2. Organisation of the Organism (Cambridge IGCSE Biology 0610 for exams in 2023,2024 and 2025)

Introduction to Cells

  • Cells are the basic unit of life, acting as building blocks for all organisms.

Structure of Animal Cells

  • Nucleus: The control unit of the cell, containing genetic material (DNA).

  • Mitochondria: Known as the powerhouse of the cell; site of aerobic respiration and energy production.

  • Cell Membrane: Regulates entry and exit of substances, providing a protective barrier.

  • Cytoplasm: Jelly-like substance where cell organelles are suspended and chemical reactions occur.

  • Ribosomes: Sites for protein synthesis; essential for producing proteins required by the cell.

Structure of Plant Cells

  • Plant cells contain all the organelles found in animal cells, plus additional ones:

    • Cell Wall: Made of cellulose; provides structural support and protection.

    • Chloroplasts: Contain chlorophyll for photosynthesis, transforming light energy into chemical energy (food).

    • Vacuole: Stores cell sap for nutrients and helps maintain cell structure by providing turgor pressure.

Functions of Cell Organelles

  • Nucleus: Coordinates cell activities and stores DNA.

  • Mitochondria: Provides energy through aerobic respiration.

  • Cytoplasm: Supports organelles and is the site for many metabolic reactions.

  • Ribosomes: Essential for making proteins.

  • Cell Membrane: Selectively permeable barrier for the cell.

Functions of Plant Cell Structures

  • Cell Wall: Offers strength and additional protection to the plant cell.

  • Chloroplasts: Perform photosynthesis to produce food for plants.

  • Vacuole: Helps store substances and maintain cellular structure.

Structure of Bacterial Cells

  • Similar organelles to animal cells but have:

    • Circular DNA: Genetic material organized in a circular fashion.

    • Plasmids: Small circular DNA molecules facilitating genetic exchange between bacteria.

Cell Division and Organization

  • New cells are produced through the division of existing cells.

  • Hierarchical organization:

    • Cells ➔ Tissues ➔ Organs ➔ Organ Systems ➔ Multicellular Organism

Specialized Cells

  • Ciliated Cells: Have cilia to move mucus in the respiratory system.

  • Root Hair Cells: Aid in water and mineral absorption.

  • Palisade Mesophyll Cells: Contain chloroplasts to maximize photosynthesis.

  • Neurons: Transmit electrical impulses across the body.

  • Red Blood Cells: Transport oxygen via hemoglobin.

  • Gametes (Sperm and Egg Cells): Involved in reproduction; nuclei fuse to form an embryo.

Understanding Size and Magnification

  • Cells typically require magnification to be viewed clearly under a microscope.

  • Magnification Formula:

    • Magnification = Image Size / Actual Size

    • Ensure both sizes are in millimeters for consistent measurement.

Example Calculation

  • For an image of a leaf:

    • Image Size = 30mm; Actual Size = 2mm.

    • Magnification = 30mm / 2mm = 15.

Unit Conversions

  • To convert units:

    • Millimeters to Micrometers: Multiply by 1000.

    • Micrometers to Millimeters: Divide by 1000.

Conclusion

  • Review the key topics within Chapter 2: Organization of the Organism to solidify understanding.

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