The Cell

• Cell — structural and functional unit of life (Robert Hooke, 1665 — cork 'cells').
• Unicellular vs multicellular organisms.
• Prokaryotic (no true nucleus) vs Eukaryotic (true nucleus) — intro.
• Cell theory: all living things made of cells; cell from pre-existing cell.

1. Discovery — Hooke observed cork; Leeuwenhoek saw free-living cells.
2. Cell theory — Schleiden (plants), Schwann (animals), Virchow (omnis cellula e cellula).
3. Unicellular — Amoeba, bacteria, Chlamydomonas.
4. Multicellular — humans, plants, most animals.
5. Prokaryote — no membrane-bound nucleus (bacteria).
6. Eukaryote — nucleus, organelles (plants, animals, fungi).
7. NCERT Ch. 5 — onion peel and human cheek cell observations.
8. Real world — stem cells; bacterial infections (prokaryotes).

Comparing onion epidermal cell and human cheek cell (NCERT slide activity)

Step 1 — Onion peel: rectangular cells, cell wall, large central vacuole, nucleus at side.
Step 2 — Cheek cell: irregular shape, **no cell wall**, small vacuoles, central nucleus.
Step 3 — Both: cell membrane, cytoplasm, nucleus (eukaryotic).
Step 4 — Stain with methylene blue to see nucleus clearly.
Conclusion: plant cells have wall + large vacuole; animal cells lack wall.

• Thinking all cells have cell wall (only plants, fungi, bacteria).
• Misconception: viruses are cells (acellular — not in cell theory).
• Confusing ** tissue** with cell.
• Assuming prokaryotes have no DNA (have nucleoid region).
• Forgetting Virchow's contribution to cell theory.

• Who discovered cells and how?
• State the three parts of cell theory.
• Distinguish unicellular and multicellular with examples.
• One difference between plant and animal cell.

Open the Practice tab for graded questions on The Cell.