Warm-up DiscussionWhat are the

important “steps” in developing and analyzing scientific investigations?

Is the process linear (meaning one step always leads to the next in the same order)? If not, explain why.

AgendaWarm-upBrainstorm: characteristics of good experiments

Special notes on hypotheses (including null hypotheses)

Design an experiment to investigate the response of isopods to environmental factorsBring bugs by Friday!!All procedures, raw data, and analysis should be

written in your lab notebook! Revisit characteristics of good experimentsGroup activity: evaluating and critiquing

experiments

Characteristics of Good Experiments

HypothesesBest to use “if-then” form

Indicates IN THE HYPOTHESIS what your independent and dependent variables will be (what you’ll change and what you’ll measure)

Examples:Poor: I think the color green is more soothing than

the color red. Doesn’t tell you enough about the experimental design!

What are you measuring?

Better: If rats are soothed by green more than red, then rats in a green chamber will have lower heart rates and respiratory rates than rats in a red chamber.

HypothesesFix these!

Poor: I think cats like tuna more than they like chicken.

Poor: I think my dog pees more on trees that other dogs have marked than on fresh trees.

Null HypothesesBasically says that there will be no significant

correlation/preference/difference/effect in your outcomes

Examples:Hypothesis: if cats prefer tuna over chicken, then cats

will eat the tuna meal more often than the chicken meal when they are given both options.

Null: if cats have no preference of tuna over chicken, then they will eat both meals with equal frequency when given both options.(or cats will have no preference between tuna and chicken)

Null HypothesesYou Try!

Hypothesis: If a white Chrysler 200 and black Chrysler 200 are left in the blazing Texas sun for 9 hours, then the white Chrysler 200 will have a lower interior temperature than the black Chrysler 200.

Null:

Null HypothesesYou Try!

Hypothesis: If bacteria grow more in sweaty versus dry environments, then more bacteria will be found on a sweaty sock than on a dry sock.

Null:

Null HypothesesYou Try!

Hypothesis: If Oxyclean is a more effective stain-fighter than Shout, then a grass-stained t-shirt washed with Oxyclean will be cleaner than a grass-stained t-shirt washed with Shout.

Null:

Null HypothesesWhy bother with a null hypothesis?

You can’t really “prove” anything in scienceIf you can statistically reject your null hypothesis,

you’re saying there is not “no difference” which is very similar to saying that there IS a difference

ExampleAbbrHyp: Cats prefer tuna over chickenNullHyp: Cats eat tuna and chicken in equal

frequencies

I can never prove unequivocally that cats prefer tuna, but I can disprove that they have no preference which supports the idea that they prefer tuna

Design an experiment to investigate the response of isopods

to environmental factorsIsopod Behavior

(or The Roly-poly Lab!)Objectives: Observe various aspects of a terrestrial isopod Conduct experiments examining the responses

of isopods to various environmental factors Design and conduct an investigation of animal

behavior

Isopod BehaviorToday: Design the LabNote any important background information that will help

you form a question about the isopod’s response to the environment

Form a questionForm a testable hypothesisForm a null hypothesisDesign an experiment that will allow you to support or

reject your hypothesis and null hypothesisIdentify independent and dependent variables (what will you

change? What will you measure?)Determine materials: choice chamber, # pill bugs, etcDetermine procedures – BE SPECIFIC! I should be able to

read your procedures and do your EXACT experiment!Sketch out what data tables you’ll need

THIS STUFF GOES IN YOUR LAB NOTEBOOK – DUE TOMORROW!! (you will type up a nice, pretty lab report later)

Tomorrow: Do the Lab (gather data, begin analysis, etc)

Factors to Investigate…Factor Materials (suggested)

Temperature cold pack, warm pack

Light lamps, flashlights, dark construction paper, aluminum foil

pH low pH (HCl), high pH (NaOH)

Substrate (surface)

soil, sand, sandpaper, bark, paper, cedar chips, gravel

Odor ammonia

Food apple, potato, fish food, lunchmeat

Revisiting Characteristics of Good Experimental Design

Critiquing ExperimentsIn your groups, you will evaluate and critique four

experimentsEach student will write their OWN answersUse “if/then” format for hypothesis, but you are not

required to use “if/then” for the null hypothesisBe sure that your conclusions are concise and

specific – it’s never enough to say that something “changed,” you must always say HOW it changed (increased, decreased, got __ °C warmer, etc…) and do not make broad generalizations that aren’t supported by the data

HypothesesPoor: I think the bugs will move toward the wet

side of the chamber.

Better: If the bugs prefer a moist environment over a dry environment, then when they are randomly placed in a choice chamber and allowed to move freely for ten minutes, more bugs will be found on the wet side of the chamber than the dry side of the chamber.

Null Hypothesis: If pill bugs are randomly placed in a choice chamber and allowed to move freely for ten minutes, then they will have no preference for moist versus dry and the same number will be found on each side of the chamber.