The Nature of
Science
Class Notes
The Scientific
Method
What is Science?
 “Science” derived from Latin ‘to know’
 Way of asking and answering questions about the world
around us
 Can only address questions that are testable
 Scientific thinking reduces personal, emotional reactions
Scientific Design
 Scientific method – common steps that scientists use to
gather information and answer questions
 There is no ONE scientific method.
 This is just a general outline to follow.
Step 1: Observe and Ask a
Question
 An observation is made about the natural world.
 Songbirds seems to be absent in the forests of Guam.
 This observation was made around the same time that
brown tree snakes were first spotted in Guam.
 The scientist will then develop a general question that
they are setting out to answer.
 Example: Is there a relationship between the lack of
songbirds in the forests in Guam and the introduction of the
brown tree snake?
Step 2: Create a Hypothesis
 Hypothesis – a possible explanation for a question or
problem that is testable and based on previous knowledge
 It is NOT an “educated guess”
 Example: If there are brown tree snakes, then they must eat
the song birds.
Step 3: Carry Out a Controlled
Experiment
 Controlled experiment – an investigation that tests a
hypothesis by the process of collecting information under
controlled conditions
 Made up of:
 Independent variable
 Dependent variable
 Control group
 Experimental group
 Controls
Experimental Design
Independent (manipulated) variable: condition or event under
study
Dependent (responding) variable: condition that could change
under the influence of the independent variable (measure this)
Controls (controlled variables): conditions which could effect the
outcome of the experiment so they must be held constant
between groups
Experimental Design
Experimental group: group(s) subjected to the independent
variable
Control group: group kept “normal”, used as measuring stick
Step 4: Analyze Data and Draw
Conclusions
 Data – information obtained from investigations
 Qualitative data: observational data
 Example: color changes, descriptions
 Quantitative data: numerical (numbers) data
 Example: time, quantities, measurements
 Examine the data for patterns and trends and make
conclusions from the data that you collected.
Step 5: Publishing Results
 Scientists then publish and share their data through
scientific journals so that other scientists can review and
use this information.
 Science is collaborative and results must be reproduced
and verified in order to be commonly accepted.
Theories and Natural Laws
 Theory: a description of the world that covers a relatively
large number of phenomena and has met many
observational and experimental tests
 Law of Nature: theory (or group of theories) that has been
tested extensively and seems to apply everywhere in the
universe
Example
 Observation: Dogs that wear the red collar seem to have
less fleas.
 Hypothesis: If dogs wear a red collars, then they will have
less fleas than dogs that wear other color collars.
Experimental Design
 Obtain 500 dogs of various breeds from local shelters.
 Randomly assign individuals to 2 groups.
 What would you do to the experimental group?
 What would you do to the control group?
 Board the dogs in identical environments and treat them
the same except for the independent variable.
 What is the independent variable?
 After 2 weeks the dogs are examined.
 What is the dependent variable? What are we measuring?
Results:
The dogs wearing the red collars were virtually free of fleas
after the 2 week period.
The dogs without the collars had about the same number of
fleas as when the experiment began.
What can we conclude??
Scientific Measurement
The metric system
• Decimal based system - scaled on multiples of 10
• AKA the International System of Units, or SI
• Two ways to solve conversion problems:
– Ladder method
– Dimensional Analysis
Kilo (k)
Hecto (h)
1/1000=0.001
1/100=0.01
Deka (da)
1/10=0.1
Meter (m) /liter (L)
/gram (g)
Deci (d)
1
Centi (c)
100
Milli (m)
1000
10
Metric
Conversions - Ladder Method
1
2
KILO
1000
Units
3
HECTO
100
Units
DEKA
10
Units
DECI
0.1
Unit
Meters
Liters
Grams
How do you use the “ladder” method?
1st – Determine your starting point.
2nd – Count the “jumps” to your ending point.
3rd – Move the decimal the same number of
jumps in the same direction.
CENTI
0.01
Unit
MILLI
0.001
Unit
4 km = _________ m
Starting Point
Ending Point
How many jumps does it take?
4. __. __. __. = 4000 m
1
2
3
Metric Conversions - Dimensional Analysis
Question: 8400mg = ___?___g
Steps:
1. Know the conversion factor (there are 1000mg in 1g).
2. Set up a multiplication problem and cancel out units on
the top and bottom of the fractions.
3. Do the math to find the answer (8.4g).
Measuring Length
Standard: meter (m)
Measuring mass
Standard: gram (g)
Measuring Volume
Standard:
liquid:Liter (L)
solid: cubic centimeters (cc)
1 Liter
1 milliliter (mL)
1 liter = 1000 cubic centimeters
Everything you ever wanted to know
about the Metric System.
Graphing
• Graph- pictoral representation of the
information recorded in a data table.
• Two common types:
– Line graph
– Bar graph
Line Graph
• Shows
relationship
between two
variables.
Bar Graph
• Used only to show comparisons.
Graphs must have…
•
•
•
•
A title
Labeled X and Y axes
Units on X and Y axes
Legends
Practice making a line graph
Table 1: Breathing rate of fish
Temp
(deg C)
10
15
18
20
23
25
27
Rate
(per
min)
15
25
30
38
60
57
25
Practice making a bar graph
Table 2: Average rainfall
Mon
th
Jan
Rain 15
fall
(mL)
Feb
Mar
Apr
May
June July
Aug
Sept Oct
Nov
Dec
21
28
24
16
8
1
2
5
10
2
3
Science Lab Safety
Lab Safety Video:
http://www.flinnsci.com/teacher-resources/teacher-resource-videos/bestpractices-for-teaching-chemistry/safety/laboratory-safety-challenge/
Safety Symbols
Flame
Poison
Dangerous Fumes
Wear Safety Goggles
Electrical Shock
Safety Rule #1
 Never perform any unauthorized
experiments or use any equipment or
instruments without proper instruction.
 Always follow all directions given by
your teacher!
Safety Rule #2
 Do not begin working on your lab unless
your teacher is present!
Safety Rule #3
 When required, proper eye protection
must be worn during the entire class
period!
Safety Rule #4
 When something breaks or spills, you
must notify your teacher so it can be
cleaned up properly.
 DO NOT TRY TO DO THIS YOURSELF!
Safety Rule #5
 When working on a lab, dangling
jewelry should be removed and long hair
should be tied back.
Safety Rule #6
 Do not eat or drink anything in the lab
at any time.
Safety Rule #7
 Consider every material used in the lab
as dangerous.
 Avoid inhaling fumes, tasting, touching,
or smelling any chemical unless your
teacher instructs you otherwise.
 Rinse anything that spills on your skin
with water immediately.
Safety Rule #8
 Nothing is to be taken from the
laboratory unless checked out to you in
writing by your teacher.
Safety Rule #9
 Never become involved in horseplay or
practical jokes in the lab.
 Use maturity at all times when working in
the lab.
Safety Rule #10
 Never point a test tube toward yourself
or anyone else.
Safety Rule #11
 Do not put anything in the sink or
garbage can unless instructed by your
teacher.
 Always clean up according to the lab
and teacher’s instructions.
Safety Rule #12
 Note the location of the safety
equipment in and around the classroom.
 Always wash your hands with soap and
water before leaving the lab.
Characteristics of
Living Things
Characteristics of Life
 All living things can be
called “organisms”.
 All organisms share the
7 characteristics of life:
 Made of cells
 Reproduce
 Grow and
develop
 Maintain
homeostasis
 Use energy
 Respond to their
environment
 Have a
metabolism
All living things are made of
cells
 A cell is the smallest unit of life and gives all
organisms an orderly structure
 Organisms can be made of one cell (unicellular)
 Example  bacteria, amoeba, paramecia
 Or, organisms can be made of many cells
(multicellular)
 Examples  plants, animals, fungi
All organisms reproduce
 All organisms must produce offspring in
order to continue the species
 Individual organisms do not need to
reproduce to survive, but they must
reproduce for the species to survive.
 Species – a group of organisms that
can interbreed and produce fertile
offspring.
All organisms grow and
develop.
 Every organism’s life begins as a single
cell.
 Some organisms will remain a single cell
that just gets larger.
 Other organisms will become many
cells that grow and develop.
 Growth – An increase in the amount of
living material
 Development – All of the changes that
take place during the life of an organism
All living things maintain
homeostasis.
 Homeostasis – regulation of an
organism’s internal environment to
maintain conditions suitable for its
survival
 Example: The temperature of your body
gets too high so you sweat to lower the
temperature.
All living things use energy.
 The cells of an organism are always hard at work.
 Just to read this sentence cells in your eyes and
brain are working. At the same time cells are
digesting your last meal, while blood cells are
moving chemicals in your body, and other cells
are repairing damage to your body. The list goes
on and on…
All organisms respond to
their environment.
 Stimulus and response
 Stimulus  anything in the organism’s
external or internal environment that
causes an organism to react
 Response  a reaction to a stimulus
 Example: The leaves of a plant will grow
towards the light.
 Stimulus  light
 Response  growth towards the light
All living things have a
metabolism
 Metabolism – All of the chemical
reactions that occur in an organism
 The cells of living things are made of
chemicals that allow an organism to
survive.
Electron Microscopes
• Used to observe VERY small objects that require
going beyond the limit of resolution of a
compound light microscope.
– Transmission electron microscopes (TEMs)-shine
beam of electrons at sample and magnify the image.
– Scanning electron microscopes (SEMs)-beam of
electrons scan across surface of object; electrons that
bounce off specimen are detected to generate the image.
Capillary
Plant cell
Mitochondria
TEM images
Hypodermic Needle
Velcro
Bedbug
SEM images
Red blood cells
Cobweb
Compound Light Microscopes
• Frequently used tools of biologists.
• Magnify organisms too small to be seen
with the unaided eye.
• To use:
– Sandwich specimen between transparent slide
and thin, transparent coverslip.
– Shine light through specimen into lenses of
microscope.
• Lens closest to object is objective lens.
• Lens closest to your eye is the ocular lens.
• The image viewed through a compound
light microscope is formed by the
projection of light through a mounted
specimen on a slide.
How does a compound light
microscope work?
• Video tutorial
Always carry a microscope with one hand
holding the arm and one hand under the base.
Eyepiece/
Body Tube
Ocular Lens
Nosepiece
Objectives or
Objective Lenses
Arm
Stage
Stage Clips
Coarse Adjustment
Diaphragm
Light Source
Fine Adjustment
Base
Always carry a microscope with one hand
holding the arm and one hand under the base.
Magnification
• The process of enlarging something in
appearance, not actual physical size.
What’s my power?
To calculate the power of magnification or total magnification,
multiply the power of the ocular lens by the power of the objective.
Power of Ocular lens X power of Objective
10 X 40
= 400
Comparing Powers of Magnification
We can see better details with higher the
powers of magnification, but we cannot see
as much of the image.
Which of these images
would be viewed at a
higher power of
magnification?
Resolution
• The shortest distance
between two points
on a specimen that
can still be
distinguished as two
points.
Limit of resolution
• As magnifying power increases, we see
more detail.
• The point where we can see no more detail
is the limit of resolution.
– Beyond the limit of resolution, objects get
blurry and detail is lost.
– Use electron microscopes to reveal detail
beyond the limit of resolution of a compound
light microscope!
Field of view
• The diameter of the circle of view when you
look down the microscope.
What happens to the size of the field of view as you increase
magnification?
Proper focusing technique
1.
2.
3.
4.
5.
Check that the light is on.
Add the slide
Check the objective lens.- low power!
Raise the stage.
Look through the eyepiece & FOCUS DOWN by
turning the coarse adjustment knob away from you
until the specimen is in focus.
6. Fine tune the focus with the fine adjustment knob.do not use the coarse adjustment knob after this
point!
7. Change objectives and re-fine tune the focus.
Proper clean up technique
1.
2.
3.
4.
5.
Clean up right away
Go back to low power
Lower the stage
Remove the slide
Proper storage
1.
2.
3.
4.
Check the stage
Check the objective
Wind the cord
Dust cover it
Proper storage technique
1. The stage must be all
the way down.
2. The low power
objective must be in
place.
3. The slide must be
removed.
4. The cord must be
wound around the
base.
5. The dust cover must
be replaced.
How to make a wet-mount slide …
1 – Get a clean slide and coverslip.
2 – Place ONE drop of water or stain in the middle of the slide. Don’t use too
much or the liquid will run off the edge! Place the specimen in the drop.
3 – Place the edge of the cover slip on one side of the liquid drop.
Hold the coverslip at a 45-degree angle in the edge of the puddle.
5 - Slowly lower the cover slip on top of the drop with fingers or forceps.
Cover
Lower slowly
Slip
5 –Place the slide on the stage and view it first with the low power objective.
Wash and dry the coverslip and slide when finished. Once you se the image,
you can rotate the nosepiece to view the slide with different objective lenses.
You do not need to use the stage clips
when viewing wet-mount slides!