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Difficulty: EasyDetermining Control Groups and Baseline Conditions

A science class designed four different experiments to study the effects of various independent variables. Match each experimental setup with the correct control group or baseline condition required to validate the results.

  • Testing the effect of a 5%5\% chemical pesticide solution on the survival rate of honeybees over a 48-hour period.Honeybees kept under identical conditions but exposed only to water containing 0%0\% pesticide.
  • Testing the effect of a 3%3\% sodium chloride (salt) solution on the germination rate of radish seeds.Radish seeds kept under identical conditions and watered only with pure distilled water containing 0%0\% salt.
  • Testing the effect of light intensity on the rate of photosynthesis in *Elodea* plants by placing them 10 cm10\text{ cm} from a light source.*Elodea* plants kept under identical conditions but placed in complete darkness with 0 lux0\text{ lux} of light.
  • Testing the effect of a new friction-reducing engine oil additive on the fuel efficiency of a car driving at 60 mph60\text{ mph}.The same car driving under identical conditions at 60 mph60\text{ mph} using standard engine oil without the new additive.

Answer

Pesticide test matches with honeybees exposed only to water containing 0%0\% pesticide; salt solution test matches with radish seeds watered only with pure distilled water; light intensity test matches with plants placed in complete darkness; engine oil additive test matches with the car using standard engine oil without the additive.
For each setup, the correct match removes the independent variable under test (e.g., setting the pesticide concentration to 0%0\%, salt to 0%0\%, light to 0 lux0\text{ lux}, or removing the additive) while keeping all other experimental conditions constant. This ensures any observed change is due solely to the independent variable.

Step-by-Step Solution

1
Identify the independent variable being manipulated in each experimental setup.
The independent variables are: pesticide concentration (5%5\% vs 0%0\%), salt concentration (3%3\% vs 0%0\%), light intensity (10 cm10\text{ cm} light vs 0 lux0\text{ lux} darkness), and presence of the oil additive.
A control group must keep all variables constant except for the specific independent variable being tested, which is set to a baseline or zero level.
2
Match each experiment with the group that lacks the active independent variable but is otherwise treated identically.
The pesticide experiment matches the group with 0%0\% pesticide; the salt experiment matches the group with 0%0\% salt (pure water); the light experiment matches the group with no light (complete darkness); the oil additive experiment matches the car running with standard oil.
This isolates the effect of the independent variable and rules out external confounding factors.

Key Concept

A control group or baseline condition is an experimental setup where the independent variable is either removed or kept at a standard, neutral level, allowing researchers to isolate the effects of the variable being tested.
Estimated Time:1m 30s
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Topics

Determining Control Groups and Baseline Conditions

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