Introduction to Experimental Design

Part A

Which of the following statements is not true of scientific experiments?

	They must be well documented.
	They yield useful results regardless of whether the hypothesis is supported or rejected.
	They must occur under carefully controlled conditions found in a laboratory.

Correct

Not all experiments are performed under laboratory conditions; many occur outdoors in uncontrolled conditions. Scientists must account for these variations when designing experiments.

Part B

In an experiment, investigators try to control all of the variables except one—the one that tests the hypothesis. Which of the following reasons is the primary rationale for controlling variables in an experiment?

	To enable investigators to repeat the test
	To eliminate alternative explanations for the results of an experiment
	To create a control group

Correct

Controlling all variables but one ensures that some other factor is not responsible for the results obtained from an experiment.

Part C

Which of the following statements could not be supported or rejected by a scientific experiment?

	College students think football is more fun to watch than baseball.
	Grass is green because it contains chlorophyll.
	The first living cell on Earth came from outer space

Correct

An experiment could not be designed to test this statement. Science neither supports nor rejects this idea.

Part D

Which of the following statements is true of a hypothesis?

	A hypothesis can be proved.
	A hypothesis can be supported or rejected through experimentation.

Correct

A hypothesis is supported or rejected based on the outcome of one or more experiments.

Part E

Which of the following variables did Pasteur change in his experiment to test the hypothesis of spontaneous generation?

	The length of time that the flasks were allowed to sit before being sampled for organisms
	The shape of the flask
	The length of time that the broth was boiled
	The broth used in each flask

Correct

By using a swan-necked flask for the experimental treatment, Pasteur ensured that no cells were entering the flask from the air. Thus, any organisms that appeared in the experimental flask would have arisen spontaneously.

Part F

In Pasteur's experiment to test the hypothesis of spontaneous generation, why did he boil the broth in both flasks?

	To provide nutrients to stimulate the growth of microorganisms
	To expose the broth to a source of organisms
	To attract dust particles to each flask
	To kill any existing organisms in the broth

Correct

Pasteur boiled the broth to kill any existing organisms, thus ensuring that the conditions in each flask were identical (i.e., lacking organisms) at the start of the experiment.

Part G

What results from the Zonosemata experiment support the sub-hypothesis that wing waving alone reduces predation by jumping spiders?

	Zonosemata flies with their own wings cut and reglued are attacked less frequently.
	Houseflies with Zonosemata wings are attacked less frequently.
	Zonosemata flies with housefly wings are attacked less frequently.
	Untreated Zonosemata flies are attacked less frequently.

Correct

This experimental group tests the effects of wing waving alone.

Part H

Suppose that Zonosemata flies whose own wings had been clipped and reattached were attacked more frequently than untreated Zonosemata flies. How would this result affect the reliability of the other experimental results?

	All results for the experimental groups involving wing surgery would be invalid.
	All results for the experimental groups using houseflies would be invalid.
	All results for the experimental groups using Zonosemata flies would be invalid.
	The reliability of the experimental results would not change.

Correct

This result suggests that the presence or absence of wing surgery itself may affect the jumping spider's responses. Thus, there is not enough information to draw conclusions from the data because there is an alternative explanation for the results of the experiment.