1. Discovery of the Cell [cite: 865-873]

• Robert Hooke (1665): Observed cork slices under a microscope. He saw "compartments" like a honeycomb and coined the term "cell". He published this in his book Micrographia.
• Antonie van Leeuwenhoek: Developed better lenses and was the first to see tiny living organisms (bacteria, blood cells). Known as the Father of Microbiology.

2. Cell Structure [cite: 951-981]

• Cell Membrane: Porous outer layer, controls entry/exit of materials.
• Nucleus: Central round structure, regulates cell activities and growth.
• Cytoplasm: Jelly-like substance where life processes occur.
• Cell Wall: Extra outer layer in plant cells (and fungi/bacteria) for rigidity and strength.
• Vacuoles: Large in plants (store nutrients/waste), small or absent in animals.
• Plastids: Found in plants (e.g., Chloroplasts containing chlorophyll).

3. Levels of Organisation [cite: 1023-1030]

Cell → Tissue → Organ → Organ System → Organism

• Unicellular: Single-celled (e.g., Amoeba, Bacteria).
• Multicellular: Many cells (e.g., Plants, Animals, Ostrich egg yolk is the largest single cell).

4. Microorganisms [cite: 1042-1215]

Tiny organisms visible only with a microscope.

• Types: Bacteria (Lactobacillus, Rhizobium), Fungi (Yeast, Mould), Protozoa (Amoeba), Algae (Spirulina), Viruses (acellular).
• Uses:
  • Curd: Lactobacillus multiplies in warm milk.
  • Fermentation: Yeast breaks down sugar → Alcohol + $CO_2$ (makes dough fluffy).
  • Manure: Microbes decompose organic waste.
  • Nitrogen Fixation: Rhizobium in root nodules of legumes.