Explain why a population of organisms that reproduces only by mitosis is less likely to survive a new disease compared to a population of the same species that reproduces by meiosis.

Mitosis produces genetically identical cells, so a population that reproduces only by mitosis is a clone – all individuals have the same genes.
Meiosis, however, creates gametes that combine to form offspring with new combinations of alleles, giving genetic variation.
If a new disease appears, every individual in the clonal population is susceptible because they all share the same susceptible genes.
In the meiotic population, some individuals may carry alleles or mutations that confer resistance to the disease.
Those resistant individuals survive, reproduce and pass the resistance allele on, allowing the population to persist, whereas the clonal population would likely be wiped out.