What is the biological "clock"? i only know it is the internal property possessed by many organisms, but what exactly is it?

Our Biological clocks drive our circadian rhythms.  The internal clocks are groupings of interacting molecules in cells throughout the body.   A "master clock" in the brain coordinates all the body clocks so that hey are in synch.  

Explanation:

in the year 2850, humans successfully colonized mars. the martian modules that were constructed could hold only a small population of people. it is now a century later, and the population on mars has grown to 600 people. of the current mars population, 45 people express the recessive phenotype for phenylketon- uria (pku) syndrome (pp genotype).

explanation: