Activity 2.3 Nutrition in Animals Solution Science Class 7
What activity asks?
Activity 2.3 asks us to run an iodine-starch experiment with one plain boiled rice and saliva treated boiled rice (Chewed rice).
Saliva treated rice does not turn blue with iodine solution. However, plain boiled rice turns blue with iodine.
We use iodine to test the presence of starch in the food. Iodine forms a starch-iodide complex and turns starch into the blue.
Boiled rice contains a large proportion of starch. So, when we put the iodine solution to it, the solution turns blue.
Our saliva contains an enzyme amylase. The enzymatic reaction between starch and saliva Amylase breaks starch and other complex carbohydrates into simple sugars. Sugar does not form a complex. As a result, chewed rice does not turn blue.
Complex carbohydrates have a large branched chain of sugar. There are some empty spaces between them. Iodine molecule forms a blue coloured complex with the chain.
See also: Activity 2.2 Nutrition in Animals.
Ref: NCERT class Science chapter 2.
Activity 2.3 Nutrition in Animals Solution Science Class 7 Chapter 2