Lab 1: Scientific Investigation
Objectives from Study Guide:
Be able to make a question, hypothesis and prediction for a given phenomenon
Know elements of good experimental design including all types of variables, use of controls, replication
Know how to tabulate and graph data
Know difference between a hypothesis and a theory
1.1
• A hypothesis must be testable and falsifiable (able to be proven false)
o Well-defined
o Measureable
o Reasonable
o Consistent with existing bodies of knowledge
• Note that a hypothesis can be falsified but never proven true
• Hypothesis v. theory: Both are falsifiable and testable, but hypothesis is tentative answer to a rather narrow
question and theory is well-supported, broadly explanatory
1.2
• Dependent variable: Variable that is measured in response to experimental conditions (can have more than
one)
• Independent variable: Variable that is manipulated to test the hypothesis (only one)
• Controlled variable: Variable kept constant during the experiment (can have more than one)
NOTE ABOUT TIME AS A VARIABLE: Time can be an independent, controlled, or
dependent variable, dependent on the experiment
If you… Measure how long it takes to do something: time is dependent on the something (time to
germination of 3 varieties of seed)
If you… Run an experiment and measure the outcome after some exact amount of time: time is a controlled
variable
If you… Measure a dependent variable at several points over the course of an experiment: time is an
independent variable (you want to know how time, as well as whatever else you are measuring, affects the
outcome).
•
•
•
•
•
Procedure: Sequence of steps to be performed for the experiment
Level of treatment: Value set for independent variable (based on knowledge of system and biological
significance of treatment level)
o Note that in some experiments, independent variables represent categories that do not have a level of
treatment (i.e. gender)
Replication: Number of times the procedure is repeated (ensures consistent results)
Control: Independent variable is held at an established level or omitted (serves as a benchmark that allows
scientists to decide whether the predicted effect is really due to the independent variable)
Prediction: Written in the form of an if/then statement: “If the hypothesis is true, then the results of the
experiment will be…”
1.3
• Allometric growth: Parts of an organism grow at different rates (example: human head)
• Isometric growth: Parts of an organism grow at the same rate (example: arms and legs)
• This experiment:
o We compared the ratios of (1) height to head and (2) height to hand in newborns and students
 Dependent variable: Height/body part ratio
 Independent variable: Adult body part selected
 Controlled variables: Age, sex, ethnicity, nutrition, etc.
 Control: Infant proportions
 Level of treatment: N/A
 Replication: Number of students in class
o Results:
 Ratio of height / head circumference in adult students was twice as large as the same ratio in
newborns
 Height to head ratio: Evidence for allometric growth strongly supported
• Ratio was 3.2 (adult) to 1.45 (child)
 Height to hand ratio: Data was inconclusive
• Ratio was 10.3 (adult) to 8.0 (child)
1.4
• Tables
o Tables used to present results that have many data points
o Also useful for displaying several independent variables
o Things to remember:
 All values of the same kind should read down the column, not across a row
 Headings of each column should indicate units of measurement
 Title
• Graphs
o Line graphs show changes in quantity of chosen variable and emphasize the rise and fall of values
over their range (used for continuous data)
 y-axis: Dependent variable
 x-axis: Independent variable
 Appropriate value range
 Legend
o Bar graphs are used for data that represent separate or discontinuous groups or non-numerical
categories
1.5
• Potential weaknesses in our experiment:
o Limited sample size
o One-time data collection
o Flexibility in definition of allometric and isometric growth
o Measurement error
o Assumed control validity
Misc.
• Evolution of humans reflects paedomorphosis, a process that leads to retention of juvenile/child characters
in the adult
o Small change in timing/rate of development can lead to relatively large change in body form (this is
why modern humans have closer resemblance to baby chimpanzee than adult chimpanzee)
• Base units for measurements (SI Units): Meter, liter, gram
• Prefixes: mega (M) - 106, kilo (k) - 103, deci (d) - 10-1, centi (c) - 10-2, milli (m) - 10-3, micro (µ) - 10-6, nano
(n) - 10-9, pico (p) - 10-12