BIO 180 EXAM 1 QUESTIONS AND VERIFIED
ANSWERS
What is the difference between a theory and a hypothesis? - Answers - Only scale--
theories deal with "big ideas" that impact large parts of the physical or natural world;
hypotheses are more focused or narrower in scope.
What is the difference between a hypothesis and a prediction? - Answers - A hypothesis
is an idea--a testable explanation; a prediction is something that follows from a
hypothesis and that you can measure
example of prediction - Answers - If you boil nutrient broth and place it in an air-tight
flask, no cells will appear in the broth
What was important about the experimental design for Pasteur's flask experiment? -
Answers - He compared results from two experimental setups which differed only in the
type of flask in which the nutrient broth was placed
How do biologists test their ideas about the natural world? - Answers - Scientists make
predictions based on hypotheses they have developed, and then design experiments or
other types of studies to test those predictions
Why is it important to perform multiple trials in an experiment -- meaning that you
include many test individuals or samples? - Answers - To make it more likely that the
results are not due to a few unusual individuals or circumstances
The remaining questions refer to this situation: Researchers do an experiment to test
the hypothesis that Douglas fir trees put more resources into reproduction when they
are infected with a fungus that causes a fatal disease. They establish study plots in a
group of 50-year-old Douglas fir where the disease is not present. At random, they inject
half the trees with the disease-causing fungus. Then they measure how many cones
and seeds are produced by infected versus uninfected trees.
What prediction follows from the hypothesis? - Answers - On average, the infected trees
will produce more seeds than uninfected trees
Which treatment would be considered the control? - Answers - The uninfected trees
Why is it important to do the experiment in the same group of same-aged trees? -
Answers - To eliminate the possibility that the results are due to differences in age, soil,
moisture, or other relevant variables
, Why is it important that they assigned trees to the infected versus uninfected groups at
random? - Answers - If assignment were not done at random, the result could be do to
something other than the difference in infection
If the hypothesis is wrong, and being infected with the fungus has no impact at all on
reproduction, what should they observe? - Answers - There will be no difference in the
number of seeds produced by infected versus uninfected seeds
A friend says that this experimental design would be better if the researchers had
injected the control group trees with a solution that was identical to that used in the
experimental group, but without the fungus. Do you agree? - Answers - Yes. As is, it
would be reasonable for a critic to claim that seed production changed because of the
injection itself, not the presence of the fungus.
What does the p in "p-value" represent? - Answers - Probability (of getting the observed
result, just by chance)
Suppose we run a statistical test, and learn that p = 0.01. What does this mean? -
Answers - There is a 1 in 100 chance of observing a difference between treatment
groups this extreme if the null hypothesis is correct.
If we want to plot the distribution of scores on Exam 1, we should use a... - Answers -
Histogram
If we want to plot the exam scores of 1st-year students versus 2nd-year students, we
would use a ... - Answers - Bar chart
If we want to compare the scores of 1st-year and 2nd-year students using a statistical
test, our null hypothesis will be... - Answers - There is no difference in exam
performance between students in year 1 and 2.
If we calculate means (averages) based on scores from 100 1st-year students and 400
2nd-year students, which is likely to have the smaller standard error? - Answers - 2nd-
year students, because we sampled more.
Which of the following statements is the best way to characterize the standard error? -
Answers - A measure of how precise our estimate of the mean is.
When sample size increases ... - Answers - Rare events have less influence on the
estimate of the average or slope.
If you are doing a linear regression, what is the slope of the line predicted by the null
hypothesis? - Answers - 0
ANSWERS
What is the difference between a theory and a hypothesis? - Answers - Only scale--
theories deal with "big ideas" that impact large parts of the physical or natural world;
hypotheses are more focused or narrower in scope.
What is the difference between a hypothesis and a prediction? - Answers - A hypothesis
is an idea--a testable explanation; a prediction is something that follows from a
hypothesis and that you can measure
example of prediction - Answers - If you boil nutrient broth and place it in an air-tight
flask, no cells will appear in the broth
What was important about the experimental design for Pasteur's flask experiment? -
Answers - He compared results from two experimental setups which differed only in the
type of flask in which the nutrient broth was placed
How do biologists test their ideas about the natural world? - Answers - Scientists make
predictions based on hypotheses they have developed, and then design experiments or
other types of studies to test those predictions
Why is it important to perform multiple trials in an experiment -- meaning that you
include many test individuals or samples? - Answers - To make it more likely that the
results are not due to a few unusual individuals or circumstances
The remaining questions refer to this situation: Researchers do an experiment to test
the hypothesis that Douglas fir trees put more resources into reproduction when they
are infected with a fungus that causes a fatal disease. They establish study plots in a
group of 50-year-old Douglas fir where the disease is not present. At random, they inject
half the trees with the disease-causing fungus. Then they measure how many cones
and seeds are produced by infected versus uninfected trees.
What prediction follows from the hypothesis? - Answers - On average, the infected trees
will produce more seeds than uninfected trees
Which treatment would be considered the control? - Answers - The uninfected trees
Why is it important to do the experiment in the same group of same-aged trees? -
Answers - To eliminate the possibility that the results are due to differences in age, soil,
moisture, or other relevant variables
, Why is it important that they assigned trees to the infected versus uninfected groups at
random? - Answers - If assignment were not done at random, the result could be do to
something other than the difference in infection
If the hypothesis is wrong, and being infected with the fungus has no impact at all on
reproduction, what should they observe? - Answers - There will be no difference in the
number of seeds produced by infected versus uninfected seeds
A friend says that this experimental design would be better if the researchers had
injected the control group trees with a solution that was identical to that used in the
experimental group, but without the fungus. Do you agree? - Answers - Yes. As is, it
would be reasonable for a critic to claim that seed production changed because of the
injection itself, not the presence of the fungus.
What does the p in "p-value" represent? - Answers - Probability (of getting the observed
result, just by chance)
Suppose we run a statistical test, and learn that p = 0.01. What does this mean? -
Answers - There is a 1 in 100 chance of observing a difference between treatment
groups this extreme if the null hypothesis is correct.
If we want to plot the distribution of scores on Exam 1, we should use a... - Answers -
Histogram
If we want to plot the exam scores of 1st-year students versus 2nd-year students, we
would use a ... - Answers - Bar chart
If we want to compare the scores of 1st-year and 2nd-year students using a statistical
test, our null hypothesis will be... - Answers - There is no difference in exam
performance between students in year 1 and 2.
If we calculate means (averages) based on scores from 100 1st-year students and 400
2nd-year students, which is likely to have the smaller standard error? - Answers - 2nd-
year students, because we sampled more.
Which of the following statements is the best way to characterize the standard error? -
Answers - A measure of how precise our estimate of the mean is.
When sample size increases ... - Answers - Rare events have less influence on the
estimate of the average or slope.
If you are doing a linear regression, what is the slope of the line predicted by the null
hypothesis? - Answers - 0
