ICSE 10 Biology Cell Short

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Table of Contents

    ⚡ Quick Revision: The Cell & Its Structure

    🔹 Core Cell Fundamentals

    • ✔ Basic Unit: The cell is the structural and functional unit of all living organisms.
    • ✔ Cell Theory: Proposed by Schleiden and Schwann; states all cells arise from pre-existing cells (Virchow).
    • ✔ Size & Shape: Vary based on function (e.g., Nerve cells are long for impulse conduction).
    Term Card

    Protoplasm: The entire living substance of a cell, consisting of the cytoplasm and the nucleus.

    Feature Prokaryotic Cell Eukaryotic Cell
    Nucleus Absent (Nucleoid) Well-defined with membrane
    Organelles No membrane-bound types Present (Mitochondria, etc.)
    ❌ Don't Confuse:

    Cell Wall with Cell Membrane. Remember: Cell wall is rigid/permeable (plants only), while membrane is thin/semi-permeable (all cells).

    ⚡ Quick Revision: Cell Organelles & Functions

    🔹 Essential Organelles

    • ✔ Mitochondria: Sites of cellular respiration; release energy as ATP.
    • ✔ Ribosomes: Small granules responsible for Protein Synthesis.
    • ✔ Nucleus: Contains genetic material (DNA); coordinates all cell activities.
    Organelle Key Characteristic Main Function
    Lysosomes Contains digestive enzymes Intracellular digestion; "Suicide bags"
    Chloroplasts Double membrane; contains chlorophyll Photosynthesis (traps solar energy)
    Centrosome Contains two centrioles Initiates cell division in animal cells
    Term Card

    Endoplasmic Reticulum: A network of tubular membranes involved in the transport of substances within the cell.

    ❌ Don't Confuse:

    Chromatin with Chromosomes. Remember: Chromatin is the thin thread-like network in a resting nucleus; Chromosomes are the thick, condensed form during cell division.

    ⚡ Quick Revision: Nucleus & Chromosome Structure

    🔹 The Command Center (Nucleus)

    • ✔ Nuclear Envelope: Double-layered membrane with pores for substance exchange.
    • ✔ Nucleolus: One or more round bodies inside the nucleus; site of ribosome production.
    • ✔ Chromatin: DNA-protein complex that condenses into chromosomes during division.
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    Term Card

    Centromere: The point on a chromosome by which it is attached to a spindle fiber during cell division.

    🔹 Chromosome Basics

    • ✔ Structure: Each chromosome consists of two identical Sister Chromatids.
    • ✔ Composition: Made of roughly 40% DNA and 60% Histones (proteins).
    • ✔ Gene: A specific DNA sequence on a chromosome that codes for a particular protein/trait.
    ❌ Don't Confuse:

    Centromere with Centrosome. Remember: Centromere holds chromatids together; Centrosome is the organelle that forms spindle poles.

    ⚡ Quick Revision: DNA Structure & Discovery

    🔹 The Double Helix

    • ✔ Discovery: Structure proposed by Watson and Crick in 1953.
    • ✔ Components: Each nucleotide consists of a Phosphate, a Sugar (Deoxyribose), and a Nitrogenous Base.
    • ✔ Base Pairing: Adenine (A) pairs with Thymine (T); Cytosine (C) pairs with Guanine (G).
    Structure of DNA Nucleotide and Helix
    Term Card

    Nucleosome: A structural unit consisting of DNA coiled around a core of eight histone proteins.

    🔹 Nitrogenous Base Complementarity

    Base Pairs with... No. of Hydrogen Bonds
    Adenine (A) Thymine (T) 2 (Double Bond)
    Guanine (G) Cytosine (C) 3 (Triple Bond)
    ❌ Don't Confuse:

    Nucleoside with Nucleotide. Remember: Nucleoside = Sugar + Base; Nucleotide = Sugar + Base + Phosphate.

    ⚡ Quick Revision: Plant vs. Animal Cells

    🔹 Structural Variations

    • ✔ Boundary: Plant cells have a rigid cellulose Cell Wall; animal cells only have a plasma membrane.
    • ✔ Vacuoles: Large and central in plants (pushing nucleus to side); small and temporary in animals.
    • ✔ Plastids: Present in plant cells for photosynthesis/storage; strictly absent in animal cells.
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    🔹 High-Yield Comparison Table

    Feature Plant Cell Animal Cell
    Centrosome Absent (except lower plants) Present (with centrioles)
    Storage Starch grains Glycogen granules
    Shape Fixed, rectangular/polygonal Irregular or oval
    Term Card

    Tonoplast: The single semi-permeable membrane that surrounds the large central vacuole in plant cells.

    ❌ Don't Confuse:

    Dictyosomes with Golgi Complex. Remember: In plant cells, the Golgi units are smaller, scattered, and called Dictyosomes.

    ⚡ Quick Revision: Final Exam Essentials

    🔹 "Must-Memorize" Discoveries

    • ✔ First Discovery: Robert Hooke (1665) observed cork cells under a crude microscope.
    • ✔ Nucleus: Discovered by Robert Brown (1831).
    • ✔ Living Cells: Antonie van Leeuwenhoek (1674) was the first to see living bacteria and protozoa.
    Exam Strategy Box

    For Diagram-based Questions, always identify if the cell is Plant or Animal first by looking for a Cell Wall or Centrioles. This saves time in subsequent identification parts.

    🔹 Quick Fact Sheet

    Category Fact
    Smallest Cell Mycoplasma (PPLO)
    Largest Cell Ostrich Egg
    Longest Cell (Human) Nerve Cell (Neuron)
    ❌ Common Error:

    Don't forget that Mature RBCs in humans lack a nucleus and mitochondria to carry more oxygen and maximize space.

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