The Study of LifeChapter 1

BiologyLife Knowledge

Biology is the branch of science that studies living things

So....

What is “life?”

How do scientists study it?

Living Non-living

Alive Dead

vs.

vs.

or

When talking about the qualities of “living things,” we are often talking about the species level rather

than the individual level. “Skunks are living things,” rather than, “That skunk is living, the one on the

road is dead.”

Scientific Inquiry

• Science is an investigation of the natural world, using evidence from nature to support explanations.

• The methods used by scientists to investigate the natural world are called Scientific Inquiry.

• Scientific Laws and Theories are products of scientific inquiry.

Scientific Evidence

• Based on natural causes.

• Uniform in time and space.

• Perceived similarly by many people.

• Objective, measurable.

Forming Hypotheses

• Scientific Inquiry is often used to test hypotheses.

• A hypothesis is a tentative explanation for an observation.

• A valid hypothesis must be specific, testable, and falsifiable.

Specific• A hypothesis is specific if it

addresses particular observations and has specific variables.

• Not specific: “Toxins in water make fish populations decline.”

• Specific: “The herbicide glyphosate causes trout embryos to die in the egg when present in water at levels of 100 parts per million or more.”

Falsifiable• A hypothesis is falsifiable if it can

be “true or false,” either supported or rejected by evidence. Note we do not say “proven” or “disproven.”

• Not falsifiable: “Black licorice is the best kind of licorice.” (Opinions cannot be true or false.)

• Falsifiable: “Over half of WOU students in our biology class prefer black licorice over red.”

Let’s test it!

1. Black licorice2. Red licorice3. No preference

Which kind of licorice do you prefer?

Testable• A hypothesis is testable if involves

specific variables in the real, physical world that can be measured directly or indirectly.

• Not testable: “Students do poorly on exams because of bad luck.”

• Testable: “Biology students who make outlines and concept maps while studying their textbook score 10% better on exams than students who only read the textbook.”

A hypothesis does not…• …have to be “true” at the start of

the experiment. We don’t know until the experiment is over whether the hypothesis is supported or not.

• …have to explain everything. It only has to address one variable at a time. If you try to write a hypothesis that explains everything, it is no longer specific.

Hypotheses often begin with an observation that leads to questions.

Questions invite possible explanations.

These possible explanations are hypotheses. To be valid, a hypothesis must be specific,

testable, and falsifiable – but it doesn’t have to be correct! In fact, you don’t know if it is correct

or not until you test it.

Each possible explanation — hypothesis — can give rise to a prediction, often stated in an

IF...THEN format.

A good prediction suggests a procedure that can test the hypothesis.

Scientists test hypotheses and accept or reject hypotheses based on data. They do not set out

to prove hypotheses or they may bias their results.

Once the procedures are carried out, scientists use the data to reach a conclusion regarding the

hypothesis.

Notice that the hypothesis is supported rather than “proven.”

• Which of the following are valid hypotheses (specific, testable, falsifiable)? Explain why.

• Salmon makes my cat throw up.

• Coffee grounds are really good for a garden.

• Students who attend more than 80% of lectures earn a higher final exam average than students who attend fewer than 50% of lectures.

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“I get good grades because I’m lucky,” is a:

1. Valid hypothesis2. Observation3. Unfalsifiable

statement

Testing Hypotheses

• Scientific inquiry is used to test hypotheses.

• Scientific inquiry can be carried out by:

• Experiments

• Observational studies

• Scientists design experiments when their questions ask, “What is the natural cause of what I am seeing?”

• Variables must be measurable. Results must be repeatable to be dependable.

• Experiments use controls and replication.

Experiments

“Does this fertilizer cause crops to mature

faster?”

“Does pond water pH affect Daphnia

survival?”

Experiments are one type of scientific

inquiry. Experiments

test variables to try to find

the cause of natural events.

• Scientists design observational studies when their questions ask, “What is happening here?”

• Observational studies may be needed to establish which variables to test in an experiment.

• In some fields, observation may be all that is possible.

Observational Studies

“What lived here long ago?”

“What lives here now?”

Much of Astronomy and Paleontology involves observational science. We can’t do experiments on things out in space or that went extinct long

ago.

Which of these questions would lead to an experimental study?

1. “What’s for dinner?

2. “What’s the best seasoning for roast beef?”

3. “Which cooking method will make roast beef most tender?”

4. “Is there any roast beef left?”

• What’s happening in this picture?

• Write an IF – THEN hypothesis and prediction based on the picture.

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Observation

Conclusion

Experiment orObservation

Prediction

Hypothesis

Question

Laws and Theories• In general:

• Scientific Laws and Theories are both products of Scientific Inquiry.

• Laws tend to be descriptions of natural phenomena in given circumstances.

• Theories tend to be explanations of how natural phenomena work.

Two misconceptions to avoid!

• Laws are NOT ideas or theories that are “proven.” They are NOT “better” than theories.

• Theories are NOT guesses that have not been “proven” yet. Scientists to NOT form theories and then “desperately” try to “prove” them!

Law of Gravity describes what

happens when you drop a rock or

launch a rocket at the moon.

Gravitational Theory explains why dropped objects fall toward the

center of the mass of the Earth.

Mendel’s Laws of Heredity:

Describe patterns of inheritance in terms of

probability.

Darwin’s Theory of Natural Selection:

Explains why inherited traits change in populations over

generations.

A Unifying Theory• The gene pool of populations

changes over time. Changing environmental conditions favor different gene combinations at different times.

• Change in the genetics of a population from generation to generation is called “evolution.”

• Evolution explains species diversity and underlies all of modern Biology.

Modern evolutionary theory explains why organisms are so diverse, yet all are related.

Three processes underlie evolution: genetic variability, inheritance, and selection.

Genetic variability in populations is normal.

Genetic variation is inherited when DNA is passed from one generation to the next. Our DNA contains

the code for all of our inheritable traits.

Natural Selection, one mechanism

that causes evolution, is a

tendency for genes for traits that help

an organism survive and

reproduce to be passed on from generation to

generation. Traits that interfere with

reproductive success tend not to be passed on.

A scientific theory is:

1. Descriptive.2. Explanatory.3. A guess.4. Not proven.

What is Life?

• The concept of “living” can be difficult to define, since many qualities of living things can be seen in non-living things:

• Crystals (non-living) can grow.

• A thermostat (non-living) responds to the environment.

• On your own paper, list all the qualities that you can think of that define “living” as opposed to “non-living” in the natural world.

• When you have finished your list, turn to a neighbor and compare lists.

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Qualities of Living Things• Living things:

• are complex, organized, and made up of cells.

• maintain homeostasis.

• respond to stimuli.

• reproduce and grow.

• use materials and energy.

• as species, adapt and evolve.

Cells are the basic unit of living things.

Complex and organized

All living things have DNA,

which contains information to build cell parts.

Organisms can be single-celled, or cells can organize

into tissues and organs.

Maintain Homeostasis

Living organisms need to maintain

an internal environment,

such as maintaining

temperature.

Respond to stimuli

All living things have ways of sensing the environment that

allow them to respond to threats and find food or favorable environments.

Reproduce and grow

Living things produce more of their kind

through reproduction. The young grow to

maturity and the cycle begins again.

Use materials and energy

In order to maintain complexity, maintain homeostasis, to grow, and to respond to the environment, organisms must take in energy

and materials. Living things have a metabolism and give off waste products as they use

materials.

Still a relevant question

“What is life?” isn’t just a question that you left behind in Kindergarten.

Astrobiologists who search for signs of life on other planets look for many of the same

characteristics of terrestrial life.

Microbiologists studying nanobacteria may

challenge our current understanding of “life.”

Life can be studied on many different levels.

What is the smallest level of organization that meets our criteria

for “living organism?”

Is this a living thing?

1. Yes2. No3. Um… I’m not

sure.

Influenza virus

Living?

• The classification systems described are applied to living organisms.

• Some particles are “proto-living” – having a few of the characteristics of living things, but not quite alive.

Viruses• A virus has:

• Genetic material

• A protein coat

• A virus lacks a metabolism and cannot reproduce on its own.

• Much, much smaller than bacteria.

HIV Virus

Viruses

Bacteria

Viruses infecting a bacteria cell.

Viroid• A viroid is only

naked RNA, often in a ring.

• Viroids can, however, act as infectious agents. Several plant diseases are caused by viroids.

Prions

• Prions are self-replicating proteins that cause disease (such as “mad cow” disease).

• How prions replicate is still not fully understood.

Recap

• Living things are complex, organized, and maintain homeostasis.

• Scientists study living things using scientific inquiry to make observations and test hypotheses.

• Laws and theories are the products of science.

• Evolution is the unifying theory of modern biology.

• Write down something new that you have learned about:

• hypotheses.

• Laws and Theories in science.

• what evolution is.

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