What is cancer? How is a cancer cell different from the normal cell ? How do normal cells attain cancerous nature?

Explanation

(a) A cancer is characterised by uncontrolled growth and division of certain body cells leading to formation of a tumour.
(b) A cancer cell differs from the normal cells in following characters:
(i) Grow and divide in an uncontrolled manner.
(ii) Size of cancer cells is much more.
(iii) Cancer cells do not show contact inhibition.
(iv) Having indefinite life
(v) Do not undergo differentiation.
(c) Certain physical, chemical, radiological or biological agents, called carcinogens, activate inactive proto- oncogenes to active oncogenes, which cause loss of control on growth and rate of their division.