Biology 12

SKILL FOCUS

Initiating and planning

Predicting

Analyzing and interpreting

Communicating results

Investigation 1 • B

Pre-lab Questions

How does the starch molecule change as a result of

hydrolysis?

What products are formed by the complete hydrolysis

of polysaccharides?

What test can be used to identify these products?

Problem

How can the products of hydrolysis of carbohydrates

be identified?

Predictions

Predict which factors will affect the rate of carbohydrate

hydrolysis. Also, predict what types of products are

formed by the hydrolysis of disaccharide and

polysaccharide molecules.

CAUTION: Hydrochloric acid is very corrosive.

Other chemicals are toxic. Avoid any contact

with skin, eyes, or clothes. Flush spills

immediately with copious amounts of cool water

and inform your teacher. Exercise care when

heating liquids and using a hot plate. Wash your

hands before leaving the laboratory.

Materials

test tubes distilled water

test tube markers 1 mol/L HCl solution

test tube brush Benedict’s solution

test tube rack Lugol solution

test tube holder potato starch

spot plates 1% solutions of glucose,

beaker for hot water bath fructose, sucrose, and

hot plate lactose

beaker tongs labels

30 mL graduated cylinder marker

medicine droppers

Procedure

Part A: Testing for the Presence of

Monosaccharides

1.Add 3 mL of each of the following 1% solutions to

separate test tubes: glucose, fructose, sucrose, and

lactose. Add 3 mL of distilled water to a fifth test tube.

2.Add five drops of Benedict’s solution to each test

tube.

Finding the Products of Hydrolysis

Indicators are often used to test for the presence of certain compounds. For

example, Benedict’s solution is a reagent that can be used to test for the presence

of monosaccharides, such as glucose. The free aldehyde group, which is present

only in the ring form of glucose, reduces the copper (II) ion (Cu^2 +) ion in Benedict’s

solution. Thus, monosaccharides are referred to as “reducing sugars.” As more

copper ions are reduced, the colour of the Benedict’s solution changes, thus

confirming the presence of glucose in a test solution. The ring structure configuration

of glucose forms only in solution (when glucose molecules are dissolved in water).

In a similar way, Lugol solution can be used to test for the presence of starches.

In this investigation, you will conduct an experiment to identify the products

formed by the hydrolysis of disaccharide and polysaccharide molecules.

24 MHR • Unit 1 Metabolic Processes

Redox Reactions

Almost every element on Earth can react with

oxygen. For instance, if oxygen combines with

calcium, the oxygen receives electrons and forms

negatively charged ions.

The addition of two electrons has decreased the

charge of the oxygen atom by two. The gain of

electrons is referred to as reduction. The calcium

loses electrons and forms positively charged ions,

as shown here:

The loss of electrons is called oxidation.

Ca Ca^2 +

calcium atom

no charge

loses two

electrons

charge of atom

oxygen atom increased by two

no charge

gains two

electrons

charge of atom

decreased by two

OO^2 −