Bio A – Intro to Scientific Practices
Name __________________Period______
Experimental Scenario Analysis
Read the following passage and use the information in the reading and the data to answer the
questions below at the bottom of the page.
Scenario 1. A group of scientists decided to perform an experiment to test the effects of caffeine on the
heart rate of female rabbits. The scientists used 5 cloned rabbits (genetically they are identical) and fed
different amounts of caffeine to the rabbits on a daily basis. One rabbit received no caffeine. At the
start of the experiment, the heart rates of all rabbits were taken (this is prior to feeding them caffeine).
This heart rate is called the initial or baseline heart rate. The heart rates were measured in BPMs (beats
per minute).
After two weeks of the experiment, the heart rates were again measured to see if there was any change
in heart rate. All rabbits were in separate cages and were given the same amount of food and water
each day.
The results of the experiment are shown below:
Rabbit #
Caffeine/day (mg)
1
2
3
4
5
2
4
6
8
No caffeine
Heart rate (BPM)
Baseline
34
32
31
31
32
Heart rate after 2
weeks (BPM)
35
50
60
80
33
Identify the following components in this experiment:
?
1. Independent variable _______________________________________________
2. Dependent variable ________________________________________________
3. Which rabbit is the control “group” ____________________________________________
4. How many experimental groups (also called treatments) are there?
5. What factors are being controlled (constant) BE CAREFUL..this is not the same as the control
group.
Bio A – Intro to Scientific Practices
Name __________________Period______
Scenario 2. Niko Tinbergen (1907-1988) was a Swedish Ethologist (animal behaviorist) famous for
studying animals in their native habitats. One of his classic experiments involved a bird called the blackheaded gull (Larus ridibundus). Black headed gulls build nests of twigs on the ground and lay light brown
eggs that are covered with dark brown spots However the inside of the egg is white in color.
Tinbergen noticed that adult gulls pick up the egg shells shortly after a chick has hatched and fly them to
a location far from the nest (and of course leave them there). Since this behavior requires expending
energy and time that could have been spent feeding and protecting the chicks, Tinbergen wanted to
know why the birds did this.
QUESTION (or PROBLEM): Why do black-headed gulls remove eggshells from the nest.
HYPOTHESIS: The white interior of the shell is not camouflaged and attracts predators to the nest.
Therefore, the gulls remove the shells to decrease predation.
EXPERIMENT: Tinsbergen and his co-workers collected gull eggs and painted 69 of them white and left
68 of them their natural color (light brown with dark brown spots). Staistically, these numbers are close
enough to be considered equal. The researchers then cattered the eggs next to a gull breeding area and
observed from a nearby blind (an area camouflaged so that the birds could not see them). Predation
rate were recorded for white versus natural colored eggs.
Color of eggs
Original number of
eggs
Eggs Taken by
Predator
Eggs not taken
White
69
43
26
Natural eggs
68
13
55
1. Do the results of this experiment support the hypothesis? Provide evidence of your reasoning (use
data).
2. Are you 100% sure (without ANY doubt) that your hypothesis is correct? (Is it proven). Why?
3. If you were working with Tinberrgen, what would you suggest be done next?
4. Identify the independent and dependent variables
5. Was this a controlled experiment? _______________ Does it have a control group?
6. Identify the type of graph you would use to display the data, and explain why. Sketch the graph.