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Els Ecosistemes

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Submitted By aidabll
Words 400
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Els ecosistemes són sistemes naturals dinàmics, formats per una comunitat natural i per un medi ambient físic que interaccionen mútuament
La biocenosi (o comunitat biòtica) és la comunitat natural d’un ecosistema, i la formen tots els éssers vius que hi habiten.
S’anomena biodiversitat al nombre d’espècies d’una comunitat.
El biòtop és el medi ambient físic d’un ecosistema. Inclou factors abiòtics (inerts) físics i químics.
Components abiòtics d’un ecosistema: sol, aire, aigua, sòl, clima, relleu, llum...
Qualsevol alteració en la biocenosi (pèrdua de biodiversitat, introducció d’espècies invasives...) o en el biòtop (esgotament de recursos, contaminació, catàstrofes naturals...) pot alterar el funcionament de tot el sistema.
Desenvolupament sostenible: aprofitament dels recursos per tal de garantir les necessitats actuals sense esgotar-los o malmetre’ls per al futur.
Els nivells tròfics (o d’alimentació) són els diferents passos per mitjà dels quals es transfereix l’energia entre els organismes d’un ecosistema.
La cadena tròfica (o d’alimentació) és la relació alimentària entre els organismes d’un ecosistema
Causants de la contaminació atmosfèrica: * Centrals elèctriques, calderes i calefaccions * Vehicles * Siderúrgia, foses, incineradores, refineries, cimenteres, indústries químiques
Problemes de la contaminació atmosfèrica:
- reducció de la capa d’ozó
- la pluja àcida
- l’efecte hivernacle

Afebliment de la capa d’ozó
La capa d’ozó, a l’estratosfera, filtra els raigs ultraviolats del Sol, nocives per als éssers vius.
De manera natural, l’ozó es genera i desintegra, mantenint l’equilibri.
La indústria i els cotxes, i els aerosols, frigorífics i aires condicionats alliberen contaminants (òxid de nitrogen, gasos orgànics; clorofluorcarbonats) que afebleixen la capa d’ozó Pluja àcida
Quan l’aigua de pluja entra en contacte amb certs gasos (òxid nitrós, òxid nítric, diòxid de sofre), produeixen àcid sulfúric, àcid nitrós i àcid nítric, convertint-se en l’anomenada pluja àcida.
De manera natural, aquest fenomen es produeix amb les erupcions volcàniques.
Aquests gasos són emesos per fàbriques, centrals elèctriques o vehicles que cremen carbó o productes derivats del petroli.
Té efectes desastrosos per animals, plantes i edificis. Afecta sobretot a vegetals i llacs i embassaments.

Efecte hivernacle
És el procés per mitjà del qual l’atmosfera no permet que els raigs infrarojos de l’energia solar s’alliberin de la superfície del planeta.
Aquest procés comporta un augment de la temperatura de la Terra.
L’efecte hivernacle es produeix de manera natural, però l’activitat humana l’ha accentuat, i és responsable de l’escalfament global del planeta.
Els anomenats gasos d’efecte hivernacle són el vapor d’aigua, el diòxid de carboni i l’ozó, entre d’altres.

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