However, nitrogen can only be used by plants in the form of the nitrate ion (NO 3

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1 The Nitrgen Cycle the cycling f nitrgen thrugh the bisphere Nitrgen is plentiful in ur atmsphere as N 2(g) Hwever, nitrgen can nly be used by plants in the frm f the nitrate in (NO 3 ) There are tw ways that nitrate is frmed nitrgen fixatin is the prcess in which atmspheric r disslved nitrgen is cnverted int nitrate ins 1

2 Lightning energy frm lightning prduces nitrates by cmbining N 2 and O 2 t make NO 3 the nitrate ins disslve in rain water and enter the sil where they are taken up by plant rts (assimilatin) the plant then makes DNA r amin acids amin acids are then made int prteins Nitrgen Fixing Bacteria sme bacteria species in sil can take N 2 and make NO 3 frm it smetimes the bacteria are fund in ndules n the rt f the plant ccurs in legumes; this is a symbitic relatinship Nitrgen and Decmpsitin when waste r dead matter is decmpsed, the nitrgen it cntains is cnverted back int N 2 thrugh a series f steps called denitrificatin cmplex nitrgen cmpunds in rganic matter > NH 3 > NO 3 > NO 2 > N 2 this is dne by bacteria in the sil called denitrifying bacteria 2

3 The Phsphrus Cycle phsphrus is needed t make cell membranes, ATP, DNA and the calcium phsphate in bnes the phsphrus cycle has 2 parts: the lng cycle invlving rcks f Earth's crust (red arrws) the shrt cycle invlving living rganisms (black arrws) phsphrus fund in phsphates (PO 4 3 ) in rcks gets erded and absrbed by plants and algae the phsphates then get passed up the fd chain When living rganisms decmpse, the phsphates can be used by phtsynthesizers again r enter the lng cycle and frm rcks again. 3

4 Human Impacts n the Nitrgen and Phsphrus Cycle Quesn: What are sme ways humans add nitrgen/phsphrus r take nitrgen/ phsphrus frm the ecsystem? Harvesng crps takes N and P in plants away frm the area leaves sil with less N and P fr next grwing seasn Quesn: Hw can we fix the prblem f nt enugh N and P in the sil? Adding ferlizer adds N and P, in the frm f nitrates and phsphates, t sil that needs it adding t much can make sil acidic excess ferlizer can run ff int streams and end up in lakes Runff frm farm perans manure can enter water ways and end up in lakes causing algal blms and speed up eutrphican Quesn: Hw can cies and twns affect the amunt f N and P that may enter rivers and streams? 4

5 Nitrgen and Phsphrus Cycle Questins (Read pgs 60 65) 1. Why d the levels f nitrgen and phsphrus in fields decline when crps are harvested? 2. Explain hw excess ferlizers might affect decmpsing rganisms. 3. (a) Why d algal blms usually ccur in spring? (b) Explain hw algal blms affect ther rganisms in freshwater ecsystems. 4. What dangers d high levels f nitrates in the drinking water present fr infants? 5. If a farmer des nt plant a crp in ne field, and then plws the field in the fall, hw wuld this help restre nitrgen and phsphrus levels in the sil? 6. Explain why nitrgen is imprtant t rganisms. 7. If nearly 79 % f the atmsphere is nitrgen, hw culd there be a shrtage f nitrgen in sme sils? 8. Hw d animals btain usable nitrgen? 9. Nitrgen fixing bacteria are fund in the rts f bean plants. Explain hw the bacteria benefit the plant and hw the plant benefits the bacteria. 10. Draw a diagram f the nitrgen cycle fr a farm r garden where manure is used. 5

6 11. Explain why it is a gd pracce t aerate lawns. 12. Explain why phsphrus is imprtant t living things. 13. Sme farmers alternate crps that require rich supplies f nitrgen, such as crn, with alfalfa. Alfalfa is usually less valuable in the marketplace than crn. Why wuld farmers plant a crp that prvides less ecnmic value? 14. Explain why bgs and swamps are usually lw in nitrgen. 15. Speculate abut why clver wuld begin t grw in an lder lawn. Hw wuld the presence f clver benefit the lawn? 16. Nitrate levels were analyzed frm living material and sil samples in three different ecsystems (grassland, temperate rain frest, and trpical rain frest) in the same mnth. T determine the mass f nitrates in living things, all living plant maer was cllected in a study area and the levels f nitrates were determined. The same analysis was cnducted fr the tp layer f sil. The results are listed in Table 1, where each ecsystem is idenfied by a number. (a) In which cmmunity des nitrgen cycle mst rapidly? Explain yur cnclusin. (b) Which ecsystem (grassland, temperate rain frest, and trpical rain frest) is study area 1, 2, and 3? Give reasns fr yur answers. (c) Speculate abut the data that might be cllected frm a tundra ecsystem. Explain yur predicn. 17. Hw is the water cycle imprtant in the cycling f nitrgen and phsphrus? 18. Peple have used ferlizers fr a lng me. Explain why we must begin changing ur views n the use f ferlizers s the ecsystems we live in will be sustainable. Why 6