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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