Unit 2: Biology as a ScienceCh. 1: The Study of Life

200

• the microscope

What is one of the most important tools of biology? Microscopy timeline

Early Microscopes• Anton van Leeuwenhoek

– Improved magnification (to ~270x)

– first to see & describe microorganisms

• “Father of Microbiology”

• Robert Hooke– improved on

Leeuwenhoek’s microscope

– first to use term “cell”• after looking at cork

• What can you see with a CLM?– live, dead, & non-living

specimens–COLOR!!!

stoma

Compound Light Microscope (CLM)

aperture

Parts of a compound light microscope

Microscope parts quiz

Interactivemicroscopeguide

You must know what the parts of the microscope are, where they are, and what they do!

Microscope Tutorial

Virtual Microscope

CLM Microscope Basics: Magnification• Microscopes magnify small objects to make

them appear bigger/easier to see.

• How does a compound light microscope magnify objects?– uses light & 2 or more

glass lenses to focus the light that passes through specimen• Why must the

specimen be thin?– light must be able to

pass through it

http://www.biologycorner.com/bio1/microscope.html

CLM Microscope Basics: Magnification

• How is the total magnification power of a compound light microscope calculated?–find the power of the:

• ocular (eyepiece)▪ 10x

• objective lens (you are using)▪ 40x

–multiply• ex. 10 X 40 =

▪ 400x total magnification

ocular

objective

CLM Microscope Basics: Magnification

• How does magnification affect the size of the “field of view”?– If increase magnification…

• diameter of field of view decreases– See less of object, but in better detail.

Low power field

Medium power field

Medium power objective

Low power objective

CLM Microscope Basics: Magnification

• Match the image to the power (low, med, high)…– Which has better detail?

• high power– Which shows a larger portion of image?

• low powerhigh low med

CLM Microscope Basics: Magnification

• Microscopes increase “resolving power”.

– the ability to distinguish two closely spaced objects as being separate from one another

• improves clarity/detail

Which image has better resolution?

Which set of images has better resolution… top or bottom?

CLM Microscope Basics: Resolving Power

Magnification changes are show from left to right.

• Focusing is affected by “depth of field”.– the thickness of the plane of focus

• as magnification increases, the depth of field decreases– can be difficult to focus all parts at the same time & need

to refocus to see different parts» especially true for thicker specimens

Depth of Field Video Depth of Field Video 2

CLM Microscope Basics: Depth of Field

Low power

CLM Microscope Basics: Making a Wet Mount Slide

• Stains are used to see colorless specimens better…– ex.

• methylene blue• crystal violet• iodine

CLM Microscope Basics: Staining Specimens

CLM Microscope Basics: Staining Specimens

Transmission Electron Microscope (TEM)

• Electrons pass through very thin non-living specimen– black & white, 2-D, image of inside

TEM simulatorPreparation of a specimen

Scanning Electron Microscope (SEM)• electrons bounce off surface

of non-living specimen– black & white, 3-D, image of

surface• micrographs can be color

enhanced using computer

SEM Interactive Virtual SEM

Comparison of Microscopes

Characteristic

Compound Light

Microscope (CLM or LM)

Transmission Electron

Microscope (TEM)

Scanning Electron

Microscope (SEM)

Resolving power

low(500 nm)

high (10 nm)

very high(2 nm)

Magnifying Power

low (up to 1,500X)

high(5,000,000+X)

moderate(~ 100,000X)

Depth of Field small moderate large

Type of Specimens

living & dead/ non-living

dead/non-living

dead/non-living

Which microscope?

Science & Technology• What is science?

– an organized process that produces a body of knowledge about nature

• based on observation of phenomenon or their effects & experimentation in order to attempt to explain the cause of those effects

• goal is to produce useful models of reality

– Can you ever truly prove anything in science?• No… there is constant refinement as new information

becomes available or information is looked at differently

• What is technology?– application of scientific knowledge for practical purposes

• Laws (describe “what”)– are generalizations, principles, or patterns in

nature derived from scientific facts• describe relationships among observable

phenomena/ behavior of the natural world (under certain conditions)

– Statement of great generality of something in nature which seems to always be true• Does not give an explanation of “mechanism” or

“why” something happens.

– often expressed as a numerical equation

What is a Law?

• Nicolas Steno’s Law of Superposition–fossils in bottom layer are oldest & in top layer youngest

• Gregor Mendel’s Law of Segregation–alleles governing a trait are separated during meiosis

Examples of Laws?

• Theories (explain “why/how”)– Most logical & complete explanation of events

that happen in nature (under certain conditions)• can be used to predict what will happen as long as

those conditions are met

– Based on evidence tested & supported many times• can change/be refuted based on new evidence

– Often explain laws– Has a broad range of significance & application

What is a theory? video clip What is a Theory?

What is a theory? video clip

• Darwin’s Theory of Evolution by Natural Selection– Organisms best suited for environment will be more

likely to survive & pass on traits...• causing change in species over time

• Refuted: Theory of Abiogenesis (spontaneous generation)– life came from non-living matter

• due to lack of proper experimentation• refuted by controlled experiments

– Redi’s “maggots from meat”

– replaced w/ Theory of Biogenesis

Examples of Theories?

• Hypotheses (are tentative explanations)– Are developed to:

• investigate a scientific question & MUST be testable• Explain observations (of patterns in nature or connections btwn 2 variables)• Predict the outcome of an experiment (based on observations or prior

scientific knowledge)• Guide investigator in seeking & paying attention to right data

– Are NOT proved true or correct (or false or incorrect)• Are supported (or negated) by the data

– Some, but not all, confirmed hypothesis become theories.

– Are NOT written as a question… Ex. “Rainbow trout suffer more lice in low water conditions b/c there is less oxygen in the water.”

• may use “If _(IV)_, then _(DV)_, because __.” format– If there are low water conditions, then rainbow trout will suffer more lice, because there

is less oxygen in the water.

– Are creative and imaginative as well as logical

What is a Hypothesis?

A. In every case, male birds are either similar or more colorful than their female counterparts.– law

• It is a statement of something which appears to always be true, but it is not an explanation of anything.

B. Zinc in the diet will lower the rate and intensity of viral outbreaks.– hypothesis

• It is a very specific prediction about the connection between one thing and one other thing.

C. There is a strong connection between nutrition and different types of heart disease.– theory

• It is a broad statement that nutrition in general can have an impact on a range of very different kinds of heart disease.

Scientific Law, Theory, or Hypothesis?

The Scientific Method

http://www.sciencebuddies.org/science-fair-projects/overview_scientific_method2.gif

Pose a problem/Ask a question

Do not necessarily have to go in order.

The Scientific MethodA. Identify

problem/question to investigate

– gather background information

B. form hypothesis– “If _(IV)_, then

_(DV)_, because __.”

The Scientific MethodC. Test hypothesis

– using a controlled experiment• experimental design

(procedure)– written so that others

can easily follow it» like a recipe

(detailed, logical sequence, amounts included, diagrams of set-up, etc.)

• to be valid has to have two parts…

What is a controlled experiment?1. tests one variable & all others are kept the same

– Independent Variable (IV)» factor being tested/changed by scientist (to see if it has an effect

on the DV)

– Dependent Variable (DV)» factor being measured (to see if it changes in response to a

change in the IV)

– Constants or (controlled variables) (Cv)» All other factors that are not being tested & must be kept the

same (so that they can not affect on the results differently)

What is a controlled experiment?2. two groups must be tested

a) control group» nothing is being tested

▪IV is absent

» “standard” which experimental group is compared to ▪to see if IV had an effect

b) experimental group» “test” group(s) ▪IV is changed (one or more variations)

» “test” group compared to “standard” control group ▪to see if IV had an effect

• Also should have multiple trials (replicates)– ensure results are accurate

D. make observations & collect data (often in tables)– quantitative (ex. numbers, measurements)– qualitative (ex. descriptive… color, shape, smell, etc.)

E. interpret data & analyze results– graphs

F. draw conclusions– support/reject hypothesis (NOT prove/disprove)

• conduct additional experiments (revise or discard hypothesis if rejected)

G. communicate results– report & publish

The Scientific Method

Which brand of mouthwash gets rid of stinky breath the best?

– Independent Variable-• Brand of mouthwash

– Dependent Variable-• Stinkyness of breath (smell of breath)

– Constants (Controlled Variables)-• Amount, time of day, how long swish, person, same thing to

eat before, how the breath is smelled (who smells it), flavor, etc.

– Experimental Group(s)-• Group(s) w/ each type of mouth wash

– Control Group-• Water (no mouthwash)