ph-IMPORTANCE

NCERT-CLASS10-SCIENCE

Are plants and animals pH sensitive?
Our body works within the pH range of 7.0 to 7.8. Living organisms can
survive only in a narrow range of pH change. When pH of rain water is
less than 5.6, it is called acid rain. When acid rain flows into the rivers, it
lowers the pH of the river water. The survival of aquatic life in such rivers
becomes difficult.
pH in our digestive system
It is very interesting to note that our stomach produces hydrochloric
acid. It helps in the digestion of food without harming the stomach.
During indigestion the stomach produces too much acid and this causes
pain and irritation. To get rid of this pain, people use bases called
antacids. One such remedy must have been suggested by you at the
beginning of this Chapter. These antacids neutralise the excess acid.
Magnesium hydroxide (Milk of magnesia), a mild base, is often used for
this purpose.
pH change as the cause of tooth decay
Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth
enamel, made up of calcium phosphate is the hardest substance in the
body. It does not dissolve in water, but is corroded when the pH in the
mouth is below 5.5. Bacteria present in the mouth produce acids by
degradation of sugar and food particles remaining in the mouth after
eating. The best way to prevent this is to clean the mouth after eating
food. Using toothpastes, which are generally basic, for cleaning the teeth
can neutralise the excess acid and prevent tooth decay.
Self defence by animals and plants through chemical warfare
Have you ever been stung by a honey-bee? Bee-sting leaves an acid
which causes pain and irritation. Use of a mild base like baking soda
on the stung area gives relief. Stinging hair of nettle leaves inject
methanoic acid causing burning pain.