Cell – The Unit of Life (NEET Notes)
All living organisms are made of cells. Cell is the basic structural and functional unit of life. Study of cell is called
Cytology. Robert Hooke (1665) first observed cells in cork. Leeuwenhoek first saw free-living cells (bacteria,
protozoa). Schleiden & Schwann proposed Cell Theory (1839). Rudolf Virchow (1855) modified it – "Omnis cellula
e cellula".
Prokaryotic vs. Eukaryotic Cells
• Prokaryotic Cells: Smaller (1–10 µm), no true nucleus, genetic material is naked circular DNA. Examples:
Bacteria, Mycoplasma, Cyanobacteria.
• Eukaryotic Cells: Larger (10–100 µm), nucleus with nuclear envelope, membrane-bound organelles present.
Examples: Plants, Animals, Protists, Fungi.
Cell Envelope (Prokaryotes)
1. Glycocalyx – outermost covering; capsule/slime layer for protection.
2. Cell wall – made of peptidoglycan (murein) in bacteria.
3. Plasma membrane – selectively permeable, fluid mosaic model (Singer & Nicolson). Functions in transport,
respiration, photosynthesis.
Eukaryotic Cell Organelles
• Nucleus – Surrounded by double membrane, contains nucleolus, DNA, chromatin.
• Endoplasmic Reticulum (ER) – RER (with ribosomes, protein synthesis), SER (lipid synthesis, detoxification).
• Golgi Apparatus – Packaging, secretion, glycosylation, lysosome formation.
• Lysosomes – Contain hydrolytic enzymes, "suicidal bags".
• Mitochondria – Double membrane, cristae, matrix; powerhouse of cell, has its own DNA & ribosomes.
• Plastids – Found in plants. Types: Chloroplast (photosynthesis), Chromoplast (color), Leucoplast (storage).
• Ribosomes – 70S (prokaryotes, mitochondria, chloroplast), 80S (eukaryotes).
• Cytoskeleton – Microtubules, microfilaments, intermediate filaments for shape, transport.
• Centrosome & Centrioles – Animal cells only, spindle formation.
• Vacuoles – Large in plants, storage, tonoplast membrane.
Plant vs. Animal Cells
• Plant Cells: Cell wall, chloroplast, large central vacuole, plasmodesmata.
• Animal Cells: No cell wall, no chloroplast, small vacuoles, centrioles present.
Important NEET Points
• Mycoplasma – smallest cell (0.3 µm).
• Ostrich egg – largest single cell.
• Prokaryotic ribosomes – 70S (50S + 30S).
• Eukaryotic ribosomes – 80S (60S + 40S).
• Semi-autonomous organelles: Mitochondria, Chloroplast.
• Fluid mosaic model proposed by Singer & Nicolson (1972).
• Cell wall of fungi – chitin; plants – cellulose; bacteria – peptidoglycan.
• Nucleus discovered by Robert Brown.
• Golgi apparatus discovered by Camillo Golgi.
• Lysosomes discovered by Christian de Duve.
• Mitochondria discovered by Kolliker; named by Benda.
• Ribosomes discovered by George Palade.
All living organisms are made of cells. Cell is the basic structural and functional unit of life. Study of cell is called
Cytology. Robert Hooke (1665) first observed cells in cork. Leeuwenhoek first saw free-living cells (bacteria,
protozoa). Schleiden & Schwann proposed Cell Theory (1839). Rudolf Virchow (1855) modified it – "Omnis cellula
e cellula".
Prokaryotic vs. Eukaryotic Cells
• Prokaryotic Cells: Smaller (1–10 µm), no true nucleus, genetic material is naked circular DNA. Examples:
Bacteria, Mycoplasma, Cyanobacteria.
• Eukaryotic Cells: Larger (10–100 µm), nucleus with nuclear envelope, membrane-bound organelles present.
Examples: Plants, Animals, Protists, Fungi.
Cell Envelope (Prokaryotes)
1. Glycocalyx – outermost covering; capsule/slime layer for protection.
2. Cell wall – made of peptidoglycan (murein) in bacteria.
3. Plasma membrane – selectively permeable, fluid mosaic model (Singer & Nicolson). Functions in transport,
respiration, photosynthesis.
Eukaryotic Cell Organelles
• Nucleus – Surrounded by double membrane, contains nucleolus, DNA, chromatin.
• Endoplasmic Reticulum (ER) – RER (with ribosomes, protein synthesis), SER (lipid synthesis, detoxification).
• Golgi Apparatus – Packaging, secretion, glycosylation, lysosome formation.
• Lysosomes – Contain hydrolytic enzymes, "suicidal bags".
• Mitochondria – Double membrane, cristae, matrix; powerhouse of cell, has its own DNA & ribosomes.
• Plastids – Found in plants. Types: Chloroplast (photosynthesis), Chromoplast (color), Leucoplast (storage).
• Ribosomes – 70S (prokaryotes, mitochondria, chloroplast), 80S (eukaryotes).
• Cytoskeleton – Microtubules, microfilaments, intermediate filaments for shape, transport.
• Centrosome & Centrioles – Animal cells only, spindle formation.
• Vacuoles – Large in plants, storage, tonoplast membrane.
Plant vs. Animal Cells
• Plant Cells: Cell wall, chloroplast, large central vacuole, plasmodesmata.
• Animal Cells: No cell wall, no chloroplast, small vacuoles, centrioles present.
Important NEET Points
• Mycoplasma – smallest cell (0.3 µm).
• Ostrich egg – largest single cell.
• Prokaryotic ribosomes – 70S (50S + 30S).
• Eukaryotic ribosomes – 80S (60S + 40S).
• Semi-autonomous organelles: Mitochondria, Chloroplast.
• Fluid mosaic model proposed by Singer & Nicolson (1972).
• Cell wall of fungi – chitin; plants – cellulose; bacteria – peptidoglycan.
• Nucleus discovered by Robert Brown.
• Golgi apparatus discovered by Camillo Golgi.
• Lysosomes discovered by Christian de Duve.
• Mitochondria discovered by Kolliker; named by Benda.
• Ribosomes discovered by George Palade.
