ICSE 9 Biology Cell Short

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Table of Contents

    ⚡ Quick Revision: Cell Theory & Discovery

    Foundational Facts

    • ✔ Robert Hooke (1665): First observed cells in a cork slice; coined the term "Cell".
    • ✔ Antonie van Leeuwenhoek: First to observe a living cell (bacteria/protozoa).
    • ✔ Cell Theory: Proposed by Schleiden and Schwann; expanded by Rudolf Virchow.
    Term Card

    Cell: The fundamental structural and functional unit of all living organisms.

    The Cell Theory Postulates

    • ✔ All living organisms are composed of one or more cells.
    • ✔ The cell is the basic unit of life.
    • ✔ Omnis cellula-e cellula: All cells arise from pre-existing cells (Virchow).
    ❌ Don't Confuse:

    The Discovery of Cell (Hooke) with the Discovery of Nucleus (Robert Brown). Both Roberts, very different findings!

    ⚡ Quick Revision: Cell Size, Shape & Types

    Size Extremes (Must-Memorize)

    • ✔ Smallest Cell: Mycoplasma (PPLO) - approx 0.1 to 0.5 μm.
    • ✔ Largest Cell: Ostrich Egg (approx 170 mm × 135 mm).
    • ✔ Longest Cell (Human): Nerve Cell (Neuron) - can be over 1 meter long.
    Cell Shape Example & Purpose
    Biconcave/Circular RBCs: To pass through narrow capillaries and carry more oxygen.
    Amoeboid WBCs: To squeeze out of blood vessel walls (diapedesis).
    Long/Branching Nerve Cells: To conduct impulses over long distances.
    Term Card

    Prokaryotic Cell: Cells lacking a well-defined nucleus and membrane-bound organelles (e.g., Bacteria).

    ❌ Don't Confuse:

    Eukaryotic with Prokaryotic. Eukaryotes have a True Nucleus (Eu = True, Karyon = Nucleus); Prokaryotes do not.

    ⚡ Quick Revision: Cell Structure - The Outer Boundaries

    1. Cell Wall (Plants Only)

    • ✔ Composition: Made of Cellulose (a non-living rigid substance).
    • ✔ Nature: Freely permeable; allows all substances to pass through.
    • ✔ Function: Provides rigidity, protection, and definite shape to the plant cell.

    2. Cell Membrane (Plasma Membrane)

    • ✔ Composition: Living, thin, and flexible layer made of Lipids and Proteins.
    • ✔ Nature: Selectively Permeable; regulates entry/exit of specific molecules.
    • ✔ Function: Maintains cell individuality and protects the internal protoplasm.
    Feature Cell Wall Cell Membrane
    Vitality Non-living Living
    Permeability Freely Permeable Selectively Permeable
    ❌ Don't Confuse:

    Permeable with Selectively Permeable. A sieve is permeable to water, but the plasma membrane "decides" which solutes get through based on size and charge.

    ⚡ Quick Revision: The Nucleus & Cytoplasm

    The Nucleus (The Brain of the Cell)

    • ✔ Components: Nuclear membrane, Nucleoplasm, Nucleolus, and Chromatin network.
    • ✔ Function: Regulates all metabolic activities and carries genetic information (DNA).
    • ✔ Chromatin: Coils into Chromosomes during cell division.
    Term Card

    Protoplasm: The entire living content of a cell, comprising the Cytoplasm + Nucleus.

    Structure Key Characteristic
    Cytoplasm Semi-liquid substance where cell organelles are embedded.
    Nucleolus One or more round bodies inside the nucleus; site of ribosome formation.
    [Diagram: Nucleus with Nuclear Pores & Chromatin]
    Structure of the Nucleus

    ⚡ Quick Revision: Cell Organelles 

    Mitochondria (Powerhouse)

    • ✔ Structure: Double-walled; inner wall folded into Cristae to increase surface area.
    • ✔ Function: Site of cellular respiration; releases energy in the form of ATP.
    • ✔ Contain their own DNA and ribosomes (semi-autonomous).

    Endoplasmic Reticulum (ER)

    • ✔ Rough ER: Studded with ribosomes; site of protein synthesis.
    • ✔ Smooth ER: Lacks ribosomes; helps in lipid/steroid synthesis and detoxification.
    • ✔ Provides an internal framework (cytoskeleton) for the cell.
    Organelle Key Nickname Main Function
    Ribosomes Protein Factories Synthesis of Proteins.
    Golgi Bodies Delivery Dispatcher Packaging and secretion of enzymes/hormones.
    Term Card

    ATP (Adenosine Triphosphate): The chemical energy currency of the cell produced during respiration.

    ❌ Don't Confuse:

    Dictyosomes with Golgi Apparatus. Dictyosomes is the term used specifically for Golgi bodies found in plant cells (they are more scattered).

    ⚡ Quick Revision: Cell Organelles 

    Lysosomes (Suicide Bags)

    • ✔ Contain strong digestive enzymes (Hydrolases).
    • ✔ Destroy foreign substances and damaged cell organelles.
    • ✔ Can digest the cell itself if it is damaged or old, hence the name.

    Plastids (Plants Only)

    • ✔ Chloroplasts: Green plastids; site of photosynthesis (contain chlorophyll).
    • ✔ Chromoplasts: Coloured (red, yellow, orange); found in fruits and flowers.
    • ✔ Leucoplasts: Colourless; used for storing starch, proteins, or fats.
    Organelle Structure/Function
    Vacuoles Large in plants (storage); small/absent in animals. Surrounded by Tonoplast.
    Centrosome Only in Animal Cells; contains Centrioles that help in cell division.
    Term Card

    Anthocyanins: Water-soluble pigments in the cell sap that give purple, blue, or pink colours to flowers/vegetables (not in plastids).

    ❌ Don't Confuse:

    Centrosome with Chromosome. Centrosomes are organizers of cell division in animals; Chromosomes are the genetic material in the nucleus.

    ⚡ Quick Revision: Plant Cell vs. Animal Cell

    Feature Plant Cell Animal Cell
    Cell Wall Present (Cellulose) Absent
    Centrosome Absent Present
    Vacuoles One large central vacuole Small and temporary
    Plastids Present Absent

    Exam Essentials: Common Terms

    • ✔ Nucleoplasm: Fluid found specifically inside the nucleus.
    • ✔ Tonoplast: The membrane surrounding the large central vacuole in plants.
    • ✔ Cell Sap: The liquid content (water, sugar, salts) inside the vacuole.
    Visualizing Cell Differences
    [Insert Side-by-Side Labeled Diagram of Plant and Animal Cells]
    Key Exam Figure
    ❌ Don't Confuse:

    Chlorophyll with Chloroplast. Chloroplast is the organelle (the container), while Chlorophyll is the green pigment inside it.

    ⚡ Quick Revision: Prokaryotic vs. Eukaryotic Cells

    Structural Differences

    • ✔ Prokaryotes: Lack a nuclear membrane; DNA is circular and lies naked in the Nucleoid.
    • ✔ Eukaryotes: Possess a well-defined nucleus with a double-layered nuclear envelope.
    • ✔ Membrane-bound organelles (Mitochondria, Plastids) are absent in Prokaryotes but present in Eukaryotes.
    Feature Prokaryotic Cell Eukaryotic Cell
    Nucleus Incipient (Nucleoid) True Nucleus
    Ribosomes Smaller (70S) Larger (80S)
    Cell Division Fission or Budding Mitosis or Meiosis
    Term Card

    Nucleoid: An irregularly shaped region within a prokaryote that contains all or most of the genetic material.

    [Simplified Diagram of Bacterial Cell vs Human Cell]
    Cell Types Comparison
    ❌ Don't Confuse:

    S-units (Svedberg) in Ribosomes. Just remember: 70S is for simple (Prokaryotic), 80S is for complex (Eukaryotic).

    ⚡ Quick Revision: Vital Cell Processes

    Movement of Substances

    • ✔ Diffusion: Movement of molecules from high to low concentration (e.g., $O_2$ and $CO_2$ exchange).
    • ✔ Osmosis: Movement of water molecules through a semi-permeable membrane.
    • ✔ Active Transport: Movement against concentration gradient using ATP energy.
    Term Card

    Hypotonic Solution: A solution with lower solute concentration than the cell; causes the cell to swell (endosmosis).

    Condition Process Resulting State
    Water Enters Endosmosis Turgid (Swollen)
    Water Leaves Exosmosis Flaccid/Plasmolysed
    ❌ Don't Confuse:

    Turgidity with Plasmolysis. Turgidity is the state of being distended by fluid, while Plasmolysis is the shrinkage of protoplasm away from the cell wall.

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