Name: green algae: forms, habitats, and roles
Uploaded: 2025-06-13T06:15:05.000Z
Duration: 1 min 21 s
Channel: JoVE

Le alghe verdi appartengono al phylum Chlorophyta nel regno Archaeplastida.La loro tonalità verde è dovuta ai cloroplasti contenenti clorofilla a e b.Abitano il suolo umido, l'acqua dolce e gli ambienti marini o esistono come simbionti nei licheni.Alcune specie di Trebouxia dell'Antartide sono fototrofi endolitici in grado di vivere all'interno di rocce porose contenenti quarzo.Le alghe verdi sono morfologicamente diverse. Sono classificati in due gruppi principali: le clorofite, come la microscopica Chlamydomonas, e le charofite, i parenti più stretti delle piante terrestri, come la Chara macroscopica.Altri esempi degni di nota includono l'Ostreococcus unicellulare, le Micrasterie multilobate unicellulari, la Dunaliella flagellata e gli Spirogyra filamentosi.Le specie di Scenedesmus esistono come pacchetti di quattro cellule, mentre le specie di Ulva formano grandi strutture multicellulari simili ad alghe.Le specie Volvox formano colonie comprendenti diverse cellule flagellate.È interessante notare che il Botryococcus braunii è noto per la produzione di biocarburanti. Ma la produzione su larga scala è ancora una sfida.

principali phyla di alghe

Green Algae

Le alghe verdi, note anche come clorofite, si distinguono dalle alghe rosse per la presenza nei loro cloroplasti di clorofilla a e b, che conferisce loro la caratteristica colorazione verde. Tuttavia, sono prive di ficobiliproteine, motivo per cui non sviluppano pigmentazioni rosse o blu-verdi come le alghe rosse. Per composizione di pigmenti fotosintetici, le alghe verdi somigliano molto alle piante, con cui condividono una stretta relazione evolutiva. Tassonomicamente, le alghe verdi appartengono al phylum Chlorophyta nel regno Archaeplastida.
Le alghe verdi sono suddivise in due gruppi principali: le clorofite, come le microscopiche Chlamydomonas e Dunaliella, e le carofite, come Chara, di dimensioni macroscopiche e spesso simili alle piante terrestri. Le carofite sono considerate le parenti pi&#249; prossime delle piante terrestri. La maggior parte delle alghe verdi si trova in ambienti di acqua dolce, sebbene alcune abitino terreni umidi o crescano persino sulla neve, conferendo una tonalit&#224; rosa agli ambienti circostanti. Altre vivono come simbionti nei licheni. Morfologicamente, le clorofite presentano una grande variet&#224; di forme, da organismi unicellulari a strutture filamentose, in cui le cellule sono disposte linearmente, fino a disposizioni coloniali dove le cellule formano aggregati. Alcune alghe verdi, come l&#8217;alga marina Ulva, raggiungono una forma multicellulare. Il ciclo vitale della maggior parte delle alghe verdi &#232; complesso e comprende fasi riproduttive sia sessuate che asessuate.
Tra gli eucarioti pi&#249; piccoli conosciuti figura l&#8217;alga verde Ostreococcus tauri, una comune specie unicellulare presente nel fitoplancton marino. Con un diametro cellulare di circa 2 micrometri, O. tauri possiede il genoma pi&#249; piccolo noto tra gli eucarioti fototrofi, pari a circa 12,6 milioni di paia di basi. Grazie al suo contenuto genomico minimo, Ostreococcus &#232; stato utilizzato come organismo modello per lo studio della riduzione genomica e della specializzazione negli eucarioti.
A livello coloniale, le alghe verdi comprendono il genere Volvox, che forma colonie costituite da diverse centinaia di cellule flagellate. Alcune di queste cellule si dedicano principalmente alla fotosintesi, mentre altre sono specializzate nella riproduzione. Le cellule all&#8217;interno di una colonia di Volvox rimangono collegate da sottili ponti citoplasmatici, permettendo un movimento coordinato dell&#8217;intera colonia. Volvox &#232; da tempo studiato come organismo modello per comprendere i meccanismi genetici alla base della multicellularit&#224; e della divisione del lavoro tra cellule in organismi multicellulari.
Alcune alghe verdi coloniali mostrano potenziale come fonti di biocarburanti. La specie Botryococcus braunii, ad esempio, secerne idrocarburi a catena lunga (C30&#8211;C36) con una consistenza simile al petrolio grezzo. Circa il 30 % del peso secco cellulare di B. braunii &#232; costituito da questi idrocarburi, suscitando grande interesse per il suo potenziale come fonte rinnovabile di petrolio. Studi basati su biomarcatori suggeriscono che alcune riserve di petrolio esistenti potrebbero derivare da antiche alghe verdi, come B. braunii, sedimentate nei letti lacustri preistorici. Se si riuscisse a superare le sfide associate alla produzione commerciale su larga scala di petrolio da alghe, le alghe verdi potrebbero contribuire all&#8217;approvvigionamento globale di petrolio tramite fotosintesi.
Alcune alghe verdi sono capaci di vivere all&#8217;interno delle rocce, caratteristica che le classifica come fototrofi endolitici. Questi organismi abitano rocce porose, in particolare quelle contenenti quarzo, e solitamente formano strati vicino alla superficie della roccia. Le comunit&#224; fototrofiche endolitiche sono comuni in ambienti estremi, come deserti o le fredde regioni aride dell&#8217;Antartide. Nelle Valli Secche di McMurdo, dove le temperature e i livelli di umidit&#224; sono eccezionalmente bassi, vivere all&#8217;interno delle rocce offre vantaggi significativi. Il sole riscalda la roccia, mentre lo scioglimento della neve fornisce una fonte costante di umidit&#224;. Inoltre, quando le rocce porose assorbono acqua, diventano pi&#249; trasparenti, consentendo una maggiore penetrazione della luce a sostegno degli strati algali interni.
Un&#8217;ampia variet&#224; di organismi fototrofi pu&#242; formare comunit&#224; endolitiche, inclusi cianobatteri e diverse alghe verdi. Oltre a esistere come fototrofi liberi, le alghe verdi e i cianobatteri spesso formano relazioni simbiotiche con i funghi, contribuendo alla formazione di comunit&#224; licheniche endolitiche. L&#8217;attivit&#224; metabolica e la crescita di queste comunit&#224; microbiche litiche contribuiscono al lento disgregamento delle superfici rocciose. Col tempo, si formano piccole fratture che permettono all&#8217;acqua di penetrare, congelarsi ed espandersi, provocando ulteriori spaccature della roccia. Questo processo crea nuovi habitat per la colonizzazione microbica e contribuisce alla degradazione della roccia in un suolo primitivo che, in condizioni favorevoli, pu&#242; supportare lo sviluppo di vita vegetale e animale.

Principali Phyla di Alghe

Le alghe verdi, note anche come clorofite, si distinguono dalle alghe rosse per la presenza nei loro cloroplasti di clorofilla a e b, che conferisce loro ...

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green algae: forms, habitats, and roles

Green algae are photosynthetic organisms with chlorophylls a and b in their chloroplasts. These pigments give them a green color. They differ from red algae because they lack phycobiliproteins, the pigments that produce red or blue-green tones in red algae. In pigment makeup, green algae are close to plants, and they share a close evolutionary relationship with them.

Green algae belong to Phylum Chlorophyta in the Kingdom Archaeplastida. They are usually divided into two main groups: chlorophytes and charophytes. Chlorophytes include microscopic species such as Chlamydomonas and Dunaliella. Charophytes, such as Chara, are often larger and can look like land plants. Charophytes are considered the closest relatives of land plants.

Most green algae live in freshwater, but some grow in moist soil or even in snow, where they can tint the surroundings pink. Others live as symbionts in lichens. Their body forms vary widely. Some are unicellular, some are filamentous with cells arranged in a line, and some form colonies. A few, such as Ulva, are multicellular.

The life cycle of most green algae includes both sexual and asexual stages. Ostreococcus tauri is one of the smallest known eukaryotes. It is a unicellular marine phytoplankton species with a cell diameter of about 2 micrometers. It also has the smallest genome of any known phototrophic eukaryote, at about 12.6 million base pairs. Because of its small genome, Ostreococcus is used to study genome reduction and specialization in eukaryotes.

Volvox is a well-known colonial green alga. Its colonies contain several hundred flagellated cells. Some cells focus on photosynthesis, while others specialize in reproduction. Thin cytoplasmic strands connect the cells and help the colony move together. Volvox is a model organism for studying multicellularity and the division of labor among cells.

Some colonial green algae may also be useful as biofuel sources. Botryococcus braunii produces long-chain hydrocarbons, from C30 to C36, that are similar to crude oil. About 30 percent of its dry cell weight is made of these hydrocarbons. This has led to interest in green algae as a possible renewable petroleum source. Biomarker studies also suggest that some petroleum reserves may have come from ancient green algae such as B. braunii that settled in prehistoric lakebeds.

Some green algae live inside rocks, where they are called endolithic phototrophs. They are often found in porous rocks, especially quartz-containing rocks, and usually grow in layers near the surface. These communities are common in harsh places such as deserts and the cold, dry regions of Antarctica. In the McMurdo Dry Valleys, rocks can provide warmth, moisture from snowmelt, and, when wet, more light for the algae inside.

Endolithic communities can include cyanobacteria, green algae, and fungi that form lichens. As these rock-dwelling microbes grow and carry out metabolism, they slowly weather the rock surface. Small gaps form, water enters, freezes, and expands. This cracks the rock further and creates new spaces for colonization. Over time, the rock breaks down into primitive soil that can support later plant and animal life.

Green Algae: Forms, Habitats, and Roles

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key terms and concepts

Explore green algae in freshwater, rocks, and lichens, plus key examples like Volvox, Ostreococcus, and Botryococcus in a student-friendly summary.

Green Algae: Forms, Habitats, and Roles | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Green Algae: Forms, Habitats, and Roles

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