Biology · Life, Evidence & Biological Scale
Observations, explanations, hypotheses and biological models
Imagine two labelled groups of seedlings. One group has greater average stem extension. That is a description of a set of measurements. 'Their light conditions caused the difference' adds an explanation that the measurements alone have not established.
No earlier biology course is needed. The data lesson explains its own arithmetic. Chemistry and mathematics offer useful next steps, but you can read this chapter before completing their maps.
Back to the Biology mapBy the end, you can
Separate what was observed from the explanation proposed for it, and identify a testable prediction.
Give each statement a job
An observation records something measured or noticed using a stated method. A hypothesis proposes an explanation that can be tested. A prediction specifies what we expect to observe if that explanation, together with relevant assumptions, is useful. A model represents selected features or relationships; it may be a diagram, a physical representation or a mathematical expression.
Our question is narrow: does changing the specified light condition alter seven-day stem extension in these seedlings? One hypothesis is that light condition contributes to the extension difference. A prediction is an average shift in the proposed direction across many comparable, controlled comparisons. Individual small cohorts may differ or reverse direction by chance. State the proposed direction before looking at the results.
Make each step answer a different question
Read the diagram in words
An observation prompts a question. An explanation produces a prediction, which a comparison tests. Evidence may revise the explanation or the question; this is an iterative guide rather than a mandatory order for every investigation.
- Observation
A difference in recorded extension
- Question
What accounts for the difference?
- Hypothesis
Light condition contributes
- Prediction
An average shift across comparable cohorts
- Comparison
Collect relevant measurements
- Revision
Update the explanation and question
Make a model's omissions visible
Draw an arrow from light condition to stem extension. This is a candidate relationship, not a discovery. Now add temperature, water and starting condition as other possible influences. The larger diagram helps us ask what must be held comparable, recorded or separately investigated.
A model's usefulness depends on its question. A diagram connecting light and extension might help plan a comparison, but it does not explain every biochemical step or predict every plant species. A diagram is easier to understand when its labels say what the arrows mean and what has been left out.
Suppose a repeated comparison does not show the predicted difference. We should check the measurements and the design, then reconsider the explanation and its assumptions. Rejecting one explanation does not automatically establish a favourite alternative. Several possibilities may remain.
Evidence can come through several routes
Not every biological question can be answered by deliberately changing a condition. Researchers can compare observations, examine historical evidence, analyse existing records and develop models as well as perform experiments. The method must fit the question, and the strength of the claim must fit the evidence.
A neat sequence from question to conclusion is a helpful reading guide. Actual investigation can return to earlier steps: an unexpected observation suggests a new question, or another researcher identifies a missing assumption. Changing a model in response to evidence is part of the work.
Worked example
Observation or explanation?
'These five values have a mean of fifty millimetres' can be checked against the data and arithmetic. 'Light increased extension' requires a comparison and a design that addresses alternatives. 'The seedlings wanted to grow faster' supplies an intention without evidence and is not a useful replacement for a biological mechanism.
Check your understanding
Does drawing an arrow between two variables establish that one caused the other?
Show reasoning
No. The arrow expresses the relationship the model proposes. Evidence and a suitable design are still needed.
Your preferred hypothesis fails a prediction. Does this prove the competing hypothesis?
Show reasoning
No. Check the test and its assumptions, then compare the remaining explanations with further evidence.
What to carry forward
Keep observation, explanation, prediction and model distinct, then connect them through a suitable test.
References
Resources supporting this lesson’s explanations and examples.