Advanced Placement (AP) Biology Practice Exam

What does density-dependent inhibition refer to?

1. Cells continue to divide regardless of their environment

2. Cells stop dividing when in contact with one another

3. Cells increase their growth factor production

4. Cells undergo apoptosis when crowded

The correct answer is: Cells stop dividing when in contact with one another

Density-dependent inhibition refers to the phenomenon in which cells cease to divide when they come into contact with each other. This mechanism plays a crucial role in regulating cell growth and maintaining tissue homeostasis. When cells are sparse, they can freely divide, but as they become more populated and start to touch one another, signals are sent that halt further division. This contact-mediated signal prevents overgrowth and helps in preventing tumor formation, ensuring that cells only proliferate when there is adequate space and resources available. The other options do not accurately describe density-dependent inhibition. Cells continuing to divide regardless of their environment suggests a lack of regulation, which is the opposite of what density-dependent inhibition entails. Increasing growth factor production is related to cell signaling and proliferation but does not capture the essence of cells stopping division when they are in close proximity. Apoptosis, or programmed cell death, may occur in certain conditions but is not a characteristic of density-dependent inhibition, which specifically involves the cessation of cell division upon contact.