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

• The light microscope

What is one of the most important tools of biology?

Early Microscopes• Hans & Zacharias Janssen: said to have invented 1st

compound microscope (late 1500s)• Galileo: improved compound microscope; added focusing

device (early 1600s)– Often given title “inventor of the microscope”

• Anton van Leeuwenhoek: improved lenses & magnification – First to observe & describe unicellular organisms

• Robert Hooke: improved on Leeuwenhoek’s microscope– First to use the term “cell”

Microscopy timeline

What are Microscope Used For?1. magnify images

– make objects appear bigger

2. increase resolving power–Improve clarity/detail

Image of pollen grain with good resolution (left) and poor resolution (right)

What are Microscope Used For?

3. Increase “depth of field”– the thickness of the

specimen that is acceptably sharp at a given focus level

• can be difficult to focus all parts at the same time

Depth of Field Video

What are Microscope Used For?

• light microscopes– simple– compound

• electron microscopes– transmission (TEM)– scanning (SEM)

Types of Microscopes

SEM

Comparison of Microscopes

Characteristic

Compound Light

Microscope (CLM or LM)

Transmission Electron

Microscope (TEM)

Scanning Electron

Microscope (SEM)

Resolution (Average) 500 nm 10 nm 2 nm

Magnifying Power up to 1,500X up to

5,000,000X ~ 100,000X

Depth of Field poor moderate high

Type of Specimens

living or non-living non-living non-living

Compound Light Microscope (CLM)• 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

ocular

objective

• How is the total magnification power calculated?– find the power of the:

• ocular (eyepiece)– 10x

• objective lens (you are using)

– 40x– multiply

• Ex. 10 X 40 = 400x total magnification

Compound Light Microscope (CLM)

• How do different powers of magnification compare?– high vs. low power:

• Which has better detail?– high

• Which shows a larger portion of image?– low

Which of the images to the left would be viewed at a higher power of magnification?

Compound Light Microscope (CLM)

high low med

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

specimens–COLOR!!!

stoma

Compound Light Microscope (CLM)

• What if we want to look at something that is colorless?–We can use a stain to see it

better…• Ex.

–methylene blue– iodine

Compound Light Microscope (CLM)

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

Making a Wet Mount Slide

Staining Specimens on a Slide

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 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

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

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

What is a Law? Examples of Laws?

• Theories (explain “why”)– 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

• 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

(flies from meat)• due to lack of proper

experimentation & refuted by controlled experiments (Redi’s “maggots from meat”)

– Replaced w/ Theory of Biogenesis

What is a Theory? Examples of Theories?

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

• investigate a scientific question & MUST be testable• Explain observations (such as patterns in nature or connections between

two 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

– 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

▪even IV is controlled

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

b) experimental group» “test” group ▪IV is changed

» “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– data tables

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-

• Dependent Variable-

• Constants (Controlled Variables)-

• Experimental Group(s)-

• Control Group-