I believe the primary determinant of basal metabolic rate is the Lean Body Mass. Basal metabolic is the rate of energy expenditure per unit time by animals at rest. It comprises the processes that the body requires to function. It is the amount of energy per unit time that a person need to keep the body operational at a state of rest.
I think the answer is D. A good indicator is the resting heart rate. Exercise strengthen your heart and it makes it more efficient. The resting heart rate shows of the heart is pumping blood normally each time it contracts. Having a normal resting heart rate would mean a healthy heart.
The colony would have less genetic variation. The Bacteria in the colony would be too genetically similar