Students believed salt water would harm hydra locomotion. They placed 100 hydra in 10% salt water and observed for a week. What was missing?

Question

Students believed salt water would harm hydra locomotion. They placed 100 hydra in 10% salt water and observed for a week. What was missing??  
A. Control  
B. Hypothesis  
C. Observation  
D. Measurement

NursesPath · Accepted Answer

Correct Answer: (A)Control. 
Rationale: The experimental design was missing a control group.A control group is essential for establishing a baseline for comparison and isolating the effect of the independent variable. In this experiment, the students tested the effect of 10% salt water (the independent variable) on hydra locomotion. They had a hypothesis (salt water harms locomotion), and they made observations/measurements. However, they only tested the experimental group (hydra in salt water). Without a parallel control group of hydra kept in their normal freshwater environment under otherwise identical conditions (same temperature, light, food, container type), they cannot attribute any changes in locomotion to the salt. The observed effects could be due to the salt, or they could be due to other factors like starvation, the stress of being transferred, natural lifecycle changes, or disease. The control group would experience all these same conditions except for the salt treatment, allowing the students to compare and determine the specific effect of salinity.A) ControlThis is the critical missing element. A proper experiment compares an experimental group (receives treatment) to a control group (does not receive treatment). The absence of a control group renders the experiment inconclusive.B) HypothesisThe students had a clear hypothesis: "salt water would harm hydra locomotion." This was stated at the beginning, so it was not missing.C) ObservationThe students performed observations by watching the hydra for a week. Observation was part of their method.D) MeasurementWhile not explicitly stated, "observed locomotion" implies some form of qualitative or quantitative measurement (e.g., speed, contraction rate). The flaw is not the lack of measurement technique but the lack of a proper comparison group against which to interpret those measurements.ConclusionThe scientific method requires controlled experimentation to draw valid conclusions. By testing only one condition, the students created a confounded experiment. Any result could have multiple explanations. Including a control group is non-negotiable for credible experimental design.

Students believed salt water would harm hydra locomotion. They placed 100 hydra in 10% salt water and observed for a week. What was missing?

A
Control

B
Hypothesis

C
Observation

D
Measurement

The experimental design was missing a control group.

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Students believed salt water would harm hydra locomotion. They placed 100 hydra in 10% salt water and observed for a week. What was missing?

A Control B Hypothesis C Observation D Measurement

The experimental design was missing a control group.

Topic Flashcards

Mini Quiz

Related Questions

A
Control

B
Hypothesis

C
Observation

D
Measurement