The ways in which molecules and cells are affected by age, with many theories aiming to explain how aging causes deterioration?

• A. Demographic shift
• B. Hayflick limit
• C. Dependency ratio
• D. Cellular aging

Answer: (D)

The main idea here is how aging affects cells and molecules inside the body, driving deterioration over time. Cellular aging captures this broad sense, describing how cells and their components change with age—things like DNA damage, telomere shortening, mitochondrial dysfunction, and protein misfolding—which together help explain why tissues and organs decline. Many aging theories are framed around these cellular and molecular processes, illustrating how deterioration arises from how cells function and fail as we grow older.

The other concepts relate to people and society rather than the biology of aging. Demographic shift and dependency ratio describe changes in population structure and the burden of dependents, not the internal processes of aging. The Hayflick limit is a specific idea within cellular aging about how many times a normal cell can divide before senescence due to telomere shortening; it’s part of the cellular aging picture but doesn’t by itself cover the wide range of cellular and molecular changes that lead to deterioration.