Tuesday means….
Homework collection…
http://tasisbiology.wordpress.com
Let’s remember…
What are the (8)
characteristics of living
things?
Characteristics of living things
From Prentice-Hall, Section 1-3, p. 15 – 17.
Living things:
1. Are composed of units called cells
2. Reproduce
3. Are based on a universal genetic code
4. Grow and develop
5. Obtain and use materials and energy
6. Respond to their environment
7. Maintain a stable internal environment
8. Change over time….when considered as a group
Today we are going to learn
about…
THE SCIENTIFIC METHOD!
The fundamental cornerstone of
ALL SCIENCE!!!
You will have a test on the Scientific
Method and Experimental Design
next Thursday 13th/ Friday14th
Today’s Resources
 Handout on the Scientific Method
 Worksheet on the Scientific Method
 Simpsons Variables Worksheet
 Prentice-Hall p. 8 – 14, 1060 - 1063
Words we will understand by the
end of today…
 Observation
 Inference
 Hypothesis…and the Null Hypothesis
 Data – quantitative and qualitative
 Variables
 Controlled experiment
 Control group
1. Observations and Inferences
 The first step of the scientific method is
OBSERVATION
 On the basis of our observations, we
develop INFERENCES
What’s the difference between an
observation and an inference?
 Inference: Conclusion based on evidence
and reasoning
 Reasoning – but not fact
 Logical – but not necessarily true…
 Inductive: Specific observations
extrapolate to general conclusions
 Deductive: General observations
extrapolate to specific results…
Meet our sewer lice….
With 2 colleagues, make as many observations and
inferences about your sewer lice
You have 5 minutes….
Observations
Inferences
It is imperative to develop an
OBJECTIVE, TESTABLE
RESEARCH QUESTION - one that
can be tested
Worksheet: P3/4: ‘Testable
Questions’
Page 3
Page 4
 Group 1: Q 1 - 6
 Group 1: Q. 2
 Group 2: Q 7 - 12
 Group 2: Q. 3
 Group 3: Q 13 - 17
 Group 3: Q 4
Words we will understand by the
end of today…
 Observation
 Inference
 Hypothesis…and the Null
Hypothesis
 Data – quantitative and qualitative
 Variables
 Controlled experiment
 Control group
 Based on our
observations, we
formulate a research
question
 Our research question is
presented as a
hypothesis, based on our
biological reasoning
 We typically present the
Null hypothesis
So why do all experiments require
a hypothesis?
 ‘If………..then………………’
 We must have a principle that we can
objectively test
 We generally state the Null Hypothesis
for cause-and-effect relationships
Words we will understand by the
end of today…
 Observation
 Inference
 Hypothesis…and the Null Hypothesis
 Data – quantitative and qualitative
 Variables
 Controlled experiment
 Control group
When does a hypothesis become
a theory?
 When a hypothesis is repeatedly confirmed by experiment
and observation (USING THE SCIENTIFIC METHOD), it
may become generally considered as a THEORY
 THEORIES are the most reliable, rigourous, and
comprehensive form of scientific knowledge
 Some well known scientific theories:
 Cell theory
 Evolutionary theory
 Theory of relativity
 Climate change theory
From hypothesis to controlled
experiment
In order to ‘test’ our
hypothesis and
understand the world
better, we must
design a
CONTROLLED
EXPERIMENT
Designing an experiment:
IDENTIFYING VARIABLES
 Variables are conditions that affect the outcome of an
experiment
 It is essential that you identify all of the variables which
could affect the outcome of your experiment BEFORE you
begin
 Ideally, you want to control (I.e. make constant) ALL of the
variables, with the exception of WHAT YOU CHANGE (the
independent variable) and WHAT YOU MEASURE (the
dependent variable)
Designing an experiment
 What do we want to CHANGE?
 What do we want to measure?
 Are there any other ‘things’ which can affect the ‘thing’ we
are measuring?
 What we change on purpose is called the INDEPENDENT
VARIABLE
 What we MEASURE is called the DEPENDENT VARIABLE
Identify the experimental
VARIABLES
 Independent – what you change
(X- axis)
 Dependent – what you measure
(Y-Axis)
 Controlled Variables – what
remains constant (what YOU
control)
 (Uncontrolled – variables which
may be hard to control)
 Ideally you should have all
variables controlled,
excepting one dependent
and one independent
variable
How do we design a
controlled experiment?
Designing a controlled
experiment
Designing a controlled
experiment
1. Formulate a focused research question
2. Identify ALL of the relevant variables (independent,
dependent, controlled, uncontrolled)
3. Decide how to manipulate the independent variable –
range
4. Decide how many repeats of the experiment you need to
do
5. Decide if you are including a control group
Identify the experimental
VARIABLES
 Dependent – what you measure
(Y-Axis)
 Independent – what you change
(X- axis)
 Controlled – what remains
constant
 (Uncontrolled – variables which
may be hard to control)
 Ideally you should have all
variables controlled, excepting
one dependent and one
independent variable
How much data is enough: designing an
experimental model?
 Experiments can be designed in many different ways….
 Simple observational study
 Simple comparison (e.g. test group and control group)
 ‘Crossover’:each group receives each ‘treatment’
 Multiple concentrations/doses etc: multiple groups
The classical five by five model
 Used for many biological
tests
 5 different test groups
 Repeat the test on each
group 5 times
 This experimental model
will provide plenty of
information!
Smithers thinks that a special juice will increase the
productivity of workers. He creates two groups of 50
workers each and assigns each group the same task
(in this case, they're supposed to staple a set of
papers).
Group A is given the special juice to drink while they work. Group B is
not given the special juice. After an hour, Smithers counts how many
stacks of papers each group has made. Group A made 1,587 stacks,
Group B made 2,113 stacks.
 1. Control Group
 2. Independent Variable
 3. Dependent Variable
No special juice
The juice
Number of papers stapled
 4. What should Smithers' conclusion be?
Stay off the juice! (The juice doesn’t work)
 5. How could this experiment be improved?
 Identify the16. Control Group
 17. Independent Variable
 18. Dependent Variable
 19. Explain whether the data supports the
advertisements claims about its product.
Homework for tomorrow
 2 questions from the Simpson’s
Worksheet (Bart and Lisa)
 Convert one of the two experiments
into a 5 X 5 model
20. Describe how Lisa would
perform this experiment. Identify
the control group, and the
independent and dependent
variables in your description.