Final answer:
Viruses and carcinogenic chemicals can cause tumors by disrupting cell division control, leading to abnormal, uncontrollable cell proliferation that results in tumors.
Step-by-step explanation:
Both viruses and carcinogenic chemicals can cause tumors by disruption of control over the rate of the cell division. This happens when there is damage to the cell's DNA, leading to mutations in the genes that regulate the cell cycle. These mutations result in abnormal cells that divide uncontrollably, often leading to the formation of a tumor. Carcinogens and certain viruses cause cancer by producing mutations in DNA which interfere with the cell cycle, thus disrupting the balance between proto-oncogenes and tumor suppressor genes, leading to unregulated cell proliferation that can form cancerous growths.