Resource 2: Mrs Mohanty’s plan for a demonstration
Topic: Test for starch
Class: VII
Duration: 40 minutes
General aim: The students will be able to understand that the presence of starch in food can be tested.
Instructional objectives: After this lesson, the students will be able to:
- list some commonly available food items that contain starch
- describe the test for starch in food items.
Introduction: The interest and curiosity of the students will be aroused and their previous knowledge in the area will also be tested by asking them simple questions such as ‘What is the necessity for food containing carbohydrates?’ and ‘How is carbohydrate stored in plants?’ Thereafter the responses will be noted on the blackboard. and use it to announce to detect the presence of starch in food a simple test can be carried out, they would see how it is done.
Equipment and materials: A test tube rack with clean test tubes, a dropper, food items of various types, tincture iodine and water.
Teaching aid: A chart with pictures of energy-giving food, and the blackboard.
The seating arrangement is planned to enable every student to view the demonstration.
| Purpose of demonstration | To generate students’ interest To show students the test for starch |
| Learning objectives | By the end of the demonstration the students will be able to:
|
| Resources needed | Different foods, e.g. roti, rice, fruits, seeds, spinach, cheese, etc. Iodine and pipette Small plates Waste bucket |
Footnotes
Table R1.1 A plan to demonstrate the presence of starch in food.| Plan of demonstration | ||
|---|---|---|
| Safety | Students will have come across the word ‘energy’ in many different contexts. This will help them to draw together what they have learnt in Physics (energy transfer), Chemistry (how to generate energy) and Biology (how living things get their energy). | |
| Position of students | Have (insert names) seated on the floor at the front, with some on chairs and taller students stand at the back. | |
| Introduction | Review work on nutrients in food Food tests identify which foods contain which nutrients |
|
| Stage 1 | Test a starchy food to show positive reaction Test non-starchy food to show negative reaction |
Ask students to describe reactions Ask student to write reactions on blackboard |
| Stage 2 | Test a few different foods. Put name of food in a results table drawn on blackboard | Students copy table and write their result and own inference(s) |
| Stage 3 | Test four more (two starchy and two not starchy) | Ask student to predict result to reinforce starchy foods |
| Stage 4 | Finish demonstration by summarising with questions | What is the test for starch? What sorts of foods are starchy? Which types of food are not starchy? |
Footnotes
Table R1.2 An example of how to do the test: what the teacher said and did.| Content | Teacher activity | Student activity | Teaching aid | Blackboard summary |
|---|---|---|---|---|
| Some foods that are rich in carbohydrates give us energy and are known as energy-giving food. Carbohydrates, an important nutrient, are stored in plants as starch and sugars | Points to the pictures of ‘energy-giving food’ and says, ‘Some food gives us energy, but tell me, will holding a bowl of rice or potatoes in our hand make this possible?’ | Respond that it is necessary to eat it | Chart with pictures of energy-giving food | Students’ responses |
| The presence of starch can be detected by testing the food with iodine | Prepares a dilute solution of iodine and says that putting iodine into starch makes it blue-black | Observe the demonstration | To test the presence of starch in food Putting iodine to starch makes it blue-black |
|
| Starch turns to a blue-black colour when iodine is added to it, so food that contains starch will only turn into blue-black colour | Puts a little food of each type in a test tube and asks the children to note the colour before and after adding iodine to them. Then adds a few (two to three) drops of iodine to the food | Respond about colour before and after adding iodine | Table indicating food and colour change | |
| Tells the students the precautions to be taken while carrying out the test | Briefly note the precautions |
Resources