Explanation:
NAD⁺ (nicotinamide adenine dinucleotide) is a coenzyme derived from vitamin B₃, serving as an electron carrier in redox reactions. Pepsin is an enzyme, collagen a structural protein, hemoglobin a transport protein. Coenzymes are organic non-protein molecules that assist enzymes.
Explanation:
The ozone layer in the stratosphere absorbs most of the Sun's harmful UV radiation. CFCs, not CO₂, cause its depletion. Ozone at ground level is a pollutant. So B is correct.
Explanation:
Nitrification is a two-step process in the nitrogen cycle where ammonia is oxidized to nitrates. First, ammonia (NH3) is converted to nitrites (NO2-) by bacteria like Nitrosomonas. Then, nitrites are converted to nitrates (NO3-) by bacteria like Nitrobacter. Nitrates are the primary form of nitrogen absorbed by plants. Denitrification is the reverse process, converting nitrates back to nitrogen gas.
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