Lab: 3—Chemical Composition of Cells: Sugars

Purpose of this lab:

To learn about sugars and the test used to identify them.

Introduction

The organic macromolecules known as sugars are a type of carbohydrate. Carbohydrates are composed of monosaccharides, which are single, sugar unit monomers. Two sugar units linked together are known as a disaccharide.

In this lab, we conducted tests on various substances with Bendict’s solution to determine which sample contained sugars. Benedict’s solution is a turquoise blue color and reacts with sugars after being heated in a boiling water bath, resulting in a color change. The color change varies with the concentration of sugar present, with strong positives indicating a high sugar concentration and weaker positives correlating with lesser concentrations of sugar. The color changes are as follows: orange-red (very high), orange (high), yellow-orange (moderate), yellow (low), green (very low), no change in color (no sugar present).

Materials and Methods:

--6 test tubes marked at 1cm and 3cm from the bottom

--Benedict’s reagent

--substances to be tested: water (control), glucose solution, onion juice, potato juice, starch suspension, and an unknown substance

--hot plate with a beaker filled with water for a boiling water bath

Each substance to be tested was filled in a separate test tube to the 1cm mark, with the exception of onion and potato juice, to which 5 drops of each were added to separate tubes and then filled with water to the 1cm mark. Benedict’s solution was added to each test tube to the 3cm mark. Each test tube was examined for any change in color before heating. All 6 tubes were heated in the boiling water bath simultaneously for 5 minutes. Color changes were noted.

Results and Discussion:

No color changes occurred before heating. After heating, glucose tested