IGCSE Biology - Organisation of the Organism

Cell as the Basic Unit of Life

  • A cell is the basic unit of life, similar to how building blocks are used to construct something.

Animal Cell Structure

  • Key organelles to identify and understand:

    • Nucleus: The control unit of the cell.

    • Mitochondria: The powerhouse of the cell where aerobic respiration occurs.

    • Cell membrane: Controls the entry and exit of substances.

    • Cytoplasm: Jelly-like substance housing cell organelles.

    • Ribosomes: Sites of protein synthesis.

Plant Cell Structure

  • Contains organelles similar to animal cells:

    • Nucleus

    • Mitochondria

    • Cell membrane

    • Cytoplasm

    • Ribosomes

  • Additional organelles:

    • Cell wall: Made of cellulose.

    • Chloroplasts: Contain chlorophyll for photosynthesis.

    • Vacuole: Contains cell sap.

Organelle Functions

Common to Animal and Plant Cells:

  • Nucleus: Contains genetic material (DNA) and controls cell activities.

  • Mitochondria: Site of aerobic respiration, provides energy for the cell.

  • Cytoplasm: Jelly-like substance where chemical reactions occur; supports organelles.

  • Ribosomes: Sites of protein synthesis.

  • Cell Membrane: Controls what enters and exits the cell, provides protection.

Plant Cell Structures:

  • Cell Wall: Provides structural support and protection, made of cellulose.

  • Chloroplasts: Contain chlorophyll; site of photosynthesis, converting light energy into food.

  • Vacuole: Contains cell sap for storage and helps maintain cell shape.

Bacterial Cell Structure

  • Contains similar organelles to animal cells but also has:

    • Circular DNA

    • Plasmids: Small circular DNA molecules allowing bacteria to exchange genetic information.

Cell Division

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

    • A single cell divides into two, then four, and so on.

Levels of Organization

  • Cells: The most basic unit.

  • Tissues: Groups of similar cells.

  • Organs: Groups of different tissues.

  • Organ Systems: Groups of organs functioning together.

  • Multicellular Organism: Combination of cells, tissues, organs, and organ systems.

Specialized Cells

  • Ciliated Cells: Have cilia for movement of mucus in the trachea and bronchi.

    • Cilia sweep mucus towards the nose and throat for removal.

  • Root Hair Cells: Absorb minerals and water in plant roots.

  • Palisade Mesophyll Cells: In leaves, contain chloroplasts for photosynthesis.

  • Neurons: Nerve cells that carry electrical impulses.

  • Red Blood Cells: Contain hemoglobin to transport oxygen.

  • Sperm and Egg Cells (Gametes): Responsible for reproduction; their nuclei fuse to develop an embryo.

Size of Specimens and Magnification

  • Microscopic objects are magnified for detailed viewing.

Magnification Formula:

  • Magnification=Image SizeActual Size\text{Magnification} = \frac{\text{Image Size}}{\text{Actual Size}}

    • Image size and Actual size must be in millimeters.

Example:

  • Image size = 30 mm, Actual size = 2 mm

  • Magnification=302=15\text{Magnification} = \frac{30}{2} = 15

    • Magnification has no units.

Unit Conversions:

  • Millimeters to Micrometers: Multiply by 1000.

  • Micrometers to Millimeters: Divide by 1000.