CDS Biology · Free notes
Cell Biology: CDS Biology
Cell Biology has 41 past-year questions in CDS General Knowledge, from 2016 (II) to 2026 (II): 24 EASY, 15 MODERATE and 2 HARD. The 2019 and 2026 papers asked eight each. Almost all of them are single facts about one part of the cell: which organelle digests, which has its own DNA, which cell has no wall or no nucleus. The organelles carry the most weight, so learn each one's job and the two or three it is usually confused with. Go from the outside in: the kinds of cell, the wall and membrane, the organelles, then the nucleus.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Kinds of Cells and the Microscope
7 PYQsHow a compound microscope makes a cell look bigger, and how a prokaryotic cell such as a bacterium differs from the eukaryotic cells of plants and animals.
Cell Wall, Membrane and Transport
11 PYQsWhich living things have a cell wall and what it is made of, how the cell membrane is built, and how substances cross it: diffusion, osmosis and active transport.
Cell Organelles
17 PYQsThe working parts of a eukaryotic cell: the endoplasmic reticulum and Golgi body, lysosomes and microbodies, mitochondria and plastids with their own DNA, and how to match each organelle to its job.
The Nucleus and Cell Division
6 PYQsWhat the nucleus holds and which cells have none, where RNA is found in a cell, how mitosis differs from meiosis, and how cancer starts and spreads.
Formula & revision sheet
1 formulas · 10 reference tables · 23 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
1 formulas · 10 reference tables · 23 gotchas across all subtopics — the exam-eve cheat-sheet
Kinds of Cells and the Microscope
Reference tables (1)
Prokaryotic and eukaryotic cells5 rows
| Feature | Prokaryotic cell | Eukaryotic cell |
|---|---|---|
| Nucleus | No nuclear membrane; DNA in the nucleoid | True nucleus inside a nuclear membraneQ Asked twice, CDS 2023 (II) and 2026 (I): the region holding a bacterium's DNA is the nucleoid. |
| Mitochondria, Golgi, ER | Absent | Present |
| Ribosomes | Present (70S) | Present (80S)Q CDS 2025 (II): of mitochondria, a nucleus, ribosomes and Golgi bodies, only ribosomes are in a prokaryotic cell. |
| Photosynthetic pigment | On membranous vesicles of the cell membrane | In chloroplastsQ CDS 2019 (II): chlorophyll in photosynthetic bacteria is held on membranous vesicles. |
| Examples | Bacteria, cyanobacteria | Plants, animals, fungi, protists |
Watch out for (4)
- Image size goes on top→ The compound microscope and magnification
- The condenser comes before the objective→ The compound microscope and magnification
- Nucleoid, not nucleolus or nucleosome→ Prokaryotic and eukaryotic cells
- Prokaryotes do have ribosomes and a wall→ Prokaryotic and eukaryotic cells
Cell Wall, Membrane and Transport
Reference tables (3)
The cell wall: who has one and what it is made of5 rows
| Living thing | Cell wall made of |
|---|---|
| Plants | Cellulose |
| Fungi, such as mushrooms | Chitin |
| Bacteria | PeptidoglycanQ CDS 2026 (I): penicillin spares human cells because it targets the bacterial cell wall. |
| Diatoms | Silica |
| Animals, including humans | No cell wallQ Asked three times: CDS 2019 (II), 2021 (I) and 2023 (II). The organism without a wall is always the animal. |
The cell membrane5 rows
| Statement about the cell membrane | True or false |
|---|---|
| It is a phospholipid bilayer with proteins and cholesterol in it | TrueQ CDS 2022 (II): the bilayer is of phospholipid, not of protein or neutral lipid. |
| It is flexible and lets the cell engulf material | TrueQ CDS 2022 (I): this is the correct statement; the other three are false. |
| It is made of cellulose | False: that is the plant cell wall |
| It lets every substance through | False: it is selectively permeable |
| It stops oxygen and carbon dioxide | False: these gases diffuse through it |
Diffusion, osmosis and active transport5 rows
| Process | Direction | Energy used | Example |
|---|---|---|---|
| Diffusion | High to low concentration | None | Oxygen entering a cell |
| Osmosis | Water, through a semi-permeable membrane, from dilute to strong solution | None | Root hairs taking in waterQ CDS 2021 (I): the membrane is semi-permeable, not fully permeable and not the cell wall. |
| Facilitated diffusion | High to low, through a protein channel | None | Na⁺ and Cl⁻ through protein channelsQ CDS 2026 (II): this is the one process in the list that is not active transport. |
| Active transport | Low to high concentration | ATP from respiration | Glucose reabsorbed in the kidney |
| Reverse osmosis | Water forced out of a strong solution | Pressure above the osmotic pressure | Desalination of sea waterQ CDS 2017 (II): the pressure applied is larger than the osmotic pressure. |
Watch out for (7)
- Fungi and bacteria do have walls→ The cell wall: who has one and what it is made of
- Not every wall is cellulose→ The cell wall: who has one and what it is made of
- A bilayer of lipid, not of protein→ The cell membrane
- Membrane and wall are different layers→ The cell membrane
- Active transport runs on respiration→ Diffusion, osmosis and active transport
- A protein channel is not active transport→ Diffusion, osmosis and active transport
- Isotonic means no change→ Diffusion, osmosis and active transport
Cell Organelles
Reference tables (4)
Endoplasmic reticulum, ribosomes and the Golgi body4 rows
| Organelle | Main work |
|---|---|
| Rough ER | Carries ribosomes on its surface; makes and transports proteinsQ CDS 2025 (I): it looks rough because of the ribosomes on its surface. |
| Smooth ER | Makes lipids and steroid hormones; detoxifies drugs in the liverQ CDS 2019 (I): protein synthesis is the one job smooth ER does not do. |
| Ribosome | Joins amino acids into proteins |
| Golgi body | Packs and dispatches products; forms lysosomesQ CDS 2018 (I): lysosomes are formed from the Golgi bodies. |
Lysosomes and microbodies5 rows
| Question about lysosomes | Answer |
|---|---|
| What do they store? | Digestive (hydrolytic) enzymesQ CDS 2019 (I): the lysosome is the storehouse of digestive enzymes. |
| What can they digest? | Food, germs, foreign particles and worn-out cell partsQ CDS 2024 (II): the organelle that digests foreign material in animal cells is the lysosome. |
| Which cell has the most? | White blood cells that engulf germsQ CDS 2026 (I): a white blood cell, not a pancreatic, ovarian or muscle cell. |
| Which organelle makes them? | The Golgi body |
| What do microbodies contain? | EnzymesQ CDS 2024 (I): microbodies in plant and animal cells contain enzymes. |
Mitochondria and plastids: energy and their own DNA5 rows
| Question | Answer |
|---|---|
| Which organelles have their own DNA and ribosomes? | Mitochondria and plastidsQ Asked twice: CDS 2020 (I) (mitochondrion) and 2021 (I) (mitochondria and plastids). |
| Which molecule is the cell's energy currency? | ATP |
| How many carbon atoms does pyruvate have? | ThreeQ CDS 2025 (I): pyruvate is a three-carbon molecule. |
| How many membranes surround a mitochondrion or chloroplast? | Two |
| Which plastids store starch? | Leucoplasts |
Matching organelles to their jobs6 rows
| Organelle | Job |
|---|---|
| Mitochondria | Respiration and ATP formationQ In all three CDS match items (2017 (II), 2023 (II), 2026 (I)) mitochondria go with respiration or ATP. |
| Chloroplast | Photosynthesis |
| Ribosome | Protein synthesis |
| Lysosome | Intracellular digestion |
| Cytoskeleton | Keeps the shape of the cellQ CDS 2026 (I): cytoskeleton with cell shape, smooth ER with detoxification in liver cells, vacuoles with storage and cell enlargement. |
| Vacuole | Storage of sap and chemicals; enlarges the plant cell |
Watch out for (8)
- Smooth ER makes fats, not proteins→ Endoplasmic reticulum, ribosomes and the Golgi body
- Lysosomes come from the Golgi→ Endoplasmic reticulum, ribosomes and the Golgi body
- Suicide bags are lysosomes, not vacuoles→ Lysosomes and microbodies
- Phagocytes, not busy secretory cells→ Lysosomes and microbodies
- Golgi, ER and lysosomes have no DNA→ Mitochondria and plastids: energy and their own DNA
- ATP is the currency, glucose is the fuel→ Mitochondria and plastids: energy and their own DNA
- Ribosome makes; rough ER carries→ Matching organelles to their jobs
- Fix one sure pair first→ Matching organelles to their jobs
The Nucleus and Cell Division
Reference tables (2)
The nucleus, and the cells that have none4 rows
| Cell or part | Nucleus |
|---|---|
| Mature red blood cell (mammal) | None: it is lost as the cell maturesQ CDS 2016 (II): red blood cells and platelets are the two without a nucleus; root hair cells and monocytes have one. |
| Platelet | None: it is a cell fragment |
| White blood cell, muscle cell | Present |
| Plant cell | Present, in its own double membrane, as each chloroplast isQ CDS 2022 (II): in plant cells the nucleus and the chloroplasts are each surrounded by their own membrane. |
Mitosis, meiosis and cancer4 rows
| Feature | Mitosis | Meiosis |
|---|---|---|
| Daughter cells | Two | Four |
| Chromosome number | Same as the parent | Half of the parent (haploid)Q CDS 2026 (II): 'the cells become haploid' is the one statement that is not true of mitosis. |
| Where it happens | Body cells everywhere | Cells that form eggs and sperm |
| Used for | Growth, repair, asexual reproduction | Making gametes |
Watch out for (4)
- Platelets have no nucleus either→ The nucleus, and the cells that have none
- RNA is not only in the nucleus→ The nucleus, and the cells that have none
- Mitosis never halves the number→ Mitosis, meiosis and cancer
- Cancer spreads by blood and lymph→ Mitosis, meiosis and cancer
PYQ weightage by concept
11 concepts · 41 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
11 concepts · 41 PYQs — where the marks actually sit, so you know what to drill first
Kinds of Cells and the Microscope7 PYQs · 17%
| Concept | PYQs | Share |
|---|---|---|
| Prokaryotic and eukaryotic cells | 5 | 12% |
| The compound microscope and magnification | 2 | 5% |
Cell Wall, Membrane and Transport11 PYQs · 27%
| Concept | PYQs | Share |
|---|---|---|
| Diffusion, osmosis and active transport | 5 | 12% |
| The cell wall: who has one and what it is made of | 4 | 10% |
| The cell membrane | 2 | 5% |
Cell Organelles17 PYQs · 41%
| Concept | PYQs | Share |
|---|---|---|
| Lysosomes and microbodies | 5 | 12% |
| Mitochondria and plastids: energy and their own DNA | 5 | 12% |
| Matching organelles to their jobs | 4 | 10% |
| Endoplasmic reticulum, ribosomes and the Golgi body | 3 | 7% |
The Nucleus and Cell Division6 PYQs · 15%
| Concept | PYQs | Share |
|---|---|---|
| The nucleus, and the cells that have none | 4 | 10% |
| Mitosis, meiosis and cancer | 2 | 5% |
Test yourself on Cell Biology
15 past CDS questions from this chapter, timed at 15 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.