Biology: Tests for Starch, Glucose, and Protein

What color does the iodine solution turn when it reacts with starch?

Which solution is used to test for glucose?

Which of the following is NOT classified as a reducing sugar?

What indicates a positive test for protein using the biuret test?

What happens to the solution when olive oil is mixed with ethanol and then added to water?

In the glucose test, what color change indicates the presence of reducing sugars after heating?

Which component is added first in the biuret test for proteins?

What is the purpose of heating the test tube with Benedict's solution?

Starch Test

A little starch is placed on a spotting tile.
A drop of iodine solution is added to the starch.
The starch turns a very dark blue or blue-black color.
This test works on solid food samples or starch suspensions.

Glucose Test

A small amount of glucose is placed in a test tube with water.
The tube is shaken to dissolve the glucose.
Several drops of Benedict's solution are added to the tube, enough to color the mixture blue.
The test tube is placed in a water bath and heated.
The solution gradually changes color to form an orange or brick red precipitate of copper(I) oxide.
All single sugars and some double sugars are reducing sugars.
Ordinary table sugar (sucrose) is not a reducing sugar.

Protein Test

A little protein (like egg white) is placed in a test tube with some water
The powder is mixed with the water by shaking.
An equal volume of dilute (5%) potassium hydroxide solution is added.
The tube shaken again
Two drops of 1% copper sulfate solution are added.
A purple color develops (or a pre-mixed "biuret solution").

Lipid Test

A drop of olive oil is placed in a test tube.
Ethanol (alcohol) is added to dissolve the oil.
The solution is poured into a test tube filled with cold water.
A white cloudy layer forms at the top of the water.
This layer is a suspension of tiny lipid droplets called an emulsion.

This quiz covers the essential tests used to identify starch, glucose, and protein in various samples. You'll learn about the procedures and chemical reactions involved in each test, including the use of iodine, Benedict's solution, and potassium hydroxide. Perfect for biology students wanting to reinforce their understanding of biochemical testing.