Lesson Notes By Weeks and Term - Senior Secondary 3

Practical on food test

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TERM – 1ST TERM

WEEK TEN

Class: Senior Secondary School 3

Age: 17 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Biology

Topic: PRACTICAL ON FOOD TEST

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Test for the presence of starch in food
  2. Test for the presence of protein in food substances
  3. Test for the presence of simple reducing sugars
  4. Test the presence of complex sugars

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers,

demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S

ACTIVITY

STEP 1

INTRODUCTION

Teacher set up the experiment in the laboratory.

Students pay

attention

STEP 2

EXPLANATION

Teacher guide the students to test for the presence of starch and and protein using the materials and equipments provided

Students carry out the practicals and record their observations

STEP 3

DEMONSTRATIO

N

Teacher guide students to test for the presence of simple reducing sugars and complex sugars in food substances

Students carry out the test and write down their observations.

STEP 4

NOTE TAKING

The teacher writes a summarized

note on the board

 

The students

copy the note in

their books

 

NOTE

PRACTICAL ON FOOD TEST

 Test for presence of starch

Material Required

To test the presence of starch, the following materials are needed:

  1. Iodine solution
  2. Test tubes
  3. Pipettes or droppers
  4. Samples containing starch(e.g.potatoes, rice, wheat etc.)
  5. Water
  6. Bunsen burner.

Procedure

Below is a general procedure for testing the presence of starch using iodine solution:

  1. Prepare Iodine Solution: Ensure you have a dilute iodine solution, typically iodine-potassium iodide (IKI) solution. It should be brown in color.
  2. Label Test Tubes: Label each test tube with the sample names or identification.
  3. Prepare Samples: Obtain the samples you want to test for the presence of starch. These could be solutions of starch or extracts from biological materials.
  4. Add Samples to Test Tubes: Using a pipette or dropper, add a small amount of each sample to the corresponding labeled test tube.
  5. Add Iodine Solution: Add a few drops of the iodine solution to each test tube containing the sample. Mix the contents gently by swirling the test tube.

Observation

Allow the mixture to stand for a few minutes. A positive result for starch will be indicated by a color change from brown to blue-black.

Test for Proteins

The presence of proteins in a sample can be detected by Biuret Test.

Material Required

To conduct the biuret test, you'll need the following materials:

  1. Biuret reagent
  2. Test tubes
  3. Pipettes or droppers
  4. Water.
  5. Samples containing protein ( e.g. meat, egg, legumes etc)
  6. Bunsen burner

Procedure

Below is a general procedure for conducting the biuret test:

  1. Prepare the Biuret Reagent: Ensure the biuret reagent is prepared and ready for use. It should have a blue color.
  2. Prepare Samples: Obtain the samples you want to test for protein content. These could be solutions of proteins or extracts from biological materials.
  3. Label Test Tubes: Label each test tube with the sample names or identification.
  4. Add Samples: Using a pipette or dropper, add a small amount of each sample to the corresponding labeled test tube.
  5. Add Biuret Reagent: Add an equal amount of biuret reagent to each test tube containing the sample. Mix the contents gently by swirling the test tube.
  6. Observe Color Change: Allow the mixture to stand for a few minutes. A positive result for proteins will be indicated by a color change.

Observation

The blue biuret reagent turns violet or pink in the presence of proteins. This indicates that the sample that is tested contains proteins.

NOTE:  Biuret reagent is composed of copper sulfate (CuSO4) and potassium hydroxide (KOH). The active ingredient in Biuret reagent is the copper ion (Cu2+).

Test for the presence of simple reducing sugar

To test for the presence of simple reducing sugars (such as glucose or fructose), you can use Benedict's test.

Materials needed

  1. Benedict's reagent
  2. Test tubes
  3. Pipettes or droppers
  4. Samples containing reducing sugar (e.g. fruits, honey, yoghurt, milk etc)
  5. Water bath or heating source
  6. Bunsen burner.

Procedure

Below is a general procedure for conducting Benedict's test:

  1. Prepare Benedict's Reagent: Ensure you have a freshly prepared Benedict's reagent. It is usually blue in color.
  2. Label Test Tubes: Label each test tube with the sample names or identification.
  3. Prepare Samples: Obtain the samples you want to test for the presence of reducing sugars. These could be solutions of sugars or extracts from biological materials.
  4. Add Samples to Test Tubes: Using a pipette or dropper, add a small amount of each sample to the corresponding labeled test tube.
  5. Add Benedict's Reagent: Add an equal amount of Benedict's reagent to each test tube containing the sample. Mix the contents gently.
  6. Heat the Mixture: Place the test tubes in a water bath or use a heating source to heat the mixture. Benedict's test is often performed by heating the reaction mixture. The temperature and duration may vary based on the specific protocol.

Observation

 A positive result for reducing sugars is indicated by a color change from blue to green, yellow, orange, or even red, depending on the concentration of reducing sugars.

NOTE: Benedict's reagent is a chemical solution used to test for the presence of reducing sugars. It consists of copper sulfate (CuSO4), sodium carbonate (Na2CO3), and sodium citrate. The active ingredient is the copper ion (Cu2+).

Test for a complex sugar.

Testing for complex sugars, such as starch, often involves specific methods to detect the presence of these polysaccharides. One common method is using iodine solution. Here's a general procedure for testing the presence of complex sugars, specifically starch:

Materials:

  1. Iodine solution (e.g., iodine-potassium iodide solution or IKI)
  2. Test tubes
  3. Pipettes or droppers
  4. Samples containing complex sugars (e.g., starch solution)
  5. Water (for dilution if necessary)

Procedure:

  1. Label Test Tubes: Label each test tube with the sample names or identification.
  2. Prepare Samples: Obtain the samples you want to test for the presence of complex sugars. Ensure the samples are in a liquid form (dissolved in water if needed).
  3. Add Samples to Test Tubes: Using a pipette or dropper, add a small amount of each sample to the corresponding labeled test tube.
  4. Add Iodine Solution: Add a few drops of iodine solution (IKI) to each test tube containing the sample. Mix the contents gently by swirling the test tube.

Observation:

 Allow the mixture to stand for a few minutes. A positive result for the presence of complex sugars (such as starch) is indicated by a color change from brown to blue-black.

EVALUATION: 1. What is your observation from your test for the presence of starch.

  1. Identify materials needed for testing the presence of simple reducing sugars

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively