Campbell Mastering Biology: Scientific Method

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

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

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B) They must occur under carefully controlled conditions found in a laboratory.

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

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?

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

C) To eliminate alternative explanations for the results of an experiment

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

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

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

C) The first living cell on Earth came from outer space

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

Which of the following statements is true of a hypothesis?

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

B) A hypothesis can be supported or rejected through experimentation.

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

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

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

A) The shape of the flask

(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.)

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

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

B) To kill any existing organisms in the broth

(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.)

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

A) Untreated Zonosemata flies are attacked less frequently.
B) Houseflies with Zonosemata wings are attacked less frequently.
C) Zonosemata flies with housefly wings are attacked less frequently.
D) Zonosemata flies with their own wings cut and reglued are attacked less frequently.

C) Zonosemata flies with housefly wings are attacked less frequently.

(This experimental group tests the effects of wing waving alone.)

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?

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

C) All results for the experimental groups involving wing surgery would be invalid.

(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.)

For each insect below, indicate whether it is part of an experimental group or a control group when placed in enclosure B. Labels may be used once, more than once, or not at all.

male snowy tree cricket: control group
female snowy tree cricket: experimental group
female field cricket: control group

(In this experiment, your hypothesis is that the male's song communicates information to potential mates. The experimental group provides a direct test of the hypothesis. Female snowy tree crickets compose the experimental group because they are the potential mates of male snowy tree crickets and therefore would be expected to uniquely respond to the male's song. Failure of the experimental group to respond to the male's song would require you to reject your hypothesis.
In addition, control groups test other factors that might influence the experimental outcome. In this experiment, the control groups test whether the male's song functions in frightening potential competitors for mates (other male snowy tree crickets) or competitors for food (female field crickets). If one or both of the control groups respond to the male snowy tree cricket's song, you would have to reject your hypothesis.
In the actual experiment, the female snowy tree crickets turn toward the male in response to his song, but the control groups move randomly in response to the song. These results support your hypothesis.)

Which three of the following statements are valid conclusions that could be drawn from the graph above?

A) The difference between the chirp rates of the two species remains fairly constant across the range of temperatures tested.
B) Crickets of these two species sing only at temperatures between 15 °C and 30 °C.
C) It is possible for a male snowy tree cricket and a male field cricket to sing with the same chirp rate, but only at different temperatures.
D) The change in chirp rate with each change in temperature is similar for the two species.

A) The difference between the chirp rates of the two species remains fairly constant across the range of temperatures tested.
C) It is possible for a male snowy tree cricket and a male field cricket to sing with the same chirp rate, but only at different temperatures.
D) The change in chirp rate with each change in temperature is similar for the two species

(Conclusions derived from the data in the graph have important biological implications for the crickets. For example, the similarity of the slopes of the two plots suggests a common biological cause for this temperature effect. In fact, the chirp rate increases with temperature for both species because metabolism (and thus the crickets' ability to move their legs or wings past each other) increases with increasing temperature.
The observation that the difference between the chirp rates of the two species does not change with temperature indicates that there is no single temperature at which both species chirp at the same rate. However, the two species can produce songs with the same chirp rate at different temperatures.)