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

Les algues vertes appartiennent à l’embranchement des Chlorophyta dans le règne des Archaeplastida.Leur teinte verte est due aux chloroplastes contenant la chlorophylle a et b.Ils habitent les sols humides, les eaux douces et les milieux marins ou existent en symbiotes dans les lichens.Certaines espèces de Trebouxia de l’Antarctique sont des phototrophes endolithiques capables de vivre dans des roches poreuses contenant du quartz.Les algues vertes sont morphologiquement diverses. Ils sont classés en deux groupes principaux : les chlorophytes, tels que les Chlamydomonas microscopiques, et les charophytes, les plus proches parents des plantes terrestres, tels que les Chara macroscopiques.D’autres exemples notables incluent l’Ostreococcus unicellulaire, les Micrasterias multilobés unicellulaires, le Dunaliella flagellé et le Spirogyra filamenteux.Les espèces de Scenedesmus existent sous forme de paquets de quatre cellules, tandis que les espèces d’Ulva forment de grandes structures multicellulaires ressemblant à des algues.Les espèces Volvox forment des colonies composées de plusieurs cellules flagellées.Il est intéressant de noter que Botryococcus braunii est connu pour produire du biocarburant. Mais la production à grande échelle reste un défi.

principaux phylums d’algues

Green Algae

Les algues vertes, &#233;galement appel&#233;es chlorophytes, se distinguent des algues rouges par leurs chloroplastes contenant de la chlorophylle a et b, ce qui leur conf&#232;re leur teinte verte caract&#233;ristique. En revanche, elles ne poss&#232;dent pas de phycobiliprot&#233;ines, ce qui les emp&#234;che de pr&#233;senter les colorations rouge&#226;tres ou bleu-vert typiques des algues rouges. Par leur composition pigmentaire, les algues vertes ressemblent beaucoup aux plantes terrestres et partagent avec elles une relation &#233;volutive &#233;troite. Taxonomiquement, elles appartiennent au phylum Chlorophyta, dans le r&#232;gne Archaeplastida.
Les algues vertes sont divis&#233;es en deux grands groupes : les chlorophytes, comme les esp&#232;ces microscopiques Chlamydomonas et Dunaliella, et les charophytes, telles que Chara, de plus grande taille, qui ressemblent parfois &#224; des plantes terrestres. Ce second groupe est consid&#233;r&#233; comme le plus proche parent des plantes terrestres. La plupart des algues vertes vivent en eau douce, bien que certaines habitent les sols humides ou m&#234;me la neige, &#224; laquelle elles donnent une teinte ros&#233;e. D&#8217;autres vivent en symbiose au sein des lichens. Les chlorophytes pr&#233;sentent une grande diversit&#233; morphologique : certaines sont unicellulaires, d&#8217;autres filamenteuses (les cellules &#233;tant dispos&#233;es en ligne) ou encore coloniales, o&#249; les cellules forment des agr&#233;gats. Certaines esp&#232;ces, comme l&#8217;algue marine Ulva, adoptent une forme multicellulaire. Leur cycle de vie est souvent complexe, incluant des phases de reproduction sexu&#233;e et asexu&#233;e.
Parmi les plus petits eucaryotes connus figure l&#8217;algue verte Ostreococcus tauri, une esp&#232;ce unicellulaire marine du phytoplancton. Avec un diam&#232;tre cellulaire d&#8217;environ 2 microm&#232;tres, O. tauri poss&#232;de le plus petit g&#233;nome connu chez un eucaryote phototrophe, environ 12,6 millions de paires de bases. Gr&#226;ce &#224; sa simplicit&#233; g&#233;nomique, Ostreococcus est devenu un organisme mod&#232;le pour l&#8217;&#233;tude de la r&#233;duction et sp&#233;cialisation g&#233;nomiques chez les eucaryotes.
Chez les esp&#232;ces coloniales, on trouve Volvox, qui forme des colonies de plusieurs centaines de cellules flagell&#233;es. Certaines cellules sont sp&#233;cialis&#233;es dans la photosynth&#232;se, d&#8217;autres dans la reproduction. Ces cellules restent connect&#233;es par de fins filaments cytoplasmiques, ce qui permet une coordination du mouvement de la colonie. Volvox est longuement &#233;tudi&#233; comme mod&#232;le de la multicellularit&#233; et de la division du travail cellulaire.
Certaines algues vertes coloniales pr&#233;sentent un fort potentiel pour la production de biocarburants. Par exemple, Botryococcus braunii s&#233;cr&#232;te des hydrocarbures &#224; longue cha&#238;ne (C30&#8211;C36), de consistance proche du p&#233;trole brut. Environ 30 % du poids sec de B. braunii est constitu&#233; de ces hydrocarbures, suscitant un vif int&#233;r&#234;t en tant que source potentielle de p&#233;trole renouvelable. Des &#233;tudes sugg&#232;rent m&#234;me que certains gisements p&#233;troliers fossiles pourraient provenir d&#8217;anciennes algues vertes comme B. braunii, accumul&#233;es dans des lacs pr&#233;historiques. Si les obstacles &#224; la production industrielle d&#8217;hydrocarbures algaux peuvent &#234;tre lev&#233;s, les algues vertes pourraient contribuer &#224; l&#8217;approvisionnement mondial en p&#233;trole par photosynth&#232;se.
Certaines algues vertes sont capables de vivre dans les roches, ce qui en fait des phototrophes endolithiques. Elles colonisent les roches poreuses, notamment les formations riches en quartz, et forment des couches proches de la surface de la roche. Ces communaut&#233;s endolithiques sont courantes dans des environnements extr&#234;mes, comme les d&#233;serts ou les r&#233;gions froides et arides de l&#8217;Antarctique. Dans les vall&#233;es s&#232;ches de McMurdo, o&#249; la temp&#233;rature et l&#8217;humidit&#233; sont tr&#232;s faibles, vivre &#224; l&#8217;int&#233;rieur des roches pr&#233;sente des avantages. La roche accumule la chaleur solaire, et la fonte des neiges fournit une source r&#233;guli&#232;re d&#8217;eau. Une fois humidifi&#233;es, les roches deviennent plus transparentes, laissant p&#233;n&#233;trer la lumi&#232;re pour la photosynth&#232;se.
Une grande diversit&#233; d&#8217;organismes phototrophes forme ces communaut&#233;s endolithiques, incluant des cyanobact&#233;ries et diverses algues vertes. Outre leur mode de vie libre, elles forment souvent des symbioses avec des champignons, donnant naissance &#224; des lichens endolithiques. Leur activit&#233; m&#233;tabolique contribue &#224; la m&#233;t&#233;orisation des roches : &#224; long terme, de petites fissures apparaissent, favorisant l&#8217;entr&#233;e de l&#8217;eau, qui en gelant, &#233;largit les fractures. Ce processus favorise la colonisation par d&#8217;autres micro-organismes et transforme peu &#224; peu la roche en sol primitif, base de nouveaux &#233;cosyst&#232;mes v&#233;g&#233;taux et animaux.

Principaux phylums d’algues

Les algues vertes, &#233;galement appel&#233;es chlorophytes, se distinguent des algues rouges par leurs chloroplastes contenant de la chlorophylle a et ...

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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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New Archaea Phyla and Their Roles

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green algae

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Alveolates: Ciliates, Dinoflagellates, Apicomplexans

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Rhizaria: Pseudopods, Tests, and Skeletons

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diversity of protists iv

Amoebozoa: Movement and Life Cycles

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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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