To investigate the effect of change in pH value on the population growth rate of Lemna sp. plants.

Problem statement	What is the effect of change in pH value on the population growth rate of Lemna sp.?
Aim	To investigate the effect of change in pH value on the population growth rate of Lemna sp. plants.
Hypothesis	The population growth rate of Lemna sp. plants is the highest in the pH 7 compared to pH 2 and pH 14.
Variables	Manipulated variable: Different pH value // pH 2, pH 7and pH 14 Responding variable: The population growth rate of Lemna sp. plants. Controlled variable: Species of Lemna sp. // plant /volume of water /intensity / time
Material & Apparatus	Materials: Lemna sp. plants, distilled water / dilute hydrochloric acid / sodium hydroxide solution, culture solution / pond water. Apparatus: Beaker // petri dish // container, measuring cylinder, pH paper / meter.
Technique	Count and record the number of Lemna sp. after 5 days. Or Calculate the population growth rate of Lemna sp. by using a formula : The population growth rate of Lemna sp. = Number of Lemna sp. 5 days

Procedure

1. Choose Lemna sp. plants of the same size.

2. Choose // take three petri dishes of the same size.

3. Label the petri dishes as A, B and C.

4. Pour 5 ml of distilled water into petri dish A, 5 ml of hydrochloric acid into petri dish B and 5 ml of sodium hydroxide solution into petri dish C.

5. Test the pH value of each solution using pH paper (and record in a table).

6. Pour 5 ml of culture solution / pond water into each petri dish.

7. Put 5 Lemna sp. plants into each petri dish.

8. Record in a table.

9. Place the petri dishes on the table / near the window in the laboratory.

10. Change the solution in the petri dishes everyday.

11. Count the number of Lemna sp. plants after 5 days.

12. Calculate the population growth rate of Lemna sp. plants.

13. Repeat the experiment / steps 1 until 11 to get the average result.

14. Observe and record the result.

15. Precaution : Change the solution in the petri dishes everyday.

Data	pH value Number of Lemna sp. plants The population growth rate of Lemna sp. plants (number/ 5 days) Day-1 Day-5 Increase / Decrease Neutral Asidic Alkali

Conclusion

The population growth rate of Lemna sp. plants is the highest in the pH 7 compared to pH 2 and pH 14. Hypothesis is accepted.