Principles of Life, 2e - Launchpad · 2014. 3. 19. · chapter 1| Principles of life 5 FIGURE 1.5 Life Consists of Organized Systems at a Hierarchy of Scales(continued) POL 2e Sinauer
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1 Principles of Life
POL 2e Sinauer AssociatesMorales Studio POL2e_01.01.ai Date 06-18-13
27
First life?
12
6
39
27 28 29 30
Each “day” represents about 150 million years.
Homo sapiens (modern humans) arose in the last 5 minutes of day 30 (around 500,000 years ago).
Recorded historycovers the last fewseconds of day 30.
Life appeared some time around day 5, a little less than 4 billion years ago.
POL 2e Sinauer AssociatesMorales Studio POL2e_01.11.ai Date 06-18-13
1. Make observations.
2. Speculate, ask a question.
4. Make a prediction: What else would be true if your hypothesis is correct?
5. Design and conduct an experiment that uses quantifiable data to test your prediction.
Reexamine theexperiment foruncontrolledvariables.
Ask newquestions.
Use statistical tests to evaluatethe significance of your results.
Significant resultssupport hypothesis.
Experiment repeated and results verified by other researchers.
Results do notsupport hypothesis.
3. Form a hypothesis to answer the question.
Revise yourhypothesis.
FIGURE 1.11 Scientific Methodology (Page 12)
FIGURE 1.12 Controlled Experiments Manipulate a Variable
HyPotHesis
Exposure to atrazine during larval development causes abnormalities in the reproductive tissues of male frogs.
MetHod
1. Establish 9 tanks in which all attributes are held constant except the water’s atrazine concentration. Establish 3 atrazine conditions (3 replicate tanks per condition): 0 ppb (control condition), 0.1 ppb, and 25 ppb.
2. Place Rana pipiens tadpoles from laboratory-reared eggs in the 9 tanks (30 tadpoles per replicate).
3. When tadpoles have transitioned into adults, sacrifice the ani-mals and evaluate their reproductive tissues.
4. Test for correlation of degree of atrazine exposure with the presence of abnormalities in the gonads (testes) of male frogs.
ResuLts
ConCLusion
Exposure to atrazine at concentrations as low as 0.1 ppb induces abnormalities in the gonads of male frogs. The effect is not pro-portional to the level of exposure.
Go to LaunchPad for discussion and relevant links for all INVESTIGATION figures.
INVESTIGATION
POL 2e Sinauer AssociatesMorales Studio POL2e_01.12.ai Date 06-18-13
Color blind note:changed colors to new spec colors
In the control condition, only one male had abnormalities.
Atrophiedtestes
Testicularoocytes
Mal
e fro
gsw
ith g
onad
al
abno
rmal
ities
(%)
0.0Control
0.1 25
Atrazine (ppb)
20
40
0
Oocytes (eggs) in normal-size testis (sex reversal)
FIGURE 1.13 Comparative Experiments Look for Differences among Groups
HyPotHesis
Presence of the herbicide atrazine in environmental water correlates with gonadal abnormalities in frog populations.
MetHod
1. Based on commercial sales of atrazine, select 4 sites (sites 1–4) less likely and 4 sites (sites 5–8) more likely to be contaminated with atrazine.
2. Visit all sites in the spring (i.e., when frogs have transitioned from tadpoles into adults); collect frogs and water samples.
3. In the laboratory, sacrifice frogs and examine their reproductive tissues, documenting abnormalities.
4. Analyze the water samples for atrazine concentration (the sample for site 7 was not tested).
5. Quantify and correlate the incidence of reproductive abnormalities with environmental atrazine concentrations.
ResuLts
ConCLusion
Reproductive abnormalities exist in frogs from environments in which aqueous atrazine con-centration is 0.2 ppb or above. The incidence of abnormalities does not appear to be propor-tional to atrazine concentration at the time of transition to adulthood.
Go to LaunchPad for discussion and relevant links for all INVESTIGATION figures.
INVESTIGATION
POL 2e Sinauer AssociatesMorales Studio POL2e_01.13.ai Date 06-18-13
Color blind note:changed colors to new spec colors
In the seven sites where atrazine was present, abnormalities, including testicular oocytes and atrophied testes, were observed.