One difference between cancer cells and normal cells is that cancer cells a. are unable to synthesize DNA. b. are arrested at the S phase of the cell cycle. c. continue to divide even when they are tightly packed together. d. cannot function properly because they are affected by density-dependent inhibition.

Verified step by step guidance

1. Understand the characteristics of normal cell division, including the concept of density-dependent inhibition, where normal cells stop dividing when they become crowded.
2. Recognize that cancer cells often exhibit uncontrolled growth and do not respond to the usual regulatory signals that control cell division.
3. Consider the options provided: (a) inability to synthesize DNA, (b) arrest at the S phase, (c) continued division despite crowding, and (d) inability to function due to density-dependent inhibition.
4. Evaluate each option: (a) Cancer cells can synthesize DNA, (b) Cancer cells are not typically arrested at the S phase, (c) Cancer cells often continue to divide even when crowded, (d) Cancer cells are not affected by density-dependent inhibition.
5. Identify the correct characteristic of cancer cells: they continue to divide even when they are tightly packed together, which is option (c).

Key Concepts

Cell Cycle Regulation

The cell cycle is a series of phases that a cell goes through to divide and replicate. Normal cells are regulated by checkpoints that ensure proper division and prevent overcrowding. Cancer cells often bypass these regulatory mechanisms, allowing them to continue dividing uncontrollably, even in dense environments.

Density-Dependent Inhibition

Density-dependent inhibition is a phenomenon where normal cells stop dividing when they become too crowded. This mechanism helps maintain tissue architecture and function. In contrast, cancer cells lose this ability, leading to excessive growth and the formation of tumors, as they ignore signals that would normally halt their division.

S Phase of the Cell Cycle

The S phase, or synthesis phase, is a part of the cell cycle where DNA is replicated. Normal cells complete this phase and proceed to mitosis, while cancer cells may become arrested in this phase or continue to replicate DNA without proper regulation, contributing to their uncontrolled growth and division.