May 26, 2006

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 should be worn at all times during this lab activity.

Materials Needed:

Fresh water sample from a local pond or aquarium

3 x 250 ml beakers

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 and pH probe

Pipettes

Procedure:

1. Working with a partner:
2. 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.
3. Label 3 beakers with a china clay pencil as follows: Beaker 1-Control

   Beaker 2-pH 3

   Beaker 3-pH 12

4. Add approximately 200 mLs of the fresh water sample to each beaker.
5. Beaker 1 is the control. Add a spig of plant material to beaker 1. Do not add any additional materials to beaker 1.
6. 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.
7. 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.
8. Place the 3 beakers in an area where they will not be disturbed. Observe the containers every day for the rest of the laboratory course.
9. On days 1-3 and 6-9, make visual observations of the plants and record the observations in the data table.
10. On days 6 and 9, 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.
11. 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:

 

Date	Day	Observations Beaker 1	Observations Beaker 2	Observations Beaker 3
	1
	2
	3
	4
	5
	6
	7
	8
	9
	10

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.