Because they are the same chemical reaction but reversed. Cellular respiration takes glucose (from nutrient/food) and oxygen (from atmosphere) in order to make CO2 (think about exhaling) and H20 (water).
(I don't remember this clearly so it may be wrong, i'll look into it and come back!)
Mitochondria is the answer to your questions
1. Chemical sedimentary rocks
2. Chemical sedimentary rocks are formed from sediments created by rocks being broken down into small particles (clasts).
3. Chemical sedimentary rocks are formed from sediments created by dissolved chemicals being precipitated out of the water they're dissolved in.
