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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!