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6.2: Procedure

  • Page ID
    49696
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    1. Each pair of students will work as a team. Each team should obtain 2 vials, 1 carrot, 1 metric ruler, a digital scale and a small knife. Sorry, no stabbing allowed!

    2. Fill each of the 2 vials 3/4 full of the appropriate solution (either H\(_2\)O/distilled water or 1 M sodium chloride/NaCl).

      Note: the “M” refers to how much stuff there is in the water. The larger the number, the more stuff there is in the water. “M” stands for “molarity.” By the way, typical molarity of NaCl inside a plant cell is 0.15. This means that 1 Molar salt water is really salty!

    3. Prepare 2 carrot sticks from the same carrot. Slice narrow rectangular strips as close to 100 mm long \(\times\) 10mm wide \(\times\) 5mm thick as possible. (The instructor will give a demonstration of this).

    4. Measure each strip’s length in millimeters and weigh each strip in grams. Place them in the cups according to the table (question 2). Be careful to keep track of which strip is in which cup! Leave the strips in the environments for 20 minutes.

    5. Meanwhile, you might want to answer some questions from the report page.

    6. After 20 minutes, remove the strips, blot dry, re-measure and re-weigh them. Record the final length and weight for each strip. Compute the change (final minus initial length). Be sure to record changes with “\(+\)” or “\(-\)”.

    7. There are lots of random factors which all influence our results. This is why we need statistics. Your instructor will lead you through a statistical analysis to determine if the group data represent significant changes.

      For each set of before and after length data, we will calculate the probability of the null hypothesis (“Carrots strips did not change in length”) using t-test.

      We will use an on-line calculator. Enter initial data on the left and final data on the right. Make sure that “groups are matched” and “two tails” are selected. Then press “calculate”. You will be given the p-value which reflects the probability of the null hypothesis. This is the probability that there was not a change. Record the p-value.

    8. Address question 3. If p-value is less than a threshold (0.05), this is an indication that the null hypothesis (“Carrots strips did not change in length”) is unlikely. Consequently, if p-value \(< 0.05\) it is likely there was a significant change so we reject the null hypothesis and fail-to-reject the hypothesis indicating change!

    9. Clean up as instructed.


    This page titled 6.2: Procedure is shared under a Public Domain license and was authored, remixed, and/or curated by Alexey Shipunov.

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