Question

Why can't plants directly use nitrogen gas from air?​

Answer 1

The molecular nitrogen (N2) in the atmosphere is very stable and the bonds are hard to break. It takes energy to break the bonds. Bacteria that do nitrogen fixing make nitrogen available for plants by making the N2 conversion to ammonia NH3. From there other organisms can then do more conversions to make nitrogen available for plants. There are a lot of steps and a lot of energy involved to make nitrogen available for plants. It wouldn’t be very efficient for the plants to do it directly from the atmosphere. And bacteria have been around a lot longer doing the conversion already.

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Answer 2

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Kink in the Mercury thermometer helps to prevents the falling of mercury present in capillary tube into bulb. It ensures that the user takes the correct reading of temperature. That's the reason a person before taking a new reading must give a sudden shake to the clinical thermometer so that the mercury level comes to normal.

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