The process of cell renewal and how it is accomplished includes which elements?

• A. Old molecules are recycled; sometimes autolysis or apoptosis occurs.
• B. The nucleus divides randomly.
• C. Cells do not remove damaged organelles.
• D. New proteins are not synthesized.

Answer: (A)

Cell renewal depends on turnover: old components are broken down and their parts are reused, while new components are built to replace them. This is achieved through autophagy, where damaged organelles and proteins are enveloped and degraded in lysosomes so their building blocks can be reused, and through programmed cell removal via apoptosis, which allows tissues to remodel and maintain health by getting rid of cells that are damaged or no longer needed. Autolysis can occur in certain contexts where cells self-digest enzymes, contributing to renewal or tissue remodeling during specific situations. Together, these processes explain how old molecules are recycled and how controlled cell removal supports renewal.

The other statements don’t fit the renewal process as a general mechanism: nucleus division is a separate, regulated form of cell division for creating new cells, not a method of renewing existing cellular components; cells do remove damaged organelles as part of quality control; and new proteins are indeed synthesized to replace degraded ones.