1.Because if this system was not functional the toxins would build up in the body.
2.Fiber is made out of cellulose. Our body doesn't synthesize an enzyme that digests cellulose(cellulase) that's why we can't metabolize it. fiber is good because it reaches the colon undigested and helps the intestinal fauna and can even prevent colon cancer
3.If the organism will stop reproducing they will eventually die and there would be no offspring left so life will die out.
4.You would consume a lot of calcium. For example milk and lactates.
5.The stem will grow towards the sun(phototropism) and the root will go towards gravity(geotropism) and minerals(chemotropism)