Peranema Figure They are found in freshwater lakes, ponds and ditches, and are often abundant at the bottom of stagnant pools rich in decaying organic material.
Although they belong to the class Euglenoidea, and are morphologically similar to the green Euglena, Peranema have no chloroplasts, and cannot feed by autotrophy. Chlamydomonas Figure Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogeneses, and genetics.
One of the many striking features of Chlamydomonas is that it contains ion channels, channelrhodopsins , that are directly activated by light.
These proteins are used in optogenetics. Gymnodinium is a genus of dinoflagellates It is one of the few naked dinoflagellates, or species lacking armor cellulosic plates. Most are marine plankton, but they are common in freshwater habitats, as well. Their populations are distributed depending on temperature, salinity, or depth.
Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey phagotrophy.
In terms of number of species, dinoflagellates form one of the largest groups of marine eukaryotes, although this group is substantially smaller than the diatoms. Some species are endosymbionts of marine animals and play an important part in the biology of coral reefs. Other dinoflagellates are unpigmented predators on other protozoa, and a few forms are parasitic. Pandorina Figure The cells are ovoid or slightly narrowed at one end to appear keystone- or pear-shaped.
Each cell has two flagella with two contractile vacuoles at their base, an eyespot, and a large cup-shaped chloroplast with at least one pyrenoid. The colonies co-ordinate their flagellar movement to create a rolling, swimming motion. Pandorina shows the beginnings of the colony polarity and differentiation seen in Volvox since the anterior cells have larger eyespots.
Asexual reproduction is by simultaneous division of all cells of the colony to form autocolonies that are liberated by a gelatinization of the colonial envelope. Sexual reproduction occurs by division of each cell of the colony into zoogametes.
Zoogametes show indications of heterogamy, a slight difference in the size and motility of the pairs that fuse to form the smooth walled zygote.
Volvox Figure It forms spherical colonies of up to 50, cells that were first reported by Antonie van Leeuwenhoek in Volvox diverged from unicellular ancestors approximately million years ago.
Each mature Volvox colony is composed of up to thousands of cells from two differentiated cell types: numerous flagellate somatic cells and a smaller number of germ cells lacking in soma that are embedded in the surface of a hollow sphere or coenobium containing an extracellular matrix made of glycoproteins. Adult somatic cells comprise a single layer with the flagella facing outward. The cells swim in a coordinated fashion, with distinct anterior and posterior poles.
The cells have anterior eyespots that enable the colony to swim towards light. An asexual colony includes both somatic vegetative cells, which do not reproduce, and large, non-motile gonidia in the interior, which produce new colonies through repeated division.
In sexual reproduction two types of gametes are produced. Volvox species can be monoecious or dioecious. Male colonies release numerous sperm packets, while in female colonies single cells enlarge to become oogametes, or eggs. Volvox is facultatively sexual and can reproduce both sexually and asexually.
The switch from asexual to sexual reproduction can be triggered by environmental conditions and by the production of a sex-inducing pheremone. Desiccation-resistant diploid zygotes are produced following successful fertilization. Oedogonium Figure Oedogonium can be free-floating, though it is usually attached to aquatic plants by a holdfast.
It appears greenish and inhabits calm, fresh water. Oedogonium can reproduce asexually by fragmentation of the filaments, through some other types of non-motile spores, and also through zoospores, which have many flagella. These develop in a zoosporangium cell, one zoospore per zoosporangium.
After settling and losing its flagella, a zoospore grows into a filament. Oedogonium can also reproduce sexually. Its sexual life cycle is haplontic, i. Antheridia produce and release sperm, and oogonia produce and release an egg,. The egg and sperm then fuse and form a zygote which is diploid 2n. The zygote then undergoes meiosis to produce the filamentous green alga which is haploid 1n. Spirogyra Figure It is commonly found in freshwater areas, and there are more than species of Spirogyra in the world.
Spirogyra can reproduce both sexually and asexually. In vegetative reproduction, fragmentation takes place, and Spirogyra simply undergoes the intercalary mitosis to form new filaments. Sexual Reproduction is of two types: 1. Scalariform conjugation requires association of two different filaments lined side by side either partially or throughout their length. One cell each from opposite lined filaments emits tubular protuberances known as conjugation tubes, which elongate and fuse, to make a passage called the conjugation canal.
The cytoplasm of the cell acting as the male travels through this tube and fuses with the female cytoplasm, and the gametes fuse to form a zygospore. In lateral conjugation, gametes are formed in a single filament.
Two adjoining cells near the common transverse wall give out protuberances known as conjugation tubes, which further form the conjugation canal upon contact.
The male cytoplasm migrates through the conjugation canal, fusing with the female. The rest of the process proceeds as in scalariform conjugation. The essential difference is that scalariform conjugation occurs between two filaments and lateral conjugation occurs between two adjacent cells on the same filament.
Foraminifera Figure Most foraminifera are marine, the majority of which live on or within the seafloor sediment i. These shells are commonly made of calcium carbonate CaCO 3 or agglutinated sediment particles. Over 50, species are recognized, both living 10, and fossil 40, Radiolaria Figure The elaborate mineral skeleton is usually made of silica.
They are found as zooplankton throughout the ocean, and their skeletal remains make up a large part of the cover of the ocean floor as siliceous ooze. Diatoms Figure Diatoms are producers within the food chain.
A unique feature of diatom cells is that they are enclosed within a cell wall made of silica hydrated silicon dioxide called a frustule. These frustules show a wide diversity in form, but are usually almost bilaterally symmetrical, hence the group name. These shells are used by humans as diatomaceous earth, also known as diatomite.
Fossil evidence suggests that they originated during, or before, the early Jurassic period. Only male gametes of centric diatoms are capable of movement by means of flagella. Diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality. Trypanosoma cruzi is a species of parasitic euglenoids.
Amongst the protozoa, the trypanosomes characteristically bore tissue in another organism and feed on blood primarily and also lymph. This behaviour causes disease or the likelihood of disease that varies with the organism: for example, trypanosomiasis in humans Chagas disease in South America. The triatomine likes the nests of vertebrate animals for shelter, where it bites and sucks blood for food.
Penetration of the infected faeces is further facilitated by the scratching of the bite area by the human or animal host.
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