Unit 1—Ch 2Biology as a Science

•Microscopes were 1st introduced in the 1600’s by Galileo. Shown here is Robert Hooke’s simple microscope.

http://www.moonmentum.com/blog/wp-content/uploads/2010/03/Robert-Hooke.jpg http://micro.magnet.fsu.edu/primer/anatomy/introduction.html

Microscopy timeline

Microscopes• use to magnify & to increase resolving power• common lab microscopes uses light passing through

an object & lens to produce a larger image– Simple light microscope– Compound light microscope

Compound Light Microscopes• Uses light & 2 or more

glass lenses to focus light– Total magnification

• Eyepiece• Objectives• Total magnification up to

2000x

• Lower resolving power• live & dead specimens• COLOR!!!• Many are portable

Light Microscopes• Shown here are an amoeba (left), stoma

in leaf (center) & onion cells (right).

stoma

Stains help us to see some specimens better…

Parts of a compound light

microscope

Microscope parts quiz

Interactivemicroscopeguide

Microscope parts

http://www.science.smith.edu/departments/Biology/Bio111/Labmanual/scope.jpg

Virtual Microscope

Making a Wet Mount Slide

Electron Microscopes• developed in 1960’s

• beam of electrons & magnetic lenses produce enlarged image

• only dead specimens

• greater resolving power & magnification than light microscope– 10,000-200,000x

Transmission Electron Microscope (TEM)• Electrons pass through very thin non-living specimen

– Black & white, 2-D, image of inside

– Specimen frozen or embedded in plastic first

• resolution: 0.5 - 10 nm• magnification: > 1,000,000x

http://nobelprize.org/educational/physics/microscopes/tem/index.html

TEM simulator

Preparation 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

• Magnification < TEM– 100,000x plus

• Resolving power < TEM

SEM Interactive

Virtual SEM

SEM Micrographs

The samples shown above are (clockwise from top left) an ant (Lasius flavus), passion fruit (Passiflora caerulea) pollen, a freshwater shrimp parasite (Epistillis sp.), sunflower

(Helianthus anuus) pollen and central, agreenbottle (Lucilia sericata) foot.

Comparison of Microscopes

Characteristic Compound Microscope

Transmission E. Microscope

Scanning E. Microscope

Resolution (Average) 500 nm 10 nm 2 nm

Resolution (Special) 100 nm 0.5 nm 0.2 nm

Magnifying Power up to 1,500X up to 5,000,000X ~ 100,000X

Depth of Field poor moderate high

Type of Objects living or non-living non-living non-living

http://universe-review.ca/R11-13-microscopes.htm

Science & Technology• Science- is 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

• Technology- Applying knowledge to real problems

The Scientific Method

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

The Scientific Method• Observations• question or problem to investigate• background information• hypothesis is formed

– “If _(IV)_, then _(DV)_, because __.”

• Test hypothesis controlled experiment

• Controlled experiment–to be valid has to have these two parts!!!!!

• 1. Tests one variable, all others kept same– Independent Variable (IV)–Dependent Variable (DV)–Controlled Variables

or Constants (Cv)

–2. Two groups must be tested.–control group (set-up)–experimental group (set-up)

• Multiple Trials (replicates)– Ensure results are accurate

• Make observations & collect data– data tables

• Interpret data & analyze results– graphs

• Draw conclusions– Support/reject hypothesis (NOT prove/disprove)

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

• Communicate results– Report & publish

The Scientific Method

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

• Independent Variable-

• Dependent Variable-

• Controlled Variables-

• Experimental Group(s)-

• Control Group-

Theories & Laws• Can you prove anything in science?

• Theory– hypothesis becomes theory when it has been

supported repeatedly by experimental evidence• ex. evolution, natural selection, relativity

– used to explain laws– as close to complete explanation as science can offer

• can change/be refuted based on new evidence.

Examples of Theories• Darwin’s finches

ex. of his theory of evolution through natural selection

• Lack of proper experimentation led to belief in abiogenesis (spontaneous generation)– Controlled experiments like

F. Redi’s “maggots from meat” experiment refuted this theory.

• Laws• Statements about events that always occur

in nature• Does not give mechanism or explanation of

phenomenon• often expressed as a numerical equation

Theories & Laws

Examples of Laws

• Newton

• Nicolas Steno’s Law of Superposition• Fossils in lowest layer

are oldest, in uppermost layer are youngest