What initiates an investigation: Marshall and Warren, Von Helmont and Spencer, and departures from the linear scientific method

1. What the syllabus asks and why these three cases

The first inquiry question of Module 5 is What are the reasons for undertaking a scientific investigation? The syllabus answers it with three named cases you must know in detail: Barry Marshall and Robin Warren (bacteria and peptic ulcers), Jan Baptist van Helmont (where a growing plant's mass comes from) and Percy Spencer (the microwave oven). For each one you need four things: the factor that initiated the investigation, the type of data the investigator was after, the hypothesis being tested, and the ways the work departed from the traditional linear model of the scientific method.

The syllabus pairs each case with a reason for investigating. Marshall and Warren were trying to explain a pattern (curved bacteria kept turning up in inflamed stomach tissue). Van Helmont was testing a previous conclusion (the ancient view that plants are built from soil). Spencer was led to a new technology by an unexpected observation, and his follow-up tests were about prediction: if microwaves heat a chocolate bar, they should heat other foods too. Learn these pairings, because short-answer questions often give a one-line stimulus and ask which reason it illustrates.

NESA examines these scientists directly. The 2024 paper asked students to identify the technology Spencer was working with and outline what led to the microwave oven; the 2025 paper asked how Marshall and Warren's methodology differed from the linear model; the 2022 paper asked about controlled variables in van Helmont's experiment; and the 2024 paper set a long question comparing a student plant-growth investigation with van Helmont's. Markers' feedback in 2024 asked students to recognise the importance of the work of scientists named within the syllabus. Vague answers ("he did an experiment and found out plants need water") score poorly. Specific answers name the apparatus, the measurement and the conclusion.

2. Marshall and Warren: a pattern nobody could explain

Initiating factor. In 1979 Robin Warren, a pathologist at Royal Perth Hospital, noticed small curved bacteria in biopsies of inflamed stomach lining. The accepted view was that the stomach was too acidic for bacteria to survive and that peptic ulcers were caused by stress, spicy food and excess acid. Warren kept seeing the same association, a pattern that the existing explanation could not account for. Barry Marshall, a junior physician, joined him in 1981.

Hypothesis. The bacteria (now Helicobacter pylori) cause gastritis and peptic ulcers. A good exam phrasing is: If H. pylori causes gastritis, then a person without gastritis who ingests H. pylori will develop gastritis.

Data sought. First, observational data linking the bacterium to disease in patient biopsies. Second, a pure culture of the organism. Their early culture attempts failed because plates were discarded after about two days; in 1982 plates left over the Easter long weekend incubated for several days and colonies grew. This is a useful example of chance contributing to a result. Third, evidence of causation, not just correlation. Animal models did not work well, so in 1984 Marshall drank a culture of the bacterium himself. Within days he developed symptoms, an endoscopy showed gastritis, and the organism was recovered from his stomach. He then treated himself with antibiotics.

Outcome. Later clinical work showed that antibiotic treatment that eradicates H. pylori greatly reduces ulcer recurrence. Marshall and Warren shared the 2005 Nobel Prize in Physiology or Medicine. Their work was published, debated, replicated by other groups and eventually accepted, which is also a good example of science correcting an established idea.

3. Van Helmont: testing an old conclusion with a balance

Initiating factor. In the early 1600s the dominant idea, inherited from Aristotle, was that plants take in their substance from the soil. Jan Baptist van Helmont set out to test this previous conclusion quantitatively, which was unusual for his time. His account was published after his death, in 1648.

Method. He dried 200 pounds of soil in a furnace, placed it in a large earthenware pot, moistened it with rainwater and planted a willow stem weighing 5 pounds. He covered the pot with a perforated lid to keep out dust, and added only rainwater (or distilled water) for five years. He then weighed the tree and re-dried and re-weighed the soil.

Results and conclusion. The willow weighed about 169 pounds 3 ounces, a gain of about 164 pounds. The soil had lost only about 2 ounces. Van Helmont concluded that the extra mass had come from the water alone.

Strengths you can credit. He measured mass quantitatively; he dried the soil before and after so that water content did not distort the soil mass; he covered the pot to control contamination; and he ran the experiment long enough to produce a large change. Limitations. One tree, so no repetition; no control (for example, a pot of soil with no tree); fallen leaves were not weighed; and he did not consider air. We now know most of the dry mass comes from carbon dioxide fixed in photosynthesis, with water also contributing. His conclusion was valid for the variables he considered, but his design could not test a variable he did not know existed.

4. Spencer: chance observation, prediction and new technology

Initiating factor. Percy Spencer was an engineer at the American company Raytheon, which built magnetrons, the vacuum tubes that generate microwaves for radar sets. Around 1945, while working near an operating magnetron, he noticed that a chocolate bar in his pocket had melted. This was an unplanned observation made by someone with the background knowledge to see its significance.

Hypothesis and prediction. Microwave radiation from the magnetron heats food. If that is true, then other foods placed near the magnetron should also heat up. Spencer tested the prediction with popcorn kernels, which popped, and with an egg, which heated so quickly that it burst. Each test was a prediction derived from the first observation, and each confirmed it.

Data sought. At first the data were qualitative (melting, popping, bursting). The development work that followed needed quantitative data on power, heating time and the design of an enclosed metal box that kept the microwaves contained. Raytheon filed a patent in 1945, and the first commercial microwave oven, the Radarange, appeared in 1947. It was large and expensive; household countertop models came decades later.

Why the case matters. Spencer's work illustrates the link between investigation and technology: a device built for one purpose (radar) led to an observation that produced a different device. It also links to Module 6, where you study how science and technology drive each other. In the 2024 exam, better responses named the magnetron precisely and outlined the chain from observation to testing to development. Weaker responses wrote "radar" or "radiation" without naming the device.

5. The linear model and how real investigations depart from it

The traditional linear model is the textbook sequence: observe, ask a question, research, form a hypothesis, design and run an experiment, analyse data, draw a conclusion, communicate. It is useful for planning, but real investigations rarely follow it in order. NESA asks you to identify specific departures, so learn them case by case.

A strong answer to "How did this investigation differ from the linear model?" names a stage of the linear model, says what the scientist actually did instead, and gives a consequence. For example: The linear model places hypothesis testing in a controlled experiment with a large sample, but Marshall tested causation by ingesting the bacterium himself. A sample of one cannot be repeated or compared with a control, so the result alone could not establish reliability; it needed later clinical trials.

The 2025 feedback noted that some students misused the word unethical. Self-experimentation is risky and unusual, but Marshall consented, so the clearest point is about sample size, repetition and controls, not consent.

6. Exam technique: identify, outline, compare

Questions on these cases come in three main forms. Practise each.

• Identify / outline (2–3 marks). "Outline the factors that led Spencer to develop the microwave oven." Give the context (Raytheon, magnetron for radar), the observation (melted chocolate), and the follow-up tests (popcorn, egg) leading to a patent. Three precise facts earn three marks.
• Explain / describe a methodology (4–5 marks). "Describe van Helmont's investigation and explain why he dried the soil." Describe the measured masses, the five-year time frame and the rainwater; then explain the purpose: drying removes water so that any change in soil mass reflects material taken up by the tree, not moisture.
• Compare / evaluate (6–9 marks). The 2024 paper gave students a modern plant-growth investigation and asked them to compare it with van Helmont's. Build a table or paired paragraphs covering hypothesis, variables, sample size, controls, measurements and conclusion. A model comparison sentence: Both investigations measured change in plant mass, but the student used ten seedlings per treatment and calculated a mean, while van Helmont used a single willow, so the student's results are more reliable.

Use the language of investigation accurately. A hypothesis is a testable statement predicting the relationship between an independent and a dependent variable. A pattern is a regularity in observations. A prediction is a specific expected result derived from a hypothesis. Mixing them up costs marks. When a question asks for a hypothesis, write one sentence that names both variables and the direction of the effect.

Finally, connect the cases to bigger ideas when the question invites it: Marshall and Warren show paradigm change and the role of peer review; van Helmont shows quantitative measurement and the limits of the variables a scientist knows to control; Spencer shows the science-technology cycle.

7. Worked response: a 5-mark question

Practice question (original): Using Marshall and Warren's work, explain how identifying a pattern can lead to a scientific investigation. (5 marks)

Plan. Pattern → hypothesis → data to test it → outcome. Name the people, the organism and at least one specific step.

Model answer. Robin Warren repeatedly observed curved bacteria in biopsies of inflamed stomach tissue, a pattern that conflicted with the accepted view that the acidic stomach was sterile and that ulcers were caused by stress and acid. The consistency of the association led Warren and Barry Marshall to hypothesise that the bacterium, later named Helicobacter pylori, causes gastritis and peptic ulcers. To test this they needed data beyond correlation. They grew the organism in pure culture in 1982, after plates were left to incubate longer than usual, and in 1984 Marshall ingested a culture. He developed gastritis, confirmed by endoscopy, and the bacterium was recovered from his stomach, supporting a causal link. Later studies showed antibiotics that eradicate the bacterium prevent ulcer recurrence. The observed pattern therefore initiated an investigation that overturned an established explanation and changed treatment from long-term acid suppression to antibiotics.

Why it scores well. It states the pattern precisely, shows why it was surprising (the prevailing view), gives a testable hypothesis, describes the data gathered in sequence, distinguishes correlation from causation, and ends with the consequence. It avoids inventing figures: you do not need sample sizes or percentages that you cannot remember accurately, and markers reward accurate qualitative detail over made-up numbers.

Common trap. Writing that Marshall "proved" bacteria cause all ulcers. Some ulcers have other causes, notably long-term use of anti-inflammatory drugs. Say the work showed that H. pylori is a major cause.