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Lecture 1

Ch 1The Scientific Method

& Diversity of Life

Dr. Terence Lee

LA Harbor College

Biology

• The science of life:

1. That branch of knowledge which treats of living

matter as distinct from matter which is not living;

2. The study of living tissue.

3. It has to do with the origin, structure,

development, function, and distribution of

animals and plants.

The Scientific Method

1. Observations

2. Form a Hypothesis or Hypotheses

3. Testing Hypotheses

4. Drawing Conclusions or

– Revising the original hypotheses

– Re-testing

Does taking echinacea reduce the intensity or duration

of the common cold?

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What is a Hypothesis?

• A statement of a possible explanation for some natural phenomenon.

1. Must be phrased such that it can be falsified.

2. It is very often confused with Assumptions and Predictions.

Experimentation

• Experimental or Treatment group

– Manipulated group

• Control group

– No manipulation

– Used to compare to experimental group

• How would you test to see if birth control

pills cause cancer?

Null and Alternative Hypotheses

� Echinacea reduces the duration and severity of

the symptoms of the common cold.

Or as a null hypothesis:

• Echinacea has no effect on the duration or severity

of the symptoms of the common cold.

Devising a Testable Prediction from a

Hypothesis

The goal is to:

� Propose a situation that will give a particular outcome

if your hypothesis is true…

� …but that will give a different outcome if your

hypothesis is not true.

Hypothesis: Echinacea reduces the duration and

severity of the symptoms of the common cold.

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Does echinacea help prevent the common cold?

Hypothesis: Echinacea reduces the duration and severity of

the symptoms of the common cold.

Hypotheses and Theories

� A theory is a hypothesis for natural

phenomena that is exceptionally well-

supported by the data.

• a hypothesis that has withstood the test of time and

is unlikely to be altered by any new evidence

� Theories are hypotheses that have been so

strongly supported by empirical observation

that the scientific community views them as

very unlikely to be altered by new evidence.

Elements Common

to Most Experiments

1. Treatment

• any experimental condition applied to individuals

2. Experimental group

• a group of individuals who are exposed to a particular treatment

3. Control group

• a group of individuals who are treated identically to the experimental group with the one exception: they are not exposed to the treatment

4. Variables

• characteristics of your experimental system that are subject to change

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The Placebo Effect

� The phenomenon in which people respond

favorably to any treatment

� The placebo effect highlights the need for

comparison of treatment effects with an

appropriate control group.

Clever Hans

Experimental Designs

� Blind experimental design

• The experimental subjects do not know which

treatment (if any) they are receiving.

� Double-blind experimental design

• Neither the experimental subjects nor the

experimenter knows which treatment the subject is

receiving.

Hallmarks of an Extremely

Well-designed Experiment

� Blind/double-blind strategies

� Randomized

• The subjects are randomly assigned into

experimental and control groups.

Take-home message 1.11

� In experiments, it is essential to hold constant all those variables we are not interested in.

� Control and experimental groups should vary only with respect to the treatment of interest.

� Differences in them can then be attributed to the treatment.

1. Pseudoscience: individuals make scientific-

sounding claims that are not supported by

trustworthy, methodical scientific studies.

2. Anecdotal observations: based on only one

or a few observations, people conclude that

there is or is not a link between two things.

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Anecdotal Observations

� do not include a

sufficiently large and

representative set of

observations of the

world

� data are more reliable

than anecdotes

Take-home message 1.15

� Pseudoscience and anecdotal observations

often lead people to believe that links between

two phenomena exist, when in fact there are no

such links.

1.16 There are limits to what science can do.

� The scientific method will never prove or

disprove the existence of God.

� Understand elegance?

� What is beauty?

One of Several Approaches to the Acquisition

of Knowledge

� The scientific method is, above all, empirical.

� Value judgments and subjective information

� Moral statements and ethical problems

Pseudo-science and Misuse

of Science

• Intelligent Design

2nd Law of

ThermodynamicsWatchmaker Appendix

Pseudo-science and Misuse of

Science

• Cane Toads

www.hermonslade.org.au/projects/HSF_07_10/hsf_07_10.html

See also Youtube -> “Cane Toads: An Unnatural History”

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What makes something alive?

Are crystals alive?

Are viruses alive?

The Science of Biology

• What makes something alive?

1. Metabolic Processes (uses energy)

2. Generative Processes (growth & reproduction)

3. Responsive Processes (Reacts to environment)

4. Control Processes (homeostasis)

5. Unique Structural Organization (Synergy)

Levels of Organization The Origin and Diversification of

Life on Earth

Carolus Linnaeus Charles Darwin

Phylogeny

• The evolutionary development and history of a

species or higher taxonomic grouping of organisms.

• Phylogeny is not Taxonomy!

Bacteria

• Bacteria are prokaryotes

– No nucleus

– Circular DNA

– Both autotrophs and heterotrophs

1. Eubacteria

– Eu- = True

– More ancient.

2. Archea– Archaios- = ancient

– Lives in extreme environments similar to ancient earth.

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Eukaryotes

• Protista

– Most diverse group

– Hard to classify

• Fungi

– Non-photosynthetic

– Decomposers

• Plantae

– All have chlorophyll and are photosynthetic.

• Animalia

– All are heterotrophs

– Simplest animal is the sponge.

See also fig 20.8

Acellular Infectious Particles

•Viruses

• Can not reproduce on its own

• Needs the cellular “machinery” of a host to

reproduce.

•Viroids

•Small strands of RNA that can infect some plants.

•Prions

• Self replicating proteins that can infect some

animals.

•Thought to be responsible for mad cow disease.

•May help explain the origins of life.

viroids virus