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 concept of density-dependent inhibition: Normal cells stop dividing when they become crowded, a phenomenon known as density-dependent inhibition. This is a regulatory mechanism that ensures cells only divide when there is enough space and resources.
2. Recognize the behavior of cancer cells: Cancer cells often lack density-dependent inhibition, meaning they continue to divide even when they are tightly packed together. This uncontrolled division is a hallmark of cancerous growth.
3. Analyze the options given in the problem: Option a suggests cancer cells are unable to synthesize DNA, which is incorrect as cancer cells do synthesize DNA to continue dividing. Option b suggests they are arrested at the S phase, which is not typical for cancer cells as they progress through the cell cycle. Option d suggests they cannot function properly due to density-dependent inhibition, which is misleading because cancer cells are not affected by this inhibition.
4. Focus on option c: This option states that cancer cells continue to divide even when they are tightly packed together, which aligns with the characteristic behavior of cancer cells lacking density-dependent inhibition.
5. Conclude that option c is the correct answer: Cancer cells continue to divide despite being tightly packed, which is a key difference from normal cells that are regulated by density-dependent inhibition.

Key Concepts

Cell Cycle

The cell cycle is a series of phases that cells go through to grow and divide. It includes the G1 phase (cell growth), S phase (DNA synthesis), G2 phase (preparation for mitosis), and M phase (mitosis). Understanding the cell cycle is crucial for identifying how cancer cells differ from normal cells, particularly in their uncontrolled division.

Density-Dependent Inhibition

Density-dependent inhibition is a regulatory mechanism where normal cells stop dividing when they become crowded. This ensures that cells grow in a controlled manner, maintaining tissue structure. Cancer cells often lose this ability, allowing them to continue dividing even when densely packed, contributing to tumor formation.

Cancer Cell Characteristics

Cancer cells exhibit several distinct characteristics compared to normal cells, such as uncontrolled growth, evasion of apoptosis, and loss of density-dependent inhibition. These traits enable cancer cells to proliferate excessively, invade surrounding tissues, and form tumors, highlighting the importance of understanding these differences in cancer biology.