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Teaching Guide
Testing for simple sugars
Counting Calories
The Anti-oxidant effects of Vitamin C
Testing for Simple Sugars
Quiz


Image of sugar bag




Click here for the PDF version of this guide


As you learned in "The Desert's Perfect Foods," the Pima Indians have a genetic predisposition to gaining weight when adhering to a contemporary Western diet. This weight gain sets the stage for a variety of health disorders including diabetes. Diabetics have difficulty in regulating their body's store of sugar. To help manage this health risk, diabetics must limit the amount of sugar they ingest. By keeping records of their meals and maintaining a low-sugar diet, they can gain some control over the ill effects of this disorder.

There are several different methods to test the sugar content of food. One laboratory technique uses Benedict's solution (a mixture of mostly copper sulfate and sodium hydroxide). When this reagent is mixed with a sample of food and heated, a color change identifies the relative concentration of sugar in the test solution. The sugars that Benedict's reagent tests for are simple sugars such as glucose and fructose. More complex sugars such as sucrose and lactose (formed by two simple sugars hooked together) cannot be identified with this test.

Note to educators

 
OBJECTIVE
This activity page will offer
  • an overview of diabetes
  • a hands-on activity using a sugar indicator solution
  • an activity to determine relative amounts of sugar in several juices esign

MATERIALS

  • Benedicts reagent (available through school catalogs or at local pharmacies)
  • Scale illustrating colors and associated sugar concentrations
  • Beaker, size 1000 ml
  • Test tubes
  • Test tube holder
  • Graduated cylinder, size 10 ml or 100 ml
  • Lime juice
  • White grape juice
  • Grapefruit juice
  • Apple juice
  • Protective goggles
  • Boiling water bath

Image of test tubes

PROCEDURE

  1. Put on your safety goggles and adhere to all laboratory precautions addressing the use of a boiling water bath.
  2. Add 4 mL of white grape juice to your test tube.
  3. Add 1 mL of Benedict's solution to the juice. Swirl the tube to ensure that it
  4. Image of hotplate with  boiling water bath
  5. mixes well.
  6. With your instructor's approval, place your test tube in the boiling water bath.
  7. Wait several minutes or until the color change is complete (blue color may turn to green, yellow. orange, red, brown). Examine and compare the color of the solution to reference color sheet. Record the relative concentration of sugar.
  8. Test the other juice samples in the same manner. Record all results in a data table.

QUESTIONS

  1. What did the Benedict's solution test for?
  2. How did the presence of a reducing sugar affect the Benedict's solution?
  3. What color would the Benedict's display if there was no sugar in the solution?
  4. What color would the Benedict's display if it tested a sugar (sucrose) solution?
  5. Did these juices contain reducing sugars? How could you tell?
  6. Which juice underwent the most dramatic color shift? Why?
  7. Which juice underwent the least change in color? Why?

EXTENSIONS

MODEL MAKING

The molecular formula for glucose is c6h12o6.


glucose molecule


Five of the carbons and one oxygen atom are joined together in a ring structure. The other carbon is attached to one of the ring carbons that is located next to the ring oxygen. The remaining five oxygen atoms are joined to hydrogen atoms to form OH groups. From this information and a supply of gumdrops and toothpicks, construct the glucose molecule.

A SWEET MATH CONNECTION

This scale illustrates the relative sweetness of several sugars based upon
sucrose = 100
Lactose (complex sugar) = 16
Galactos (simple sugar) =32
Sucrose (complex sugar) =100
Fructose (simple sugar) =173

Using this scale, answer the following questions:

QUESTIONS

  1. Which is the sweetest of these four sugars?
  2. How many times sweeter is sucrose than lactose?
  3. How many grams of fructose would be needed to replace 10 grams of sucrose in order to produce the same sweetness?
  4. Suppose a recipe calls for 5 grams of sucrose to sweeten a dish. How much lactose would be needed if you substituted sugars?

Primer on Diabetes
Diabetes is a chronic disorder that results in an increased level of sugar (glucose) in the bloodstream. It is caused by the inadequate production or use of insulin, a hormone produced within the pancreas that allows the body to use and store glucose. With an insufficient level of this hormone, high levels of sugar remain in the blood resulting in symptoms including increased urine production and excessive thirst. The body responds to the low insulin levels by breaking down fat and producing damaging metabolic bi-products called ketones. Diabetes may be regulated by regular doses of insulin, which quickly lowers the blood sugar level. If, however, the level of insulin is too high, excessive sugar is removed from the blood. In order to regain this delicate sugar balance, an individual may require a quick "fix" of sugar that is available in orange juice and other sweet liquids.

QUESTION

If a diabetic has a low blood sugar level, that person may drink orange juice. Orange juice contains a high concentration of sugar that is readily used by the body. In contrast, some foods contain sugars that must be broken down before they can be used. These slow-release sugars may offer a diabetic a window in which a compromised insulin response has sufficient time to deal with the slowly rising sugar level. Think about it. Should a diabetic who is suffering from low sugar levels be given a food containing a slow-release sugar? Explain.

WEB CONNECTION

What the Hunter/Gatherers Ate
A review of Paleolithic nutrition

Diabetes Knowledge Test
An interactive, multiple-choice diabetes test

Nutrient Data Laboratory
Nutrient database for all foods maintained by the USDA

AIDA
A sophisticated diabetes software simulator program


Answers

The activities in this guide were contributed by Michael DiSpezio, a Massachusetts-based science writer and author of "Critical Thinking Puzzles" and "Awesome Experiments in Light & Sound" (Sterling Publishing Co., NY).

Academic Advisors for this Guide:

Corrine Lowen, Science Department, Wayland Public Schools, Wayland, MA
Suzanne Panico, Science Department, Fenway High School, Boston, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland, MA

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