Advanced Placement (AP) Biology Practice Exam

Density-dependent inhibition primarily occurs in which type of cells?

1. Transformed cancer cells

2. Normal animal cells

3. Prokaryotic cells

4. Stem cells

The correct answer is: Normal animal cells

Density-dependent inhibition is a key regulatory mechanism in normal animal cells. This phenomenon occurs when the growth and division of cells are inhibited as a result of the crowding and interaction with neighboring cells. In normal tissue, once the cells reach a certain density, they receive signals that slow down or stop their division. This is a crucial aspect of maintaining homeostasis and proper tissue architecture, ensuring that cells do not proliferate unchecked. In contrast, transformed cancer cells typically evade density-dependent inhibition, allowing them to grow uncontrollably regardless of cell density. Prokaryotic cells generally do not rely on density-dependent inhibition, as their growth patterns are influenced by different regulatory mechanisms. Stem cells have unique properties and potential for growth but do not uniformly exhibit density-dependent inhibition like normal cells do. Thus, normal animal cells exemplify the concept of density-dependent inhibition in a way that directly ties into their physiological role in maintaining orderly growth.