Controlling variables (age 11+) · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Writing a hypothesis and planning a fair test

Science · Scientific Inquiry · ages 11-12
Name ______________________   Date ____________

  1. Priya tests whether water temperature affects sugar's dissolving time. What is her independent variable?

    • The dissolving time she records during each trial
    • The water temperature she changes between conditions
    • The sugar mass she keeps fixed throughout the trials

  2. Which prediction about sugar dissolving gives a scientific reason?

    • Warmer water will shorten the time because its particles move faster.
    • Warmer water will shorten the time because I enjoy using warmer water.
    • Warmer water will shorten the time because that is the result I want.

  3. Control variables are conditions kept the same to help make a fair comparison.

    Circle one:   True   False

  4. Plants can differ naturally. Priya has time for eight height readings at each light level. Which starting plan checks both differences between plants and variation in repeated measurements of each plant?

    • Four plants, two readings each: compare plants and check repeat variation.
    • One plant, eight readings: let repeated readings stand for different plants.
    • Eight plants, one reading each: treat differences between plants as repeat variation.

  5. Priya changes water temperature and times how long a fixed mass of sugar takes to dissolve. What is the dependent variable?

    • The water temperature selected for each trial
    • The water volume kept fixed throughout each trial
    • The dissolving time recorded during each trial

  6. Priya has time for 12 height readings. She plans at least three readings per plant under the same conditions. What is the largest number of separate plants she can include?

    Answer: ______________

  7. A class investigates sugar dissolving in hot water. Which plan reduces the risk of a scald?

    • Have a pupil test the hot water with a finger before pouring it into the cups.
    • Have a pupil hold each cup in one hand while pouring hot water with the other.
    • Have an adult pour into suitable containers on a stable, heatproof surface.

  8. Bilal writes, 'I predict that plants given more light will grow taller.' He has named a change and an expected outcome. What should he add to meet this lesson's prediction plan?

    • The amount of light as the condition he changes
    • A scientific reason for the growth he predicts
    • The plant height as the outcome he will measure
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Writing a hypothesis and planning a fair test W1-mt_Ae56umVlTT-s1

  1. The water temperature she changes between conditions · Water temperature is the condition Priya deliberately changes, so it is the independent variable.
  2. Warmer water will shorten the time because its particles move faster. · Particle movement gives a scientific reason. A preference or a desired result does not explain dissolving.
  3. True · Keeping relevant conditions fixed helps separate the effect of the condition being changed.
  4. Four plants, two readings each: compare plants and check repeat variation. · Four plants provide separate objects to compare. Two readings of each plant allow a repeat comparison. All three plans use eight readings, but only this plan checks both kinds of variation.
  5. The dissolving time recorded during each trial · The dependent variable is the measured outcome. Here, it is dissolving time.
  6. 4 · Reserve three readings for each plant. The largest sample that fits is 12 ÷ 3 = 4 plants. Five plants would need at least 15 readings.
  7. Have an adult pour into suitable containers on a stable, heatproof surface. · Adult handling and suitable containers on a stable surface reduce the risk from hot water. They do not remove every risk.
  8. A scientific reason for the growth he predicts · Bilal names the change and predicts taller plants. He still needs to explain his expectation using science.
Worksheet · LightMySky