
• Cell wall = made of cellulose (plants); present in plants, fungi, bacteria – NOT in animal cells
• Prokaryotic cells: no