cellulose
some bacteria secrete enzymes that help in the making of some foods. other kinds of bacteria help the human body big time, like the intestinal flora. These help the body break down cellulose, plus they provide an intestinal surface cover layer to prevent pathogenic bacteria from taking a place to settle down in the body, and finally they can secrete chemicals to fight some invading pathogenic microbes.
Intestinal flora
It is broken down by bacteria.
Broken down into starch and glycose
Viruses, bacteria, and organelles that a cell ingests are broken down in the mitochondria.
by enzymes
in the digestive process, complex foods are broken down into simpler substances like what?
If you mean flatus, it's produced by the action of intestinal bacteria. Beans are commonly known for producing flatulence. They contain complex polysaccharides that cannot be broken down by human digestive enzymes, but intestinal flora does have the necessary enzymes to break these down (with a resultant production of methane, the principal constituent by volume of "gas").
corn....and sand
food not plastics or metals
Sewage
Bacteria. Yes, but much of it can't be broken down and it is passed in the feces.