Tuesday, May 8, 2012

May 8th, 2012

Today in class: For the entire period, we worked on the What Nutrients are in Foods? lab (which is a separate packet from our regular unit packet). Mrs. Andrews also collected our "Design a Quiz" projects.

As far as homework goes: ~ Finish the nutrient lab that we worked on in class today
                                             ~ Work on review packets (TEST this thursday)


As you probably all know, the purpose of the Nutrient lab was to test different foods (about 10 of them) for the presence of macromolecules (particularly starch, simple sugars, protein, and fats or lipids).  Because of the many different parts to this lab, your group of four (which were predetermined) had to divide up the work, so one person would find the results for each test, all working at the same time.  At the end of the period, the individual groups met with each other and exchanged data from each test.

In part 1 of the lab, your job was to set up the control for the various experiments.  The iodine test was first, where you observed the color change when with the mixtures starch and water, water and Lugol's iodine, and starch, water, ad Lugol's iodine all together.  If the mixture turned DARK PURPLE, that would be an indication that simple or complex starches were present (as it should have happened with the mixture of all three substances in this first experiment--the rest of the tests should have provided results that indicated there was no starch present).

To test for simple sugars, you had four different test tubes, two contained the mixture of glucose and Benedict's solution, and two contained the mixture of water and Benedict's solution.  One of each mixture was to be heated, and the other two were just supposed to be mixed together and observed.  Every one of the test tubes should have provided you with a negative result EXCEPT the test tube that had glucose and Benedict's solution that was heated--the color of that particular mixture should have been red, testing positive for glucose.

Next, you had to test for proteins.  The three test tubes in this experiment had the mixtures egg albumen, egg albumen and Biuret reagent, and water and Biuret reagent.  If the solution turned PURPLE, then this was an indicator for the presence of protein (the rest should have had negative results).

Lastly, you had to test for lipids.  One square of an unglazed brown paper bag should have been labeled "oil" and the second, "water."  You then had to wait until each substance evaporated to see whether or not the paper was translucent (light can go through, but one cannot see a clear image through the translucent substance)--if it was, lipids were present.  If not, than there were no lipids in the substance (distilled water tested negative, the oil tested positive).

After all of these "control tests," we had to perform the same experiments to test foods for each of the four different macromolecules (9 listed substances, and 1 from home).

To review, Benedict's test is an indicator for simple sugars, Biuret's test is an indicator for proteins, Lugol's iodine solution shows the presence or absence of starches, and an unglazed paper bag can be used to test for lipid (fats).

Think about this:

Which of the four macromolecules from the lab could be present in this chicken dinner?

This is basically what we did in the lab today--just think about what is in the food we eat and how the digestive system breaks it down/absorbs its nutrients! :)


  1. Can I have some of your turkey?
    And regarding your post...you did a really comprehensive job describing the process of each test and the kind of results you had to look for. I could definitely do a lab like this with no problem just by following your directions above. The color coding was a really cool touch too!

  2. This was really well done and described. I liked how you explained each part of the lab but also talked about the macro molecule being described in each experiment as well. It really helped me out and made it less confusing. Great job!

  3. Nice post Emma! It was good how descriptive you were in your information. The color coding was pretty helpful too. Thanks for the recap!