The Cell – Basic Unit of Life

📚 Key Concepts

🔹 What is a Cell?

A cell is the smallest structural and functional unit of life. All living organisms are made up of one or more cells.

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Cell Theory (Fundamental Principles):

  1. All living things are made of cells
  2. Cell is the basic unit of life
  3. All cells come from pre-existing cells

🔹 Basic Structure of a Cell

Three Main Components:

1. Cell Membrane

  • Thin outer boundary of the cell
  • Controls entry and exit of materials
  • Semi-permeable (selective barrier)
  • Present in ALL cells

2. Cytoplasm

  • Jelly-like substance inside the cell
  • Contains water, proteins, carbohydrates, fats
  • Site of most cellular activities
  • Fills space between membrane and nucleus

3. Nucleus

  • Control center of the cell
  • Contains genetic material (DNA)
  • Regulates all cellular activities
  • Controls growth and reproduction

🔹 Plant vs Animal vs Bacterial Cells

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🔹 Specialized Cell Structures

Additional Plant Cell Components:

  • Chloroplasts: Green structures containing chlorophyll for photosynthesis
  • Vacuole: Large storage compartment for water and nutrients
  • Cell Wall: Rigid outer layer providing support and protection

Cell Shape and Function Relationship:

  • Muscle cells: Spindle-shaped for contraction
  • Nerve cells: Long and branched for message transmission
  • Cheek cells: Flat for protective lining
  • Root hair cells: Extended for water absorption

🧪 Important Formulas and Concepts

🔸 Cell Size: Usually measured in micrometers (μm)

  • 1 micrometer = 0.001 millimeter
  • Most cells: 1-100 μm
  • Ostrich egg: Largest single cell (130-170 mm diameter)

🔸 Magnification = Image size ÷ Actual size