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The Nature of Science


2-1 The Scientific Method

Tries to find general principles to explain why things are as they are and why things happen the way they do.

Specialists: physicists, chemists, astronomers, earth scientists, biologists

Universal approach


Defining the Problem

Question - usually followed by a thorough search for information

data from reports from scientific journals

existing knowledge

no duplication


Formulating a Hypothesis

Define: a possible explanation for an observed set of facts.

Critical step


Testing the Hypothesis - Experimentation

To test a hypothesis - carry out same experiments that established the pattern or relationships

Good hypothesis will predict other types of patterns that have not been observed.

Design will prove or disprove the hypothesis

Repeated effects from experiment

controlled experiment - two identical setups

variable - isolate and test a single factor

control - set up has no change and serves as a reference


Observing and Measuring

Must include observations

Generalizations are not very useful

Accurate measurements and statement of results in numeral or quantitative form

Special tools and instruments


Analyzing and Drawing Conclusions

Data need to be analyzed

Interpret results and draw conclusions

Data can provide evidence to support, modify, or reject a hypothesis or to formulate a new hypothesis


Reporting Observations

No secrecy

Reported in detail

Experiment must be repeated by other investigators for results to be valid

Publish a paper

Scientific Journals

Reviewed by other scientists

Correct scientific methodology

Results reported clearly

Conclusions supported by experimental data

Criticisms and suggestions passed on to original scientist


Theories and Laws

Theories- explanations that apply to a broad range of phenomena and that are supported by experimental evidence.

Germ theory, Louis Pasteur

Scientific Law- is a statement that describes some aspect of a phenomenon that is always true. A law does not explain how or why something occurs as it does

scientists can state a law only after they have observed the particular events


Scientific Measurement

SI - International System of Units

Metric system

meters, grams, liter,second, Celsius or Kelvin

Biologists use small units - micrometers

micron - m , one-millionth of a meter 0.001 mm


2-1 Section Reviews answers



2-2 Tools of the Biologist

Observations and measurements are the backbone of scientific investigation.

The Light Microscope

Any device that uses light to produce enlarged view of an object

image - object

magnification - ratio of image size to object size

lenses - curved glass, bends light


The Simple Microscope

Magnifying glass

single lens

10 th century

still used today

used to make quick observations in the field


The Compound Microscope

Uses two lenses

Optical system

objective, ocular, low-power objective, high-power objective

Mechanical system

base, arm, stage, two clips, body tube, nosepiece, coarse adjustment, fine adjustment



Enlargement of an image

Magnifying power

100 x

Total magnification

multiply power of objective by the magnification power of the ocular



Shows two points that are close together as separate images

Sharpness of a image

Depends on precision and quality of the lens


Preparations of Specimens

Thin enough for light to pass through it

Fixationc- cut thin and soak

Embedded - liquid wax or plastic and hardened

sliced or sectioned

microtome - instrument for slicing

Glass slide and stained

Vital stains - do not kill cells


The Phase-Contrast Microscope

A special compound microscope that allows the details within living specimens to be seen without staining

Enhances the differences


The Stereomicroscope

Light that is used to study the external or surface structures of specimens

Three dimensional image

Image not reversed



TEM- Transmission Electron Microscope

SEM- Scanning Electron Microscope

Laboratory Techniques



Tissue Culture








2-2 Section Reviews answers

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