Since plant species evolved for survival in different environments, their internal solute concentrations should be different from their marine ancestors. Which hypothesis do you think is more likely to be true?
PART III: DESIGN YOUR OWN EXPERIMENT
Do plants living in a freshwater pond have the same solute concentrations inside their cells as plants living in the salty ocean or on dry land? All plants are thought to have evolved from a common ancestor – single-celled green algae living in the ocean. In Part III you will design an experiment to test one of the following hypotheses:
Hypothesis 1: Since water is so critical for the life’s biochemical process, all plant cells should maintain the same internal solute concentrations as found in their marine ancestors.
Hypothesis 2: Since plant species evolved for survival in different environments, their internal solute concentrations should be different from their marine ancestors. Which hypothesis do you think is more likely to be true? Circle 1 or 2.
8.3 Exercise 3 – Comparing solute concentrations (isotonic points) inside plant cells from different environments
Using the plasmolysis threshold technique from Part II, design and carry out an experiment to determine whether the isotonic points of terrestrial and freshwater plants are the same or different than the isotonic points of marine plants. Procedure 1. Work in groups of 3-4. Write your partners’ names here:
Partner’s name Discussion leader’s name
2. Select three or four organisms from those available in the Central Study Area. In table 4A-D, record the names of the organisms and where they live. a. freshwater algae b. salt water algae c. terrestrial plants d. other plants, including any you bring in yourself
57
3. Based on the hypothesis you circled above (that is, that the cells will have the same or different internal concentrations), formulate a reasonable prediction about the outcome you expect. Your prediction should have the general form: Prediction: “If my hypothesis (1 or 2) is correct, then the isotonic point should be (higher/lower/the same) in cells from (aquatic, marine and/or terrestrial) environments than in cells from (aquatic, marine and/or terrestrial) environments. Write below the prediction you plan to test: Prediction: If my hypothesis is true, then… 4. Working with your group, test your prediction by following the procedures used in Exercise 2. Enter your results in Table 4A-D. Table 4A: Plasmolysis of the cells of ____________________________________in different concentrations of salt solution. This species lives in ____________________________________________________
Salt concentration
Number of cells plasmolyzed
Number of cells counted
Percent of cells plasmolyzed
58
Table 4B: Plasmolysis of the cells of ____________________________________in different concentrations of salt solution. This species lives in ____________________________________________________
Salt concentration
Number of cells plasmolyzed
Number of cells counted
Percent of cells plasmolyzed
Table 4C: Plasmolysis of the cells of ____________________________________in different concentrations of salt solution. This species lives in ____________________________________________________
Salt concentration
Number of cells plasmolyzed
Number of cells counted
Percent of cells plasmolyzed
Table 4D: Plasmolysis of the cells of ____________________________________in different concentrations of salt solution. This species lives in ____________________________________________________
Salt concentration
Number of cells plasmolyzed
Number of cells counted
Percent of cells plasmolyzed