{"id":10643,"date":"2020-11-25T16:49:27","date_gmt":"2020-11-25T15:49:27","guid":{"rendered":"http:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/?p=10643"},"modified":"2021-01-18T14:59:42","modified_gmt":"2021-01-18T13:59:42","slug":"per-que-les-fulles-canvien-de-color-a-la-tardor","status":"publish","type":"post","link":"https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/general\/per-que-les-fulles-canvien-de-color-a-la-tardor\/","title":{"rendered":"Per qu\u00e8 les fulles canvien de color a la tardor?"},"content":{"rendered":"<p style=\"text-align: left;\">Aquesta tardor ens hem despla\u00e7at als centres escolars del Pallars Sobir\u00e0 per a dur a terme una activitat sobre les fulles amb els nens i nenes de cicle inicial. Ten\u00edem l&#8217;objectiu de parlar del m\u00f3n dels vegetals i en concret de la import\u00e0ncia de les fulles en els vegetals.<\/p>\n<p>Per fer-ho, vam enviar una activitat pr\u00e8via a les escoles que consistia en un &#8220;concept cartoon&#8221; on diferents nens i nenes opinaven sobre la pregunta: <strong>Les plantes, com les persones, necessiten aliment per cr\u00e9ixer, per\u00f2, &#8230;qu\u00e8 mengen les plantes?<\/strong><\/p>\n<p>En el mateix &#8220;concept cartoon&#8221; hi sortien diverses opinions al respecte:<\/p>\n<ul style=\"list-style-type: square;\">\n<li>Les plantes mengen l\u2019aliment que hi ha al terra.<\/li>\n<li>Les plantes mengen l\u2019aliment que hi ha a l\u2019aire.<\/li>\n<li>Les plantes mengen l\u2019aliment que hi ha a l\u2019aigua que absorbeixen les seves arrels.<\/li>\n<li>Les plantes mengen l\u2019aliment que fabriquen les seves fulles amb llum del Sol.<\/li>\n<\/ul>\n<p>La idea era establir un debat a partir d&#8217;aquestes idees i mica en mica aproximar-nos al concepte de &#8220;fotos\u00edntesi&#8221; i la import\u00e0ncia que hi juguen les fulles i en especial els pigments fotosint\u00e8tics en aquest proc\u00e9s.<\/p>\n<p>El dia que els v\u00e0rem visitar a l&#8217;escola, vam recuperar el debat de l&#8217;activitat pr\u00e8via i despr\u00e9s varem sortir al voltant de l&#8217;escola amb l&#8217;objectiu de recol\u00b7lectar i estudiar les fulles dels arbres i dels arbusts que an\u00e0vem trobant. Totes les fulles s\u00f3n iguals? Quines parts podem identificar en una fulla? N&#8217;hi ha de simples i n&#8217;hi ha de compostes! I les formes? S\u00f3n totes iguals? Durant la sortida tamb\u00e9 comprovem que hi ha arbres de fulla caduca, \u00e9s a dir que quan arriba la tardor les fulles canvien de color i cauen. En canvi hi ha arbres de fulla perenne que mantenen les fulles durant l&#8217;hivern.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignright size-large wp-image-10659\" src=\"https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/1603965140569-COLLAGE-1024x1024.jpg\" alt=\"\" width=\"1024\" height=\"1024\" srcset=\"https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/1603965140569-COLLAGE-1024x1024.jpg 1024w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/1603965140569-COLLAGE-150x150.jpg 150w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/1603965140569-COLLAGE-300x300.jpg 300w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/1603965140569-COLLAGE-768x768.jpg 768w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/1603965140569-COLLAGE.jpg 2046w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/p>\n<p>Dediquem una estona a classificar les fulles, primer per lliure i a proposta dels nens i nenes: per color o per la forma; i despr\u00e9s utilitzant un petit joc de cartes on vam poder classificar m\u00e9s a fons les fulles segons si s\u00f3n simples o compostes, segons la seva forma, segons el tipus de marge que t\u00e9, &#8230; Aix\u00f2 ens ajudar\u00e0 m\u00e9s endavant a saber utilitzar les claus dicot\u00f2miques o les claus que ens ajuden a identificar les esp\u00e8cies. \u00c9s molt dif\u00edcil con\u00e8ixer i aprendre els noms de totes les plantes! \u00c9s interessant aprendre a utilitzar recursos que ens ajudin.<\/p>\n<p>Al final del mat\u00ed, tornem a recuperar aquella pregunta que ens hem fet quan hem sortit a recol\u00b7lectar les fulles. <strong>Per qu\u00e8 canvien de color les fulles dels arbres a la tardor?\u00a0<\/strong><\/p>\n<p>Proposem a l&#8217;escola que dugui a terme un petit experiment a l&#8217;aula per visualitzar els diferents pigments fotosint\u00e8tics que contenen les fulles. Per fer-ho,\u00a0 duran a terme <strong>una cromatografia<\/strong> que \u00e9s una t\u00e8cnica de separaci\u00f3 dels components d&#8217;una mescla. En aquest cas, amb un morter, una mica d&#8217;alcohol, un pot de vidre i una mica de paper de filtre es pot dur a terme molt f\u00e0cilment.<\/p>\n<p>Es tracta d&#8217;esmicolar i triturar les fulles que volem analitzar per separat. Cada fulla esmicolada la posem en un vas de precipitats o en un got de vidre i hi afegim una mica d&#8217;alcohol. Emplacem un paper de filtre verticalment a dins del got i esperem unes hores a veure el resultat.<\/p>\n<p>Us compartim unes quantes de les imatges que ens han fet arribar les escoles de quan van realitzar l&#8217;experiment. La veritat \u00e9s que els va sortir molt b\u00e9!<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"alignright size-large wp-image-10644\" src=\"https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/cromatografia-1024x1024.jpg\" alt=\"\" width=\"1024\" height=\"1024\" srcset=\"https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/cromatografia-1024x1024.jpg 1024w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/cromatografia-150x150.jpg 150w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/cromatografia-300x300.jpg 300w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/cromatografia-768x768.jpg 768w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/cromatografia.jpg 2047w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/p>\n<p>&nbsp;<\/p>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<div><\/div>\n<p><strong>Qu\u00e8 han pogut observar en aquest experiment?<\/strong><\/p>\n<p>L&#8217;alcohol ha transportat i dipositat en el paper de filtre els diferents pigments de les fulles. El fet de que els pigments es dipositin en bandes \u00e9s degut a la diferent composici\u00f3 qu\u00edmica d&#8217;aquests pigments. Els menys densos es dipositen m\u00e9s amunt del paper de filtre i viceversa. D&#8217;altra banda, l&#8217;amplada de la banda tamb\u00e9 ens dona informaci\u00f3 sobre l&#8217;abund\u00e0ncia de cada pigment en les fulles.<\/p>\n<p>Aquest experiment ens permet comprovar que les fulles tenen m\u00e9s d&#8217;un pigment. El pigment m\u00e9s abundant a les fulles durant la primavera i l&#8217;estiu \u00e9s la clorofil\u00b7la, que \u00e9s la responsable de que les fulles tinguin un color verd\u00f3s.\u00a0 Per qu\u00e8? Perqu\u00e8 els pigments absorbeixen llum per\u00f2 tamb\u00e9 en reflexen. Aquella llum que reflexen \u00e9s el color que nosaltres veiem.<\/p>\n<p><span style=\"font-family: inherit; font-size: 1em;\"><strong>Per qu\u00e8 \u00e9s important la clorofil\u00b7la? <\/strong>\u00c9s important perqu\u00e8 \u00e9s el pigment responsable de la fotos\u00edntesi, que \u00e9s el proc\u00e9s pel qual les plantes fabriquen el seu propi aliment.\u00a0<\/span><\/p>\n<div>\n<figure id=\"attachment_10649\" aria-describedby=\"caption-attachment-10649\" style=\"width: 191px\" class=\"wp-caption alignleft\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-10649\" src=\"https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/molsa-400x2.jpg\" alt=\"\" width=\"191\" height=\"196\" srcset=\"https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/molsa-400x2.jpg 901w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/molsa-400x2-292x300.jpg 292w, https:\/\/serveiseducatius.xtec.cat\/cda-vallsdaneu\/wp-content\/uploads\/usu1375\/2020\/11\/molsa-400x2-768x788.jpg 768w\" sizes=\"auto, (max-width: 191px) 100vw, 191px\" \/><figcaption id=\"caption-attachment-10649\" class=\"wp-caption-text\"><i>\u00a0 \u00a0c\u00e8l\u00b7lules d&#8217;una molsa<\/i><\/figcaption><\/figure>\n<p>En aquesta imatge podeu observar les c\u00e8l\u00b7lules d&#8217;un fil\u00b7lidi d&#8217;una molsa. Els fil\u00b7lidis vindrien a ser estructures semblants a les d&#8217;una fulla en una planta superior. En aquestes c\u00e8l\u00b7lules podem observar uns saquets rodonets de color verd. S\u00f3n els cloroplasts, els org\u00e0nuls que contenen la clorofil\u00b7la i on es produeix aquesta captura (absorci\u00f3) de l&#8217;energia de la llum per poder realitzar la fotos\u00edntesi o producci\u00f3 d&#8217;aliment.<\/p>\n<p><strong>Per\u00f2 les fulles nom\u00e9s contenen clorofil\u00b7les? O tamb\u00e9 contenen altres pigments fotosint\u00e8tics? <\/strong>Amb l&#8217;experiment realitzat comprovem que les fulles no nom\u00e9s contenen clorofil\u00b7la sin\u00f3 que tamb\u00e9 tenen altres pigments que tamb\u00e9 absorbeixen radiaci\u00f3 i que s\u00f3n els responsables de les coloracions taronges (carotens) i grogoses (xantofil\u00b7les). Aquests pigments tamb\u00e9 col\u00b7laboren en la fotos\u00edntesi, per\u00f2 en menor escala.<\/p>\n<p><strong>Per qu\u00e8 cauen les fulles? Per qu\u00e8 canvien de color?<\/strong><\/p>\n<p>Finalment responem a la pregunta d&#8217;aquest article. Quan arriba la tardor, les hores de llum del dia s&#8217;escurcen i la intensitat de la radiaci\u00f3 solar tamb\u00e9 \u00e9s menor. Quan comencen les primeres gelades, la disponibilitat d&#8217;aigua i nutrients per a les plantes tamb\u00e9 \u00e9s menor. Tots aquests factors dificulten el proc\u00e9s de la fotos\u00edntesi, de manera que l&#8217;estrat\u00e8gia de moltes plantes \u00e9s deixar anar les seves fulles per no haver-les de mantenir mentre no tenen possibilitat de produir aliment.<\/p>\n<p>El fet de que canvi\u00efn de color \u00e9s degut a que el fred i les poques hores de llum degraden la clorofil\u00b7la i aquesta comen\u00e7a a descompondre&#8217;s deixant al descobert altres pigments fotosint\u00e8tics de les fulles (carotens i xantofil\u00b7les).<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Aquesta tardor ens hem despla\u00e7at als centres escolars del Pallars Sobir\u00e0 per a dur a terme una activitat sobre les [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":10644,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_bbp_topic_count":0,"_bbp_reply_count":0,"_bbp_total_topic_count":0,"_bbp_total_reply_count":0,"_bbp_voice_count":0,"_bbp_anonymous_reply_count":0,"_bbp_topic_count_hidden":0,"_bbp_reply_count_hidden":0,"_bbp_forum_subforum_count":0,"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center 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