We have looked at abiotic and biotic factors and have identified their interactions. We have looked at various plant and animal communities (biomes) and have traced how energy flows through a biome. Now it is time to experiment with how biotic factors interact with abiotic factors. That's right! This assignment is an experiment.

We use many chemicals that affect the Earth’s spheres. Simple things like the Miracle-Gro that you spray on your flowers may be affecting nearby streams or even far-off lakes. How does fertilizer affect our lakes and streams? Finding out is your task.


· sample of water that is NOT drinkable. The water may come from a pond, creek, stream, canal, reservoir, river or puddle.

· fertilizer (any type will work)

· available light source for algae growth (anything light that could make a plant grow)


1. Determine what you want to find out when you do your experiment. Do you want to know the effect of fertilizer on algae growth in pond water? Write down the QUESTION that you are trying to answer.

2. Predict what you think the outcome of your experiment will be.

3. Design an experiment to test your prediction.

There are a couple of things about designing experiments that you need to keep in mind.

First, you must have a CONTROL. A control is the part of the experiment that you do NOT change. For example, suppose you decide you want to find out what the effect of fertilizer is on the growth of algae in pond water. So you must get TWO identical samples of pond water. You will add fertilizer to one. The fertilizer is your variable. You will leave the other alone. The one that you left alone is the control. A control is necessary so that you can compare the results of your experimental variable, the fertilizer in this case, to what happens without the variable. Let us pretend for a moment that you did not use a control. You put fertilizer in the water, put it in the sunlight and checked it everyday for five days. Nothing happened. You don’t know if the fertilizer killed the algae or if the algae was never there to grow in the first place. If you have a control and the algae in the control grew, then you can probably conclude that the fertilizer killed the algae. Remember to use a CONTROL in your experiment.

Second, you need to know that most pond water, if left in a sunny location, will show increased algae growth in about five days. The water will become greener and murkier. Use this fact when you are planning your experiment.

Now, design your experiment. Be very specific. Tell me exactly what you plan to do. Tell me how much of everything you plan on using. Tell me how long you plan on running the experiment and how often you will check it. Tell me how you will record your data. I want details!!!

4. STOP!!! Submit your experimental design to me via email before going any further. My I promise to give you feedback on your design within three days. If the design is scientifically sound, you may go ahead and conduct your experiment. If it has flaws, we will work together until you have designed a valid, reliable experiment---then you may go ahead and conduct your experiment.

5. AFTER you have received my go-ahead, conduct your experiment. Be sure to keep detailed lab notes. Your lab notes should contain a record of everything you did as well as all the data you collected.

6. When you are done collecting your data, answer the analysis questions below.


A. Re-send me your original question, your hypothesis, and your experimental plan.

B. Send me your lab notes. I want to the observations that you recorded. Do not simply send me a summary of your results. I want to see a record of your daily observations.

C. Based on your observations, write a conclusion. What does your data tell you? What did you learn from your experimental results?

D. What kind of relationships did you find between biotic and abiotic factors?

E. Do your findings support your hypothesis? Why or why not?

F. If you were to do this again, what would you change? Why?

G. What additional experiments could be performed?

H. What effects would a dairy farm have on a pond downstream?

Please, send me the information requested in analysis questions A-H.


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