Biology • Year 12 • Module 6 • Lesson 2
Mutagens — How Genetic Damage Is Increased
Lock in the mutagen-vs-mutation distinction, the three mutagen categories (radiation, chemical, biological/natural), and the mechanism words a Band 4 answer needs.
1. Label the mutagen-categories diagram
The diagram below sorts the mutagens covered in this lesson into their three HSC categories and shows the mechanism each one uses to increase mutation risk. Fill in the missing labels for boxes A–H. Each label is drawn from the lesson's Key Terms or from Cards 1–4. 8 marks
- A — category name (electromagnetic / ionising parent category) _______________________
- B — DNA-level mechanism caused by UV sunlight _______________________
- C — DNA-level mechanism caused by X-rays / gamma rays _______________________
- D — category name (covers base-modifying compounds and base analogues) _______________________
- E — DNA-level mechanism caused by base-analogue chemicals _______________________
- F — category name (includes background radiation and certain viruses) _______________________
- G — DNA-level mechanism by which a virus increases mutation risk _______________________
- H — the general outcome shared by all six mutagens (one phrase, two words) _______________________
| Box | Your label |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F | |
| G | |
| H |
2. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: mutagen, mutation, UV radiation, ionising radiation, chemical mutagen, base analogue, background radiation, insertion effect, DNA repair, strand break. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 2.1 | Any agent that increases the rate of mutation by damaging DNA or interfering with replication. | |
| 2.2 | The lasting DNA sequence change that remains after damage is unrepaired and copied during replication. | |
| 2.3 | Electromagnetic radiation (e.g. from sunlight) that can cause abnormal bonding between neighbouring bases. | |
| 2.4 | High-energy radiation such as X-rays or gamma rays that can remove electrons from atoms and break DNA strands. | |
| 2.5 | A chemical that alters bases, mimics bases or interferes with the accuracy of DNA replication. | |
| 2.6 | A molecule that resembles a normal DNA base and is incorporated during replication, increasing the chance of mispairing in a later cycle. | |
| 2.7 | Naturally occurring low-level ionising radiation from rocks, soil and cosmic sources. | |
| 2.8 | A change caused when foreign genetic material (e.g. a viral genome) is inserted into host DNA, disrupting a gene or its regulation. | |
| 2.9 | The cellular processes that can correct DNA damage before it is copied, preventing damage from becoming a permanent mutation. | |
| 2.10 | A more severe form of DNA damage — typically caused by ionising radiation — in which one or both backbones of the double helix are cut. |
3. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version on the line below. 10 marks (1 for T/F, 1 for the correction where needed)
3.1 A mutagen and a mutation are two words for the same biological event. T / F
3.2 Exposure to a mutagen guarantees that a permanent mutation will occur in the exposed cell. T / F
3.3 UV radiation and ionising radiation damage DNA by the same mechanism. T / F
3.4 Background radiation is naturally occurring, so it cannot be considered a mutagen. T / F
3.5 DNA damage caused by a mutagen can be corrected by DNA repair before it is copied and fixed into the sequence. T / F
4. Mechanism recall
Answer each in 1–2 sentences using precise mechanism vocabulary from the lesson. 10 marks (2 each)
4.1 What is the function of DNA repair in determining whether mutagen exposure becomes a lasting mutation?
4.2 How does UV radiation damage DNA at the level of bases?
4.3 How does ionising radiation damage DNA differently from UV radiation?
4.4 How does a base-analogue chemical mutagen increase mutation risk during replication?
4.5 How does a mutagenic virus increase mutation risk in its host cell (the "insertion effect")?
5. Build a concept map
Draw labelled arrows between the five terms below to show how they connect from exposure through to a lasting mutation. Each arrow must carry a linking phrase (e.g. "damages", "may be corrected by", "becomes"). Aim for at least 5 labelled arrows. 5 marks
Supplied terms: mutagen · DNA damage · DNA repair · replication · mutation.
Q1 — Labelled diagram
A: radiation (radiation mutagens). B: abnormal bonding between neighbouring bases (DNA distortion that interferes with replication). C: DNA strand break(s) / severe strand disruption. D: chemical (chemical mutagens). E: mispairing during a later replication cycle. F: naturally occurring (natural / biological) mutagens. G: insertion effect — viral genetic material is inserted into host DNA and disrupts a gene or its regulation. H: increased mutation rate / increased mutation risk.
Q2 — Term–definition matches
2.1 mutagen • 2.2 mutation • 2.3 UV radiation • 2.4 ionising radiation • 2.5 chemical mutagen • 2.6 base analogue • 2.7 background radiation • 2.8 insertion effect • 2.9 DNA repair • 2.10 strand break.
Q3 — True / false with correction
3.1 False. Correction: a mutagen is an agent that raises mutation rate; a mutation is the resulting DNA sequence change. They are linked but not the same event.
3.2 False. Correction: exposure to a mutagen increases the chance of mutation. DNA repair may correct the damage before replication, and not all damage is copied into the genome.
3.3 False. Correction: UV typically causes abnormal bonding between neighbouring bases and DNA distortion; ionising radiation has enough energy to remove electrons and can cause DNA strand breaks — a more severe form of damage.
3.4 False. Correction: background radiation is a mutagen — it is low-level ionising radiation that can damage DNA over time. "Natural" does not mean "harmless".
3.5 True.
Q4.1 — Function of DNA repair
DNA repair removes or corrects damaged bases or strand breaks before the cell replicates its DNA. If repair is successful, the damage does not become a permanent sequence change, so the exposed cell carries no mutation despite mutagen exposure. Repair is therefore the main reason why exposure increases risk rather than guaranteeing mutation.
Q4.2 — How UV radiation damages DNA
UV radiation can cause abnormal bonding between neighbouring bases (especially pyrimidines), distorting the DNA molecule. This distortion can interfere with accurate replication and increase mutation risk if the damage is copied.
Q4.3 — How ionising radiation damages DNA differently
Ionising radiation (X-rays, gamma rays) has enough energy to remove electrons from atoms in or around DNA. This can break one or both strands of the double helix, producing more severe and large-scale damage than the base-distortion caused by UV.
Q4.4 — How a base-analogue chemical works
A base analogue is a chemical that resembles a normal DNA base. During replication it can be inserted into a new strand in place of the correct base, then mispair with the wrong partner in a later replication cycle — fixing a base substitution into the sequence.
Q4.5 — How a mutagenic virus works (insertion effect)
A mutagenic virus inserts its own genetic material into the host cell's DNA. The inserted sequence can interrupt a coding region of a gene or change how a gene is regulated, producing a mutation in host gene function — even though the virus is a "natural" source.
Q5 — Sample concept map
A correct map should include arrows such as:
- mutagen — causes → DNA damage
- DNA damage — may be corrected by → DNA repair
- DNA repair — prevents → mutation (no mutation results)
- DNA damage — if copied during → replication
- replication — fixes damage as → mutation
Any biologically valid linking phrases are accepted. Award full marks for at least 5 correctly labelled arrows that respect the cause-effect direction.