What do you think of Raman's statement, "All starches are carbohydrates but not all carbohydrates are starches." Describe the design of an activity to test your answer.
Raman's statement is correct.
Starch is one type of carbohydrate, but there are other carbohydrates like sugar (sucrose, glucose) that are not starch.
Activity design:
(1) Collect food items known to contain starch (potato, rice, bread) and food items containing other carbohydrates like sugar (glucose, common sugar).
(2) Place small quantities of each on separate dishes.
(3) Add 2-3 drops of diluted iodine solution to each food item.
(4) Observe the colour change.
Expected results: Potato, rice, and bread will turn blue-black (presence of starch), while glucose and common sugar will not change colour (absence of starch).
This confirms that all starches are carbohydrates, but not all carbohydrates are starches.
Explanation
The chapter mentions that glucose is an example of a carbohydrate and that common sugar is also a type of carbohydrate. The iodine test described in Activity 3.5 specifically tests for starch—a blue-black colour indicates starch presence. The chapter states that cereals like wheat, rice, maize, and vegetables like potato contain carbohydrates (starch). Sugar, though a carbohydrate, does not give a positive iodine test because it is not starch.
Solution Steps
Raman's statement is correct: starch is one type of carbohydrate, but sugars are also carbohydrates that are not starch.
Collect food items containing starch (potato, rice, bread) and other carbohydrates like sugar (glucose, common sugar).
Add 2-3 drops of diluted iodine solution to each food item and observe colour change.
Starch-containing foods turn blue-black; sugar does not change colour.
This confirms that all starches are carbohydrates, but not all carbohydrates are starches.