A.

Morphallaxis - Regeneration of two transversely cut equal pieces of a Hydra into two small Hydras

Morphallaxis is the type of regeneration in which lost body parts are replaced by the remodelling of the remaining tissue. In this type, little or no cellular proliferation takes place. Eg, Hydra.

When a Hydra is cut into two pieces, two Hydra will be regenerated, both smaller than the parental Hydra. Once regeneration is completed, the two Hydra can continue to grow and reach the size of their original parent.

Epimorphosis require active cellular proliferation prior to the replacement of the lost body part. Eg, Planarian are flatworms, regenerate using a mechanism in which pre- existing cells, known as neoblasts, begin to proliferate and migrate to the injured site in response to injury. These cells later form mass of proliferating cells known as regenration blastema. These further differentiate into specialized cells. 

D.

Atrial natriuretic factor (ANF) is released by wails of the cardiac atrium in response to high sodium concentration, high extracellular fluid volume, or high blood volume. It then acts via various mechanisms to excrete Na, and to cause vasodilation in the circulatory system. It also decreases Na resorption in the renal distal convoluted tubule and cortical collecting duct. It also inhibits renin secretion.

Gastrin is a polypeptide hormone produced by the enteroendocrinc cells of the stomach. It plays an important role in the control of gastric acid secretion.

Inhibin hormone is secreted from corpus luteum, placenta and testes. It supplements the effect of excess sex hormones for depressing gonadotrophic activity (FSH, LH, ICSH) target of inhibin is anterior lobe of pituitary.

Duodenal enterokinase converts trypsinogcn to activate trypsin which, in turn, activates the other pancreatic enzymes.

B.

Thymus - starts undergoing atrophy after puberty

The thymus gland is located behind the sternum and between lungs. It is only active until puberty. After puberty, the thymus starts to shrink slowly and become replaced by fat.

The thyroid gland is a vital hormone gland. It plays an important role in the metabolism growth and development of the human body. It helps to regulate many body functions by constantly releasing a steady amount of thyroid hormones into the bloodstream. Cretinism is a type of mental retardation and bodily malformation caused by severe, uncorrected thyroid deficiency.

The major function of parathyroid gland is to maintain the body's calcium and phosphate levels within a very narrow range, so that the nervous and muscular systems can function properly. It secretes parathyroid hormone. It also enhances the excretion of phosphate by the kidneys and its uptake by the cells.

Pancreas is an organ present in abdomen. It plays an essential role in converting the food we eat into fuel for the body's cells. Delta cells is a type of cell found in Islets of Langerhans in pancreas. They form somatostatin, a hormone that inhibits the release of numerous hormones in the body.

B.

excess of nitrates in drinking water

Blue baby syndrome is a blood related condition mostly found in babies due to nitrate poisoning. It particularly limits blood's ability to carry oxygen thereby causing baby to look blue and hence known as metheamoglobanemia. It is a serious illness in infants which is caused when nitrate is converted into nitrite in the infant's body. Nitrite interferes with the oxygen carrying capacity of the child's blood and therby replaces the oxygen on the red blood cells. It is an acute disease and symptoms develop in infants.

B.

scapula and canines

MRI is a non-invasive technique which uses strong magnetic field for generating resonance and low radio frequency in protons present in body. Most common protons are H nuclei of H₂O molecules. Scapula and canine are osteocytic structures with negligible H₂O content. Also, in MRI we can only see soft tissues, fluids, nerves, vessels, fat and CSF, spinal fluids, brain and eyes.