Step 3: The nitrates and nitrites are used by plants to make amino acids which are then used to make plant proteins.

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1 The Nitrgen Cycle Organisms require nitrgen t prduce amin acids. Nitrgen makes up seventy-eight percent f the atmsphere, but mst rganisms can nt use this frm f nitrgen, and must have the fixed frm. The nitrgen cycle prduces the fixed frm f nitrgen these rganisms need. Step 1: A special type f bacteria called nitrgen fixing bacteria take in atmspheric nitrgen and prduce ammnia (NH3). Step 2: Other bacteria use this ammnia t prduce nitrates and nitrites, which are nitrgen and xygen cntaining cmpunds. Step 3: The nitrates and nitrites are used by plants t make amin acids which are then used t make plant prteins. Step 4: Plants are cnsumed by ther rganisms which use the plant amin acids t make their wn. Step 5: Decmpsers cnvert the nitrgen fund in ther rganisms int ammnia and return it t the sil. A few f these type f bacteria return nitrgen t the atmsphere by a prcess called denitrificatin, hwever this amunt is small.

2 Water cycle Over tw thirds f the earth's surface is cvered by water. It frms an imprtant cmpnent f mst life frms, with up t 70% f plants and animals being cmpsed f water. Vast quantities f water cycle thrugh Earth's atmsphere, ceans, land and bisphere. This cycling f water is called the water r hydrlgical cycle. The cycling f water is imprtant in determining ur weather and climate, supprts plant grwth and makes life pssible. Evapratin: mst water evaprates frm the ceans, where water is fund in highest abundance. Hwever sme evapratin als ccurs frm lakes, rivers, streams and fllwing rain. Transpiratin: is the water lss frm the surface area (particularly the stmata) f plants. Transpiratin accunts fr a massive 50% f land-based evapratin, and 10% f ttal evapratin.. Evaptranspiratin: the prcesses f evapratin and transpiratin are ften cllectively referred t as evaptranspiratin. Cndensatin: the prcess by which water vapur is cnverted back int liquid is called cndensatin. Yu may have bserved a similar prcess ccurring when dew drps frm n a blade f grass r n cld glass. Water in the atmsphere cndenses t frm cluds. Precipitatin: water returns t earth thrugh precipitatin in the frm f rain, sleet, snw r ice (hail). When rain ccurs due t precipitatin, mst f it runs ff int lakes and rivers while a significant prtin f it sinks int the grund. Infiltratin: the prcess thrugh which water sinks int the grund is knwn as infiltratin and is determined by the sil r rck type thrugh which water mves. During the prcess f sinking int the Earth's surface, water is filtered and purified. Depending n the sil type and the depth t which the water has sunk, the grund water becmes increasingly purified: the deeper the water, the cleaner it becmes. Melting and freezing: sme water freezes and is "lcked up in ice, such as in glaciers, and ice sheets. Similarly, water smetimes melts and is returned t ceans and seas.

3 Oxygen cycle Oxygen is ne f the main gases fund in the air, alng with nitrgen. Oxygen is recycled between the air and living rganisms in the fllwing ways: Breathing and respiratin: rganisms such as animals and plants take in xygen frm the air, during breathing and gaseus exchange prcesses. The xygen is used fr cellular respiratin t release energy frm rganic nutrients such as glucse. Phtsynthesis: during phtsynthesis, plants absrb carbn dixide frm the air t synthesize sugars, and release xygen. There is a cmplementary relatinship between phtsynthesis and respiratin in that the frmer prduces xygen and the latter cnsumes xygen.

4 Carbn cycle Carbn is the basic building blck f all rganic materials, and therefre, f living rganisms. Mst f the carbn n earth can be fund in the crust. Other reservirs f carbn include the ceans and atmsphere. Carbn mves frm ne reservir t anther by these prcesses: Cmbustin: burning f wd and fssil fuels by factry and aut emissins transfers carbn t the atmsphere as carbn dixide. Phtsynthesis: carbn dixide is taken up by plants during phtsynthesis and is cnverted int energy rich surces, such as glucse, which cntains carbn. Cellular respiratin: animals eat plants fr fd, taking up the carbn. Plants and animals release carbn int the atmsphere as carbn dixide during gaseus exchange Metablism: rganisms cnvert carbn int rganic mlecules like fats, carbhydrates and prteins when they eat plants r animals. Precipitate: carbn dixide in the atmsphere can als precipitate as carbnate in cean sediments. Decay: carbn dixide gas is als released int the atmsphere during the decay f all rganisms.

5 Krebs Cycle a) Krebs cycle ccurs in matrix f mitchndria. b) Only ccurs if O2 present. c) Link Reactin: Pyruvate mves int matrix & lses 1 carbn as 1 CO2. 1 mre NADH is made. d) The remaining 2C mlecule enters the Krebs Cycle. In several steps, e) energy & hydrgens are remved frm the 2 carbns and changed t mre NADH & FADH2. These migrate t Electrn Transprt. f) 1 mre ATP is made. The cell can use this. g) each remaining carbn is remved as CO2 & released t air. Phsphrus Cycle

6 Phsphrus (P) is anther ne f the essential elements that cycle thrugh the ecsystem. It is an element that is fund in the grund and then taken up by plants and animals. Phsphrus starts its existence as phsphate ins (PO4) in the rcks f the wrld. When it rains, the phsphates and ther minerals are remved frm the rcks and distributed in sils and the water all ver the planet. Plants Need It Plants n land take in the inrganic (cmpunds withut carbn) phsphrus cmpunds frm the sil. The phsphrus atms are then incrprated int many rganic cmpunds that are used in cells. Animals can get their phsphrus by eating plants r drinking water. Algae and water plants are able t absrb the ins frm the water. Unlike carbn and nitrgen, the phsphrus cycle is nt a true cycle. There is a great deal f phsphrus lst. Lsing The Element Phsphrus has a tendency t wind up at the bttm f the cean. Once at the bttm, the phsphate ins are lst t the wrld. Smetimes the phsphates are fund in runff water and g t the bttm and smetimes human pp cntains phsphate and thse phsphates are returned t the cean. The prblem is that all usable phsphrus surces are n the surface The atms are useless nce they reach the bttm f the cean. Slwly but surely the surface f the Earth is running ut f easy places t find phsphrus.

7 Elemental Cncern Why is there a sudden cncern? Phsphrus nly gets int the sil by the weathering prcess n rcks. When plants die in the natural wrld, the phsphates return t the sil. In farming, the crps are taken away and then ver many years the sil runs ut f phsphrus cmpunds. We have created a situatin where we must artificially replenish the nutrients in the land. Phsphrus is heavily used in the farming industry and fertilizersfilled with phsphates are used all ver the wrld t help plants grw.