Final answer:
Eukaryotes need telomeres to protect the ends of their linear chromosomes from progressive shortening during replication, while prokaryotes do not face this issue because they have circular chromosomes that do not require telomeres. The correct option is D.
Step-by-step explanation:
Eukaryotes need telomeres because they have multiple, linear chromosomes that get progressively shorter during cell division due to the end-replication problem. Prokaryotes do not have this issue because they have a single, circular chromosome that doesn't require a specific end replication mechanism.
So, the correct answer to why eukaryotes need telomeres but prokaryotes do not is D) Eukaryotes have linear chromosomes; prokaryotes have circular chromosomes.
In the replication of linear DNA, some sequences are lost with each round of DNA replication because the DNA polymerase can add nucleotides only in the 5' to 3' direction, leading to the end-replication problem. This is where telomeres come into play, protecting the ends of chromosomes from degradation.
Prokaryotes, which replicate much faster, have a single origin of replication and do not face this problem due to their circular DNA, thus lacking telomerase.