Final answer:
A difference in the molecular structure of cytochrome c can arise in a small population that becomes geographically isolated through accumulation of small genetic changes over time. This difference can then spread in the population through natural selection.
Step-by-step explanation:
In a small population that becomes geographically isolated, a difference in the molecular structure of cytochrome c can arise through accumulation of small genetic changes over time. This can happen through random mutations in the DNA sequence, which can lead to variations in the amino acid sequence of cytochrome c. These variations in the molecular structure can then spread in the population through natural selection.
For example, imagine a population of organisms that have a certain gene for producing cytochrome c. Due to random mutations, a few individuals in the population may have a slightly different version of this gene, resulting in a slightly different molecular structure of cytochrome c. If this difference provides any advantage in terms of cellular respiration or energy production, individuals with the new version of the gene are more likely to survive and reproduce, passing on the new gene to their offspring. Over time, this can lead to the spread of the difference in the molecular structure of cytochrome c within the population.