The first step of chemical digestion starts in the mouth. Saliva, the fluid released by the salivary glands in the mouth, contains an enzyme that breakdowns food starch and turns it into simple sugars. This enzyme is called amylase or also known as alpha-amylase or ptyalin.
I believe the answer is receptor sites, but correct me if I'm wrong.
Hope this helps!
Answer: Is A
Explanation:
Lichens break down rock from there the soil start to create life i don't how to explain it