Questions, Variables & Fair Investigations — Practice · Grade 7 Science

Chapter: Scientific Inquiry & Diversity of Life

What this practice covers

By the end of Questions, Variables & Fair Investigations you should be able to:

8 questions, written answer, multiple choice and numeric, each with a worked explanation.

Vocabulary used: testable question, independent variable, dependent variable, controlled variable, confound.

Problem 1

Why does defining the outcome before testing help?
Answer and explanation

It keeps the comparison consistent and reduces the temptation to choose whichever observation later supports a favorite explanation.

Problem 2

Two plant groups differ in both soil and water. What claim is too strong?
Answer and explanation

A claim that water alone caused their difference is too strong because soil could also influence growth; separate or control the factors.

Problem 3

Why should an unexpected trial remain in the record?
Answer and explanation

It may represent real variation or reveal a problem worth investigating. Removing it only because it disagrees with a prediction biases the evidence.

Problem 4

Does repeating an unfair test make it fair?
Answer and explanation

No. Repetition can reveal variability while repeating the same confound. The method must change to separate the competing explanations.

Problem 5

Illustrative record: Group A receives 10 mL daily and bright light; Group B receives 5 mL and dim light. After seven days, A gains 4 cm and B gains 1 cm. Identify the intended variable, measured outcome, and confound. Propose a fairer comparison and explain what the current data do establish.
Answer and explanation

The record shows a 3 cm difference in height gain, but both water and light differ. It cannot isolate water’s effect. A revised comparison would keep light, species, starting conditions, and times comparable while changing only the defined water treatment; independent seedlings and recorded variation would strengthen the evidence.

Identify water amount as the intended factor.

Measure height change in centimeters over seven days.

Recognize light as an additional changed factor.

Match light and other conditions, then use several seedlings per group.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A class repeats this same light-confounded comparison ten times. Can it now identify water’s separate effect?
Answer and explanation

No. Repetition does not remove the linked light difference. Redesign the comparison so light is comparable, and use independent seedlings with recorded starting sizes.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which is the dependent variable in a water-and-growth test?
  1. Daily water amount
  2. Height change
  3. Container material
  4. Plant species
Answer and explanation

Height change

Height change is the measured response; daily water is the changed factor.

Problem 8

A seedling starts at 3 cm and ends at 8 cm. Find height change.
Answer and explanation

5 cm

Final minus initial: 8−3=5 cm.

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