Tumours, cancers and plant galls

Unit 2 · Chemical and Cellular Basis of Life

How uncontrolled cell division gives tumours and cancer in animals, benign and malignant tumours, metastasis, and galls in plants.

Tumours and cancers in animals

The cell cycle is driven by external and internal factors, which may be chemical or physical.

• Cancer cells do not respond to the body's control mechanisms. They divide excessively and invade other tissues, and if nothing stops them they can kill the organism.
• They ignore the normal signals that regulate the cell cycle. They do not need growth factors, because they either make their own or carry on without them. Their cell-cycle control system is abnormal.
• The trouble starts when one cell of a tissue changes from normal to abnormal. If the immune system cannot recognise and destroy it, the cell multiplies and forms a tumour.

	Benign tumour	Malignant tumour
Where the cells stay	At the original site	Invade nearby tissue
Effect	Usually no serious problem	Impairs the function of one or more organs
Treatment	Can be removed completely by surgery	A person with a malignant tumour is said to have cancer

A few cells of a malignant tumour may break away, enter blood vessels or lymph and form new tumours elsewhere. This spread of cancer cells to a distant site is metastasis.

Galls in plants

• A gall is a swelling or growth that develops on some part of a plant after it is invaded by certain organisms.
• Galls come from uncontrolled mitotic division of plant cells.
• Plant cell division is kept in check by a balance between plant growth regulators such as auxins and cytokinins. When the balance is lost, a mass of undifferentiated cells forms.
• The causes are viruses, fungi, bacteria, insects and mites. They get into the tissue in some way and reprogramme the host cells into abnormal growth.

Exam tip: Define benign and malignant by what the cells do (stay put or invade), and remember that only malignant tumours are called cancer and can show metastasis.

Deshapriya Senevirathne. B.Sc. (Hons) Biology Special, University of Peradeniya — graduated with a class pass. All the content and lessons in A/L Biology on Paadama are reviewed by Deshapriya Senevirathne, and the lessons are taught by him.