identifying variables - Free Printable

Let's solve each of the four experiments by identifying the Independent Variable, Dependent Variable, and Control Variable.

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1) Different rose bushes are grown in a greenhouse for two months. The number of flowers on each bush is counted at the end of the experiment.

- a. Independent Variable: *Type of rose bush*
(This is what is being changed or tested — different varieties of rose bushes.)

- b. Dependent Variable: *Number of flowers on each bush*
(This is what is being measured or observed as a result of the independent variable.)

- c. Control Variable: *Growing conditions (e.g., amount of light, temperature, water, soil type, time period)*
(These factors are kept constant so that only the type of rose bush affects the outcome.)

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2) You water three sunflower plants with salt water. Each plant receives a different concentration of salt solutions. A fourth plant receives pure water. After a two-week period, the height the plant reaches is measured.

- a. Independent Variable: *Concentration of salt solution*
(The different levels of salt in the water are being manipulated.)

- b. Dependent Variable: *Height of the plant*
(This is what is being measured after the treatment.)

- c. Control Variable: *Amount of water given, type of plant, light exposure, soil, container size, temperature, duration of experiment*
(All other conditions are kept the same to isolate the effect of salt concentration.)

> Note: The fourth plant receiving pure water acts as the control group.

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3) Three redwood trees are kept at different humidity levels inside a greenhouse for 12 weeks. One tree is left outside in normal conditions. Height of the tree is measured once a week.

- a. Independent Variable: *Humidity level*
(Different humidity levels are applied to the trees.)

- b. Dependent Variable: *Height of the tree*
(Measured weekly to see how growth is affected.)

- c. Control Variable: *Type of tree, amount of light, temperature, soil, watering schedule, duration of experiment*
(These are kept consistent across all trees except for humidity.)

> Note: The tree left outside under normal conditions serves as the control group.

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4) Pea plant clones are given different amounts of water for a three-week period. The first pea plant receives 400 milliliters a day. The second receives 200 milliliters a day. The third receives 100 milliliters a day. The fourth receives no extra water (only natural rainfall). The height of pea plants is recorded daily.

- a. Independent Variable: *Amount of water given per day*
(This is what is being changed: 400 mL, 200 mL, 100 mL, or none.)

- b. Dependent Variable: *Height of the pea plant*
(This is what is being measured over time.)

- c. Control Variable: *Type of plant (clones), sunlight exposure, soil type, pot size, temperature, initial plant size, duration of experiment*
(All these factors are held constant so that only water amount affects growth.)

> Note: The fourth plant (no extra water) acts as the control group.

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✔ Summary Table:

| Experiment | Independent Variable | Dependent Variable | Control Variable |
|----------|------------------------|--------------------|------------------|
| 1 | Type of rose bush | Number of flowers | Light, temperature, water, soil, time |
| 2 | Salt concentration in water | Plant height | Plant type, light, soil, amount of water, time |
| 3 | Humidity level | Tree height | Light, temperature, soil, water, time |
| 4 | Amount of water given daily | Plant height | Plant type, light, soil, pot size, temperature, time |

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✔ Key Definitions Recap:
- Independent Variable: The factor you change or manipulate.
- Dependent Variable: The outcome you measure.
- Control Variable: Factors kept constant to ensure a fair test.

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