Unit 03 Lab Walkthrough:      

Many thanks to science teacher Edward Shapard for his guidance in helping students learn.  The science lab 'Walkthrough' is his idea, process and format.

Follow along below and I'll show you exactly what to do for this lab in a step-by-step fashion.  This lab takes approximately 45 minutes to complete. The lab will open in a new tab. So anytime you want to refer to the 'Walkthrough' you can click on that tab.

The purpose of a lab report is to share your scientific knowledge with others.  Lab reports must be written so that your peers can understand 1) what you did in your experiment, 2) what data you collected and 3) what conclusions you made, based on your data.  Write as if you are writing for someone who did not do the experiment.  You are sharing what you learned. 

What's in this walkthrough:

 

The purpose of this lab is to learn:  How does biodegradable waste affect dissolved oxygen levels?

Purpose : Understand the relationship between biodegradable waste and dissolved oxygen found in the world’s water-based ecosystems. Eutrophication is the process by which an ecosystem, such as a body of water, becomes contaminated with chemical nutrients such as from fertilizer. Excessive nutrients cause too much plant matter (such as algae) to grow, which can make the water unlivable for other aquatic life. This lab serves to demonstrate those effects.


Background: When microorganisms such as fungi and bacteria eat biodegradable waste, they use large quantities of oxygen. Consequently, more biodegradable waste means there is less dissolved oxygen for fish, plants, and other aquatic life. In this experiment, we will investigate that relationship. Yeast will represent the microorganisms that produce biodegradable waste, and various reagents will indicate how much oxygen was consumed. A reagent is a substance used in a chemical reaction to examine other substances. The solution will turn blue when there is no more oxygen present. The color change is actually from a yellowish-brown to blue once enough drops of reagent have been added. A yellowish-brown solution indicates the presence of dissolved oxygen gas.


Why do we measure the amount of dissolved oxygen in water? When we measure the amount of dissolved oxygen in a sample, we are measuring the amount of oxygen gas that is “trapped” between water molecules. This amount is important because without dissolved oxygen, fish, and other aquatic organisms could not survive. Fish need oxygen gas, too, but since they don’t have lungs, they take oxygen gas from the water in which they live. The oxygen in the water available to fish is called dissolved oxygen (oxygen that is dissolved in the water). Fish use gills to take oxygen gas from water just as we use our lungs to take oxygen gas from air. Since many aquatic organisms prefer to live in water with high levels of dissolved oxygen, a measurement of dissolved oxygen can let us know whether an aquatic ecosystem would be a good habitat. Certain species of fish—such as salmon or trout, for example—can only live in ecosystems with high levels of dissolved oxygen.

 

Keywords and Pronunciation

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Lab Report  

Download the Lab Report Document


The Tutorial

The tutorial will reset when you know how to use the chemicals, pipette, test tube, stopper, timer, reagent dropper bottles and preparation of yeast solution.   When the tutorial instructs you on how to gently swirl the test tube make sure you 'click and hold' (hold the click for about 2 seconds until you see the test tube shake)

 View the Tutorial  

In the Tutorial you will do one of the trials of the actual lab.  Make sure you keep track of how many drops of Reagent you use to turn the solution blue and record the data on your data sheet below in the column for 0.25mL of yeast.

  How to answer the questions on the Lab Report

#1.  Use your data sheet (above) to fill in the data (15 Points)  

 

#2    Since the number of Reagent D drops represents oxygen content, the more drops you have to add to acquire the blue color, the more oxygen was present in the tube. Thus, the tube sample you added the most drops of Reagent D to would be the more favorable environment for marine life. The fewer drops you had to add to the test tube to achieve the blue color, the less oxygen it had to begin with.    Note eutrophication  (yoo-TROH-fuh-KAY-shuhn):  enrichment of nutrients in an aquatic environment that causes excessive growth of aquatic plants, especially algae, which increases bacterial growth and consumption of oxygen, resulting in depletion of oxygen in the environment.  (make sure your answers are in a complete sentences.)

 

#3   Don't make this answer too complicated.  You just did an experiment showing how and increase in waste, affect the amount of oxygen available to the health of the water environments.  Image what would happen if there too much waste in a river.  (make sure your answers are in a complete sentences.)

 

#4   Use your algebra!  If 1 hour makes 8 bacteria, how many bacteria in 15 hours?   What do you have to multiply 1 hour by to get 15 hours.  Use that same factor to multiply the 8 bacteria by to get the total number of bacteria.

 

#5   Look at your data.  Which sample took the most drops of D?  How much yeast was in that test tube?  Aha....what does that tell you about the quality of water without the yeast?   (make sure your answers are in a complete sentences.)

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Troubleshooting the virtual labs

  • Note: The virtual labs are known not work well with Chrome and sometimes internet explorer.
    • If you have technical difficulties with the virtual lab, try Firefox, it's free.
  • If you're using Firefox and you still have technical problems with the virtual lab try:

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Submitting your lab report

Click on the dropbox

 

You will see:  Click on 'Add a File'

 

 Look in 'My Computer' Upload and Add your lab report:

Submit

 

Viewing your score and grading notes

Give me a few days to grade your work and then click on the dropbox again. You'll see your grade along with my comments in the inbox section.

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How to improve your grade on this lab

Correct your lab and turn it back in for more points!

You get unlimited re-takes for labs if you're in my class (Mrs. Lilly). Just read the comments I give you when I turn back your lab (see section above) to figure out what wasn't right about the lab, fix it in your lab report, and turn the new report back in to me. If you're in another teacher's class, ask them about their retake policy for labs.

You can keep doing this until you get a perfect score, but near end of the semester, we stop accepting labs, so don't wait until the last minute!

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Many thanks to science teacher Edward Shapard for his guidance in helping students learn.  The science lab 'Walkthrough' is his idea, process and format.

 


Procedure


When you have finished the tutorial and recorded your data in the data sheet, click the home button and reset the lab if necessary.

Click to    Begin the Lab

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Data for 0 mL of yeast

  1. Rinse the test tube and fill with water by picking it up and putting it under the water tap to the left.

  2. You are starting the experiment by measuring how much oxygen is in the water.  DO NOT ADD THE YEAST TO THE TEST TUBE FOR THIS FIRST TRIAL.

  3. Again add 5 drops of A and 5 drops of B to the test tube, put the stopper on, shake and return to the test tube holder.  Put the timer on for 2 minutes.

  4. Add 5 drops of C  put the stopper on, shake and return to the test tube holder.  Put the timer on for 2 minutes.

  5. Add Reagent D to the test tube.  You know how many drops it took to turn blue when there were 0.25mL of yeast.  It would be reasonable to add that many drops to start.  Put on the stopper, shake and return to the test tube holder.

  6. For the remainder of this trial, add 1 drop of Reagent D at a time, put on the stopper, shake and return to the test tube holder.

  7. Continue adding 1 drop of D at time until the solution turns blue.  Record your data on the Data Sheet in the column of '0 mL' of yeast.

  8. When finished take the test tube to the water tap, empty, clean and refill with water.  Return it to the test tube holder.

Data for 0.25 mL of yeast

  1. You did this in the tutorial, make sure the data is on your data sheet

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Data for 0.50 mL of yeast

  1. Make the yeast solution- The beaker has 40 mL of water and you put in 1 teaspoon (4 mL)  of yeast and put in beaker and stir.  The beaker solution now contains .25 mL per drop from the pipette.

  2. In this next trail put two pipettes of yeast into the test tube for a total of 0.5mL of yeast.  Add two pipettes of the yeast solution to the test tube.

  3. Again add 5 drops of A and 5 drops of B to the test tube, put the stopper on, shake and return to the test tube holder.  Put the timer on for 2 minutes.

  4. Add 5 drops of C  put the stopper on, shake and return to the test tube holder.  Put the timer on for 2 minutes.

  5. Add Reagent D 1 drop at a time, put the stopper, shake and return to the test tube holder.

  6. When the solution burns blue, record the number of drops on your data sheet.

  7. Take the test tube to the water tap to empty, clean and refill for the next trial.

Data for 1.0mL of yeast in the test tube.

  1. Again add 5 drops of A and 5 drops of B to the test tube, put the stopper on, shake and return to the test tube holder.  Put the timer on for 2 minutes.

  2. Add 5 drops of C  put the stopper on, shake and return to the test tube holder.  Put the timer on for 2 minutes.

  3. Add Reagent D 1 drop at a time, put the stopper, shake and return to the test tube holder.

  4. When the solution burns blue, record the number of drops on your data sheet.

Your have now completed the lab

                                                                          DATA SHEET

One pipette (dropper) of the yeast solution is 0.25 mL. The number of drops of Solution D needed to turn the solution blue is the amount of dissolved oxygen that was in the water in parts per million (ppm).

) Amount of yeast
0 mL 0.25 mL 0.50 mL 1.0 mL
Drops of Reagent D        
         
Amount of dissolved oxygen in the sample (ppm        
         
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