Which of the following is a unique characteristic of birds (Class Aves)?
A. Poikilothermic nature
B. Presence of mammary glands
C. Presence of external pinnae
D. Body covered with feathers
Answer: Option D
Solution (By JKExamLibrary)
The most unique and defining characteristic of Class Aves (birds) is the presence of feathers, which are modified scales used for flight and insulation. Birds are warm-blooded (homeothermic), have a four-chambered heart, and possess a beak instead of jaws. Mammary glands and external pinnae are features of mammals.
Explanation:
Calcitonin, secreted by parafollicular (C) cells of the thyroid, decreases blood calcium by inhibiting osteoclasts and promoting calcium deposition in bones. Parathyroid hormone (PTH) raises calcium.
Explanation:
Decomposition involves several steps. Leaching is the process where water-soluble inorganic nutrients (like nitrates, phosphates) are washed out of the decomposing organic matter (detritus) and move deep into the soil profile, where they may become unavailable to plants. Fragmentation is the breakdown of detritus by detritivores (like earthworms).
Explanation:
Chiasmata become clearly visible during the diplotene stage of Prophase I. While the actual exchange of genetic material (crossing over) occurs during the pachytene stage, the homologous chromosomes begin to repel each other and move apart in diplotene, remaining connected only at the sites of crossing over, which appear as X-shaped chiasmata. Exam tip: Pachytene = crossing over; Diplotene = chiasmata visible.
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