Both viruses and carcinogenic chemicals can cause tumors by __________.

• A. stimulating the immune system to destroy cancer cells
• B. increasing the rate of apoptosis in healthy cells
• C. inducing mutations in the DNA of host cells
• D. directly converting normal cells into stem cells

Answer: (C)

Verified step by step guidance

1. Understand the question: The problem is asking how both viruses and carcinogenic chemicals can cause tumors. Tumors are abnormal growths of cells, often caused by disruptions in normal cellular processes.
2. Review the options provided: The options include stimulating the immune system, increasing apoptosis, inducing mutations in DNA, and converting normal cells into stem cells. Analyze each option to determine its relevance to tumor formation.
3. Eliminate incorrect options: Tumor formation is not caused by stimulating the immune system to destroy cancer cells, as this would help prevent tumors. Similarly, increasing apoptosis (programmed cell death) in healthy cells does not directly lead to tumor formation, as apoptosis is a protective mechanism to remove damaged cells. Converting normal cells into stem cells is not a known mechanism for tumor formation.
4. Focus on the correct mechanism: Tumors are often caused by mutations in the DNA of host cells. Viruses and carcinogenic chemicals can induce these mutations, disrupting normal cell cycle regulation and leading to uncontrolled cell division.
5. Conclude: The correct answer is 'inducing mutations in the DNA of host cells,' as this is the primary mechanism by which both viruses and carcinogenic chemicals contribute to tumor formation.