The type of fossil formed when minerals replace organic material, preserving the original structure, is called: MCQ with Answer and Explanation

Explanation:
Nitrogen fixation is the conversion of inert atmospheric N₂ into ammonia (NH₃) by free-living (e.g., Azotobacter) or symbiotic (e.g., Rhizobium) bacteria, or by industrial processes. Nitrification is the oxidation of ammonia to nitrites then nitrates. Denitrification converts nitrates to N₂ gas. Ammonification is the release of ammonia from organic nitrogen by decomposers. Fixed nitrogen is essential for plant growth.

Explanation:
Marasmus is a form of severe malnutrition caused by a deficiency of both calories and protein. It results in extreme wasting of muscle and subcutaneous fat, making the child look emaciated or 'wasted'. Unlike kwashiorkor, marasmus typically does not present with edema. The child is extremely weak, has a 'old man' face, and is highly susceptible to infections.

Explanation:
Parathyroid Hormone (PTH) is a peptide hormone secreted by the chief cells of the four parathyroid glands in response to low blood calcium levels (hypocalcemia). Its primary function is to increase blood calcium levels (hypercalcemic effect). It achieves this by: 1) Stimulating osteoclasts to break down bone, releasing calcium. 2) Increasing calcium reabsorption and stimulating the activation of Vitamin D in the kidneys. 3) Indirectly increasing calcium absorption in the gut via active Vitamin D. It has the opposite effect of calcitonin.