Lesson 2

Does a change in pH affect the growth and survival rate of aquatic plants?

Objectives:
Students will be able to:

determine if changes in pH affect the growth and survival rates of aquatic plants.
evaluate the optimal pH levels for the growth of aquatic plants.

Note: Safety goggles and aprons should be worn at all times during this lab activity.

Materials:
Fresh water sample from a local pond or aquarium
3 250 ml beakers or containers
3 portions of duckweed or elodea
Dissecting microscope or hand lenses
Petri dishes for microscopic observations
1% NaOH in dropper bottles
1% HCl in dropper bottles
Wide range pH paper, pH test kit or pH probe
Pipettes

Procedure:
Working with a partner:
1. Using a hand lens or a dissecting microscope, examine a portion of the plant to be used in this experiment.
Describe the characteristics of a healthy plant.

2. Label 3 beakers or containers as follows:

Beaker 1-Control
Beaker 2-pH 3
Beaker 3-pH 12

3. Add approximately 200 milliliters of the fresh water sample to each beaker.
4. Beaker 1 is the control. Add a spig of plant material to beaker 1. Do not add any additional materials to beaker 1.
5. Beaker 2 should have a pH of 3. Add 1% HCl dropwise to beaker 2 until the water has a pH of 3. Test with pH paper after the addition of each drop. When a pH of 3 is reached, add a spig of plant material to the beaker.
6. Beaker 3 should have a pH of 12. Add 1% NaOH dropwise to beaker 3 until the water has a pH of 12.Test with pH paper after the addition of each drop. When a pH of 12 is reached, add a spig of plant material to the beaker.
7. Place the 3 beakers in an area where they will not be disturbed. Observe the containers
every day for a ten day period.
8. On days 1-4 and 6-9, make visual observations of the plants and record the observations
in the data table.
9. On days 5 and 10, make microscopic observations of the plant material and determine
any changes which have taken place since the initial observations. Record your observations on the data table.
10. Based on the pH of each container, hypothesize about which plants will growth and survive or which plants will wither and die.

Hypothesis:

Data Table:

After the observations are complete, answer the following questions.

Conclusions:
1. Based on your observations, what would be the optimal pH level for the growth and development of aquatic plants?

2. Based on your observations, what would happen to plants in an aquatic ecosystem if the pH decreased or increased?

3. How would this effect the aquatic ecosystem as a whole? (Consider other organisms such as macroinvertebrates and fish)

4. Research the cause behind the acidification of an aquatic ecosystem. Write a short paragraph explaining the causes, the effects, and the solutions.

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