In many eukaryotes, there are repetitive sequences called telomeres at the ends of chromosomes. After successive rounds of DNA replication, the strand becomes shorter. In some cells, an enzyme called repairs the shortened strand

An image of plasma membrane shows the phospholipid bilayer, embedded proteins, and cholesterol molecules. The membrane separates the extracellular space, outside of the cell, from the cytosol inside the cell. The plasma membrane is the border between the interior and exterior of a cell. I hope this helps you :)