Scientific Variables Answer Key

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Date:

🔬 Part 1: Variable Identification - Answer Key

1. Plant Growth Experiment: A scientist waters three groups of plants with different amounts of water (50ml, 100ml, 150ml) daily for two weeks and measures their height.

Independent Variable: Amount of water given daily (50ml, 100ml, 150ml)

Dependent Variable: Height of plants (what is measured)

Constants: Type of plants, soil type, pot size, sunlight exposure, temperature, time period (2 weeks)

2. Paper Airplane Experiment: Students test how different paper types (notebook, construction, cardboard) affect how far paper airplanes fly when thrown with the same force.

Independent Variable: Type of paper used (notebook, construction, cardboard)

Dependent Variable: Distance the airplane flies

Constants: Airplane design/fold pattern, throwing force, throwing angle, indoor location, same person throwing

3. Ice Melting Experiment: Ice cubes are placed in three different temperatures of water (32°F, 70°F, 100°F) and the time for complete melting is recorded.

Independent Variable: Temperature of water (32°F, 70°F, 100°F)

Dependent Variable: Time for ice to melt completely

Constants: Size of ice cubes, amount of water, container type, room temperature, starting time

📝 Part 2: Multiple Choice - Answer Key

4. What is the variable that the scientist deliberately changes in an experiment?

Dependent variable

✓

Independent variable

Constant

Control group

Explanation: The independent variable is what the scientist changes on purpose to test its effect.

5. In an experiment testing how fertilizer affects plant growth, what is the dependent variable?

Type of fertilizer

✓

Plant growth/height

Amount of water

Type of soil

Explanation: Plant growth is what you measure - it depends on the fertilizer treatment.

6. Which of these should be kept the same in ALL groups of an experiment? (Check all that apply)

✓

Temperature

✓

Time period

Independent variable

✓

Materials used

Explanation: Constants (temperature, time, materials) must stay the same. Only the independent variable should change.

📊 Part 3: Grading Criteria for Student Experiment Design

Grading Checklist (4 points each):

□ Clear Research Question: Student asks a testable question about cause and effect

□ Independent Variable Identified: Correctly identifies what will be changed (1 thing only)

□ Dependent Variable Identified: Correctly identifies what will be measured

□ Constants Listed: Lists at least 3 things that will stay the same

□ Fair Test Design: Only one variable changes, multiple trials planned

Common Student Errors to Watch For:

• Changing multiple variables at once

• Confusing independent and dependent variables

• Not identifying enough constants

• Questions that can't be tested scientifically

• No plan for multiple trials or measurements

Scoring Guide:

20-18 points: Excellent understanding of variables
17-14 points: Good understanding, minor errors
13-10 points: Basic understanding, needs improvement
Below 10 points: Requires reteaching