GS Paper III · Science & Technology · Biology · Cell Biology · NCERT Class 8/11
🌿 Plant Cell vs Animal Cell — Complete UPSC Notes
Cell Discovery · Cell Types & Shapes · Cell Wall · Plasma Membrane · All Organelles · Plant vs Animal Comparison · Osmosis & Plasmolysis · PYQs & MCQs
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Introduction — Cell as the Basic Unit of Life
Robert Hooke · Cell theory · Prokaryote vs Eukaryote · Cell size & shape
📖 Definition
The cell is the fundamental structural and functional unit of all living organisms. Cells carry out all metabolic activities — energy production, protein synthesis, reproduction, and response to stimuli. Robert Hooke first observed cells in 1665 using a primitive optical microscope, observing cork cells and naming them "cells" (from Latin cellula = small room). Cell Theory (Schleiden & Schwann, 1838–39; Virchow, 1855): (1) All living things are made of cells. (2) Cells are the basic unit of life. (3) All cells arise from pre-existing cells (Omnis cellula-e cellula).
Diversity of Cell Shapes. Cells vary greatly in shape based on their function. Red blood cells: biconcave disc — maximises surface area for O₂ transport. White blood cells: amoeboid — can change shape to engulf pathogens. Columnar epithelial cells: long, narrow — line intestines, maximise absorption. Nerve cell: branched and extremely long — for signal transmission over distances. Tracheid: elongated — for water transport in plants. Mesophyll cells: round/oval — contain chloroplasts for photosynthesis.
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Cell Sizes
Smallest: Mycoplasma (~0.3 μm — among smallest known bacteria)
Bacteria: 3–5 μm
Human RBC: ~7 μm diameter
Animal cell: 10–20 μm
Plant cell: 10–100 μm
Largest single cell: Ostrich egg (~15 cm)
Longest cell: Nerve cell (up to 1 metre!)
Bacteria: 3–5 μm
Human RBC: ~7 μm diameter
Animal cell: 10–20 μm
Plant cell: 10–100 μm
Largest single cell: Ostrich egg (~15 cm)
Longest cell: Nerve cell (up to 1 metre!)
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Prokaryote vs Eukaryote
Prokaryote: No true nucleus, no membrane-bound organelles, 70S ribosomes, 0.5–5 μm. Examples: Bacteria, Cyanobacteria, Archaea.
Eukaryote: True membrane-bound nucleus, membrane-bound organelles, 80S ribosomes (cytoplasm), 10–100 μm. Examples: Plants, Animals, Fungi, Protists.
Eukaryote: True membrane-bound nucleus, membrane-bound organelles, 80S ribosomes (cytoplasm), 10–100 μm. Examples: Plants, Animals, Fungi, Protists.
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Cell Shapes
Disc-like (RBC), Polygonal (epithelial), Columnar (intestinal), Cuboid (kidney tubules), Thread-like/Elongated (nerve, muscle), Irregular (WBC), Spindle-shaped (smooth muscle), Branched (neurons), Spherical (eggs).
Plant cells: typically square/rectangular. Animal cells: irregular/round.
Plant cells: typically square/rectangular. Animal cells: irregular/round.
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Animal Cell & Plant Cell — Labelled Diagrams
All organelles labelled · Structural differences visible · Chloroplast · Cell wall · Vacuole
Animal Cell Anatomy. No cell wall, no chloroplasts, no large central vacuole. Has centrioles (for cell division), lysosomes (suicide bags), cilia (movement). Irregular shape. Nucleus is usually central. Cholesterol in plasma membrane.
Plant Cell Anatomy. Has cell wall (cellulose), large central vacuole, chloroplasts (green, for photosynthesis), plasmodesmata (cytoplasmic connections between cells). Rectangular shape. No centrioles (in most). Sterols (not cholesterol) in plasma membrane.
Animal Cell — Detailed Cross-section. Shows all major organelles in context: Nucleus (central, membrane-bound, contains Nucleolus) surrounded by Rough ER (studded with ribosomes). Smooth ER (lipid synthesis, detoxification). Mitochondria (multiple, for ATP). Lysosomes (green, digestive organelles). Golgi Body (packaging). Centrioles (cell division, only in animal cells). Microtubules (cytoskeleton).
🧱
Plasma Membrane & Cell Wall
Fluid mosaic model · Phospholipid bilayer · Cholesterol · Cellulose · Selective permeability · Plasmodesmata
Plasma Membrane — Fluid Mosaic Model. The cell membrane is a phospholipid bilayer — two layers of phospholipid molecules arranged with hydrophilic (water-loving) heads facing outward and hydrophobic (water-fearing) tails facing inward. Proteins are embedded in and span this bilayer — acting as channels, receptors, enzymes, and transporters. Animal cells contain Cholesterol between phospholipids (regulates membrane fluidity). Plant cells use related sterols instead. The membrane is selectively permeable — controls what enters and exits the cell.
🧱 Plasma Membrane — Key Facts
Composition: Phospholipid bilayer + proteins + carbohydrates (glycocalyx) ± cholesterol (animal) or sterols (plant/fungi)
Model: Fluid Mosaic Model (Singer & Nicolson, 1972) — membrane is fluid (lipids can move) and mosaic (proteins dotted throughout)
Functions: Selective permeability (controls entry/exit), cell signalling (receptor proteins), transport (channel proteins, carrier proteins), structural support
Transport types:
• Passive: Simple diffusion, Facilitated diffusion (no energy)
• Active: Requires ATP (against concentration gradient)
• Bulk: Endocytosis (phagocytosis, pinocytosis), Exocytosis
Model: Fluid Mosaic Model (Singer & Nicolson, 1972) — membrane is fluid (lipids can move) and mosaic (proteins dotted throughout)
Functions: Selective permeability (controls entry/exit), cell signalling (receptor proteins), transport (channel proteins, carrier proteins), structural support
Transport types:
• Passive: Simple diffusion, Facilitated diffusion (no energy)
• Active: Requires ATP (against concentration gradient)
• Bulk: Endocytosis (phagocytosis, pinocytosis), Exocytosis
🌿 Cell Wall — Plant Exclusive
Present in: Plants, Fungi (chitin), Bacteria (peptidoglycan). Absent in animals.
Plant cell wall composition:
• Primary wall (young cells): Cellulose + Hemicellulose + Pectins + Proteins. Flexible — allows growth.
• Secondary wall (mature cells): Cellulose + Lignin (wood). Rigid — no more growth.
• Algae: Cellulose + Galactans + Mannans + Calcium carbonate (in some)
Functions: Structural support, shape maintenance, protection against mechanical damage and pathogens, prevents over-expansion (prevents lysis when water enters)
Plasmodesmata: Channels through cell walls connecting adjacent plant cells — allow cytoplasm communication (symplast pathway)
Plant cell wall composition:
• Primary wall (young cells): Cellulose + Hemicellulose + Pectins + Proteins. Flexible — allows growth.
• Secondary wall (mature cells): Cellulose + Lignin (wood). Rigid — no more growth.
• Algae: Cellulose + Galactans + Mannans + Calcium carbonate (in some)
Functions: Structural support, shape maintenance, protection against mechanical damage and pathogens, prevents over-expansion (prevents lysis when water enters)
Plasmodesmata: Channels through cell walls connecting adjacent plant cells — allow cytoplasm communication (symplast pathway)
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Cell Organelles — Structure & Function
Nucleus · Mitochondria · Chloroplast · Ribosome · ER · Golgi · Lysosome · Vacuole · Centrosome
Nucleus — Control Centre. Double-membrane Nuclear Envelope with Nuclear Pores (selective gate for molecules). Nuclear Lamina maintains shape. Inside: Nucleoplasm (fluid), Chromatin (DNA + histone proteins — condenses to chromosomes during division), Nucleolus (rRNA synthesis, ribosome assembly). ER connects to outer nuclear membrane.
🧬 Nucleus — Key Facts
Present in all eukaryotic cells. Usually one per cell (exceptions: RBC = none; Muscle fibres = many nuclei = multinucleate).
Functions: Controls all cell activities. Stores genetic information (DNA). Directs protein synthesis (sends mRNA). Ribosome assembly (Nucleolus).
Nuclear Pores: ~3,000–4,000 per nucleus. Allow selective passage of mRNA, proteins, ribosomes.
Chromatin: DNA + histone proteins. Euchromatin = active (loosely packed). Heterochromatin = inactive (densely packed).
Functions: Controls all cell activities. Stores genetic information (DNA). Directs protein synthesis (sends mRNA). Ribosome assembly (Nucleolus).
Nuclear Pores: ~3,000–4,000 per nucleus. Allow selective passage of mRNA, proteins, ribosomes.
Chromatin: DNA + histone proteins. Euchromatin = active (loosely packed). Heterochromatin = inactive (densely packed).
Special case: Mature human Red Blood Cells (RBCs) have NO nucleus — ejected during maturation to make more room for haemoglobin (maximum oxygen-carrying capacity). RBCs also have no mitochondria — use anaerobic glycolysis only.
Mitochondria — Powerhouse of the Cell. Outer membrane: smooth, permeable to small molecules. Inner membrane: highly folded into Cristae — massive surface area for ATP synthase enzymes. Intermembrane space: H⁺ ion gradient drives ATP synthesis (chemiosmosis). Matrix: contains enzymes for Krebs cycle, own circular DNA (70S ribosomes — endosymbiotic origin).
⚡ Mitochondria — Key Facts
"Powerhouse of the cell" — produces ATP by aerobic respiration.
Double membrane-bound. Has own circular DNA + 70S ribosomes → endosymbiotic origin.
Number varies: 0 (RBC) to thousands (liver cells, muscle cells).
Aerobic respiration: Glucose + O₂ → CO₂ + H₂O + 36–38 ATP.
Stages: Glycolysis (cytoplasm) → Krebs cycle (matrix) → Oxidative phosphorylation (inner membrane).
Present in BOTH plant and animal cells.
Double membrane-bound. Has own circular DNA + 70S ribosomes → endosymbiotic origin.
Number varies: 0 (RBC) to thousands (liver cells, muscle cells).
Aerobic respiration: Glucose + O₂ → CO₂ + H₂O + 36–38 ATP.
Stages: Glycolysis (cytoplasm) → Krebs cycle (matrix) → Oxidative phosphorylation (inner membrane).
Present in BOTH plant and animal cells.
Endosymbiotic Theory (Lynn Margulis): Mitochondria originated from ancient aerobic bacteria engulfed by primitive eukaryotic cells ~2 billion years ago. Evidence: own circular DNA (like bacteria), own 70S ribosomes, own membrane, can self-replicate. Same theory applies to chloroplasts (from cyanobacteria).
Plant Cell Central Vacuole. Occupies up to 90% of a mature plant cell's volume. Surrounded by Tonoplast (single membrane). Contains Cell Sap (water, salts, sugars, organic acids, pigments). Functions: turgor pressure (keeps plant upright — wilting = loss of turgor), storage of nutrients/waste, pigmentation (anthocyanins give flower colour), lysosomal functions (digestion) in plants.
Lysosome — Suicide Bag. Single membrane-bound vesicle containing ~50 types of Hydrolytic Enzymes (acid hydrolases — active at pH 5). Digest carbohydrates, proteins, lipids, nucleic acids. Transport Proteins export digested products. Found in animal cells (and white blood cells especially). Plant cells use vacuoles for similar functions. Autolysis = lysosome rupture → cell self-destruction (tadpole tail loss, finger development).
| Organelle | Structure | Function | 🌿 Plant | 🐾 Animal | Key UPSC Fact |
|---|---|---|---|---|---|
| Ribosome | Two subunits (large + small). No membrane. Prokaryote: 70S (30S+50S). Eukaryote: 80S (40S+60S) | Protein synthesis. Site of translation. | ✅ | ✅ | Only organelle with NO membrane. Found on RER and free in cytoplasm. Mitochondria/Chloroplasts have 70S ribosomes. |
| Rough ER (RER) | Membrane system studded with ribosomes | Synthesis of secretory and membrane proteins. Protein folding and modification. | ✅ | ✅ | Ribosomes on surface → "rough" appearance. Proteins enter ER lumen → transported to Golgi. |
| Smooth ER (SER) | Membrane system, no ribosomes | Lipid synthesis, steroid hormones (testosterone, oestrogen), drug/toxin detoxification (liver), calcium storage (muscle cells) | ✅ | ✅ | Abundantly developed in liver cells (detox) and gonads (hormones). Sarcoplasmic reticulum in muscle = specialised SER. |
| Golgi Apparatus | Stack of flattened membrane sacs (cisternae). Cis face (receives) → Trans face (sends) | Protein sorting, modification, packaging. Produces lysosomes. Secretory pathway. | ✅ | ✅ | "Post office of the cell." Camillo Golgi discovered it. Adds sugars to proteins (glycosylation). Vesicles bud off trans face. |
| Chloroplast | Double membrane. Thylakoids (stacked = Grana). Stroma (fluid). Own DNA + 70S ribosomes. | Photosynthesis. Light reactions (thylakoid). Dark reactions/Calvin cycle (stroma). | ✅ Only plant | ❌ | Endosymbiotic origin from cyanobacteria. Chlorophyll in thylakoid membranes. Leucoplasts = starch. Chromoplasts = colour. |
| Centrosome / Centrioles | Two centrioles (9+3 microtubule arrangement) at right angles | Organises spindle fibres during cell division (mitosis/meiosis). Cell motility. | ❌ (most) | ✅ | Absent in most plant cells (plants use other structures for spindle). Animal cell division requires centrioles. |
| Peroxisome | Single membrane-bound, contains oxidative enzymes | Breaks down fatty acids, amino acids, and hydrogen peroxide (H₂O₂ → H₂O + O₂ via catalase) | ✅ | ✅ | Detoxifies H₂O₂. Important in liver and kidney cells. In plants: photorespiration. |
| Cytoskeleton | Microfilaments (actin), Intermediate filaments, Microtubules (tubulin) | Cell shape, movement, intracellular transport, cell division | ✅ | ✅ | Microtubules form spindle during mitosis. Cilia and flagella are made of microtubules (9+2 arrangement). |
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Plant Cell vs Animal Cell — Master Comparison High Yield
All differences · Presence / Absence · UPSC direct question
| Feature | 🌿 Plant Cell | 🐾 Animal Cell |
|---|---|---|
| Cell wall | ✅ Present (cellulose + hemicellulose + pectin + lignin in secondary) | ❌ Absent |
| Shape | Square / Rectangular (fixed by rigid cell wall) | Irregular / Round (no fixed shape) |
| Size | Larger: 10–100 μm | Smaller: 10–20 μm |
| Plasma membrane | ✅ Present — contains sterols (NOT cholesterol) | ✅ Present — contains Cholesterol |
| Nucleus | ✅ Present (usually peripheral — pushed by vacuole) | ✅ Present (usually central). RBC = no nucleus. |
| Nucleolus | ✅ Present | ✅ Present |
| Mitochondria | ✅ Present (but fewer — chloroplasts supplement energy) | ✅ Present (more abundant — sole energy source) |
| Chloroplast | ✅ Present (photosynthesis — chlorophyll, carotenoids) | ❌ Absent |
| Plastids | ✅ Chloroplasts (green), Leucoplasts (starch), Chromoplasts (colour) | ❌ Absent |
| Vacuole | One large central vacuole (up to 90% of cell volume). Tonoplast membrane. | Multiple small vacuoles (contractile vacuoles in Amoeba) |
| Lysosome | ❌ Usually absent — vacuoles perform lysosomal functions | ✅ Present (especially abundant in WBCs) |
| Centriole / Centrosome | ❌ Absent in most (lower plants like mosses/ferns have them) | ✅ Present — organises spindle during cell division |
| Plasmodesmata | ✅ Present — cytoplasmic channels connecting adjacent cells | ❌ Absent (have gap junctions instead) |
| Ribosome | ✅ 80S in cytoplasm; 70S in chloroplasts & mitochondria | ✅ 80S in cytoplasm; 70S in mitochondria |
| ER (Rough & Smooth) | ✅ Present | ✅ Present |
| Golgi Apparatus | ✅ Present (called Dictyosomes in plants) | ✅ Present |
| Cilia / Flagella | ❌ Absent (pollen tubes grow; gametes in lower plants have flagella) | ✅ Present in some cells (sperm = flagellum; respiratory = cilia) |
| Cytoskeleton | ✅ Present (actin, microtubules) | ✅ Present (more prominent) |
| Peroxisome | ✅ Present (photorespiration) | ✅ Present (H₂O₂ breakdown) |
| Energy | Photosynthesis (chloroplast) + Aerobic respiration (mitochondria) | Aerobic respiration only (mitochondria) |
🧠 Memory — What ONLY Plant Cells Have (The Exclusive 4)
"C-V-C-P" — Cell wall, Vacuole (large central), Chloroplasts, Plasmodesmata
And what ONLY Animal Cells have: C-L-C — Centrioles, Lysosomes (usually), Cholesterol (in membrane)
Note: Lysosomes ARE present in plant cells in some references — but UPSC typically states they are absent in plant cells (vacuoles take over that function).
And what ONLY Animal Cells have: C-L-C — Centrioles, Lysosomes (usually), Cholesterol (in membrane)
Note: Lysosomes ARE present in plant cells in some references — but UPSC typically states they are absent in plant cells (vacuoles take over that function).
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Osmosis, Plasmolysis & Turgor Pressure
Semipermeable membrane · Hypertonic · Hypotonic · Isotonic · Plasmolysis · Turgidity · Flaccidity
📖 Osmosis
Osmosis is the movement of water molecules through a selectively permeable membrane from a region of higher water concentration (lower solute) to a region of lower water concentration (higher solute). This is a type of passive diffusion — no energy required. The plasma membrane is the selectively permeable barrier in cells.
💧→🧂
Hypertonic Solution
Solute concentration OUTSIDE > INSIDE cell. Water moves OUT. Cell shrinks.
Plant cell: Plasmolysis (membrane shrinks away from cell wall). Cell becomes flaccid.
Animal cell: Crenation (cell shrivels). RBC in salt water shrinks.
Plant cell: Plasmolysis (membrane shrinks away from cell wall). Cell becomes flaccid.
Animal cell: Crenation (cell shrivels). RBC in salt water shrinks.
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Isotonic Solution
Solute concentration OUTSIDE = INSIDE cell. No net water movement. Cell stays same size.
Both cells: Normal appearance. Normal saline (0.9% NaCl) is isotonic to human RBCs.
Both cells: Normal appearance. Normal saline (0.9% NaCl) is isotonic to human RBCs.
🧂→💧
Hypotonic Solution
Solute concentration OUTSIDE < INSIDE cell. Water moves IN. Cell swells.
Plant cell: Becomes turgid (rigid, firm). Cell wall prevents bursting. Turgor pressure.
Animal cell: Lysis (bursts). RBC in pure water swells and bursts.
Plant cell: Becomes turgid (rigid, firm). Cell wall prevents bursting. Turgor pressure.
Animal cell: Lysis (bursts). RBC in pure water swells and bursts.
🧠 Why Plants Don't Burst in Hypotonic Solutions — Cell Wall Saves Them!
When a plant cell is placed in pure water (hypotonic), water rushes in by osmosis → cytoplasm swells → pushes against the cell wall → cell wall resists (it's rigid cellulose) → builds up turgor pressure (like inflating a tyre inside a metal cage — the cage doesn't break). This turgor pressure keeps plants upright and firm. If water is lost (drought/salt water) → turgor pressure drops → plant wilts → plasmolysis (in extreme cases, cytoplasm peels away from cell wall). Animal cells have no cell wall → burst immediately in hypotonic solutions (osmotic lysis).
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PYQs & Practice MCQs
UPSC pattern · Cell theory · Organelle functions · Plant vs animal · Osmosis · Mitochondria
📜 UPSC Pattern — Cell Organelles Statements
Pattern Q
Q. Consider the following statements about cell organelles:
- Mitochondria and Chloroplasts both have their own DNA and 70S ribosomes, which supports the Endosymbiotic Theory that they originated from ancient prokaryotes.
- Lysosomes are absent in plant cells because vacuoles perform the digestive function by containing hydrolytic enzymes.
- Centrioles, which help organise the spindle fibres during cell division, are found in all plant cells and all animal cells.
- The Rough Endoplasmic Reticulum (RER) is studded with ribosomes and is involved in the synthesis of proteins destined for secretion or membrane incorporation.
- a) 1 and 4 only
- b) 2 and 3 only
- c) 1, 2 and 4 only ✓
- d) 1, 2, 3 and 4
Statement 1 CORRECT: Both mitochondria (own circular DNA + 70S ribosomes, evolved from aerobic bacteria) and chloroplasts (own circular DNA + 70S ribosomes, evolved from cyanobacteria) show evidence of endosymbiotic origin. Key evidence: own circular DNA (like bacteria), 70S ribosomes (bacterial size — different from cytoplasmic 80S), double membranes, self-replication. Lynn Margulis proposed the Endosymbiotic Theory.
Statement 2 CORRECT: Lysosomes are generally absent in plant cells. The large central vacuole (enclosed by tonoplast membrane) contains hydrolytic enzymes and performs digestive functions (autophagy, breaking down damaged organelles). This is why the plant vacuole is functionally analogous to the animal lysosome.
Statement 3 WRONG: Centrioles are found in animal cells and lower plant cells (mosses, ferns, algae), but are absent in most higher plant cells (angiosperms and gymnosperms). Higher plants organise spindle fibres during cell division using other structures (nuclear envelope, smooth ER, plasmalemma) — without centrioles. This is one of the key differences between plant and animal cell division.
Statement 4 CORRECT: Rough ER (RER) gets its "rough" appearance from ribosomes studded on its cytoplasmic surface. These ribosomes synthesise proteins that are threaded into the ER lumen — these are proteins destined for: secretion (antibodies, digestive enzymes, insulin), the plasma membrane (receptor proteins, channel proteins), other organelles (lysosomes). The RER is continuous with the outer nuclear envelope.
Statement 2 CORRECT: Lysosomes are generally absent in plant cells. The large central vacuole (enclosed by tonoplast membrane) contains hydrolytic enzymes and performs digestive functions (autophagy, breaking down damaged organelles). This is why the plant vacuole is functionally analogous to the animal lysosome.
Statement 3 WRONG: Centrioles are found in animal cells and lower plant cells (mosses, ferns, algae), but are absent in most higher plant cells (angiosperms and gymnosperms). Higher plants organise spindle fibres during cell division using other structures (nuclear envelope, smooth ER, plasmalemma) — without centrioles. This is one of the key differences between plant and animal cell division.
Statement 4 CORRECT: Rough ER (RER) gets its "rough" appearance from ribosomes studded on its cytoplasmic surface. These ribosomes synthesise proteins that are threaded into the ER lumen — these are proteins destined for: secretion (antibodies, digestive enzymes, insulin), the plasma membrane (receptor proteins, channel proteins), other organelles (lysosomes). The RER is continuous with the outer nuclear envelope.
🧪 Practice MCQs — Plant Cell vs Animal Cell (Click to attempt)
Q1. Which of the following combinations correctly lists features found ONLY in plant cells and NOT in animal cells?
- (a) Cell wall, Mitochondria, Ribosome, Vacuole
- (b) Chloroplast, Centriole, Cell wall, Golgi apparatus
- (c) Cell wall, Chloroplast, Plasmodesmata, Large central vacuole
- (d) Nucleus, Cell wall, Lysosome, Chloroplast
Option (c) is correct.
Cell wall (cellulose) ✅ Plant only. Chloroplast ✅ Plant only. Plasmodesmata ✅ Plant only — cytoplasmic channels connecting adjacent plant cells (animal cells have gap junctions instead). Large central vacuole ✅ Plant only — can occupy 90% of cell volume, surrounded by tonoplast.
Option (a) wrong: Mitochondria and Ribosomes are present in BOTH plant and animal cells.
Option (b) wrong: Centrioles are present in animal cells (not plant cells), and Golgi apparatus is in both.
Option (d) wrong: Nucleus is in both; Lysosomes are typically in animal cells (not plant cells).
Cell wall (cellulose) ✅ Plant only. Chloroplast ✅ Plant only. Plasmodesmata ✅ Plant only — cytoplasmic channels connecting adjacent plant cells (animal cells have gap junctions instead). Large central vacuole ✅ Plant only — can occupy 90% of cell volume, surrounded by tonoplast.
Option (a) wrong: Mitochondria and Ribosomes are present in BOTH plant and animal cells.
Option (b) wrong: Centrioles are present in animal cells (not plant cells), and Golgi apparatus is in both.
Option (d) wrong: Nucleus is in both; Lysosomes are typically in animal cells (not plant cells).
Q2. A plant cell is placed in a concentrated sugar solution. After 30 minutes, the cell contents (cytoplasm and vacuole) are observed to have shrunk away from the cell wall. What has occurred and what is the key difference from an animal cell in the same solution?
- (a) The plant cell has undergone Turgidity — sugar entered the cell by active transport; the animal cell would also become turgid since both lack a way to prevent solute entry.
- (b) The plant cell has undergone Plasmolysis — the hypertonic sugar solution drew water out by osmosis, causing the plasma membrane to pull away from the rigid cell wall (which cannot shrink). An animal cell in the same solution would undergo Crenation (shrivel) — it has no cell wall, so the whole cell including membrane shrinks uniformly.
- (c) The plant cell has undergone Cytolysis — the sugar dissolved the cell wall, releasing the cytoplasm. The animal cell would also lyse but more quickly since it lacks a cell wall protection.
- (d) Both plant and animal cells would respond identically — both undergo plasmolysis, with the plasma membrane peeling away from the wall in both cases, since both have similar membrane structures.
Plasmolysis occurs when a plant cell is placed in a hypertonic solution (more concentrated than cell contents). Water exits the cell by osmosis → cytoplasm + vacuole shrink → the plasma membrane pulls away from the cell wall. The cell wall remains in place because it is rigid (cellulose) and does not contract — creating a gap between membrane and wall. This state is called plasmolysis; the cell is called flaccid.
Animal cell in hypertonic solution → Crenation: water leaves by osmosis → the entire cell (membrane + contents) shrinks and becomes spiky/shrivelled — because there is no rigid cell wall to stay in place. The cell membrane itself contracts with the shrinking cytoplasm.
Reversing plasmolysis: If the plasmolysed plant cell is returned to water (hypotonic solution), water re-enters → cytoplasm re-expands → membrane re-contacts cell wall → deplasmolysis. The cell recovers its turgidity. This is reversible if not taken too far (protoplast must remain intact).
Animal cell in hypertonic solution → Crenation: water leaves by osmosis → the entire cell (membrane + contents) shrinks and becomes spiky/shrivelled — because there is no rigid cell wall to stay in place. The cell membrane itself contracts with the shrinking cytoplasm.
Reversing plasmolysis: If the plasmolysed plant cell is returned to water (hypotonic solution), water re-enters → cytoplasm re-expands → membrane re-contacts cell wall → deplasmolysis. The cell recovers its turgidity. This is reversible if not taken too far (protoplast must remain intact).
Q3. Consider these statements about the Golgi apparatus:
1. It receives vesicles from the Rough ER at its cis face and dispatches vesicles from its trans face.
2. It produces lysosomes in animal cells.
3. In plant cells, it is called Dictyosomes and also helps in cell wall formation.
4. It is absent in mature plant cells.
1. It receives vesicles from the Rough ER at its cis face and dispatches vesicles from its trans face.
2. It produces lysosomes in animal cells.
3. In plant cells, it is called Dictyosomes and also helps in cell wall formation.
4. It is absent in mature plant cells.
- (a) 1 and 2 only
- (b) 1, 2 and 4 only
- (c) 1, 2 and 3 only
- (d) 1, 2, 3 and 4
Answer: (c) 1, 2 and 3 only.
Statement 1 CORRECT: The Golgi apparatus works as a processing and dispatch system. Vesicles from RER fuse with the cis face (receiving/entry face, closest to ER). Contents are modified as they move through cisternae. Vesicles bud off from the trans face (sending/exit face) carrying processed proteins/lipids to: lysosomes, plasma membrane, secretion outside cell.
Statement 2 CORRECT: Lysosomes are formed by budding from the trans face of the Golgi apparatus in animal cells. The Golgi packages hydrolytic enzymes (made on RER) into membrane-bound vesicles → these become lysosomes.
Statement 3 CORRECT: In plant cells, the Golgi apparatus is called Dictyosomes. Besides protein processing, Dictyosomes play a role in cell wall formation — they package pectin and hemicellulose components into vesicles that fuse with the plasma membrane and contribute to the growing cell wall (especially during cell division).
Statement 4 WRONG: The Golgi apparatus is present in all living eukaryotic cells — both plant and animal, both young and mature. It is continuously active in protein secretion and membrane maintenance. It is absent in prokaryotes (bacteria) but NOT absent in mature plant cells.
Statement 1 CORRECT: The Golgi apparatus works as a processing and dispatch system. Vesicles from RER fuse with the cis face (receiving/entry face, closest to ER). Contents are modified as they move through cisternae. Vesicles bud off from the trans face (sending/exit face) carrying processed proteins/lipids to: lysosomes, plasma membrane, secretion outside cell.
Statement 2 CORRECT: Lysosomes are formed by budding from the trans face of the Golgi apparatus in animal cells. The Golgi packages hydrolytic enzymes (made on RER) into membrane-bound vesicles → these become lysosomes.
Statement 3 CORRECT: In plant cells, the Golgi apparatus is called Dictyosomes. Besides protein processing, Dictyosomes play a role in cell wall formation — they package pectin and hemicellulose components into vesicles that fuse with the plasma membrane and contribute to the growing cell wall (especially during cell division).
Statement 4 WRONG: The Golgi apparatus is present in all living eukaryotic cells — both plant and animal, both young and mature. It is continuously active in protein secretion and membrane maintenance. It is absent in prokaryotes (bacteria) but NOT absent in mature plant cells.
⚡ Quick Revision — Plant Cell vs Animal Cell
| Topic | Key Facts |
|---|---|
| Cell Discovery | Robert Hooke, 1665 — observed cork cells. Cell Theory: Schleiden & Schwann (1838–39) + Virchow 1855 ("Omnis cellula-e cellula" — all cells from pre-existing cells). |
| Prokaryote vs Eukaryote | Prokaryote: no nucleus, 70S ribosomes, 0.5–5 μm (bacteria, cyanobacteria). Eukaryote: true nucleus, 80S ribosomes, 10–100 μm (plants, animals, fungi, protists). |
| Only in Plant Cells | Cell wall (cellulose), Chloroplasts, Large central vacuole (tonoplast), Plasmodesmata. Golgi = Dictyosomes in plants. |
| Only in Animal Cells | Centrioles (most plant cells lack them), Lysosomes (usually), Cholesterol in plasma membrane. Cilia and flagella in some cells. |
| In Both | Nucleus, Mitochondria, Ribosomes (80S cytoplasm), Rough ER, Smooth ER, Golgi apparatus, Peroxisome, Cytoskeleton, Plasma membrane, Vacuoles (different sizes). |
| Plasma Membrane | Fluid Mosaic Model (Singer & Nicolson, 1972). Phospholipid bilayer + proteins. Animal: cholesterol. Plant: sterols. Selectively permeable. Active + passive transport. |
| Nucleus | Double membrane, Nuclear pores (~3000–4000), Nucleolus (rRNA synthesis), Chromatin (DNA+histones). RBC = no nucleus. Muscle = multinucleate. |
| Mitochondria | Powerhouse. Double membrane, Cristae (inner membrane folds), Matrix (Krebs cycle). Own circular DNA + 70S ribosomes (endosymbiotic theory — from ancient aerobic bacteria). Present in both plant and animal. |
| Chloroplast | Plant only. Thylakoids (light reactions, chlorophyll) + Stroma (dark reactions/Calvin cycle). Own DNA + 70S ribosomes (endosymbiotic from cyanobacteria). Leucoplast = starch, Chromoplast = pigment. |
| Lysosome | Animal cells mainly. Single membrane, hydrolytic enzymes (acid hydrolases). "Suicide bag" — autolysis. Made by Golgi apparatus. Plant vacuoles do same job. |
| Osmosis | Water moves from low solute (high water) to high solute (low water) through semipermeable membrane. Hypertonic = cell loses water (plasmolysis in plants, crenation in animals). Hypotonic = water enters (turgidity in plants — cell wall prevents burst; lysis in animals). Isotonic = no net movement. |
🚨 5 UPSC Traps — Plant Cell vs Animal Cell:
Trap 1 — "Lysosomes are present in plant cells" → DEBATED, but for UPSC: Absent in plant cells. For UPSC purposes, lysosomes are absent in plant cells — the large central vacuole performs digestive functions using hydrolytic enzymes. This is the standard NCERT position. Some advanced texts mention that plant cells do have lysosome-like structures, but in UPSC questions, the accepted answer is that plant cells lack lysosomes (vacuoles substitute).
Trap 2 — "Centrioles are present in all plant cells for spindle formation" → WRONG! Centrioles are absent in most higher plant cells (angiosperms, gymnosperms). Lower plants (mosses, ferns, algae) and fungi DO have centrioles. Higher plants form spindle fibres during cell division without centrioles — using other structures. Statement 3 in the PYQ above directly tests this. Animal cells always have centrioles.
Trap 3 — "Mitochondria and Chloroplasts have 80S ribosomes like other eukaryotic organelles" → WRONG! Mitochondria and Chloroplasts have 70S ribosomes — the bacterial size. The cytoplasm of eukaryotic cells has 80S ribosomes, but these two organelles retain 70S ribosomes as evidence of their prokaryotic ancestral origin (Endosymbiotic Theory). This is why some antibiotics targeting 70S ribosomes can cause mitochondrial side effects at high doses.
Trap 4 — "Plant cells don't undergo osmosis because the cell wall prevents water entry" → WRONG! The cell wall is permeable — it does NOT prevent water from entering. Water passes freely through the cell wall. Osmosis still occurs in plant cells through the plasma membrane (which IS selectively permeable). The cell wall's role is to resist the turgor pressure that builds up after water enters — preventing the cell from bursting, not preventing water entry.
Trap 5 — "All plant cells have chloroplasts" → WRONG! Not all plant cells have chloroplasts. Only cells exposed to light (mesophyll cells in leaves) have chloroplasts. Root cells, vascular tissue cells, and cells in dark environments do NOT have chloroplasts (they may have leucoplasts instead). Also, the plastid story: Chloroplast (green, photosynthesis) → Leucoplast (colourless, starch storage) → Chromoplast (coloured, flower/fruit colour) — these are all interconvertible forms of plastids found in plants.
Trap 1 — "Lysosomes are present in plant cells" → DEBATED, but for UPSC: Absent in plant cells. For UPSC purposes, lysosomes are absent in plant cells — the large central vacuole performs digestive functions using hydrolytic enzymes. This is the standard NCERT position. Some advanced texts mention that plant cells do have lysosome-like structures, but in UPSC questions, the accepted answer is that plant cells lack lysosomes (vacuoles substitute).
Trap 2 — "Centrioles are present in all plant cells for spindle formation" → WRONG! Centrioles are absent in most higher plant cells (angiosperms, gymnosperms). Lower plants (mosses, ferns, algae) and fungi DO have centrioles. Higher plants form spindle fibres during cell division without centrioles — using other structures. Statement 3 in the PYQ above directly tests this. Animal cells always have centrioles.
Trap 3 — "Mitochondria and Chloroplasts have 80S ribosomes like other eukaryotic organelles" → WRONG! Mitochondria and Chloroplasts have 70S ribosomes — the bacterial size. The cytoplasm of eukaryotic cells has 80S ribosomes, but these two organelles retain 70S ribosomes as evidence of their prokaryotic ancestral origin (Endosymbiotic Theory). This is why some antibiotics targeting 70S ribosomes can cause mitochondrial side effects at high doses.
Trap 4 — "Plant cells don't undergo osmosis because the cell wall prevents water entry" → WRONG! The cell wall is permeable — it does NOT prevent water from entering. Water passes freely through the cell wall. Osmosis still occurs in plant cells through the plasma membrane (which IS selectively permeable). The cell wall's role is to resist the turgor pressure that builds up after water enters — preventing the cell from bursting, not preventing water entry.
Trap 5 — "All plant cells have chloroplasts" → WRONG! Not all plant cells have chloroplasts. Only cells exposed to light (mesophyll cells in leaves) have chloroplasts. Root cells, vascular tissue cells, and cells in dark environments do NOT have chloroplasts (they may have leucoplasts instead). Also, the plastid story: Chloroplast (green, photosynthesis) → Leucoplast (colourless, starch storage) → Chromoplast (coloured, flower/fruit colour) — these are all interconvertible forms of plastids found in plants.
