NDA Biology · Formula sheet
Cell Biology formulas
2 formulas, 22 reference tables and 25 common traps for NDA Biology Cell Biology, grouped by subtopic.
Cell Structure Fundamentals — What Every Cell Has
Learn this subtopic in the notesThe increasing-complexity sequence
| 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 features
| 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. |
When a statement says 'ALL cells have X', check it against this table — ribosomes pass, cell wall and organized nucleus fail.
Common traps
Organism is the LAST rung, not an early one
Distractors scramble the order by sliding 'organism' forward (Protein–Organism–Tissue–Organ). The organism is the complete individual — it can never come before the organ or tissue that builds it.
Beware the word 'ALL' in statement questions
'All cells have a cell wall' and 'all cells have a well-organized nucleus' are both FALSE traps. Only the plasma membrane, cytoplasm, ribosomes and DNA are truly universal. Read each statement against the universal list.
Animal cell types: monocyte, basophil, lymphocyte, chondrocyte
A 2024 question listed monocyte, chondrocyte, basophil and lymphocyte and asked how many are animal cells — the answer is all four. Three are white blood cells; the chondrocyte is a cartilage cell. All belong to animals.
Microscopy — Discovering the Cell
Learn this subtopic in the notesWho discovered the cell — the scientist table
| 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 microscope
| 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'. |
Common traps
Hooke saw the cell; Leeuwenhoek saw LIVE cells
Robert Hooke (1665) saw dead cork cells and coined the word 'cell'. Leeuwenhoek later saw living organisms. The question 'who FIRST discovered the cell' wants Hooke.
Retina = eye, not microscope
Mirror, stage and clip are all microscope parts; the retina is the light-sensitive layer of the eye. In a 'which is NOT a part' question, the body-part imposter is the answer.
Cell Wall and Cell Membrane — the Cell's Boundaries
Learn this subtopic in the notesThe plasma membrane — fluid mosaic model
| 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 kingdom
| 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 membrane
| Cell type | Cell membrane? | Cell wall? |
|---|---|---|
| Animal | Yes | No |
| Plant | Yes | Yes (cellulose) Plant cells have BOTH; animal cells have the membrane ONLY. |
Common traps
'Phospholipids only' and 'proteins only' are both traps
The membrane is NOT made of one component. The complete fluid-mosaic recipe is phospholipids + proteins + cholesterol. Options listing a single ingredient are distractors.
Fungus = chitin, NOT cellulose
A statement that 'the fungal cell wall is made of cellulose' is FALSE — fungal walls are chitin. Cellulose is the PLANT wall. This swap is the most common cell-wall distractor (2023 statement question).
Plant cells don't have 'only a wall'
A trap option says plant cells have 'only a cell wall, not a membrane'. False — plant cells have BOTH. The membrane lies inside the wall in every plant cell.
Cell Organelles and Functions — the Chapter's Core
Learn this subtopic in the notesThe organelle map — who does what
| 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 DNA
| 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'
| 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, detox
| 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 osmoregulation
| 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, leucoplast
| 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 organelles
| 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 |
Common traps
Ribosomes have rRNA, but no DNA genome
A ribosome contains rRNA, so 'does it have nucleic acid?' is yes — but it has no DNA genome encoding proteins. When the question asks which organelle lacks 'its own genetic material encoding proteins', the answer is the ribosome.
Plasma membrane has NO nucleic acid
Unlike the nucleus, chloroplast or ribosome, the plasma membrane is purely lipid + protein. In 'which does NOT possess nucleic acid', it is the answer.
Lysosomes digest ORGANIC, not 'all inorganic'
A statement saying lysosomes 'break down all inorganic materials' is FALSE — their hydrolytic enzymes act on organic macromolecules (proteins, lipids, nucleic acids). Watch for this in 'which statement is NOT correct' questions.
Smooth ER detoxifies; rough ER does proteins
The SER's 'additional function' is detoxification — NOT protein synthesis (that's the rough ER). Don't pick 'protein synthesis' for a smooth-ER question.
Vacuoles are NOT absent in animal cells
A common false statement says 'vacuoles are absent in animal cells'. Animal cells have vacuoles too — just smaller and more numerous than the plant central vacuole. Mark this statement as incorrect.
Storage plastid = leucoplast, not chloroplast
The colourless leucoplast is the storage plastid (starch, oil, protein). The green chloroplast photosynthesises. Don't pick chloroplast for a storage question. (There is no 'xanthoplast' — a distractor.)
Mature RBC = no nucleus AND no mitochondria
Distractors say the RBC keeps a nucleus or mitochondria. The mature mammalian RBC has neither, nor an ER — it sacrifices organelles for maximum haemoglobin.
Prokaryotic vs Eukaryotic Cells
Learn this subtopic in the notesProkaryote vs eukaryote — the contrast table
| 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) |
Cell wall, plasma membrane and ribosomes are in BOTH — so they can never be the answer to 'what's exclusive / what's missing'. Look for the membrane-bound feature.
The nucleoid and 'naked' bacterial DNA
| 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) |
Common traps
Cell wall is NOT eukaryote-exclusive
Bacteria (prokaryotes) have a cell wall, so 'cell wall' can never be the answer to 'what is exclusive to eukaryotes'. The eukaryote-only answer is a membrane-bound structure — the nucleus or mitochondria.
Nucleoid vs nucleolus vs nucleosome
The prokaryotic DNA region is the NUCLEOID. The nucleolus (makes ribosomes) and the nucleosome (DNA wound on histones) are EUKARYOTIC structures — both are distractors here.
Osmosis and Tonicity — Water Across the Membrane
Learn this subtopic in the notesOsmosis — the direction water moves
Osmosis — direction of water flow
Naming the water-movement processes
| 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 haemolysis
| 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. |
Common traps
Osmosis vs diffusion — the membrane is the tell
Diffusion needs no membrane and can be any particle; osmosis is specifically WATER across a selectively permeable membrane. If a semi-permeable membrane is mentioned, the answer is osmosis.
Plasmolysis is a PLANT-cell word
Plasmolysis = the membrane shrinking away from the cell WALL, so it applies to walled (plant) cells in a hypertonic solution. An animal cell, with no wall, simply shrinks (crenates) or in extreme cases the opposite — bursts in hypotonic solution (haemolysis).
Detergent bursts the RBC — it doesn't shrink it
A 2% detergent solution dissolves the RBC's lipid bilayer, so water floods in and the cell SWELLS and BURSTS. The trap answer 'the RBC will shrink' describes a hypertonic salt solution, not a detergent.
Cellular Respiration and ATP — the Cell's Energy
Learn this subtopic in the notesATP — the energy currency of the cell
| 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 cytoplasm
| 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 synthesised
| 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) |
Common traps
ATP, not ADP — and not NAD
The energy CURRENCY is ATP. ADP and AMP are spent/lower-energy forms; NAD is an electron carrier in respiration. For 'source of energy in cells', choose ATP.
Glycolysis gives pyruvate + energy, NOT pyruvate + CO2
A favourite distractor pairs pyruvate with carbon dioxide or oxygen. Glycolysis produces pyruvate + energy only — CO2 is released later in the Krebs cycle inside the mitochondrion.
ATP is made at the INNER membrane, not the matrix or outer membrane
ATP synthase and the electron transport chain sit in the INNER mitochondrial membrane. The matrix runs the Krebs cycle and the outer membrane is just a boundary — neither is the ATP-synthesis site.
Cell Division and DNA Replication
Learn this subtopic in the notesPloidy and double fertilization (N, 2N, 3N)
Double fertilization products
- one set of chromosomes (haploid)
- two sets (diploid) — the zygote
- three sets (triploid) — the endosperm
DNA replication and cell division — the sequence
| 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. |
Common traps
Prokaryote and eukaryote division differ
A statement claiming 'both prokaryotes and eukaryotes have the same process for cell division' is FALSE. Prokaryotes split by binary fission; eukaryotes use mitosis (body cells) or meiosis (gametes).
Endosperm is 3N, not 2N
The zygote is 2N (one sperm + egg). The endosperm is 3N because the second sperm fuses with TWO polar nuclei (N + 2N = 3N). Don't give both products the same ploidy.