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A placer deposit is a deposit of earth, sand, or gravel formed due to the differential settling of the denser, heavier components. The placer contains particles of valuable mineral and it is found usually in the bed of a river or lake.
Answer:
Role of organisms in the nitrogen cycle:
Bacteria play a central role: Nitrogen-fixing bacteria, which convert atmospheric nitrogen to nitrates. Bacteria of decay, which convert decaying nitrogen waste to ammonia. Nitrifying bacteria, which convert ammonia to nitrates/nitrites.
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Migraines are frequent intense aches of the head of neck
that are not caused by another physical disorder. Severe pain may usually be
felt on either one side or both sides of the head. Pain usually is felt in the temples.
Migraine could last for hours or couple of days.