On farms the main sources of organic matter are plant litter (plant roots, stubble, leaves, mulch) and animal manures. Earthworms and microorganisms decompose these materials. The process of decomposition releases nutrients which can be taken up by plant roots.
Effector , sensor, control center
Through reproduction. dark fur is a dominant trait and eventually if offspring of the one dark furred mouse reproduce enough, it will eventually spread to the whole population because it is a dominant gene and will overpower recessive genes of the other parent organism that the dominant mouse is reproducing with.
I believe proteins would be the correct answer, but of course I just learnt this stuff 2 weeks ago. xD