NDA Biology · Teaching notes
Cell Biology — NDA Biology
Cell Biology is one of the most reliably-tested NDA Biology chapters — 44 PYQs across 2017–2026, almost all EASY or MODERATE, and almost all pure named-fact recall. The single biggest cluster is cell organelles (17 of 44 questions): which organelle has its own DNA, which one digests, which one builds lipids. Memorise that table and you bank a third of the chapter. The chapter teaches in eight movements, building from what a cell is up to how it divides: (1) Cell structure fundamentals — what every living cell must have, the levels-of-organization ladder, and the cell theory; (2) Microscopy — who discovered the cell and the parts of a compound microscope; (3) Cell wall and cell membrane — the fluid-mosaic membrane and the cellulose / chitin / peptidoglycan wall facts; (4) Cell organelles — the powerhouse, the suicide bags, the transport network and the DNA-bearing organelles (the chapter's core); (5) Prokaryotic vs eukaryotic cells — nucleoid vs nucleus, naked DNA, and what a prokaryote lacks; (6) Osmosis and tonicity — water movement, plasmolysis and haemolysis; (7) Cellular respiration and ATP — glycolysis, the mitochondrion, and where ATP is made; (8) Cell division and DNA replication — ploidy, double fertilization, and how prokaryotes and eukaryotes divide differently. Most concepts are reference tables: learn the table, win the marks.
Subtopic notes
Cell Structure Fundamentals — What Every Cell Has
6 PYQsThe cell is the smallest unit of life; every living cell — whether a bacterium or a human nerve cell — must have a plasma membrane, cytoplasm, ribosomes and genetic material, while only some have a cell wall or an organized nucleus.
Open note
Microscopy — Discovering the Cell
2 PYQsThe cell was discovered with the microscope: Robert Hooke first saw and named 'cells' in cork in 1665, and the compound microscope (mirror, stage, clip, lenses) is the tool that made all of cell biology possible.
Open note
Cell Wall and Cell Membrane — the Cell's Boundaries
4 PYQsEvery cell has a plasma (cell) membrane — a fluid mosaic of phospholipids, proteins and cholesterol; only plants, fungi and bacteria add a rigid cell wall on top, made of cellulose, chitin and peptidoglycan respectively.
Open note
Cell Organelles and Functions — the Chapter's Core
17 PYQsOrganelles are the tiny working compartments of a eukaryotic cell — the mitochondrion makes energy, the lysosome digests, the endoplasmic reticulum transports and builds lipids, and three organelles (mitochondria, chloroplasts, nucleus) carry their own DNA.
Open note
Prokaryotic vs Eukaryotic Cells
5 PYQsProkaryotic cells (bacteria) have no membrane-bound nucleus — just a 'nucleoid' of naked circular DNA — and no membrane-bound organelles; eukaryotic cells (plants, animals, fungi) have a true nucleus and organelles like mitochondria.
Open note
Osmosis and Tonicity — Water Across the Membrane
4 PYQsOsmosis is the net movement of water across a selectively permeable membrane from a dilute (high-water) solution to a concentrated (low-water) one; tonicity decides whether a cell swells, shrinks or bursts.
Open note
Cellular Respiration and ATP — the Cell's Energy
4 PYQsCells release energy from glucose in stages: glycolysis in the cytoplasm splits glucose into pyruvate (+ ATP), and the mitochondrion finishes the job, making most of the cell's ATP — the universal energy currency — at its inner membrane.
Open note
Cell Division and DNA Replication
2 PYQsBefore a cell divides it copies its DNA (replication); the loose chromatin then coils into rod-shaped chromosomes. Eukaryotes divide by mitosis/meiosis, but prokaryotes divide differently — by binary fission.
Open note
PYQ weightage by concept
25 concepts · 44 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
25 concepts · 44 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Universal vs optional cell features | 5 | 11% |
| The increasing-complexity sequence | 1 | 2% |
| Levels of organization — molecules to organismfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Who discovered the cell — the scientist table | 1 | 2% |
| Parts of a compound microscope | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| Cell wall composition by kingdom | 2 | 5% |
| The plasma membrane — fluid mosaic model | 1 | 2% |
| Animal vs plant cell — wall and membrane | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| Organelles with their own DNA | 7 | 16% |
| Lysosomes — the digestive 'suicide bags' | 3 | 7% |
| Endoplasmic reticulum — transport, lipids, detox | 3 | 7% |
| Vacuoles — storage and osmoregulation | 2 | 5% |
| Plastids — chloroplast, chromoplast, leucoplast | 1 | 2% |
| Red blood cells — a cell with almost no organelles | 1 | 2% |
| The organelle map — who does whatfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Prokaryote vs eukaryote — the contrast table | 3 | 7% |
| The nucleoid and 'naked' bacterial DNA | 2 | 5% |
| Concept | PYQs | Share |
|---|---|---|
| Naming the water-movement processes | 2 | 5% |
| Tonicity outcomes — plasmolysis and haemolysis | 2 | 5% |
| Osmosis — the direction water movesfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Glycolysis — breaking glucose in the cytoplasm | 2 | 5% |
| ATP — the energy currency of the cell | 1 | 2% |
| The mitochondrion — where ATP is synthesised | 1 | 2% |
| Concept | PYQs | Share |
|---|---|---|
| DNA replication and cell division — the sequence | 1 | 2% |
| Ploidy and double fertilization (N, 2N, 3N) | 1 | 2% |
Formula & revision sheet
2 formulas · 22 reference tables · 25 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
2 formulas · 22 reference tables · 25 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (2)
The increasing-complexity sequence4 rows
| Step | Level | What it is |
|---|---|---|
| 1 (simplest) | Protein | A molecule — chemical building block |
| 2 | Tissue | Group of similar cells doing one job |
| 3 | Organ | Several tissues working together |
| 4 (most complex) | Organism | The whole living individual Organism is ALWAYS last — any option listing it earlier is a distractor. |
Universal vs optional cell features6 rows
| Feature | In all cells? | Note |
|---|---|---|
| Plasma membrane | Yes — universal | Outer boundary of every cell |
| Cytoplasm | Yes — universal | The cell's internal fluid |
| Ribosomes | Yes — universal | Even prokaryotes have them (70S) |
| Genetic material (DNA) | Yes — universal | Present in every cell |
| Cell wall | No — optional | Plants/fungi/bacteria have it; animal cells do NOT 'All cells have a cell wall' is FALSE — animal cells lack one. |
| Well-organized nucleus | No — optional | Eukaryotes only; prokaryotes have a nucleoid 'All cells have a well-organized nucleus' is FALSE — prokaryotes don't. |
Watch out for (3)
- Organism is the LAST rung, not an early one→ The increasing-complexity sequence
- Beware the word 'ALL' in statement questions→ Universal vs optional cell features
- Animal cell types: monocyte, basophil, lymphocyte, chondrocyte→ Universal vs optional cell features
Reference tables (2)
Who discovered the cell — the scientist table4 rows
| Scientist | Famous for |
|---|---|
| Robert Hooke | First observed and NAMED the cell (cork, 1665) 'Who FIRST discovered the cell?' → Robert Hooke. |
| Anton van Leeuwenhoek | First saw living cells (bacteria, protozoa) |
| Robert Brown | Discovered the nucleus |
| Rudolf Virchow | All cells come from pre-existing cells |
Parts of a compound microscope4 rows
| Part | Microscope or not? |
|---|---|
| Mirror | Yes — reflects light to the specimen |
| Stage | Yes — holds the slide |
| Clip | Yes — secures the slide |
| Retina | No — part of the EYE, not the microscope The retina is the odd-one-out answer in 'which is NOT a microscope part'. |
Watch out for (2)
- Hooke saw the cell; Leeuwenhoek saw LIVE cells→ Who discovered the cell — the scientist table
- Retina = eye, not microscope→ Parts of a compound microscope
Reference tables (3)
The plasma membrane — fluid mosaic model3 rows
| Component | Role in the membrane |
|---|---|
| Phospholipid bilayer | The basic two-layer sheet (heads out, tails in) |
| Proteins | Channels, pumps, receptors embedded in the bilayer |
| Cholesterol (a lipid) | Regulates membrane fluidity The full recipe = phospholipids + proteins + cholesterol — not lipids 'only' or proteins 'only'. |
Cell wall composition by kingdom4 rows
| Organism | Cell wall material | Note |
|---|---|---|
| Plant | Cellulose | A carbohydrate polymer |
| Fungus | Chitin | NOT cellulose — this is the plant-vs-fungus trap Fungal walls are chitin, not cellulose — the bank tests this directly. |
| Bacterium | Peptidoglycan | Also called murein |
| Animal | None | Extracellular matrix of sugars + proteins instead |
Animal vs plant cell — wall and membrane2 rows
| Cell type | Cell membrane? | Cell wall? |
|---|---|---|
| Animal | Yes | No |
| Plant | Yes | Yes (cellulose) Plant cells have BOTH; animal cells have the membrane ONLY. |
Watch out for (3)
- 'Phospholipids only' and 'proteins only' are both traps→ The plasma membrane — fluid mosaic model
- Fungus = chitin, NOT cellulose→ Cell wall composition by kingdom
- Plant cells don't have 'only a wall'→ Animal vs plant cell — wall and membrane
Reference tables (7)
The organelle map — who does what8 rows
| Organelle | Job |
|---|---|
| Mitochondrion | Makes ATP — the powerhouse |
| Chloroplast | Photosynthesis (plant cells) |
| Nucleus | Stores DNA, controls the cell |
| Ribosome | Protein synthesis |
| Endoplasmic reticulum | Transport; smooth ER makes lipids |
| Golgi body | Packaging and secretion |
| Lysosome | Intracellular digestion |
| Vacuole | Storage; water expulsion in unicellulars |
Organelles with their own DNA6 rows
| Organelle | Own DNA? | Note |
|---|---|---|
| Mitochondrion | Yes | Own DNA + ribosomes; makes some proteins Mitochondria + chloroplasts are the 'has its own DNA AND ribosomes' pair. |
| Chloroplast / plastid | Yes | Own DNA + ribosomes (plant cells) |
| Nucleus | Yes | Holds the cell's main DNA |
| Ribosome | No | Carries rRNA (structural), not its own genome |
| Plasma membrane | No | No nucleic acid at all — lipid + protein 'Which organelle does NOT possess nucleic acid?' → plasma membrane. |
| Golgi body / ER / lysosome | No | No own genome |
Lysosomes — the digestive 'suicide bags'4 rows
| Fact about lysosomes | Correct? |
|---|---|
| Rich in hydrolytic (digestive) enzymes | True |
| Waste-disposal system of the cell | True |
| Called 'suicide bags' | True |
| They break down all INORGANIC materials | False Lysosomes digest ORGANIC matter — 'breaks down all inorganic materials' is the wrong statement. |
Endoplasmic reticulum — transport, lipids, detox4 rows
| ER role | Which type | Note |
|---|---|---|
| Transport of materials | ER (general) | Moves substances through cytoplasm/nucleus |
| Lipid synthesis | Smooth ER | A cell that can't make lipids has a defective SER Can't synthesise lipids → the smooth ER is defective. |
| Detoxification | Smooth ER | The SER's 'additional' function (liver cells) SER's extra job = detoxification, not protein synthesis. |
| Protein synthesis | Rough ER | Ribosome-studded surface |
Vacuoles — storage and osmoregulation4 rows
| Vacuole fact | Correct? |
|---|---|
| Large central vacuole can be ~90% of a plant cell | True |
| Provides turgidity and rigidity in plants | True |
| Expels excess water in unicellular organisms | True (contractile vacuole) |
| Vacuoles are absent in animal cells | False Animal cells DO have vacuoles (smaller) — 'absent in animal cells' is the wrong statement. |
Plastids — chloroplast, chromoplast, leucoplast3 rows
| Plastid | Colour | Function |
|---|---|---|
| Chloroplast | Green | Photosynthesis |
| Chromoplast | Red/yellow/orange | Colour of flowers and fruits |
| Leucoplast | Colourless | Stores starch, oil and protein Stores starch + oil + protein granules → leucoplast (not chloroplast). |
Red blood cells — a cell with almost no organelles4 rows
| RBC component | Present? |
|---|---|
| Nucleus | Absent |
| Mitochondria | Absent |
| Endoplasmic reticulum | Absent Mature RBC = NO nucleus, NO mitochondria, NO ER — maximises haemoglobin. |
| Haemoglobin | Present — the cell is packed with it |
Watch out for (7)
- Ribosomes have rRNA, but no DNA genome→ Organelles with their own DNA
- Plasma membrane has NO nucleic acid→ Organelles with their own DNA
- Lysosomes digest ORGANIC, not 'all inorganic'→ Lysosomes — the digestive 'suicide bags'
- Smooth ER detoxifies; rough ER does proteins→ Endoplasmic reticulum — transport, lipids, detox
- Vacuoles are NOT absent in animal cells→ Vacuoles — storage and osmoregulation
- Storage plastid = leucoplast, not chloroplast→ Plastids — chloroplast, chromoplast, leucoplast
- Mature RBC = no nucleus AND no mitochondria→ Red blood cells — a cell with almost no organelles
Reference tables (2)
Prokaryote vs eukaryote — the contrast table5 rows
| Feature | Prokaryote | Eukaryote |
|---|---|---|
| Nucleus | Nucleoid (no membrane) | True membrane-bound nucleus 'Not present in a prokaryote' → the nucleus. |
| Mitochondria | Absent | Present 'Exclusively in eukaryotes' → mitochondria (membrane-bound). |
| Cell wall | Present | Present (plants/fungi) |
| Plasma membrane | Present | Present |
| Ribosomes | Present (70S) | Present (80S) |
The nucleoid and 'naked' bacterial DNA3 rows
| Term | Meaning |
|---|---|
| Nucleoid | The membrane-less DNA region of a prokaryote Nucleoid — not nucleolus (eukaryotic) or nucleosome (DNA+histone unit). |
| 'Naked' DNA | Bacterial DNA NOT bound to histone proteins 'Naked because not associated with' → proteins (histones). |
| Chromosome number | Usually 1 (a single circular chromosome) |
Watch out for (2)
- Cell wall is NOT eukaryote-exclusive→ Prokaryote vs eukaryote — the contrast table
- Nucleoid vs nucleolus vs nucleosome→ The nucleoid and 'naked' bacterial DNA
Reference tables (2)
Naming the water-movement processes3 rows
| Description | Process |
|---|---|
| Water moves dilute → concentrated through a semi-permeable membrane | Osmosis Membrane + water = osmosis, not plain diffusion. |
| Particles spread from high to low concentration (no membrane) | Diffusion |
| Animal cell in lower-water (hypertonic) medium | Cell loses water |
Tonicity outcomes — plasmolysis and haemolysis2 rows
| Surrounding solution | Plant cell | Animal cell |
|---|---|---|
| Hypertonic (water leaves) | Plasmolysis (membrane shrinks from wall) | Shrinks / crenates Epidermal leaf peel in a hypertonic solution → plasmolysis. |
| Hypotonic (water enters) | Becomes turgid (wall holds) | Swells and may burst (haemolysis) RBC in 2% detergent → membrane disrupted → swells and bursts. |
Watch out for (3)
- Osmosis vs diffusion — the membrane is the tell→ Naming the water-movement processes
- Plasmolysis is a PLANT-cell word→ Tonicity outcomes — plasmolysis and haemolysis
- Detergent bursts the RBC — it doesn't shrink it→ Tonicity outcomes — plasmolysis and haemolysis
Reference tables (3)
ATP — the energy currency of the cell4 rows
| Molecule | Role |
|---|---|
| ATP | Energy currency — the form the cell spends Source of energy in cells → ATP (not ADP, AMP or NAD). |
| ADP | Lower-energy form (after ATP is used) |
| AMP | Adenosine monophosphate — lowest energy |
| NAD | Electron carrier, not the energy currency |
Glycolysis — breaking glucose in the cytoplasm3 rows
| Glycolysis fact | Detail |
|---|---|
| Location | Cytoplasm (not the mitochondrion) |
| Products | Pyruvate + energy (ATP) Glucose breakdown in cytoplasm → pyruvate + energy. NO CO2 here. |
| Lactic acid is made from | Pyruvate (under low oxygen) Muscle cramps: pyruvate → lactic acid when oxygen is short. |
The mitochondrion — where ATP is synthesised3 rows
| Mitochondrial part | Role |
|---|---|
| Outer membrane | Smooth boundary |
| Inner membrane (cristae) | Site of ATP synthesis (electron transport chain) ATP-synthesising reactions take place at the INNER membrane. |
| Matrix | Inner fluid (Krebs cycle reactions) |
Watch out for (3)
- ATP, not ADP — and not NAD→ ATP — the energy currency of the cell
- Glycolysis gives pyruvate + energy, NOT pyruvate + CO2→ Glycolysis — breaking glucose in the cytoplasm
- ATP is made at the INNER membrane, not the matrix or outer membrane→ The mitochondrion — where ATP is synthesised
Reference tables (1)
DNA replication and cell division — the sequence3 rows
| Statement | Correct? |
|---|---|
| DNA replicates when chromatin is opened up | True |
| Chromatin forms rod-shaped chromosomes before division | True |
| Prokaryotes and eukaryotes divide by the same process | False Prokaryotes = binary fission; eukaryotes = mitosis/meiosis. NOT the same. |
Watch out for (2)
- Prokaryote and eukaryote division differ→ DNA replication and cell division — the sequence
- Endosperm is 3N, not 2N→ Ploidy and double fertilization (N, 2N, 3N)