Biochemistry Lab: Testing Foods for Organic Compounds.

What types of organic compounds are contained in the foods we eat? Sometimes an old idea is still the best way to teach a concept.  That is how I feel about this lab, "Testing Foods for Organic Compounds."  I have been doing this lab for over 30 years, and I never tire of doing it.  Granted, it is a bit messy and the observed results are sometimes a little subjective, but my students always love these two days in the lab.

This lab is best used during your units on Biochemistry and the Organic Compounds.  Teaching the characteristics of carbohydrates, proteins, and lipids can be dry and tiresome to students, and this lab is a great way to break the monotony of lecturing on these topics.  This lab activity is a two-part activity.  First, students will learn the indicator tests for sugars, starches, proteins, fats, vitamin C, and salt using known solutions.  Once the students understand how to complete these tests, they will test a wide variety of foods to see what compounds are contained in each food.

Before any testing of foods is carried out, students must "practice" to learn the indicator test for each compound.  For example, in order to determine if milk contains simple sugars, students must know how to carry out the test for simple sugars.  This is the purpose of the first part of the lab.  Students are given known solutions so that they can see what the positive test for a particular compound looks like.  Then, when the foods are tested, the students will recognize and understand the results they are getting.  Students will learn the positive and negative tests for the following:

• Students will test for starch using iodine.
• Students will test for simple sugars using Benedict's solution.
• Students will test for proteins using Biuret reagent.
• Students will test for lipids using the brown paper test.
• Students will test for the presence of vitamin C using indophenol.
• Students will test for salt using silver nitrate.

Please note: Obviously, salt is not an organic compound.  However, it is a fun test for the students to carry out, and it provides interesting information about the foods we eat.

Once students know how to use the above indicators, the real fun can begin! Choose a variety of foods that you would like for your students to test.  While you can theoretically use any foods in the experiment, some are easier to test than others.  For example, students will probably be frustrated if you ask them to test dark purple grape juice.  They simply will not be able to see the results of the tests.  I have the best results when testing the following:  Milk, yogurt, egg whites, egg yolks, potatoes, celery, cereals, and an assortment of fruit juices.  The liquid foods can be used straight from their containers.  For solids foods, you will need to prepare a solution of the food using a blender.

What are the benefits of doing this lab?

• First and foremost, it is just plain FUN!  If students love your lab activities, they will be excited about your class.  These days, having your students excited about your class solves a host of other problems.
• This lab reviews and reinforces the concepts you have been teaching in your classroom.  Facts about the macromolecules are easier to learn and remember when the students see a practical application of the information.
• This lab teaches good lab techniques, how to organize data, and how to work in cooperative learning groups.
• Students lean that a particular food that they thought was "healthy" is really nothing more than sugar and salt.
• Working through detailed lab procedures teaches a student to read, understand, and follow directions.
• Students must use their critical thinking and problem solving skills.

Below you can see the lab handouts that I use with my students.  Clicking here or on the image below will lead you to this lab in my TpT store. Complete teacher guide is included that contains an answer key to all questions, directions for preparing the solutions, and tips and suggestions for the successful completion of this lab activity.  

Using Poinsettia Leaves as an Acid / Base pH Indicator

Click image to view this resource in my TpT store.

I LOVE this fun holiday activity!

We science teachers know that many plants contain pigments that can be used as pH indicators.  I think we have all created a stink in our homes or labs by boiling red cabbage to use the "juice" as an acid/base indicator!



Did you know that you can do the same with the pigments found in red Poinsettia leaves?

These plants contain anthocyanins, which are water soluble pigments.  These pigments are responsible for the the red, purple, and blue colors seen in flowers, fruits, and vegetables. Anthocyanins respond to changes in pH.  I absolutely love lab activities that use items like this in the lab.  My students are often surprised and excited to discover that household items, such as the Poinsettia or red cabbage, can be used for scientific purposes.  Using the Poinsettia leaves as an acid/base indicator makes for a super fun lab activity around the holidays.

In this lab, the students will use a pigment solution extracted from the leaves of the poinsettia to establish a known pH baseline.  Students will then use this baseline to predict the pH of common household items.

The images below will give you a great idea of all that is involved with this lab. Click on any image below to view this resource in my TpT store.

I hope you find this useful in your science classes.  Enjoy the holiday season!

Helping Students Review and Reinforce Biochemistry and Organic Compounds

Master the Information with this Organic Compounds Mix/Match Game 

It's that time of year again.  Time to teach the dreaded unit on Biochemistry!  (Insert scary music here.)

I love the phrase, "Nothing in Biology makes sense, except in the light of evolution."  I would like to add to that, "...except in the light of evolution and biochemistry."  In my mind, there is simply no way to teach cell physiology, cell division, photosynthesis, enzymatic reactions, or cellular respiration without first teaching a solid unit on biochemistry and organic compounds.

The concepts of biochemistry are difficult, and unfortunately, this is the unit that our biology students are usually faced with at the very beginning of the school year. Teaching strategies, labs, and review activities are especially important at this time. This mix/match review game will provide the review and reinforcement that you are looking for.

The set includes 4 larger cards, each with the name of one of the groups of organic compounds.  There are 75 smaller answer cards. Students must match the answer card statements to the correct group of organic compounds.

One of the things that I love best about this activity is that the game can be customized for different grade levels and ability levels.  An advanced class should use all of the cards.  A younger grade or slower-paced class should use only the answer cards that are appropriate.  Remove any answer cards that you have decided not to use.  The game can be made easy or hard based on your particular students.   It is very easy to differentiate within the same class. By placing the game pieces into small Ziplock bags, you can easily give a "customized" bag to each group of students in your class.

Once the students have completed the card sort, have them record the answer card statements on the student answer sheet.  When students write, it helps them learn and commit the information to memory.  Students can easily do this on their own notebook paper as well.  Blank cards are included so you can add additional answer card statements.

Click image to view product.

I make these cards available to my students before school, after school, and/or during their study hall.  It is a great way to review for the unit test. Best of luck as you teach your unit on biochemistry!  Have a great school year!

How much Vitamin C is in your fruit juice?

Lab: Determining the Amount of Vitamin C in Fruit Juices

I  have been doing this lab every year for a long, long time.  I always enjoy it, and so do my students. I often do this lab with my biology students when teaching about nutrition and digestion, but my favorite use of this lab is with my chemistry classes.  This lab is perfect to introduce the idea of titrations, equivalents, and as a review of dimensional analysis.

In this experiment the student will use a lab procedure known as a titration to determine the amount of Vitamin C found in a 6 ounce serving of various fruit juices.  I most often use orange juice, pineapple juice, and apple juice. 

A titration is the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.  Titration provides a means of determining the chemically equivalent amounts of two substances.  

The materials list is short and consists of items found in almost all labs..... no fancy equipment required!  You will need:  Spot plate, Thin stemmed or microtip Beral pipets  (or medicine droppers),  White paper for background, Ascorbic acid standard solution,  Apple juice,  Orange juice,  Pineapple juice, Starch solution,  Iodine solution and Plastic Toothpick (stirrer).

In order to determine the amount of Vitamin C in the fruit juice, the student must first do a titration using a vitamin C (ascorbic acid) solution of known concentration.  An iodine/starch complex is used so that a color change can be detected.  The number of drops of iodine added will be used to determine the amount of Vitamin C present in the juice.  

When ascorbic acid (Vitamin C) comes into contact with iodine, it is oxidized to form dehydroascorbic acid.  When Vitamin C and iodine are in solution together, they will form iodide.  As iodine is added during the titration, iodide will continue to be formed until there is no more Vitamin C left in the solution.  At this point, iodine becomes present in the solution and the starch turns a blue-black color.  The starch is used as an indicator because it turns black in the presence of iodine, but not for iodide.  The amount of iodine that is added during the titration can be used to indicate the amount of Vitamin C present in the fruit juice.

Set up for the lab is quick and easy, and does not take a lot of advance preparation.  

This lab is available in my TpT store and can be viewed here:  Determining the Amount of Vitamin C in Fruit Juices.

The Effect of the Enzyme Amylase on Starch

This is a fun lab that students enjoy and it teaches important concepts about enzymes.

Make your biology class more appealing and exciting by incorporating a variety of fun and interesting labs into your weekly lesson plans.  This inquiry-based lab allows students to discover basic information about the functioning of enzymes within cells.  Enzymes are biological catalysts that speed up the chemical reactions within cells.  Without the aid of enzymes, the chemical reactions of the body would proceed so slow that the reaction would be of no use to the cell.

Purpose:  In this lab, the student will observe the effect of the enzyme amylase on its substrate, starch.  The student will perform various experiments with the enzyme amylase and will compile a list of facts concerning enzymes.

Students are given the task of trying to determine what happens to starch in the presence of the enzyme amylase.  There are essentially four mini-experiments in the lab that will lead the student to the appropriate conclusion.

1. The student mixes together a solution of of amylase and starch and determines the length of time it will take until the starch has been completely broken down into end products.  This is done by removing a drop of the solution each minute and testing it for the presence of starch.
2. Now the student must determine the end products of the reaction.  Benedict's solution is used in this second portion of the lab to determine that the end product is a simple sugar.
3. In the third portion of the experiment, students use glucose test strips to determine that glucose is NOT one of the end products.
4. Finally, the student will test the solution for the presence of proteins to determine that the enzyme is still present when the reaction is complete.

This lab is designed for a typical high school biology class for students in grades 9 – 12.  It is appropriate for both standard and honors classes as well as for first or second year biology students.  I have used this lab in both my freshman biology I class as well as my AP biology class.

Happy Teaching!