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8/10/2015
1
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.
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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
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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.
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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??
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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) 1/1000=0.001
Hecto (h) 1/100=0.01
Deka (da) 1/10=0.1
Meter (m) /liter (L)
/gram (g)
1
Deci (d) 10
Centi (c) 100
Milli (m) 1000
KILO
1000
Units HECTO
100
Units
DEKA
10
Units DECI
0.1
Unit CENTI
0.01
Unit MILLI
0.001
Unit
Meters
Liters
Grams
Metric Conversions - Ladder Method
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.
4 km = _________ m
1
2 3
How many jumps does it take?
Starting Point Ending Point
4. 1
__. 2
__. 3
__. = 4000 m
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).
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Measuring Length
Standard: meter (m)
Measuring mass
Standard: gram (g)
1 liter = 1000 cubic centimeters
1 Liter
1 milliliter (mL)
Measuring Volume
Standard:
liquid:Liter (L)
solid: cubic centimeters (cc)
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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.
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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)
Rate
(per
min)
10 15
15 25
18 30
20 38
23 60
25 57
27 25
Practice making a bar graph Table 2: Average rainfall
Mon
th
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Rain
fall
(mL)
15 21 28 24 16 8 2 1 2 3 5 10
Science Lab Safety
Lab Safety Video:
http://www.flinnsci.com/teacher-resources/teacher-resource-videos/best-
practices-for-teaching-chemistry/safety/laboratory-safety-challenge/
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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!
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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.
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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.
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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
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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…
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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.
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Mitochondria Capillary
Plant cell TEM images
Hypodermic Needle Velcro
Bedbug
Cobweb
Red blood cells
SEM images
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
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Always carry a microscope with one hand
holding the arm and one hand under the base.
Body Tube
Nosepiece
Objectives or
Objective Lenses
Stage Clips
Light Source
Eyepiece/
Ocular Lens
Arm
Stage
Coarse Adjustment
Fine Adjustment
Always carry a microscope with one hand
holding the arm and one hand under the base.
Base
Diaphragm
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
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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?
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Proper focusing technique
1. Check that the light is on.
2. Add the slide
3. Check the objective lens.- low power!
4. Look through the eyepiece & FOCUS DOWN by
turning the coarse adjustment knob away from you
until the specimen is in focus.
5. Fine tune the focus with the fine adjustment knob.-
do not use the coarse adjustment knob after this
point!
6. Change objectives and re-fine tune the focus.
Proper clean up technique
1. Clean up right away
2. Go back to low power
3. Lower the stage
4. Remove the slide
5. Proper storage
1. Check the stage
2. Check the objective
3. Wind the cord
4. 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 –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.
5 - Slowly lower the cover slip on top of the drop with fingers or forceps. Cover
Slip Lower slowly
You do not need to use the stage clips
when viewing wet-mount slides!