Biology Test 322

• Goitre is the enlargement of the thyroid gland which occurs due to deficiency of iodine in the body. Iodine is needed for the synthesis of thyroid hormone. When the iodine levels are low, the thyroid gland becomes hyperactive and enlarged to compensate for the deficiency of thyroid hormone in the body. The enlarged thyroid gland is visible as a swelling in the throat known as goitre.
• Grave's disease or exophthalmic goitre occurs due to over secretion of thyroid hormone as the thyroid gland becomes hyperactive. In exophthalmic goitre, protrusion of eyeballs occurs due to the deposition of excess fat behind the eyes. 
• The thyroid gland may also become hyperactive due to hypersecretion of TSH (Thyroid-stimulating hormone) from the anterior pituitary and this can occur due to pituitary adenoma (benign tumours of the pituitary gland).

Excessive intake of exogenous thyroxine can't cause goitre.

The first antibiotic was discovered by Alexander Fleming from the fungus Penicilliumnotatum in 1928.

Antibodies in our body are present in the blood in form of glycoproteins. They produce antigens in response to foreign particles to provide immunity against the pathogen.

Memory cells are formed in lymphocytes of WBC. Immunization against the particular disease based on the function of memory cell induced due to mild, heat killed pathogen administrated during immunization.

• Physiological barriers to the entry of microorganisms into the human body are tears in the eyes, saliva in the mouth and HCl in the stomach.
• The enzymes lysozymes are found in tears and saliva and inhibit the synthesis of peptidoglycan present in the cell wall of microorganisms especially eubacteria.
• Disease-causing microorganism enters through different routes into the body. The physiological barrier prevents their entry. Tears act as a physiological barrier for entry of pathogen.

Skin and respiratory allergy problems arise in hilly areas due to allergen present in these areas. Allergen induce inflammatory reaction in the body.

AIDS is caused by Human immunodeficiency virus of member of group of virus called retrovirus. It is a type of RNA virus that inserts a copy of its genome into the DNA of a host cell that it invades, thus changing the genome of that cell.

AIDS day is celebrated on December 1 all over the world. Its aim is to create awareness about this dreaded disease.

A tumor enclosed within a capsule is called benign tumor. Benign tumors normally remain confined to their original location and do not spread to other parts of the body and cause little damage.

AIDS can be transmitted from infected person to healthy person through blood transfusion. The most common way of transmission of AIDS is during sexual intercourse with multiple partners without protection.