1. Why does pepper make us sneeze?
Pepper contains an alkaloid of pyridine called piperine that gives the pepper its flavour. Piperine, when gets into the nostrils, irritates the nerve endings inside the mucous membrane which cause the brain to trigger the muscles inside the nose and throat to kick out the foreign particles by the action of sneezing.
2. Why does milk rise up on boiling, but water doesn’t?
Milk contains about 87% of water and its remaining part constitutes proteins, fats, and sugar. As the milk is heated, the water in its structure starts converting into vapour and the fats and proteins get separated which being lighter form a creamy layer at the top. The rising water vapour gets trapped below this layer. On further heating of milk, the water vapour expands and creates enough pressure to raise the thick creamy layer and escapes out causing the milk to spill down.
3. Why does our mouth water at the sight of delicious food?
When we see delicious food, our brain gets deluded into believing that we are going to eat that food and it triggers our salivary glands to produce more saliva because saliva contains amylase enzymes that help in digestion of food before it enters the stomach. It also helps in spreading the taste of food all over the mouth.
4. Why do the leaves of touch me not plant close as soon as we touch it?
At the base of every leaf of mimosa plant there is a fluid filled sac-like structure called pulvinus. As soon as we touch the plant, its cells produce electrical signals in response to which the pulvinus flushes out all its fluid. Due to this loss of fluid from the pulvinus, its cells lose the rigidity causing the leaf to droop.
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