Class 12th Biology 2014 Set3 Delhi Board Paper Solution

(a) Tissue culture is the technique that has helped scientists propagate the desired crops on a large scale in a short duration. The following steps are carried out to propagate crops by tissue culture:

Nutrient media contain a carbon source (such as sucrose), organic salts, vitamins, amino acids and phytohormones. Hence, propagation is achieved for a large number of plants in a short duration. This process is called micropropagation. All the plants obtained by tissue culture are called somaclones since they are genetically identical to each other as well as the parent plant.

(b) Somatic hybrids are obtained by the method of somatic hybridisation. In this method, the somatic parts of two plants are hybridised. Protoplasts are isolated and fused to get a hybrid protoplast that grows further to form a new plant. For example, protoplasts of potato and tomato have been actually fused to form a pomato. But this plant is not commercially viable, as it does not have all the desired combination of characteristics for its commercial utilisation.

OR

(a) Normal cells have the property of contact inhibition (stoppage of growth on coming in contact with other cells) but cancer cells lose this property. As a result, cancer cells divide continuously to give rise to a mass of cells (tumours). Metastasis- This property is exhibited by malignant tumours. It is the pathological process of spreading cancerous cells to the different parts of the body. These cells divide uncontrollably, forming a mass of cells called tumour. From the tumour, some cells get sloughed off and enter the blood stream. From the blood stream, these cells reach distant parts of the body and therefore, initiate the formation of new tumours by dividing actively.

(b) Cellular oncogenes (c-onc) or proto-oncogenes are the group of genes that have been identified in normal cells. These genes when activated under certain conditions, could lead to oncogenic transformation of the cells.

(c) Techniques such as radiography, CT (Computed Tomography) and MRI (Magnetic Resonance Imaging) are useful to detect cancers of internal organs.

(d) The biological response modifiers such as α-interferons are given to cancer patients as part of their treatment because it activates a patient's immune system and helps in destroying the tumour.