La fotosintesi clorofilliana e i segreti del rapporto tra piante e luce solare.
di
Luca Longo
12 febbraio 2021
4 min di lettura
di
Luca Longo
12 febbraio 2021
4 min di lettura
Sappiamo che l’eccesso di anidride carbonica (CO2) in atmosfera è la principale causa del cambiamento climatico. Abbiamo capito che la Terra si sta surriscaldando perché nell’ultimo secolo o due abbiamo bruciato un sacco di combustibili fossili che avevano impiegato centinaia di milioni di anni per formarsi ed accumularsi nelle viscere del nostro pianeta.
Per fortuna, sulla superficie della Terra esistono i cacciatori di CO2 che passano la loro vita a catturare senza pietà l’anidride carbonica. La spaccano, liberano parte dell’ossigeno e rimontano insieme quello che resta, un po’ d’acqua e un pizzico di altre sostanze per produrre semi, frutti, foglie e altre cose buone. Le piante – i nostri cacciatori di CO2– da circa due miliardi e mezzo di anni sanno realizzare una cosa che tutti gli animali presenti sulla Terra non hanno ancora imparato a fare. Compresi noi che negli ultimi tempi (geologici) stiamo dominando il Pianeta. Per comprendere questo processo abbiamo bisogno di partire dalla definizione di fotosintesi clorofilliana.
Lafotosintesi clorofilliana è un meccanismo piuttosto complicato che permette a minuscoli organelli specializzati presenti sulle foglie –i cloroplasti– di convertire la luce solare in energia. I fotoni provenienti dal Sole che riescono a superare la barriera dell’atmosfera hanno una lunghezza d’onda compresa fra i 380 e i 750 nanometri (nm; un nanometro è un miliardesimo di metro). La regione dello spettro solare che le piante riescono a sfruttare per la fotosintesi va dai 400 nm (blu) ai 700 nm (rosso).
A differenza degli animali, le piante utilizzano i raggi solari della giusta lunghezza d’onda per eccitare alcuni elettroni in speciali molecole. L’energia del Sole convertita in energia di eccitazione di questi elettroni subisce numerose altre trasformazioni a catena ed alla fine permette di produrre carboidrati. Questi carboidrati possono essere zuccheri, amidi, cellulosa, lignina e glicogeno.
In pratica, le piante sfruttano il Sole per costruire ordine dal disordine. Convertono sostanze disordinate (l’anidride carbonica dispersa in atmosfera, l’acqua e una manciata di altre sostanze elementari sparse nel terreno) in strutture altamente ordinate e in grado di conservare un sacco di energia all’interno dei loro legami chimici. Grazie a questa gentilezza da parte delle piante, quando ne abbiamo bisogno possiamo bruciare l’energia contenuta negli zuccheri e negli amidi per fare i dolci e la pastasciutta o bruciare cellulosa e lignina per costruire oggetti di legno o per scaldarci davanti al fuoco. Ovviamente, quando abbiamo voglia di una bistecca, di uova o di latte, possiamo anche usare queste scorte concentrate di energia per allevare animali. E non dimentichiamo che il sottoprodotto di tutto questo lavorio delle piante è proprio l’ossigeno che ci permette di respirare!
Tutte le piante –dal trifoglio alla quercia– per fare la fotosintesi usano due molecole speciali in grado di interagire con la luce: la Clorofilla A e la Clorofilla B. Le alghe verdi funzionano quasi nello stesso modo, mentre le alghe rosse usano –insieme all’onnipresente A– anche la Clorofilla D al posto della B. Infine le alghe brune preferiscono la Clorofilla C. Queste differenti molecole sono costruite in modo da lavorare al meglio quando vengono colpite da raggi di luce di un colore preciso, cioè da onde elettromagnetiche di un certo intervallo di lunghezze d’onda.
In particolare, la A assorbe la luce attorno a 435 nm (blu violetto) e 670-680 nm (rosso). Invece, la B preferisce lavorare con le lunghezze d’onda 480 nm (blu) e 650 nm (arancione). Oltre alle clorofille, anche i carotenoidi e i licopeni danno il proprio contributo all’assorbimento della luce visibile –soprattutto nella zona del verde–, i primi sono i responsabili dell’arancione delle carote mentre i secondi fanno rossi i pomodori. Quindi, tenendo conto di tutte le componenti, le piante assorbono la luce viola-blu e rosso-arancione, mentre non sono in grado di utilizzare la luce nelle lunghezze d’onda del giallo e del verde. Tutti i raggi di luce giallo-verdi, quindi, vengono riflessi dalle foglie.
THIS WEBSITE (AND THE INFORMATION CONTAINED HEREIN) DOES NOT CONTAIN OR CONSTITUTE AN OFFER OF SECURITIES FOR SALE, OR SOLICITATION OF AN OFFER TO PURCHASE SECURITIES OR IS NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION, DIRECTLY OR INDIRECTLY, IN OR INTO THE UNITED STATES (INCLUDING ITS TERRITORIES AND POSSESSIONS, ANY STATE OF THE UNITED STATES AND THE DISTRICT OF COLUMBIA) OR FOR THE ACCOUNT OR BENEFIT OF ANY U.S. PERSON AS THAT TERM IS DEFINED IN THE SECURITIES ACT (A "U.S. PERSON"), AUSTRALIA, CANADA, JAPAN OR SOUTH AFRICA OR ANY OTHER JURISDICTION WHERE SUCH AN OFFER OR SOLICITATION WOULD REQUIRE THE APPROVAL OF LOCAL AUTHORITIES OR OTHERWISE BE UNLAWFUL (THE "OTHER COUNTRIES"). THE SECURITIES REFERRED TO HEREIN HAVE NOT BEEN AND WILL NOT BE REGISTERED UNDER THE U.S. SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR PURSUANT TO THE CORRESPONDING REGULATIONS IN FORCE IN AUSTRALIA, CANADA, JAPAN, SOUTH AFRICA OR THE “OTHER COUNTRIES” AND MAY NOT BE OFFERED OR SOLD IN THE UNITED STATES OR TO A U.S. PERSON UNLESS THE SECURITIES ARE REGISTERED UNDER THE SECURITIES ACT, OR AN EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT IS AVAILABLE. NO PUBLIC OFFERING OF SUCH SECURITIES IS INTENDED TO BE MADE IN THE UNITED STATES, AUSTRALIA, CANADA, JAPAN OR IN THE “OTHER COUNTRIES.”
In any Member State of the European Economic Area ("EEA"), the information contained in this website is only directed at and may only be communicated to persons who are "qualified investors" ("Qualified Investors") within the meaning of Article 2(e) of Regulation (EU) 2017/1129 (the "Prospectus Regulation").
The information to which this website gives access is directed only at persons (i) who are persons falling within Article 49(2)(a) to (d) ("high net worth companies, unincorporated associations etc.") of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 (the "Order") or (ii) who have professional experience in matters relating to investments falling within Article 19(5) of the Order or (iii) to whom it may otherwise lawfully be communicated (all such persons together being referred to as "relevant persons"). Any investment or investment activity to which this communication relates is only available to relevant persons and will be engaged in only with relevant persons, or in the EEA, with Qualified Investors. Any person who is not a relevant person, a Qualified Investor or otherwise permitted under applicable law or regulation to access the information, should not act or rely on the information contained herein.
Confirmation of Understanding and Acceptance of Disclaimer
These materials are for informational purposes only and are not directed to, nor are they intended for, access by persons located or resident in the United States, Australia, Canada, Japan or South Africa or any of the Other Countries. I certify that:
I am not resident of, or located in, the United States, Australia, Canada, Japan or South Africa or any of the Other Countries or I am not a U.S. Person; or
If I am a resident of, or located in, the EEA, I am a Qualified Investor within the meaning of Article 2(e) of the Prospectus Regulation; or
If I am a resident of, or located in, the United Kingdom, I am a Qualified Investor and a relevant person.
I have read and understood the disclaimer set out above. I understand that it may affect my rights. I agree to be bound by its terms and I am permitted under applicable law and regulations to proceed to the following parts of this website.
WARNING: the above certification constitutes a "self-certification" pursuant to Decree of the President of the Italian Republic No. 445 of 28 December 2000. False certifications are punishable by law.
You must read the following information before continuing.
The information contained in this segment of the website is not intended for, and must not be accessed or distributed or disseminated to persons resident or physically present in the United Kingdom, Canada, Australia, Japan or any other jurisdiction in which it is unlawful to do so. The information also is not intended for, and must not be accessed or distributed or disseminated to persons resident or physically present in Italy who are not “qualified investors” (investitori qualificati), as defined in Article 2, letter e) of Regulation (EU) 2017/1129 (the “Prospectus Regulation”) pursuant to Article 1, fourth paragraph, letter a) of the Prospectus Regulation as implemented in Italy by Article 35, paragraph 1, letter d) of CONSOB regulation No. 20307 of February 15, 2018.
By clicking the button below labeled “I agree”, you are certifying that (A) if you are in the European Economic Area, you are a “Qualified Investor”; (B) you are not accessing this portion of the website from the United Kingdom, Australia, Canada or Japan; (C) if you are a resident or physically present in Italy, you are a qualified investor as defined under the Prospectus Regulation as implemented in Italy by Article 35, paragraph 1, letter d) of CONSOB regulation No. 20307 of February 15, 2018; and (D) you are not located in a jurisdiction where it is unlawful to access this portion of the website.
You acknowledge that the information and statements contained in the document you are accessing on this website speak only as of the date of such document (or such other date(s) specified therein), and such information and statements may become inaccurate, stale and/or out-of-date thereafter and should not be relied upon for any investment decision.
You acknowledge that the materials on this website that you are accessing are confidential and intended only for you and you agree you will not forward, reproduce, copy, download or publish any of such materials (electronically or otherwise) to any other person if this is not in accordance with the law.
You acknowledge that the access to information and documents contained on this portion of the website may be illegal in certain jurisdictions, and only certain categories of persons may be authorized to access this portion of the website. If you are not authorized to access the information and document contained on this portion of the website or you are not sure that you are permitted to view these materials, you should leave this portion of the website.
You acknowledge that no registration or approval has been obtained and Eni Gas e Luce S.p.A. società benefit and its affiliates assume no responsibility if there is a violation of applicable law and regulation by any person.
By clicking the button below labeled “I agree”, you are confirming that you have read and understood the disclaimer above.
If you cannot so confirm, you must exit this portion of the website
