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Unit 1Methods of Biological Science

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The Goals of Science

1. Deals only with the natural world

2. Collect and Organize Information

3. Propose explanations that can be tested

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Summarizing..............

SCIENCE is a body of knowledge thatexplains the natural world.

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Steps of the Scientific Method

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Assumption

vs.Inference

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Assumption:

Beliefs or ideas that we hold to be true, somethingwe take for granted or presuppose. Statements

that are accepted or believed to be true without

evidence

Inference - a logical interpretation based on prior

knowledge or experience (Ex. You see a window

broken and a baseball on the floor next to the

shattered glass. You can -infer- that a baseball broke

your window)

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Ex. 1Inferences about the eating habits of each animal

A B

C

How did you determine what these animals eat?

What inferences did you make?

Did you make any assumptions?

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Skull A

The teeth are not the only evidence that could be used tosupport inferences about the feeding habits of theanimals. What other features might provide important

clues?

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Exercises 2 and 3:

Using observations to generate a causal explanation,and designing experiments to test a hypothesis

Hypothesis

Experiment

Prediction

Dependent

Variable

IndependentVariable

Replication

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Definitions HYPOTHESIS

Once there is a specific critical question, then a hypothesis must

be developed. Hypotheses are tentative answers to the scientific

questions.

For every critical question there are a vast number of hypotheses

(tentative answers). PREDICTION

To be useful, a scientific hypothesis must be testable in some way.

This means that scientific hypotheses must lead to specific

predictions that can be tested by further observations orexperiments.

Each prediction begins by restating the hypothesis and then

stating a specific event that will occur if the hypothesis is valid.

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What was your causal explanations/ hypothesis for whathappened in the jar?

What prediction canyou make based onyour hypothesis?

Describe anexperiment thatwould test the

hypotheses youproposed.

What prediction can you make based on your hypothesis?

a) 2 liquids in the jar react together

b) the liquid reacts with the air in the jar c) the liquid reacts with the underside of the lid

Liquid= glucose + potassium hydroxide + blue dye

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Hypotheses and Predictions Observation-

When I shake the jar the liquid turns blue.

Hypothesis-

Statement ofwhysomething happens. When I shake the jar the liquid turns blue

because it becomes oxygenated.

Prediction-

Statement of what will happen if the

hypothesis is correct.

If I remove all the oxygen from the jar and

shake the liquid, it will not turn blue.

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Designing an Experiment

Experiment- test of a hypothesis

Control group- removes the independent

variable (manipulation), or keeps it as in

nature; compare other groups to this one

Treatment group(s)- alterations/variations

of the independent variable

Replication- builds evidence, providesgreater support for/against claim,

minimizes error

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Some possible observations include:

The shrimp is associated with the algae.

The shrimp seems to be eating the algae.The algae are green.The shrimp is green.

The shrimp and the algae are similar in color.

OBSERVATION

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Some possible questions include:Why are the algae green?Why is the shrimp green?

Is the shrimp eating the algae?Is the shrimp color related to the algae color?

CRITICAL QUESTIONS

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Some possible hypotheses include:The color of the shrimp is not related to the color of the algae.The color of the algae is derived from the color of the shrimp.Shrimp color is derived from the color of the algae.

HYPOTHESIS

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Some possible predictions based on the selected hypothesis include:If shrimp color is derived from the color of the algae, then:... shrimp will change color when their diet changes.... shrimp will change color when placed in a tank with algae of a differentcolor.

PREDICTION

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EXPERIMENTA method to verify the accuracy of the predictions made from ahypothesis

-One hundred adult shrimp are divided at random into two equallysized groups and maintained under identical conditions except for theirfood.-The control group is fed the same green algae that led to the originalobservation.-The experimental group is fed algae of a different color.

-The shrimp in the two groups are observed periodically for severalmonths, and detailed records of shrimp color are maintained for bothgroups.

The Independent variable is whatyou, the experimenter, changes orenacts in order to do yourexperiment. The dependentvariable is what changes when theindependent variable changes

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RESULTS (DATA)

Once the experiment is done anddata are collected, there will beresults to analyze.

Result A: Control shrimp aregreen and experimental shrimp are

brown.

Result B: Control shrimp aregreen and experimental shrimp arealso green.

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Question

Annie was studying the effect of temperature on how quickly fish

are able to reproduce (time to reproduction). She placed 25juvenile catfish in each of 3 tanks. One tank contained water at anormal temperature (23C), the second tank contained water at30C, and the third tank contained water at 35C.

What is the dependent variable in this experiment?

time to reproductionWhat is the independent variable in this experiment?

temperatureWhat is the control group in this experiment?

tank with normal temperature

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Collecting Data

A scientist carefully collects and organizes data from theexperiment

Data should always be presented in a neat fashion, usuallytables or graphs

Data Table Example Data can be powerfullydisplayed as a graph

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Calculating and Analyzing Data

Exercise 4: Calculation of themean

The mean that you calculated for 15shells, was it closed to the grand mean?

Grand mean: 89.8based on 10,000 shells

Why do you suppose there is so much variation in theseestimates of the mean?

Generalization

Sampling Error: Inaccuracy due to inadequate sample sizeUse larger sample. Sampling must be random

Experimental Error: Inaccuracy due toprocedural faults

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Test question

Noah measures 5 microliters of plasmafor his radioimmunoassay instead of 5

milliliters. What specific type of error didNoah commit?

Experimental error

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Graphic summaries of data

Histogram show frequency of a continuous variable

within a given range. You can decide how big

each range is.

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Graphic summaries of data Ba

r gra

phs compare one (or more) variables across different

groups of similar things

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Histogram vs. Bar Graph

Similarity: Both may measure number ofsomething-- or frequency.

Difference: X-axis is continuous in ahistogram, and categorical/discrete in abar graph.

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Graphic summaries of data

Line graphs show the functional relationship betweentwo variables

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X-axis: independent variable

Line graphs

X axis = independent variable

Y axis = dependent variable

Best fit line is drawn through the pointsto show the nature of the relationship

Best fit line does NOT have to be straight,and does not always connect points.

Y-axis:

dependentvariable

What you manipulate

What you measure

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Best-fit line

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Interpreting graphs

Interpolation - estimation of an unmeasuredquantity based on the trend shown by datapoints on either side of the unmeasured

quantity (inside the data range).

Extrapolation - estimation of unmeasuredquantities based on extending the graph linebeyond the measured data (outside the datarange).

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Graphic summaries of data

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Type ofGraph

Histogram, since data are clearly presentedas frequency counts

Bar graph, since the independentvariable is a set of categories

Line graph, even though there are categories of organisms,the independent variable (generation time) is continuous

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Graph Rules

Title descriptive, use both variables ifpossible

Axis independent vs. dependent

Labels Units for what you measured

Form Use @ least 50-75% of your graph

paper (use continuity breaks if needed); starttrend line at first point and end it at last point;

best fit line, CAN CURVE

Do not connect the dots!

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Sampling error

EXTRAPOLATION

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Objectives:

1. Distinguish between inferences and assumptions

2. Formulate hypotheses and describe the relationship

between hypotheses and predictions

3. Recognize the dependent and independent variables in

an experiment and describe the role of a control group

4. Distinguish between experimental error and sampling

error

5. Construct histograms and bar graphs

6. Construct graphs of data showing functionalrelationships between two variables

7. Distinguish between interpolation and extrapolation

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Skull

A

What sort of action do you think thefront teeth can accomplish clipping, grinding, or tearing?

What do you think the teeth in backof the jaw are used for?

What type of food do you think thisanimal eats and why?

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SkullB

What sort of action do you believe the front teeth can accomplish clipping,grinding, or tearing?

What about the other teeth near the back of the jaw? What do you think

these are used for?

What type of food do you think this animal eats? Why?

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SkullC

What sort of action do you believe the frontteeth can accomplish clipping, grinding, ortearing?

What are the other teeth used for?

What type of food do you think this animaleats? Why?