Cell = basic structural & functional unit of life. AMU asks 2–3 MCQs from this chapter — focus on cell theory, membrane transport, prokaryotic vs eukaryotic, organelles, and mitosis vs meiosis.
1) Cell discovery — key scientists
| Scientist | Year | Discovery |
|---|---|---|
| Robert Hooke | 1665 | Discovered cells (cork slice → "little rooms" or cellulae); first to use microscope on biological specimen |
| Antonie van Leeuwenhoek | 1674 | First to observe living cells (bacteria, protozoa, RBCs, sperm) — "animalcules" |
| Robert Brown | 1831 | Discovered the nucleus in orchid root cells |
| M. J. Schleiden & T. Schwann | 1838–39 | Cell Theory — all plants/animals composed of cells |
| Rudolf Virchow | 1855 | "Omnis cellula e cellula" — all cells arise from pre-existing cells |
2) Cell theory
Classical cell theory (Schleiden, Schwann, Virchow):
• All living organisms are composed of one or more cells.
• The cell is the basic structural and functional unit of life.
• All cells arise from pre-existing cells (Virchow's addition).
Modern additions:
• Cells contain hereditary information (DNA) passed from cell to cell.
• Energy flow occurs within cells (metabolism).
• All cells have similar chemical composition.
• All living organisms are composed of one or more cells.
• The cell is the basic structural and functional unit of life.
• All cells arise from pre-existing cells (Virchow's addition).
Modern additions:
• Cells contain hereditary information (DNA) passed from cell to cell.
• Energy flow occurs within cells (metabolism).
• All cells have similar chemical composition.
3) Plasma membrane (Cell membrane)
• Composition: Phospholipid bilayer + proteins (integral & peripheral) + cholesterol + carbohydrates → Fluid Mosaic Model (Singer & Nicolson, 1972).
• Selectively permeable membrane — allows some substances to pass through, not others.
• Functions: Encloses cell contents, regulates entry/exit of substances, cell-to-cell communication, structural support.
• Selectively permeable membrane — allows some substances to pass through, not others.
• Functions: Encloses cell contents, regulates entry/exit of substances, cell-to-cell communication, structural support.
3.1 Transport across the membrane
| Type | Energy? | Direction | Examples |
|---|---|---|---|
| Diffusion | Passive (no ATP) | High → low concentration | O₂, CO₂ movement; perfume spreading; tea diffusing in water |
| Osmosis | Passive (no ATP) | High water potential → low water potential (water moves across semipermeable membrane) | Water absorption by roots; RBC in hypotonic solution → bursts (haemolysis) |
| Facilitated diffusion | Passive (no ATP) | High → low; via carrier/channel proteins | Glucose entry into cells (carrier); Na⁺/K⁺ channels |
| Active transport | Requires ATP | Low → high (against gradient) | Na⁺/K⁺ pump; mineral uptake by roots; glucose reabsorption in kidney |
Key terms:
• Endocytosis — cell engulfs material (solid = phagocytosis, liquid = pinocytosis). Found in Amoeba, WBCs.
• Exocytosis — cell expels material via vesicles (e.g. hormone secretion, neurotransmitter release).
• Plasmolysis — cell shrinks when placed in hypertonic solution (water moves out); used to prove semipermeable nature of membrane.
• Endocytosis — cell engulfs material (solid = phagocytosis, liquid = pinocytosis). Found in Amoeba, WBCs.
• Exocytosis — cell expels material via vesicles (e.g. hormone secretion, neurotransmitter release).
• Plasmolysis — cell shrinks when placed in hypertonic solution (water moves out); used to prove semipermeable nature of membrane.
🔥 AMU PYQ: The movement of water molecules from a region of higher water concentration to lower water concentration through a semipermeable membrane is called:
(A) Diffusion (B) Osmosis (C) Active transport (D) Plasmolysis
Ans: B
(A) Diffusion (B) Osmosis (C) Active transport (D) Plasmolysis
Ans: B
4) Cell wall
• Found in plants (cellulose, hemicellulose, pectin), bacteria (peptidoglycan), fungi (chitin), some protists.
• Functions: Structural support, prevents bursting in hypotonic environment (turgor pressure), protection.
• Permeable — allows all substances to pass through freely.
• Middle lamella (outermost) cements adjacent plant cells together.
• Functions: Structural support, prevents bursting in hypotonic environment (turgor pressure), protection.
• Permeable — allows all substances to pass through freely.
• Middle lamella (outermost) cements adjacent plant cells together.
5) Nucleus (Control centre)
• Discovered by Robert Brown (1831).
• Parts: Nuclear envelope (double membrane with pores), Nucleoplasm, Chromatin (DNA + histones), Nucleolus (rRNA synthesis).
• Functions: Contains genetic material (DNA), controls all cellular activities (via mRNA → protein synthesis), cell division.
• Parts: Nuclear envelope (double membrane with pores), Nucleoplasm, Chromatin (DNA + histones), Nucleolus (rRNA synthesis).
• Functions: Contains genetic material (DNA), controls all cellular activities (via mRNA → protein synthesis), cell division.
5.1 Chromosomes, DNA, genes
| Term | Definition |
|---|---|
| DNA | Deoxyribonucleic acid — the genetic material; double helix (Watson & Crick, 1953) |
| Gene | Segment of DNA coding for a specific protein/trait; basic unit of heredity |
| Chromosome | Condensed, coiled DNA + histone proteins; visible during cell division |
| Chromatin | Uncoiled, thread-like DNA-protein complex in interphase nucleus |
🔥 AMU PYQ: The organelle that controls all cellular activities is:
(A) Mitochondria (B) Nucleus (C) Ribosome (D) Golgi body
Ans: B
(A) Mitochondria (B) Nucleus (C) Ribosome (D) Golgi body
Ans: B
6) Prokaryotic vs Eukaryotic cells
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | Absent (nucleoid — no membrane) | Present (membrane-bound) |
| Membrane-bound organelles | Absent | Present (ER, Golgi, mitochondria, etc.) |
| Ribosomes | 70S (smaller) | 80S (larger; 70S in mitochondria/plastids) |
| Cell wall | Peptidoglycan (in bacteria) | Cellulose (plants), chitin (fungi) |
| DNA | Circular, plasmids present | Linear, associated with histones |
| Size | 0.1–5 µm | 10–100 µm |
| Examples | Bacteria, Archaea, Cyanobacteria | Animals, Plants, Fungi, Protists |
7) Cell organelles — structure and function
| Organelle | Structure | Function |
|---|---|---|
| Endoplasmic Reticulum (ER) | Network of membrane-bound tubules & sacs (cisternae) | RER (with ribosomes) → protein synthesis & transport; SER (no ribosomes) → lipid synthesis, detoxification, Ca²⁺ storage |
| Golgi apparatus | Stacked, flattened membranous sacs (cisternae) | Modification, packaging & sorting of proteins (into vesicles); formation of lysosomes; secretion |
| Lysosomes | Single membrane; contains hydrolytic enzymes (acid hydrolases) | Digestion of waste, old organelles (autophagy), pathogens; "suicide bags" — burst in damaged cells → self-digestion (autolysis) |
| Mitochondria | Double membrane; inner membrane folded into cristae; own DNA & 70S ribosomes | "Powerhouse" — ATP production (aerobic respiration); semi-autonomous |
| Plastids | Double membrane; own DNA & 70S ribosomes | Chloroplasts (chlorophyll) → photosynthesis; Chromoplasts → colour (carotenoids); Leucoplasts → storage (amyloplasts → starch) |
| Vacuoles | Membrane-bound (tonoplast in plants); fluid-filled | Storage (water, nutrients, waste); turgor pressure in plants (large central vacuole); contractile vacuole in Amoeba (osmoregulation) |
| Ribosomes | No membrane; rRNA + proteins; 2 subunits | Protein synthesis (translation); 70S in prokaryotes/mito/plastids; 80S in eukaryotic cytoplasm |
| Cytoskeleton | Microtubules, microfilaments, intermediate filaments | Cell shape, movement (cilia, flagella), intracellular transport |
| Centrosome | Pair of centrioles (9+0 microtubule arrangement); in animal cells only | Spindle fibre formation during cell division |
| Peroxisomes | Single membrane; oxidative enzymes | Breakdown of fatty acids; detox of H₂O₂ (catalase converts it to H₂O + O₂) |
Fig: Eukaryotic cell showing major organelles
🔥 AMU PYQ: The powerhouse of the cell is:
(A) Nucleus (B) Mitochondria (C) Golgi body (D) Ribosome
Ans: B (Mitochondria — site of ATP production)
(A) Nucleus (B) Mitochondria (C) Golgi body (D) Ribosome
Ans: B (Mitochondria — site of ATP production)
🔥 AMU PYQ: Lysosomes are known as:
(A) Powerhouse (B) Suicidal bags (C) Protein factory (D) Packaging unit
Ans: B (Contain hydrolytic enzymes; autolysis when damaged)
(A) Powerhouse (B) Suicidal bags (C) Protein factory (D) Packaging unit
Ans: B (Contain hydrolytic enzymes; autolysis when damaged)
8) Cell division — mitosis vs meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Gamete formation (sexual reproduction) |
| Divisions | One (equational) | Two (meiosis I & II — reductional then equational) |
| Daughter cells | 2 (diploid, identical to parent) | 4 (haploid, genetically different) |
| Chromosome number | Same as parent (2n → 2n) | Half (2n → n) |
| Crossing over | No | Yes (prophase I — exchange of genetic material) |
| Occurs in | Somatic cells (body cells) | Germ cells (ovary, testis) |
| Phases | PMAT (Prophase → Metaphase → Anaphase → Telophase) + Cytokinesis | Meiosis I: Prophase I (with crossing over), Metaphase I, Anaphase I, Telophase I + Meiosis II (PMAT II) |
Mitosis phases briefly:
• Prophase: Chromosomes condense, nuclear envelope breaks, spindle forms.
• Metaphase: Chromosomes align at equator; spindle fibres attach to centromeres.
• Anaphase: Sister chromatids separate → opposite poles.
• Telophase: Nuclear envelope reforms, chromosomes decondense → 2 nuclei → cytokinesis (cleavage furrow in animals, cell plate in plants).
• Prophase: Chromosomes condense, nuclear envelope breaks, spindle forms.
• Metaphase: Chromosomes align at equator; spindle fibres attach to centromeres.
• Anaphase: Sister chromatids separate → opposite poles.
• Telophase: Nuclear envelope reforms, chromosomes decondense → 2 nuclei → cytokinesis (cleavage furrow in animals, cell plate in plants).
🔥 AMU PYQ: In which phase of mitosis do chromosomes align at the equator?
(A) Prophase (B) Metaphase (C) Anaphase (D) Telophase
Ans: B
(A) Prophase (B) Metaphase (C) Anaphase (D) Telophase
Ans: B
9) AMU PYQs — quick revision
Q1. Who discovered the nucleus?
(A) Hooke (B) Brown (C) Virchow (D) Schwann Ans: B
(A) Hooke (B) Brown (C) Virchow (D) Schwann Ans: B
Q2. Cell theory was proposed by:
(A) Hooke & Leeuwenhoek (B) Schleiden & Schwann (C) Darwin & Wallace (D) Watson & Crick Ans: B
(A) Hooke & Leeuwenhoek (B) Schleiden & Schwann (C) Darwin & Wallace (D) Watson & Crick Ans: B
Q3. The "suicide bags" of the cell are:
(A) Ribosomes (B) Lysosomes (C) Nucleus (D) Mitochondria Ans: B
(A) Ribosomes (B) Lysosomes (C) Nucleus (D) Mitochondria Ans: B
Q4. The semi-fluid matrix inside the cell is called:
(A) Nucleoplasm (B) Cytoplasm (C) Protoplasm (D) Cytosol Ans: B
(A) Nucleoplasm (B) Cytoplasm (C) Protoplasm (D) Cytosol Ans: B
Q5. Which organelle is involved in protein synthesis?
(A) Mitochondria (B) Ribosome (C) Lysosome (D) Golgi body Ans: B
(A) Mitochondria (B) Ribosome (C) Lysosome (D) Golgi body Ans: B
Q6. Plasmolysis occurs when a plant cell is placed in:
(A) Hypotonic solution (B) Hypertonic solution (C) Isotonic solution (D) Water Ans: B
(A) Hypotonic solution (B) Hypertonic solution (C) Isotonic solution (D) Water Ans: B
Q7. Which cell organelle is semi-autonomous?
(A) Ribosome (B) Mitochondria (C) Golgi (D) ER Ans: B (has own DNA, 70S ribosomes)
(AMU 2021)
(A) Ribosome (B) Mitochondria (C) Golgi (D) ER Ans: B (has own DNA, 70S ribosomes)
(AMU 2021)
Q8. The number of daughter cells formed by mitosis is:
(A) 1 (B) 2 (C) 4 (D) 8 Ans: B
(A) 1 (B) 2 (C) 4 (D) 8 Ans: B
Q9. Crossing over occurs during:
(A) Mitosis (B) Meiosis I (C) Meiosis II (D) Both B and C Ans: B (Prophase I)
(A) Mitosis (B) Meiosis I (C) Meiosis II (D) Both B and C Ans: B (Prophase I)
Q10. Which of the following is present in prokaryotes?
(A) Nucleus (B) Mitochondria (C) 70S ribosomes (D) ER Ans: C
(A) Nucleus (B) Mitochondria (C) 70S ribosomes (D) ER Ans: C
Q11. The membrane of the vacuole is called:
(A) Tonoplast (B) Plasmalemma (C) Nuclear envelope (D) Cell wall Ans: A
(A) Tonoplast (B) Plasmalemma (C) Nuclear envelope (D) Cell wall Ans: A
Q12. Which plastid is responsible for photosynthesis?
(A) Chromoplast (B) Chloroplast (C) Leucoplast (D) Amyloplast Ans: B
(A) Chromoplast (B) Chloroplast (C) Leucoplast (D) Amyloplast Ans: B
📝 Pro Tip for AMU: High-weight topics: cell theory (names & years), membrane transport (diffusion vs osmosis), nucleus (control centre), mitochondria (powerhouse), lysosomes (suicidal bags), plastids (types), mitosis vs meiosis (purpose, chromosome number, crossing over). Prokaryotic vs eukaryotic is a guaranteed MCQ — focus on 70S vs 80S ribosomes.