1. Introduction to Biology

Experimental Design

Research Methods: Experimental Design

Variables

Gene density is the number of genes per million base pairs (Mbp). Using Figure 20.5b, find the approximate number of genes estimated in water fleas and in humans, and note the size of each genome. Calculate the gene density in water fleas relative to that in humans.

 Yes, an experiment should test only one variable at a time. That way, the experiment will have to be performed only once. 

 No. Experimental results must be repeated before they are considered valid. 

 No, it is not necessary to test only one variable per experiment, especially when time is of the essence. 

 No. That is why scientific research is so time-consuming: It requires time and care. 

 As long as the experiment is repeated a sufficient number of times, it does not matter how many variables are used. 

 No. It does matter. Repetition of confusion does not eliminate the confusion. 

 Yes, an experiment should test only one variable at a time. This ensures that the experimental outcome is clearly due to one identifiable factor. 

Consider the process of hypothesis-based scientific inquiry.

Should an experiment test only one variable at a time? Why or why not?

 measure the amount of sodium in a few bean plants 

 No. The presence of sodium in the plant tissue does not indicate that sodium is a required bean plant nutrient. 

 measure how fast radioactive sodium enters the plant 

 No. The movement of sodium into the bean plant tissue does not indicate that sodium is a required nutrient. 

 look for sodium in leaf tissues using autoradiography 

 No. The presence of sodium in the leaf tissue does not indicate that sodium is a required bean plant nutrient. 

 grow bean plants with and without sodium 

Consider the process of hypothesis-based scientific inquiry that involves the proposing and testing of hypothetical explanations or hypotheses.

The best method for determining whether bean plants require sodium is to __________.

Animation: Metric System Review

 No. However, any study does need to be replicated before the results can be considered valid. 

 nonsystematic observation and analysis of data 

 No. Observational data were collected systematically and presumably quantitatively analyzed. 

How would you improve this study?

Radon is a radioactive gas that seeps into homes from the soil. It is thought to be a cause of lung cancer. A research team investigates this hypothesis. The members of the team gather large amounts of data on basement radon concentrations and lung cancer rates and conclude that the more radon there is in a home, the more likely are people living in the home to develop lung cancer. After the study is published, other researchers criticize it by asserting that the studied neighborhoods with higher radon concentrations also have a higher percentage of older people and a higher percentage of cigarette smokers than the low-radon neighborhoods. Both advanced age and cigarette smoking increase the risk of lung cancer. This criticism, if correct, shows that the radon study suffered from __________.

Nature of Science

What Is Experimental Design? | Chemistry Matters

 No. The experimental plot is the plot that received the experimental treatment or the variable being tested. 

 No. In this experiment, the plot is not a variable. 

Consider the hypothesis-based process of scientific inquiry. What are the components of a well-designed experiment?

A team of scientists has devised a new chemical fertilizer that its members believe will increase crop yields. The team planted three garden plots with corn. The soil was similar in each, and equal amounts of water were applied to each plot. One plot was treated with a common commercial fertilizer, another was treated with the new fertilizer, and the third plot was not given any fertilizer. The experimenters measured yields as bushels of corn from each plot. The plot that did not receive fertilizer was the __________.

A relationship between two factors, for instance, between outside temperature and the number of people with active colds in a population, is known as a(n) a. a. significant result;
b. correlation;
c. hypothesis;
d. alternative hypothesis;
e. experimental test

Introduction to experimental design | High school biology | Khan Academy

What Are Independent, Dependent And Controlled Variables?

Control subjects in an experiment                   .
a. should be similar in most ways to the experimental subjects;
b. should not know whether they are in the control or experimental group;
c. should have essentially the same interactions with the researchers as the experimental subjects;
d. help eliminate alternative hypotheses that could explain experimental results;
e. all of the above

In an experiment to test the effect of temperature bacterial reproduction rate, temperature would be the:

A controlled experiment is one that
a. proceeds slowly enough that a scientist can make careful records of the results.
b. tests experimental and control groups in parallel.
c. is repeated many times to make sure the results are accurate.
d. keeps all variables constant.

Jonathan wants to know which style/model of paper airplane is going to win the contest by traveling the furthest. He designs 5 different models of paper airplanes and drops each of them from the same height of 20 meters. He records the distance that each plane travels before it hits the ground. What are the independent and dependent variables of Jonathan’s experiment?&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Independent Variable: ______________________________________&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Dependent Variable: _______________________________________

 that the drug is effective and testing on humans should begin 

 No. The difference between the control and experimental groups is very small. Statistical methods should be used to determine whether the small difference is likely to be due to chance variation. 

 nothing because no independent variable could be identified 

 No. There is an independent variable in this experiment: the administration of the drug to only one of the two groups of pregnant rats inoculated with the virus. 

 nothing because no control group was used in the test of the drug 

 No. The pregnant rats that were inoculated with the virus and that did not receive the new drug represent the control group for the experiment. 

 that the drug seems to have little effect on viral transmission at the dosage given 

Consider the process of hypothesis-based scientific inquiry. How are data analyzed?

A company was testing a new drug it thought would help decrease the risk of transmission of viruses from mother to fetus. In an experiment to test the compound, an investigator gave 400 pregnant female rats a small dose of the experimental drug and inoculated each with a type of virus known to cause disease in rats. At the same time, 400 other pregnant rats were given only the virus. Of the rat pups born to the females that received both the virus and the drug, 197 showed no symptoms of the disease; 205 rat pups born to the virus-only females showed symptoms. From these data, we can best conclude __________.

A scientist wants to study the effects of nitrogen on wheat plants. They set up an experiment with 4 groups of plants: group A gets 20 pounds of nitrogen per acre, group B gets 40 pounds per acre, group C gets 60 pounds per acre, and group D gets 0 pounds per acre. Which of the following is the control group? Is it a positive or negative control group?

Animation: Atomic Number and Atomic Mass

Experimental Design Example 1 

An experiment in which neither the participants in the experiment nor the technicians collecting the data know which individuals are in the experimental group and which ones are in the control group is known as                   .
a. controlled;
b. biased;
c. double-blind;
d. falsifiable;
e. unpredictable

Sex of the baby alligator and temperature respectively.

Temperature and sex of the baby alligator respectively.

Size of the incubator and size of the baby alligator respectively.

Number of offspring and temperature in the incubator respectively.

The temperature at which an alligator's egg is incubated will determine the sex of the offspring. The dependent and the independent variables in this experiment are ________.

Animation: Introduction to Experimental Design

Negative & Positive Controls

Animation: Electron Distribution Diagrams

False Positives/Negatives

Experimental Research Design: The Art and Practice of Experimental Design (LE: Module 1, Part 1)

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2. Chemistry

3. Water

4. Biomolecules

5. Cell Components