Food Tests for Starch, Protein and Sugars for SS 3

Class: SS 3
Term: First Term
Week: 10
Age: 16 years
Duration: 45 minutes
Subject: Biology
Curriculum Theme: Practical Biology
Previous Lesson: Theories, Evidence and
Topic: PRACTICAL ON FOOD TEST
Subject Matter: . Test for presence of starch;. Test for presence of protein;. Test for the presence of simple reducing sugar;. Test for a complex sugar

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Identify the reagents used for testing starch, protein, simple reducing sugar, and complex sugar.
• State the expected colour changes for positive and negative results for each food test.
• Explain the purpose of each step in the food test procedures.

Psychomotor Domain

• Demonstrate the correct procedure for testing for starch using iodine solution.
• Perform the Biuret test accurately to detect the presence of protein.
• Conduct the Benedict’s test to identify simple reducing sugars.
• Carry out the test for complex sugars, including the hydrolysis step.
• Draw and label diagrams of the experimental setups and observed results.

Social Domain

• Work collaboratively in groups to perform the food tests.
• Maintain a clean and organised laboratory workstation during the experiment.
• Adhere to safety rules and guidelines during practical activities.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Essential Biology for Senior Secondary Schools
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Test tubes and test tube racks
• Beakers
• Bunsen burner or spirit lamp
• Tripod stand and gauze mat
• Droppers
• Food samples (e.g., yam, rice, egg albumin, glucose solution, sucrose solution, groundnut, palm oil)
• Iodine solution
• Benedict’s solution
• Sodium hydroxide solution (NaOH)
• Copper(II) sulphate solution (CuSO₄)
• Dilute hydrochloric acid (HCl)
• Sodium bicarbonate solution
• Water bath
• Safety goggles

Rationale for the Lesson

This lesson is important as it provides students with practical skills in identifying major food components, which is fundamental to understanding nutrition and dietetics. It helps students connect theoretical knowledge of food classes with observable laboratory results. The practical experience reinforces scientific inquiry and accurate observation skills.

Prerequisite/Previous Knowledge

Students should have prior knowledge of the major classes of food (carbohydrates, proteins, lipids) and their importance in the body. They should also be familiar with basic laboratory safety rules and equipment.

Lesson Content/Board Summary

PRACTICAL ON FOOD TEST

Test for Starch

This test uses iodine solution to detect the presence of starch.

1. Add a small amount of the food sample (e.g., a piece of yam or rice flour) into a test tube.
2. Add 2-3 drops of iodine solution to the food sample.
3. Observe any colour change.
4. Observation: A positive result is indicated by a blue-black colouration. If starch is absent, the iodine solution remains yellowish-brown.

Test for Protein (Biuret Test)

The Biuret test is used to detect the presence of protein.

1. Place a small amount of the food sample (e.g., egg albumin solution or groundnut paste) into a test tube.
2. Add 2 ml of 10% sodium hydroxide solution (NaOH) to the sample and shake thoroughly.
3. Add 2-3 drops of 1% copper(II) sulphate solution (CuSO₄) to the mixture.
4. Shake gently and observe the colour change.
5. Observation: A positive result is indicated by a violet or purple colouration. If protein is absent, the solution remains blue (colour of CuSO₄) or colourless.

Test for Simple Reducing Sugar (Benedict’s Test)

Benedict’s test is used to detect the presence of simple reducing sugars (e.g., glucose, fructose, maltose).

1. Add 2 ml of the food sample solution (e.g., glucose solution) into a test tube.
2. Add 2 ml of Benedict’s solution to the test tube.
3. Place the test tube in a boiling water bath for 5-10 minutes.
4. Observe the colour change.
5. Observation: A positive result is indicated by a colour change from blue to green, yellow, orange, or brick-red precipitate, depending on the concentration of the reducing sugar. If reducing sugar is absent, the solution remains blue.

Test for Complex Sugar (Non-reducing Sugar, e.g., Sucrose)

Complex sugars like sucrose are non-reducing and require hydrolysis before they can be detected by Benedict’s test.

1. Add 2 ml of the food sample solution (e.g., sucrose solution) into a test tube.
2. Add 1 ml of dilute hydrochloric acid (HCl) to the solution.
3. Heat the mixture gently in a boiling water bath for 5 minutes. This step hydrolyses the complex sugar into simple reducing sugars.
4. Allow the test tube to cool.
5. Neutralise the acid by adding sodium bicarbonate solution drop by drop until effervescence stops.
6. Now, perform the Benedict’s test on this neutralised solution:
   1. Add 2 ml of Benedict’s solution to the test tube.
   2. Heat the mixture in a boiling water bath for 5-10 minutes.
7. Observation: A positive result is indicated by a colour change from blue to green, yellow, orange, or brick-red precipitate, showing the presence of simple sugars after hydrolysis. If complex sugar was absent, the solution would remain blue.

Teaching Methods/Instructional Techniques

Demonstration, Practical Activity, Guided Practice, Observation, Question and Answer, Group Work

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Recalling/Motivation

Teacher’s Activity: The teacher greets the students and asks them to recall the major classes of food and their importance. The teacher then introduces the topic of food tests and explains that today’s lesson will be a practical session to identify these food components.

Pupils’ Activity: Students respond to questions about food classes and listen attentively to the introduction.

Learning Point: Review of food classes

Step 2: Demonstration of Starch Test

Time: 8 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher demonstrates the test for starch using iodine solution on a known starch sample (e.g., yam paste) and a control (e.g., water). The teacher explains each step and the expected colour changes, emphasising safety.

Pupils’ Activity: Students observe the demonstration, ask questions, and note the procedure and results.

Learning Point: Starch test procedure

Step 3: Guided Practice for Starch Test

Time: 7 minutes

Teaching Skill: Guided Practice/Supervision

Teacher’s Activity: The teacher divides students into groups and provides them with food samples and iodine solution. The teacher guides each group to perform the starch test on various samples, ensuring correct technique and safety.

Pupils’ Activity: Students in groups perform the starch test, observe results, and record their findings.

Learning Point: Practical starch identification

Step 4: Demonstration of Protein Test

Time: 7 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher demonstrates the Biuret test for protein using egg albumin solution and a control. The teacher explains the role of sodium hydroxide and copper(II) sulphate, and the expected violet colour for a positive result.

Pupils’ Activity: Students observe the demonstration, paying attention to the reagents and colour changes.

Learning Point: Protein test procedure

Step 5: Guided Practice for Protein Test

Time: 7 minutes

Teaching Skill: Guided Practice/Supervision

Teacher’s Activity: The teacher supervises groups as they perform the Biuret test on protein-rich samples (e.g., groundnut paste, milk) and controls, ensuring accurate measurement and observation.

Pupils’ Activity: Students perform the protein test in groups, record observations, and discuss results.

Learning Point: Practical protein identification

Step 6: Demonstration and Guided Practice for Sugar Tests

Time: 7 minutes

Teaching Skill: Demonstration/Guided Practice

Teacher’s Activity: The teacher first demonstrates the Benedict’s test for simple reducing sugars (e.g., glucose solution), emphasising the need for heating and the colour progression. Then, the teacher demonstrates the hydrolysis and Benedict’s test for complex sugars (e.g., sucrose solution). Students then perform these tests in groups under supervision.

Pupils’ Activity: Students observe the demonstrations, then carry out the sugar tests in their groups, noting all steps and colour changes.

Learning Point: Sugar test procedures

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What reagent is used to test for starch?
2. Describe the positive result for the Biuret test.
3. Why is heating necessary for Benedict’s test?
4. What additional step is needed to test for complex sugars?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding food test results

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes, including procedures, observations, and inferences for each food test, into their notebooks. They are also encouraged to draw their experimental setups.

Pupils’ Activity: Pupils/students copy the notes and draw diagrams carefully into their notebooks.

Learning Point: Recording practical observations

Step 9: Conclusion

Time: 2 minutes

Teaching Skill: Summarisation

Teacher’s Activity: The teacher briefly summarises the importance of food tests in identifying nutrients and reminds students to always follow safety protocols during practicals. The teacher commends students for their participation.

Pupils’ Activity: Students listen and ask any final questions.

Learning Point: Reinforcement of food tests

Continuous Assessment/Further Study

Type: Homework/Practical Report

Instruction: In your biology practical notebook, write a detailed report on today’s food tests. Your report should include:

1. Title of the experiment.
2. Aim of the experiment.
3. Materials used.
4. Procedure for each test (starch, protein, simple sugar, complex sugar).
5. Observations for each test with actual food samples used.
6. Inference/Conclusion for each test.
7. Well-labelled diagrams of your experimental setups and results.

Lesson Keywords

• Starch – A complex carbohydrate found in plants, tested with iodine solution.
• Protein – A large biomolecule made of amino acids, tested with Biuret reagent.
• Simple reducing sugar – Sugars like glucose that can reduce other compounds, tested with Benedict’s solution.
• Complex sugar – Sugars like sucrose that are non-reducing and need hydrolysis before testing.
• Iodine solution – Reagent for starch test, turns blue-black in presence of starch.
• Benedict’s solution – Reagent for reducing sugar test, changes colour from blue to green, yellow, orange, or brick-red upon heating.
• Biuret reagent – Reagent for protein test, turns violet/purple in presence of protein.
• Hydrolysis – Chemical process where a compound reacts with water, breaking into smaller units.

Differentiation

For weaker learners, the teacher will provide pre-labelled reagents and step-by-step instruction cards for each test. They will also be paired with stronger learners for support. Stronger learners will be encouraged to explore additional food samples not provided by the teacher and research the chemical principles behind the observed colour changes.

Suggested Lesson Videos

For further understanding, students can search for “Food tests for starch protein and sugars” on YouTube.

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure all reagents (iodine solution, Benedict’s solution, 10% NaOH, 1% CuSO₄, dilute HCl, sodium bicarbonate solution) are correctly prepared and labelled. Gather a variety of food samples, including known positives and negatives for each test. Set up the laboratory with adequate test tubes, racks, burners, and water baths. Emphasise laboratory safety rules, especially when handling chemicals and using heat. Guide students through each test, first demonstrating and then allowing them to perform the tests in groups. Circulate among groups to provide assistance, correct techniques, and ensure accurate observations. During the note-taking step, ensure students correctly record their procedures, observations, and inferences, and encourage them to draw simple diagrams. Check their understanding throughout the practical session and during the evaluation questions. Provide specific feedback on their practical skills and report writing.