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Respiratory System Investigation Design Lab

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Problem: How does the salinity level of water affect the rate of gas exchange for aquatic organisms like algae?



* Mass of algae

* Volume of water

* Room temperature

* Humidity/air pressure


* Rate of gas exchange per minute


* Salinity of the water


– 3 beakers of 100mL in capacity or more

– algae

– graduated cylinder

– distilled water

– table salt

– paper towel

– glass stirring rod

– small fish net

– measuring balance

– large beaker of spring / pond water (to feed algae / keep them alive for further trials)

– respirometer


1. Create tables similar to the three shown.

2. Pour distilled water into the graduated cylinder, measuring out 100mL. Then pour this water into the beaker.

3. Place a piece of paper towel onto of the balance and press the tare button. Then measure out the indicated amount (between 0 – 20g) of table salt.

4. Record the measured mass and then pour the salt into the beaker filled with 100mL of water.

5. Using a stirring rod, stir the water until all of the salt dissolves.


6. Using the small fish net, pace a planarian from the large beaker of spring / pond water into each of the five beakers and wait around 10 minutes.

7. Measure the rate of respiration for the planarian in the beaker with no salt by placing the respirometer into the water close by to the planarian.

8. Remove the respirometer and record the results. Also, record the changes in the appearance and state of the algae if any, in the qualitative chart.

9. Repeat the entire procedure for two more trials.

10. Take the average result of the three trials. Record the averages from each of the groups from the class. Plot the data onto the graph provided in figure 1.

Qualitative Observations

Group’s Qualitative Observations

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