Cell Biology — 10 Essential Sentences

1. The Cell Theory (Schleiden & Schwann, 1838–39) states that all organisms are made of cells, and Virchow added that every cell arises from a pre-existing cell.

2. Prokaryotic cells lack a membrane-bound nucleus, have 70S ribosomes, peptidoglycan cell walls, mesosomes, and divide by binary fission.

3. Eukaryotic cells have a true nucleus with a double-membraned nuclear envelope, 80S cytoplasmic ribosomes, and membrane-bound organelles.

4. The endomembrane system — ER → Golgi → Lysosomes → Vacuoles — handles intracellular protein processing and secretion.

5. Lysosomes, derived from the Golgi, contain hydrolytic enzymes and are called "suicide bags" because their rupture causes autolysis.

6. Mitochondria and chloroplasts are semi-autonomous organelles with their own circular DNA and 70S ribosomes, consistent with endosymbiotic origin from prokaryotes.

7. The Fluid Mosaic Model (Singer & Nicolson, 1972) describes the plasma membrane as a fluid phospholipid bilayer with integral and peripheral proteins and glycoproteins.

8. Plant cells have cellulose cell walls (middle lamella = calcium pectate), plastids, large central vacuoles, and plasmodesmata; animal cells have centrioles and lysosomes instead.

9. Eukaryotic cilia and flagella have a 9+2 microtubule arrangement (tubulin + dynein), while prokaryotic flagella are made of flagellin with no 9+2 organization.

10. The most NEET-tested concept is that mitochondria and chloroplasts have 70S ribosomes despite being inside eukaryotic cells — because of their prokaryotic evolutionary origin.