CBSE Class 9 Answered

In cancer, a group of cells display uncontrolled growth by dividing beyond their normal limits, intrusion on and destruction of adjacent tissues, and sometimes metastasis i.e spreading to other locations in the body via lymph or blood.

In our body, cell growth and differentiation is highly controlled and regulated. In cancer cells, there is a breakdown of these regulatory mechanisms. Cancer cells have lost teh property of contact inhibition. Hence they continue to divide giving rise to masses of cells called tumors, which may be benign or malignant. Benign tumors do not spread to other parts of the body whereas malignant tumors spread to different parts of the body. The cells of malignant tumors grow very rapidly, and invade and damage the surrounding normal tissues. As these cells actively divide and grow they also starve the normal cells by competing for vital nutrients. Cells separated from such cancers reach distant sites and start a new tumor wherever they get lodged in the body. This property is called metastasis.