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. Step 1: Understand the question. The question is asking for a difference between cancer cells and normal cells.
2. Step 2: Review each of the answer choices. Let's start with option a. Cancer cells are not unable to synthesize DNA. In fact, they often have increased DNA synthesis as they divide uncontrollably. So, option a is incorrect.
3. Step 3: Move on to option b. Cancer cells are not arrested at the S phase of the cell cycle. They often have a dysregulated cell cycle, but they are not stuck in the S phase. So, option b is also incorrect.
4. Step 4: Consider option c. This statement is correct. Normal cells stop dividing when they come into contact with each other, a phenomenon known as contact inhibition. Cancer cells, however, continue to divide even when they are tightly packed together. So, option c is correct.
5. Step 5: Even though we've found our answer, let's evaluate option d for completeness. Normal cells are affected by density-dependent inhibition, meaning they stop dividing when they reach a certain density. Cancer cells, however, are not affected by this inhibition and can continue to divide. So, option d is incorrect. The correct answer 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. In contrast, cancer cells often bypass these regulatory mechanisms, leading to uncontrolled division and growth.

Density-Dependent Inhibition

Density-dependent inhibition is a phenomenon where cell growth and division are halted when cells become too crowded. Normal cells exhibit this behavior, stopping division when they are in close contact with neighboring cells. Cancer cells, however, ignore this signal, allowing them to proliferate despite high cell density.

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 progress through the cycle in a regulated manner. Cancer cells may become arrested in this phase or continue to replicate DNA uncontrollably, contributing to tumor growth.