The answer would be bacteria and and fungi
Roots will always grow down due to geotropism. It is caused by the statocytes in the root cap. They sense the force of gravity and grow down according to it. But if the root does not have a root cap, then the plant will not necesarily grow down. And if the seed is layed on a flat place like a counter, then the roots will grow any which-way
E-coli is a significant virus
Single cell division is mitosis i think
The gray rabbits would stand out and their population would decrease. For these problems, think about colors; simply, what color is not being "hidden" (by the rocks for example) compared to the rest of the populations.