What you need to know
- Unit 6Decide whether repeats are appropriate, deal with health and safety, and identify ethical issues in the use of living organisms.
Follow the school’s approved organisms and reagents. These notes do not authorise a protocol and they are not clinical advice. Ethical comment is not a substitute for the hazard control, and a hazard control is not a substitute for an ethical comment when that is what was asked.
By the end, you should be able to…
- Say whether repeats help, and which error they do not remove.
- Pair a hazard with an action.
- Identify an ethical issue for the organism actually used, and a way to reduce it.
Build your understanding
Repeats answer scatter, not a broken method
Repeats are appropriate when one reading is a poor guide to the next: different quadratA square frame of known area used to sample organisms., different seeds, an end-point judged by eye, or a zone diameter. They let you see the spread and calculate a mean.
They do not repair a systematic problem. If every respirometer leaks, or every plate is incubated in a way the question did not allow, more repeats copy the same fault. Say that if the question asks whether “do it three times” would solve the problem.
Name the hazard and the action
A useful risk line has two parts. Illustrative pairs, not a local risk assessment, include eye protection when heating reagents, a holder for hot glass, no tasting of laboratory solutions, and closed plates plus disinfectant when microorganisms are cultured. Do not incubate unknown microbes at human body temperature unless the question’s own method says so.
Ethanol near a flame is a fire hazard: keep them apart in the way your teacher specifies. “Be careful” without a named hazard does not show that you judged this experiment.
Ethics matches the organism
The specification asks you to identify ethical issues in the use of living organisms. Name the organism and what the method does to it. Plants can often be identified without uprooting a whole patch. Animals in a trap need a way to be checked and released if the question’s method allows that. A harmful treatment of an animal is hard to justify when a seed, a culture, or a chemical test would answer the same question.
A human volunteer in an exercise or breathing investigation is also a living subject. Do not collect names, do not turn the answer into medical advice, and do not invent a fitness test the question did not set. Ethics is a separate sentence from goggles. Benefits of the science do not replace either sentence.
| The question asks about | Write | Do not write only |
|---|---|---|
| Repeats | Yes or no, and whether the problem is scatter or bias | “Three times” with no reason |
| Health and safety | The hazard of this method and the control | A general benefit of the research |
| Ethics | What happens to the named organism, and a reduced-harm alternative where one exists | Eye protection |
| A controlled variable | How a factor is kept the same | A moral judgement about the organism |
Make your reasoning visible
Answer the sentence that was asked
A risk question needs a hazard and a control. An ethics question needs the organism and the impact. One stock paragraph will not do both.
Repeats: yes, no, or not enough
If the method already has a bias in every trial, say that more trials will not remove it.
Avoid this misconception
The claim: An ethical comment means refusing every investigation that uses a living organism.
The correction: Identify the issue and a way to reduce harm or avoid an unnecessary use. Many specified practicals use organisms. The comment has to match the method you were given.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
An illustrative field method leaves pitfall traps overnight and checks them the next afternoon. Give one ethical problem and one change.
Show suggested answer
Animals may be trapped for a long time without food, water or shelter. Check and empty the traps at shorter stated intervals and release the animals, if that still answers the question. This is a comment on the method, not a field protocol you should invent beyond the question.
Practice question
Retrieval and explanation · suggested answer
Why might repeat quadrats be appropriate when comparing two areas, and what would they not fix?
Show suggested answer
Vegetation varies from place to place, so several quadrats of the same area give a mean and show the spread. They would not fix a quadrat size that was larger in one area than the other, because that bias is in the method.
Practice question
Retrieval and explanation · suggested answer
Write one hazard and one matching control for culturing bacteria from a leaf surface on agar plates.
Show suggested answer
The culture may grow microbes you did not intend, including ones that could be harmful. Keep plates closed, do not open them to smell the colonies, disinfect surfaces, and dispose of plates as your teacher specifies. Do not incubate at human body temperature unless the question’s method says so.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
An unfamiliar plan tests whether a plant extract slows germination by placing brine shrimp in the extract and timing how long they keep swimming. The stated aim is germination, not animal physiology. Give an ethical objection, a safer measurement that still tests the aim, and one hazard that remains.
Show a hint
The organism should be able to answer the question that was asked.
Explore the reasoning
The shrimp are being used for a question about seed germination, so the animal use is unnecessary. Germinate seeds on filter paper with and without a stated volume of extract and record how many germinate, or the time to germinate. Extract and solvent can still be irritant or flammable, so eye protection and keeping the extract off a flame remain hazard controls. The assumption is that germination of these seeds is the dependent variable the question set.
Recall this lesson
Lesson recall questions
Question 1 of 5: A candidate plans to test whether light wavelength affects the rate of photosynthesis. State a suitable null hypothesis.
Unit 6 planning
Practice question
Retrieval and explanation · suggested answer
A candidate plans to test whether light wavelength affects the rate of photosynthesis. State a suitable null hypothesis.
Lesson: P1: A null hypothesis and the variables
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Replace, reduce, refine — when animals are actually the subject
P3 · Repeats, risk and living organismsThe NC3Rs describes three principles for more humane animal research: replacement with methods that do not use animals, reduction by using well-designed studies, and refinement by reducing pain,…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
The NC3Rs describes three principles for more humane animal research: replacement with methods that do not use animals, reduction by using well-designed studies, and refinement by reducing pain, suffering and distress. School practicals are not research laboratories. The principles are enrichment, not a Pearson mark scheme and not a ban you should quote in place of the question. The 3Rs are used when animal research is genuinely proposed. They do not mean that every school seed or yeast investigation needs the same argument. For any living subject, ask what harm the method might cause and whether a less harmful method could answer the question. If human volunteers are involved, their choice and privacy are separate ethical concerns. The response must match the organism in the question.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Planning Plan an investigation: formulate a null hypothesis, identify variables, choose and calibrate apparatus, consider repeats, safety and ethics, and state how data will be used.
Use the science
A plan uses fifty animals where a pilot could have shown that five, properly controlled, would answer the question. Which of the three ideas does that problem illustrate?
Explore a possible response
Reduction: the number of animals is higher than the design needs. It is not, by itself, a reason to skip a hazard control or to change the variables.
Explore the source
- NC3Rs: the 3RsNC3Rs
A volunteer is more than a data point
P3 · Repeats, risk and living organismsUS human-research guidance treats informed consent as an ongoing process: a participant receives relevant information, understands it and chooses voluntarily. A school exercise practical is not automatically a…Specification Unit 6 · PlanningRead & use the scienceClose article
Why this matters
US human-research guidance treats informed consent as an ongoing process: a participant receives relevant information, understands it and chooses voluntarily. A school exercise practical is not automatically a regulated clinical study, but it still involves a person who should be able to decline, stop and avoid sharing identifying health details. This extends Unit 6’s instruction to identify ethical issues with living organisms. It is separate from the physical safety of exercise equipment. A safe protocol can still be unethical if participation is pressured or private measurements are displayed publicly.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 6, pp. 39–42. The application extends beyond required recall.
- Unit 6 · Planning Plan an investigation: formulate a null hypothesis, identify variables, choose and calibrate apparatus, consider repeats, safety and ethics, and state how data will be used.
Use the science
Why are a clear stop rule and voluntary participation two different safeguards in a breathing investigation?
Explore a possible response
A stop rule reduces physical risk if someone becomes unwell; voluntary participation respects the person’s choice to take part at all. Both matter, and neither replaces the other.
Explore the source
- Informed consent FAQsU.S. Department of Health and Human Services