Biology (Part-2) (CDS-Solved Paper)

Both the statements are individually true, but statement II is not the correct explanation of statement I. Exposure to UV radiation is the main factor that causes skin cells to become cancerous cells.

Almost all skin cancers are caused by too much UV radiation from the sun or other sources such as solaria (Solariums, Sunbeds and Sun lamps). Skin cancer develops in the cells in the epidermis-the top or outer layer of the skin. The UV rays reaches the earth from the sun through stratosphere.

Strontium-90, iodine-131 and cesium-137, all three are radioactive substances that enter the human body through food chain and cause many physiological disorders in all form of individuals involved in food chain.

Polynucleotide chain of DNA contains a nitrogenous base, deoxyribose sugar and a phosphate group. Polynucleotides are two DNA strands as they are composed of simple monomer units called nucleotides.

The process of copying genetic information from one strand of DNA into RNA is termed as transcription. It is the first step of gene expression, in which a particular segment of DNA is copied into RNA (especially mRNA) by the enzyme RNA polymerase. Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. It consists of three steps–initiation, elongation and termination.

The transmission of HIV infection generally occurs through transfusion of contaminated blood, blood products, donated semen or organ of infected person. It can also be transmitted from infected mother to her child before birth or quite possibly by breast-fed milk.

The cell growth and differentiation are highly controlled and regulated in human body, but in cancer cells there is breakdown of these regulatory mechanisms leading to the formation of benign and malignant tumours. This abnormal and uncontrolled division of cells destroy surrounding tissues and causes cancer. Cancer cells do not remain confined to one part of the body and penetrate to adjoining tissues and disrupt their functions.

Most viruses that infect plants possess single-stranded RNA. Like all other viruses, plant viruses are also obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses are pathogenic to higher plants, e.g. Tobacco Mosaic Virus (TMV).

Syngamy results in formation of diploid zygote. It is also called fertilisation. It involves the complete and permanent fusion of two haploid gametes to form a zygote. It is the most common mode of sexual reproduction in higher plants and animals.

The given symptoms are due to the deficiency of vitamin-C. It is also called as ascorbic acid. It cannot be made by human body and so is an essential component of our diet. Vitamin-C is needed to make a substance called collagen, which is required for the health and repair of various tissues in the body, including skin, bone, cartilage, blood vessel walls, teeth, ligaments and tendons.

Kwashiorkor disease in children is caused by sufficient carbohydrates and fats, but deficiency of protein in diet. It is a form of severe protein-energy malnutrition characterised by oedema, irritability, ulcerating dermatoses, and an enlarged liver with fatty infiltrates. It is a result of sufficient calorie intake, but with insufficient protein consumption.