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Plants and nitrogen

Plants and nitrogen. Plants need nitrogen to grow . It’s present in DNA, RNA, the amino acids that make up proteins, ATP , chlorophyll and most vitamins. The air is 78% nitrogen gas BUT nitrogen gas CANNOT be taken up by plants – it is insoluble so cannot be absorbed

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Plants and nitrogen

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  1. Plants and nitrogen • Plants need nitrogen to grow. • It’s present in DNA, RNA, the amino acids that make up proteins, ATP, chlorophyll and most vitamins. • The air is 78% nitrogen gas • BUT nitrogen gas CANNOT be taken up by plants – it is insoluble so cannot be absorbed • So the nitrogen cycle is essential to enable plants to get nitrogen in a form they CAN absorb

  2. How can plants obtain nitrogen? • 2 ways: • Nitrification • Nitrogen fixation • Both require help from bacteria! • Nitrifying bacteria • Free-living nitrogen-fixing bacteria in the soil • Nitrogen-fixing bacteria in root nodules

  3. Nitrifying bacteria • Decomposition by decomposers produces ammonia (NH3) from the nitrogen in compounds like DNA, proteins etc. • This conversion process is called ammonification. • The ammonia is oxidised by nitrifying bacteria • First to NITRITE (NO2-) • Then to NITRATE (NO3-) • This process is called NITRIFICATION • Plant roots can absorb the nitrates • These can be combined with carbohydrates from photosynthesis to form amino acids & then proteins & other nitrogen-containing compounds.

  4. Nitrogen-fixing bacteria in root nodules • Leguminous plants have root nodules • E.g. clover, beans, peas • Nodules contain millions of nitrogen-fixing bacteria • They have a symbiotic relationship with the plant i.e. both bacteria & plant benefit • They convert nitrogen gas in the soil into ammonia • They do this using an enzyme called nitrogenase • The plant can convert this ammonia directly into amino acids etc. as it is already inside the plant roots

  5. Nitrogen-fixing bacteria in root nodules • The reduction of atmospheric nitrogen is a complex process that requires a large input of energy to proceed. • The nitrogen molecule is composed of two nitrogen atoms joined by a triple covalent bond, thus making the molecule highly inert and nonreactive. • Nitrogenase catalyses the breaking of this bond and the addition of three hydrogen atoms to each nitrogen atom. • The plant provides sugars from photosynthesis that are utilized by the nitrogen-fixing bacteria to produce the energy it needs for nitrogen fixation. • In exchange for these carbon sources, the bacteria provide fixed nitrogen to the host plant for its growth.

  6. Free-living nitrogen-fixing bacteria • Free-living nitrogen-fixing bacteria also convert nitrogen gas in the soil into ammonia • These bacteria must find their own source of energy to do this, typically by oxidizing organic molecules released by other organisms or from decomposition. • The bacteria use the ammonia to make amino acids & proteins etc. • When the bacteria die, their proteins decompose, releasing ammonia back into the soil • This ammonia can be converted to nitrates by nitrifying bacteria, & nitrates can be absorbed by the plant roots

  7. BAD bacteria! • Another type of bacteria use nitrates as an energy source and convert them into nitrogen gas • These are DENITRIFYING bacteria • DENITRIFICATION reduces the amount of nitrate in the soil – BAD for plants!

  8. Lightning • The energy from lightning causes nitrogen gas (N2) and water to combine to form ammonia (NH3) and nitrates (NO3). • Precipitation carries these to the ground, where they can be absorbed by plants

  9. NITROGEN GAS (N2) AMMONIA (NH3) NITROGEN GAS (N2) DECOMPOSITION (AMMONIFICATION) AMMONIA (NH3) NITROGEN FIXATION FREE-LIVING NITROGEN-FIXING BACTERIA DENITRIFICATION DENITRIFYING BACTERIA DEATH & DECOMPOSITION NITROGEN FIXATION NITROGEN-FIXING BACTERIA IN ROOT NODULES • NITRIFICATION NITRIFYING BACTERIA NITRITE (NO2-) NITRIFYING BACTERIA NITRATE (NO3-)

  10. Plants and nitrogen • Plants need ………………. to ……………. • It’s present in DNA, RNA, the ……………….. that make up proteins, ………, chlorophyll and most vitamins. • The air is ………% nitrogen gas • BUT nitrogen gas CANNOT be taken up by plants – it is ……………….. so ………………. be ………………….. • So the ……………………… is essential to enable plants to get nitrogen in a form they CAN …………..

  11. How can plants obtain nitrogen? • 2 ways: • ………………………… • ………………………… • Both require help from bacteria! • ………………… bacteria • Free-living ………………………. bacteria in the soil • Nitrogen-fixing bacteria in …………………………….

  12. Nitrifying bacteria • …………………… by decomposers produces …………….. (NH3) from the nitrogen in compounds like DNA, proteins etc. • This conversion process is called ………………………… • The ammonia is …………………. by …………………… bacteria • First to ………………… (NO2-) • Then to ………………….. (NO3-) • This process is called ……………………. • Plant …………….. can ……………… the …………………. • These can be combined with carbohydrates from ………………………… to form amino acids & then proteins & other nitrogen-containing compounds.

  13. Nitrogen-fixing bacteria in root nodules • …………………… plants have root ………………. • E.g. ……………………………………. • Nodules contain millions of ……………………….. bacteria • They have a …………………… relationship with the plant i.e. both bacteria & plant benefit • They convert nitrogen …….. in the ……… into …………….. • They do this using an enzyme called ………………….. • The plant can ……………. this ammonia directly into ………………….. etc. as it is already ……………… the plant roots

  14. Nitrogen-fixing bacteria in root nodules • The reduction of atmospheric nitrogen is a complex process that requires a large input of energy to proceed. • The nitrogen molecule is composed of two nitrogen atoms joined by a triple covalent bond, thus making the molecule highly inert and nonreactive. • Nitrogenase catalyses the breaking of this bond and the addition of three hydrogen atoms to each nitrogen atom. • The plant provides sugars from photosynthesis that are utilized by the nitrogen-fixing bacteria to produce the energy it needs for nitrogen fixation. • In exchange for these carbon sources, the bacteria provide fixed nitrogen to the host plant for its growth.

  15. Free-living nitrogen-fixing bacteria • Free-living nitrogen-fixing bacteria also convert ………………. in the ………. into ………………… • These bacteria must find their own source of …………… to do this, typically by oxidizing organic molecules released by other organisms or from decomposition. • The bacteria use the ………………. to make ………………… & proteins etc. • When the bacteria ……., their ………………………………….., releasing …………………. back into the ……….. • This ammonia can be converted to …………….. by ………………. bacteria, & nitrates can be ……………….. by the plant …………

  16. BAD bacteria! • Another type of bacteria use ……………. as an ……………. and convert them into nitrogen …… • These are ……………………… bacteria • …………………………. reduces the amount of nitrate in the soil – BAD for plants!

  17. Lightning • The …………….. from lightning causes ……………. …….. (N2) and …………… to combine to form …………….. (NH3) and …………… (NO3). • ……………….. carries these to the ………………, where they can be ………………… by …………….

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