Distinguish movement from sensitivity
Connect a change in position with detection and response, including plants.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Read the stated observations before choosing a group.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Can movement involve only one part of an organism?
What you will learn
- Describe movement of an organism or one of its parts.
- Explain sensitivity using a stimulus and a response.
Two processes may appear in one event
Movement means that an organism, or part of it, changes position. A seedling bending toward a light source shows movement even though its roots stay in the same place. Movement does not require walking, a nervous system or a change of location by the whole organism.
Sensitivity links detection of a change to a response. The change can be outside the organism, such as illumination, or inside it, such as blood glucose concentration. Naming a stimulus without naming the resulting response leaves the explanation unfinished.
Use an observation as evidence
When a pupil becomes smaller in brighter light, changing illumination is the stimulus and the change in pupil size is the response. The iris muscles move. The event can therefore illustrate both sensitivity and movement; the two terms answer different questions.
A rolling pebble changes position but does not detect a stimulus and produce a biological response. One physical change alone cannot establish that an object is living.
Sources for this lesson
Pause and explain
Which explanation identifies sensitivity?
Worked example
A shoot bends toward light. Explain which two characteristics are illustrated.
Show the worked solution
- The shoot changes position, which is movement.
- Directional light is the external change.
- The response to that change is evidence of sensitivity.
Answer Movement of the shoot and sensitivity to light.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A leaf folds when touched. Identify movement, stimulus and response.
Give me a hint
Separate the event from its trigger.
Compare my reasoning
- The leaf changes position.
- Touch is the change detected.
- Folding is the response.
Movement: folding; stimulus: touch; response: the leaf folds.
Look for these in your work
- Name the part that moves.
- Distinguish touch from folding.
An organism moves away when the surrounding water becomes more acidic. Explain sensitivity.
Give me a hint
What changed, and what followed?
Compare my reasoning
- Acidity changed in the external environment.
- The organism detected the change.
- Moving away is its response.
Detection of changed acidity followed by moving away.
Look for these in your work
- State the environmental change.
- Give the linked response.
A toy car and a woodlouse both change position. Why is movement alone insufficient to classify them as living?
Give me a hint
Consider the wider collection of life processes.
Compare my reasoning
- Both observations show position changes.
- The toy can move using an external mechanism.
- Evidence about biological processes is also needed.
A position change can be non-biological, so other life processes must be considered.
Look for these in your work
- Avoid claiming that anything moving is alive.
- Identify the missing biological evidence.
Common mistakes
- Plants can move parts without locomotion.
- Do not use one isolated observation as proof of all life processes.
What can you explain now?
A pupil narrows after illumination increases. What is the stimulus?
Compare with the explanation
The increase in light intensity.
The pupil narrowing is the response, whereas the light change is the stimulus.
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Make it stick
Without notes, define movement and sensitivity using two different examples.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.