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Observations

Observations. DI Water 40% Ethanol. Statement of Problem. Why does the pigment look faded with 40% ethanol?. Hypotheses. Ha1 Ethanol enters the cell and breaks down the pigment. Ha2 Ethanol breaks down the cell membrane releasing contents of the cell including the pigment.

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Observations

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  1. Observations • DI Water • 40% Ethanol

  2. Statement of Problem • Why does the pigment look faded with 40% ethanol?

  3. Hypotheses • Ha1 Ethanol enters the cell and breaks down the pigment. • Ha2 Ethanol breaks down the cell membrane releasing contents of the cell including the pigment.

  4. Methods • Control = chopped onions added to water. • Treatment = chopped onions added to 40% ethanol. • Measure amount of pigment in two solutions with spectrometer.

  5. Spectrometer Measures light intensity of different wavelengths (colors) Sensor

  6. Predictions • Ha1 Ethanol enters the cell and breaks down the pigment. • Ha2 Ethanol breaks down the cell membrane releasing contents of the cell including the pigment. • If Ha1, then the control solution will have the same or more pigment than the treatment. • If Ha2, then the control solution will have less pigment than the treatment.

  7. Measures of Central Tendency 3 4 4 5 6 7 7 7 7 8 8 Mean = (sum)/n = 66/11 = 6 Median = center value = 7 *If n is even, median = avg. of the two middle numbers ex. 1 4 4 6 9 15 median = 5

  8. Indices Mathematical manipulations of the data to assist with interpretation Ex. Diet Studies typically record: N = numerical percentage M = mass percentage F = frequency of occurrence Index of Relative Importance = (N+M)*F Another example: Shannon Weaver’s Index of Diversity

  9. Graphs t Continuous independent variables

  10. Graphs Cascades frog stomach contents at fish-containing and fishless lakes Discrete independent variables Bar graphs need error bars

  11. Graphs • X-axis is the independent variable • Y- axis is the dependent variable • Need titles or legends • Bar graphs need error bars, usually +/- SE • SE=Standard Error • Onto stats…

  12. Statistics for this lab Procedure #2 Bar graphs need to have error bars Error bars will represent the standard error (SE) 3 4 4 5 6 7 7 7 7 8 8 Dataset A Mean = 66/11 = 6 -200 -58 -20 -15 4 7 7 40 43 70 188 Dataset B Mean = 66/11 = 6 What’s the difference? SEA = 0.52 SEB = 28.18

  13. Standard Error SE represents the amount of variation within a sample SE = (standard deviation) / (sqrt(N)) N is the sample size Standard deviation:

  14. T-tests & Statistical Hypotheses Ho: Treatment (alcohol) absorption = control (water) absorption. Ha: Treatment absorption ≠ control absorption. T-tests use means and standard errors to determine whether two discrete groups are significantly different.

  15. T-tests P value  Probability(type I error) Level of significance = P “Statistically significant” Type I error: rejecting a true null hypothesis Type II error: accepting a false null hypothesis Generally, scientists try to minimize the probability of making a type I error.

  16. T-tests Ho: Treatment (alcohol) absorption = control (water) absorption. Ha: Treatment absorption ≠ control absorption. ex. if P=0.48 48% chance that we are wrong to reject Ho. Thus, we do not reject Ho. P<0.05 acceptable for most things ex. If P=0.03, we would reject Ho and accept Ha.

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