Name: alveolates: ciliates, dinoflagellates, apicomplexans
Uploaded: 2025-06-12T09:27:31.000Z
Duration: 1 min 27 s
Channel: JoVE

Os alveolados incluem ciliados, dinoflagelados e apicomplexanos. Eles são caracterizados por alvéolos - sacos citoplasmáticos localizados abaixo da membrana celular. Ciliados como o Paramecium são reconhecidos pela presença de cílios que auxiliam no movimento. Os ciliados possuem dois tipos de núcleos - macronúcleos e micronúcleos - que estão envolvidos na regulação das funções celulares básicas e da reprodução sexuada, respectivamente. Os dinoflagelados são protistas fotossintéticos. Eles se movem com um movimento giratório usando dois flagelos de comprimentos diferentes posicionados em ângulos diferentes. As espécies de Gonyaulax produzem bioluminescência, emitindo luz quando perturbadas, criando um efeito cintilante nas águas costeiras. Apicomplexans são protistas imóveis, não fotossintéticos e parasitas. Esses organismos normalmente produzem esporozoítos - estruturas especializadas que auxiliam na infecção do hospedeiro. Os apicomplexanos também contêm apicoplastos, que são cloroplastos degenerados que contribuem para a biossíntese de ácidos graxos, isoprenóides e heme. Os apicomplexos mais conhecidos são o Plasmodium, que causa a malária, e o Toxoplasma, que causa a toxoplasmose.

diversidade de protozoários

Diversity of Protists II

Os alveolados constituem um grupo de organismos reconhecido pela presen&#231;a de alv&#233;olos, que s&#227;o sacos citoplasm&#225;ticos localizados sob a membrana celular. Embora sua fun&#231;&#227;o ainda n&#227;o esteja completamente esclarecida, os alv&#233;olos podem auxiliar na regula&#231;&#227;o do equil&#237;brio h&#237;drico, controlando a quantidade de &#225;gua que entra e sai da c&#233;lula. Em dinoflagelados, essas estruturas podem atuar como placas de prote&#231;&#227;o. Existem tr&#234;s tipos principais de alveolados: os ciliados, que se locomovem por meio de c&#237;lios; os dinoflagelados, que utilizam flagelos para o movimento; e os apicomplexos, que s&#227;o parasitas e infectam seres humanos e outros animais.
Os ciliados possuem c&#237;lios em algum momento do seu ciclo de vida. Essas estruturas pequenas e semelhantes a pelos auxiliam na locomo&#231;&#227;o e podem cobrir toda a c&#233;lula ou se apresentar em tufos ou fileiras, dependendo da esp&#233;cie. Um dos ciliados mais conhecidos &#233; o Paramecium, que utiliza os c&#237;lios tanto para locomo&#231;&#227;o quanto para alimenta&#231;&#227;o. O Paramecium consome bact&#233;rias e outras part&#237;culas, conduzindo-as para um sulco oral em forma de funil. O material &#233; ent&#227;o transportado at&#233; a boca celular, ou guloso, onde &#233; envolvido em uma vac&#250;olo por meio da fagocitose. Enzimas digestivas decomp&#245;em o conte&#250;do para a obten&#231;&#227;o de nutrientes.
Os ciliados s&#227;o &#250;nicos entre os protistas por possu&#237;rem dois tipos de n&#250;cleos: micron&#250;cleos e macron&#250;cleos. O macron&#250;cleo gerencia fun&#231;&#245;es celulares essenciais como crescimento e alimenta&#231;&#227;o, enquanto o micron&#250;cleo est&#225; envolvido na reprodu&#231;&#227;o sexuada. No Paramecium, a reprodu&#231;&#227;o sexuada ocorre quando duas c&#233;lulas se fundem parcialmente e trocam os micron&#250;cleos. O genoma macronuclear do Paramecium cont&#233;m aproximadamente 40.000 genes, quase o dobro da quantidade encontrada nos seres humanos.
Muitas esp&#233;cies de Paramecium e outros protistas servem como hospedeiros de bact&#233;rias, arqueias ou eucariotos endossimbi&#243;ticos, como as algas verdes. Esses organismos simbi&#243;ticos frequentemente fornecem nutrientes essenciais ao seu hospedeiro, incluindo vitaminas ou fatores de crescimento. Alguns ciliados, especialmente aqueles presentes no trato digestivo de cupins, abrigam arqueias endossimbi&#243;ticas que convertem hidrog&#234;nio e di&#243;xido de carbono em metano. Al&#233;m disso, alguns ciliados anaer&#243;bios s&#227;o encontrados no r&#250;men de animais ruminantes, onde contribuem para os processos de digest&#227;o e fermenta&#231;&#227;o.
Embora a simbiose seja comum, alguns ciliados s&#227;o parasitas. Um exemplo &#233; o Balantidium coli, um parasita intestinal encontrado principalmente em animais dom&#233;sticos, mas que ocasionalmente infecta seres humanos, causando sintomas semelhantes &#224; disenteria. Esse parasita forma cistos que permitem a transmiss&#227;o da doen&#231;a por meio de alimentos ou &#225;gua contaminados.
Os dinoflagelados s&#227;o organismos diversos encontrados em ambientes marinhos e de &#225;gua doce. Adquiriram a capacidade de realizar fotoss&#237;ntese por meio da endossimbiose secund&#225;ria. Esses organismos movimentam-se com o aux&#237;lio de dois flagelos de comprimentos diferentes, posicionados em &#226;ngulos distintos. O movimento desses flagelos faz com que os dinoflagelados girem, o que se reflete em seu nome, derivado do termo grego para &#8220;rodopiar&#8221;. Alguns dinoflagelados s&#227;o de vida livre, enquanto outros vivem em simbiose com animais de recifes de corais, fornecendo alimento em troca de abrigo.
Certos dinoflagelados produzem bioluminesc&#234;ncia, emitindo luz quando perturbados &#224; noite, criando um efeito cintilante nas &#225;guas costeiras. No entanto, algumas esp&#233;cies s&#227;o nocivas. Por exemplo, Gonyaulax forma densas flora&#231;&#245;es conhecidas como &#8220;mar&#233;s vermelhas&#8221;, que podem levar &#224; morte de peixes e intoxica&#231;&#227;o humana quando os moluscos acumulam as neurotoxinas desses organismos. Essa condi&#231;&#227;o, chamada intoxica&#231;&#227;o paral&#237;tica por moluscos, pode causar dorm&#234;ncia, tontura e dificuldades respirat&#243;rias, com casos graves levando &#224; insufici&#234;ncia respirat&#243;ria. Outro dinoflagelado nocivo, Pfiesteria piscicida, libera esporos t&#243;xicos que infectam e matam peixes. Essas toxinas tamb&#233;m provocam les&#245;es, permitindo que bact&#233;rias invadam o tecido danificado dos peixes. Seres humanos expostos ao Pfiesteria podem desenvolver erup&#231;&#245;es cut&#226;neas e problemas respirat&#243;rios.
Os apicomplexos s&#227;o parasitas n&#227;o fotossintetizantes que causam doen&#231;as graves em seres humanos e animais. Exemplos incluem Plasmodium, respons&#225;vel pela mal&#225;ria; Toxoplasma, que causa toxoplasmose; e Eimeria, que provoca coccidiose. Os apicomplexos adultos n&#227;o possuem mobilidade e absorvem nutrientes diretamente atrav&#233;s da membrana celular.
Esses organismos produzem esporozo&#237;tos, estruturas especializadas que auxiliam na infec&#231;&#227;o do hospedeiro. O nome &#8220;apicomplexo&#8221; deriva da presen&#231;a de um complexo de organelas em uma extremidade do esporozo&#237;to que ajuda o parasita a invadir as c&#233;lulas hospedeiras. Os apicomplexos tamb&#233;m cont&#234;m apicoplastos, que s&#227;o cloroplastos degenerados que n&#227;o realizam mais fotoss&#237;ntese, mas que ainda contribuem para a bioss&#237;ntese de &#225;cidos graxos, isopren&#243;ides e heme. Acredita-se que os apicoplastos tenham se originado de algas vermelhas que foram englobadas por um ancestral apicomplexo em um evento de endossimbiose secund&#225;ria. Com o tempo, o cloroplasto perdeu a capacidade de realizar fotoss&#237;ntese e passou a desempenhar outras fun&#231;&#245;es na c&#233;lula apicomplexa.
Os apicomplexos infectam tanto vertebrados quanto invertebrados, e algumas esp&#233;cies requerem dois hospedeiros para completar seu ciclo de vida. Por exemplo, certas esp&#233;cies de Plasmodium, que causam a mal&#225;ria, alternam entre hospedeiros humanos e mosquitos. Os cocc&#237;deos infectam principalmente aves, mas tamb&#233;m podem afetar outros animais. A mal&#225;ria, que tem sido uma das doen&#231;as mais letais ao longo da hist&#243;ria da humanidade, continua sendo uma grande amea&#231;a &#224; sa&#250;de p&#250;blica mundial.

Diversidade de protozoários

Os alveolados constituem um grupo de organismos reconhecido pela presen&#231;a de alv&#233;olos, que s&#227;o sacos citoplasm&#225;ticos localizados sob a ...

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alveolates: ciliates, dinoflagellates, apicomplexans

Alveolates are protists with tiny sacs called alveoli beneath the cell membrane. These sacs may help control water balance by limiting how much water moves in and out of the cell. In dinoflagellates, alveoli may also act like armor plates.

The three main alveolate groups are ciliates, dinoflagellates, and apicomplexans. Ciliates move with cilia, which are short hair-like structures that can cover the whole cell or appear in rows or tufts. One well-known ciliate is Paramecium, which uses cilia for movement and for feeding on bacteria and other small particles.

Paramecium sweeps food into a funnel-shaped oral groove. The food then moves to the gullet, or cell mouth, where it is enclosed in a vacuole by phagocytosis. Digestive enzymes break the food down so the cell can absorb nutrients. Ciliates are also unusual because they have two nuclei. The macronucleus controls everyday cell functions such as growth and feeding, while the micronucleus is involved in sexual reproduction.

In Paramecium, sexual reproduction happens when two cells partially join and exchange micronuclei. The macronuclear genome of Paramecium has about 40,000 genes, which is nearly twice as many as humans. Many Paramecium species and other protists also host endosymbiotic bacteria, archaea, or eukaryotes such as green algae. These partners often supply vitamins or growth factors to the host.

Some ciliates have more specialized symbioses. Ciliates in termite digestive tracts can contain archaea that turn hydrogen and carbon dioxide into methane. Other anaerobic ciliates live in the rumen of ruminant animals and help with digestion and fermentation. Not all ciliates are helpful, though. Balantidium coli is an intestinal parasite that mainly infects domestic animals but can sometimes infect humans and cause dysentery-like symptoms. It spreads through cysts in contaminated food or water.

Dinoflagellates live in both marine and freshwater habitats. They gained photosynthesis through secondary endosymbiosis. They move with two flagella of different lengths that are set at different angles. This movement makes the cell spin, which fits the name dinoflagellate, from a Greek word meaning “whirling.”

Some dinoflagellates live freely, while others live with coral reef animals and provide food in exchange for shelter. Certain species also produce bioluminescence, so they glow when disturbed at night. Other dinoflagellates can be harmful. Gonyaulax can form red tides, which may kill fish and poison humans when shellfish collect its neurotoxins. This can cause paralytic shellfish poisoning, with numbness, dizziness, breathing trouble, and in severe cases respiratory failure. Pfiesteria piscicida is another harmful dinoflagellate. It releases toxic spores that infect and kill fish, and the toxins can also cause lesions that let bacteria enter damaged tissue. Humans exposed to Pfiesteria may develop skin rashes and breathing problems.

Apicomplexans are non-photosynthetic parasites that cause serious disease in humans and animals. Examples include Plasmodium, which causes malaria; Toxoplasma, which causes toxoplasmosis; and Eimeria, which causes coccidiosis. Adult apicomplexans do not move and absorb nutrients through their cell membrane. They form sporozoites, which help start infection in a host. Their name comes from a special organelle complex at one end of the sporozoite that helps the parasite enter host cells.

Apicomplexans also contain apicoplasts. These are degenerate chloroplasts that no longer do photosynthesis, but they still help with fatty acid, isoprenoid, and heme synthesis. Scientists think apicoplasts came from red algae in a secondary endosymbiotic event. Apicomplexans infect both vertebrates and invertebrates, and some need two hosts to finish their life cycle. In some Plasmodium species, the parasite alternates between mosquito and human hosts. Coccidia mainly infect birds, but they can also affect other animals. Malaria has been one of the deadliest diseases in human history and remains a major health threat worldwide.

Alveolates: Ciliates, Dinoflagellates, Apicomplexans

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diversity of protists i

Excavata Protists and Their Adaptations

Excavata protists show many different ways of living, from photosynthesis to parasitism. This group includes organisms that can use chemical energy, light, or both. Some also live in low-oxygen, or anaerobic, environments where they survive without normal oxygen-based metabolism. Among the main Excavata groups are diplomonads and parabasalids. These are flagellated protists, meaning they move with whip-like tails, and they lack mitochondria and chloroplasts. They often live in anoxic habitats,...

diversity of protists ii

Alveolates are protists with tiny sacs called alveoli beneath the cell membrane. These sacs may help control water balance by limiting how much water moves in and out of the cell. In dinoflagellates, alveoli may also act like armor plates. The three main alveolate groups are ciliates, dinoflagellates, and apicomplexans. Ciliates move with cilia, which are short hair-like structures that can cover the whole cell or appear in rows or tufts. One well-known ciliate is Paramecium, which uses cilia...

diversity of protists iii

Rhizaria: Pseudopods, Tests, and Skeletons

Rhizaria are unicellular protists with threadlike pseudopodia, which are thin cytoplasmic extensions used for movement and feeding. Their amoeboid shape once caused taxonomic confusion, but molecular phylogenetics has since shown where they fit on the evolutionary tree. This group includes Chlorarachniophyta, Radiolaria, and Foraminifera, and each lineage has adapted to a different ecological niche and metabolic strategy. Chlorarachniophyta are unicellular phototrophic protists found in marine...

diversity of protists iv

Amoebozoa: Movement and Life Cycles

Amoebozoa are a diverse group of terrestrial and aquatic protists. They move and feed with lobe-shaped pseudopodia. This feature sets them apart from Rhizaria, which have threadlike pseudopodia. The group includes gymnamoebas, entamoebas, and the plasmodial and cellular slime molds. Phylogenetic evidence also shows that Amoebozoa split from a lineage that later gave rise to fungi and animals. Gymnamoebas are free-living protists that live in water and soil. They move by amoeboid movement,...

key terms and concepts

Learn how alveolates include ciliates, dinoflagellates, and apicomplexans, from Paramecium feeding to red tides, parasites, and malaria.

Alveolates: Ciliates, Dinoflagellates, Apicomplexans | 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

Alveolates: Ciliates, Dinoflagellates, Apicomplexans

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