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Biology & life sciences · 05 / 12

Scientific experiments: control and conclusion

High school foundations · Worked example and 4 exercises with solutions, at your pace.

UnderstandSee an exampleGuided exercise3 progressive challenges

The principle, simply

Experiments test hypotheses by comparing conditions. A control gives a reference; the manipulated variable is the proposed cause. Repeated measurements, other controlled conditions and uncertainty support interpretation. Conclusions remain bounded by protocol and data; no detected effect is not absolute proof of no effect.

THE PICTURE TO REMEMBERScientific experiments: control and conclusion
  1. 01Hypothesis
  2. 02Control and variable
  3. 03Measurements and variation
  4. 04Bounded conclusion

WORKED EXAMPLE

From principle to reasoning

Comparable plant groups receive equal water and light, but only one gets extra nutrient. Growth differences can support an effect if other factors, sample size and variability are examined.

Solve a problem in this subject

  1. Frame a question

    State the relationship to explain and its scale: molecule, cell, organism, population or geological time.

  2. Describe evidence

    Give a measurable observation, unit, comparison and conditions before explaining it. Observation and inference do different jobs.

  3. Connect a mechanism

    Use a precise concept and label arrows as production, transfer, action or transformation. Sequence alone does not prove causation.

  4. Answer with a limit

    Connect evidence and knowledge to the question. Distinguish the simplified model from living systems and identify a missing condition.

YOUR TURN

01 · Try before checking

Why does changing both water and light prevent clear attribution to light?

One hint

Two explanations change together.

Reveal and understand the solution

Differences may result from water, light or interaction. The design must distinguish these effects.

Compare method, conditions and answer; identify the exact part to revisit.

IMPROVE THROUGH PRACTICE

Three additional challenges with solutions

Start with the first challenge. Write your method before opening a hint; use the solution to find the first step that needs work.

Reflect after practising
02 · Recognise and understandLink to this exercise

When testing light effects on plants, what should differ between groups?

A hint to get started

An interpretable comparison limits other differences.

Step-by-step solution
  1. The tested variable is illumination.
  2. Relevant factors such as temperature, water and species should be controlled.
  3. Several plants per group help separate effects from individual variation.

Which step did you miss? Retry without help, then explain why the method works.

03 · Apply the methodLink to this exercise

Does a confirmed prediction prove a hypothesis forever?

A hint to get started

Another explanation might predict the same observation.

Step-by-step solution
  1. The result supports the hypothesis under the tested conditions.
  2. Consider alternatives and reproducibility.
  3. Confirmation is not universal, final proof.

Which step did you miss? Retry without help, then explain why the method works.

04 · Go furtherLink to this exercise

Two groups have different means but large scatter. What should be checked?

A hint to get started

A mean alone does not show uncertainty.

Step-by-step solution
  1. Inspect sample size, spread and measurement methods.
  2. Check comparability of groups and conditions.
  3. Suitable statistical analysis may be needed; the mean difference alone is insufficient.

Which step did you miss? Retry without help, then explain why the method works.

The trap to avoid

Supporting one hypothesis does not eliminate every alternative.

Without notes, can you…

  • Explain the principle in your own words?
  • Rebuild the diagram and its connections?
  • Solve the exercise and justify the method?

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