← Module 5: Scientific Investigations

NSWInvestigating ScienceSyllabus dot point

Inquiry Question 1: What are the steps and considerations necessary to plan and conduct a scientific investigation?

Develop and evaluate questions and hypotheses for scientific investigation

A focused answer to the HSC Investigating Science Module 5 dot point on inquiry questions and hypotheses. Covers what makes a question testable, the difference between a hypothesis and a prediction, falsifiability, and worked HSC past exam questions.

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What this dot point is asking

NESA wants you to construct a testable hypothesis from an inquiry question, distinguish a hypothesis from a prediction, and evaluate whether a proposed hypothesis is scientifically valid. Hypothesis construction is examined every year in Investigating Science.

The answer

A scientific investigation starts with an inquiry question that frames what we want to know. A good inquiry question is specific, answerable through observation or experiment, and connects to existing scientific knowledge.

From inquiry question to hypothesis

An inquiry question becomes a testable investigation through a hypothesis.

Hypothesis
A proposed explanation for an observation, written as a statement that names the variables and predicts a relationship. A scientific hypothesis must be falsifiable: there must be possible observations that would disprove it.
Example inquiry question
Does temperature affect the rate of an enzyme-catalysed reaction?
Hypothesis
As temperature increases from 10 to 40 degrees Celsius, the rate of catalase-mediated decomposition of hydrogen peroxide will increase, reaching a maximum near 37 degrees Celsius and then decreasing as the enzyme denatures.

Hypothesis versus prediction

These are related but distinct.

  • A hypothesis is a general statement about the relationship between variables.
  • A prediction is a specific, measurable outcome derived from the hypothesis under defined experimental conditions, usually phrased "if... then...".

Example. Hypothesis: temperature affects enzyme activity. Prediction: if catalase is exposed to 70 degrees Celsius for 5 minutes, then the rate of oxygen production will fall to less than 10 per cent of the rate at 37 degrees Celsius.

Falsifiability (Popper)

Philosopher Karl Popper argued that the defining feature of a scientific claim is that it can be proven wrong. A hypothesis like "consciousness influences quantum events" cannot be falsified by any conceivable experiment and is therefore not scientific. "Aspirin reduces fever in adults at 500 mg doses" can be falsified by a controlled trial and is therefore scientific.

What makes a good hypothesis

A scientifically valid hypothesis:

  1. Names the variables. Independent variable (what you change) and dependent variable (what you measure).
  2. Predicts a direction. Increase, decrease, or no change.
  3. Is measurable. "Better" or "more" are not measurements. Specify units.
  4. Is falsifiable. There must be possible outcomes that would disprove it.
  5. Is based on existing knowledge. Not a wild guess, but a reasoned proposal grounded in prior science.

Past exam questions, worked

Real questions from past NESA papers on this dot point, with our answer explainer.

2022 HSC3 marksDistinguish between a hypothesis and a prediction, using an example.
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A 3-mark answer needs clear definitions, the relationship between the two, and a worked example.

Hypothesis
A testable proposed explanation for an observation, written as a statement that can be supported or falsified by evidence. A good hypothesis names the variables and the expected relationship.
Prediction
A specific, measurable outcome derived from the hypothesis under defined conditions, often phrased "if... then...".
Example
Observation: bean plants near a window grow taller than those in the cupboard.

Hypothesis: Light intensity affects the growth rate of bean plants.

Prediction: If bean plants are grown under 1000 lux for two weeks, then they will be at least 50 per cent taller than identical plants grown under 100 lux.

The hypothesis names the relationship between variables. The prediction states what we expect to observe if the hypothesis is correct. Markers reward both definitions and a worked example that clearly shows the difference.

2024 HSC4 marksA student wrote: 'Plants grow better with music.' Evaluate this as a scientific hypothesis.
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A 4-mark answer needs identification of the flaws, an explicit judgement, and a corrected version.

The statement is not a scientifically valid hypothesis.

  1. Undefined variables. "Better" is not measurable. Growth could mean height, leaf number, biomass or flowering rate. The hypothesis must specify the dependent variable.

  2. Undefined treatment. "Music" is not specified. Classical at 60 dB and heavy metal at 90 dB are different stimuli with different vibration patterns.

  3. Not falsifiable as stated. Without measurable variables, there is no way to design an experiment that could disprove the claim.

Improved hypothesis. "Exposure to 60 dB classical music increases the height of Phaseolus vulgaris seedlings after 14 days compared to silent controls."

This version names the independent variable (60 dB classical music), the dependent variable (height after 14 days), the organism (a specific species) and is falsifiable: an experiment will either show a measurable difference or it will not. Markers reward identification of measurable-variable problems, falsifiability and a corrected version.

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