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The micrograph on the left shows a sphere about 400 microns across with round green cells about 50 microns across inside. The middle micrograph shows a similar view at higher magnification. The micrograph on the right shows a broken sphere that has released some of the cells, while other cells remain inside.
Volvox aureus is a green alga in the supergroup Archaeplastida. This species exists as a colony, consisting of cells immersed in a gel-like matrix and intertwined with each other via hair-like cytoplasmic extensions. (credit: Dr. Ralf Wagner)

True multicellular organisms, such as the sea lettuce, Ulva , are represented among the chlorophytes. In addition, some chlorophytes exist as large, multinucleate, single cells. Species in the genus Caulerpa exhibit flattened fern-like foliage and can reach lengths of 3 meters ( [link] ). Caulerpa species undergo nuclear division, but their cells do not complete cytokinesis, remaining instead as massive and elaborate single cells.

This underwater photo shows fern-like plants growing on the sea bottom.
Caulerpa taxifolia is a chlorophyte consisting of a single cell containing potentially thousands of nuclei. (credit: NOAA)

Amoebozoa

The amoebozoans characteristically exhibit pseudopodia that extend like tubes or flat lobes, rather than the hair-like pseudopodia of rhizarian amoeba ( [link] ). The Amoebozoa include several groups of unicellular amoeba-like organisms that are free-living or parasites.

The micrograph shows amoebas with lobe-like pseudopodia.
Amoebae with tubular and lobe-shaped pseudopodia are seen under a microscope. These isolates would be morphologically classified as amoebozoans.

Slime molds

A subset of the amoebozoans, the slime molds, has several morphological similarities to fungi that are thought to be the result of convergent evolution. For instance, during times of stress, some slime molds develop into spore-generating fruiting bodies, much like fungi.

The slime molds are categorized on the basis of their life cycles into plasmodial or cellular types. Plasmodial slime molds are composed of large, multinucleate cells and move along surfaces like an amorphous blob of slime during their feeding stage ( [link] ). Food particles are lifted and engulfed into the slime mold as it glides along. Upon maturation, the plasmodium takes on a net-like appearance with the ability to form fruiting bodies, or sporangia, during times of stress. Haploid spores are produced by meiosis within the sporangia, and spores can be disseminated through the air or water to potentially land in more favorable environments. If this occurs, the spores germinate to form ameboid or flagellate haploid cells that can combine with each other and produce a diploid zygotic slime mold to complete the life cycle.

 Illustration shows the plasmodium slime mold life cycle, which begins when 1n spores germinate, giving rise to cells that can convert between amoeboid and flagellated forms. Fertilization of either cell type results in a 2n zygote. The zygote undergoes mitosis without cytokinesis, resulting in a single-celled, multinucleate mass visible to the naked eye. A photo inset shows that the plasmodium is bright yellow and looks like vomit. As the plasmodium matures, holes form in the center of the mass. Stalks with bulb-shaped sporangia at the top grow up from the mass. Spores are released when the sporangia burst open, completing the cycle.
The life cycle of the plasmodial slime mold is shown. The brightly colored plasmodium in the inset photo is a single-celled, multinucleate mass. (credit: modification of work by Dr. Jonatha Gott and the Center for RNA Molecular Biology, Case Western Reserve University)

The cellular slime molds function as independent amoeboid cells when nutrients are abundant ( [link] ). When food is depleted, cellular slime molds pile onto each other into a mass of cells that behaves as a single unit, called a slug. Some cells in the slug contribute to a 2–3-millimeter stalk, drying up and dying in the process. Cells atop the stalk form an asexual fruiting body that contains haploid spores. As with plasmodial slime molds, the spores are disseminated and can germinate if they land in a moist environment. One representative genus of the cellular slime molds is Dictyostelium , which commonly exists in the damp soil of forests.

 The cellular slime mold asexual life cycle begins when 1n spores germinate, giving rise to solitary amoeboid cells. The solitary amoebas undergo mitosis, and may aggregate to form aggregated amoebas. The aggregated amoebas are able to migrate. A stalk with a fruiting body at the top forms in the aggregated amoebas. Cells migrate up the stalk and form spores that disperse, completing the asexual life cycle. The cellular slime mold sexual life cycle begins when solitary amoebas undergo fertilization, resulting in a 2n zygote. The zygote undergoes mitosis and meiosis, resulting in more 1 n solitary amoebas.
Cellular slime molds may exist as solitary or aggregated amoebas. (credit: modification of work by “thatredhead4”/Flickr)

View this video to see the formation of a fruiting body by a cellular slime mold.

Opisthokonta

The opisthokonts include the animal-like choanoflagellates, which are believed to resemble the common ancestor of sponges and, in fact, all animals. Choanoflagellates include unicellular and colonial forms, and number about 244 described species. These organisms exhibit a single, apical flagellum that is surrounded by a contractile collar composed of microvilli. The collar uses a similar mechanism to sponges to filter out bacteria for ingestion by the protist. The morphology of choanoflagellates was recognized early on as resembling the collar cells of sponges, and suggesting a possible relationship to animals.

The Mesomycetozoa form a small group of parasites, primarily of fish, and at least one form that can parasitize humans. Their life cycles are poorly understood. These organisms are of special interest, because they appear to be so closely related to animals. In the past, they were grouped with fungi and other protists based on their morphology.

Section summary

The process of classifying protists into meaningful groups is ongoing, but genetic data in the past 20 years have clarified many relationships that were previously unclear or mistaken. The majority view at present is to order all eukaryotes into six supergroups: Excavata, Chromalveolata, Rhizaria, Archaeplastida, Amoebozoa, and Opisthokonta. The goal of this classification scheme is to create clusters of species that all are derived from a common ancestor. At present, the monophyly of some of the supergroups are better supported by genetic data than others. Although tremendous variation exists within the supergroups, commonalities at the morphological, physiological, and ecological levels can be identified.

Art connections

[link] Which of the following statements about Paramecium sexual reproduction is false?

  1. The macronuclei are derived from micronuclei.
  2. Both mitosis and meiosis occur during sexual reproduction.
  3. The conjugate pair swaps macronuclei.
  4. Each parent produces four daughter cells.

[link] C

[link] Which of the following statements about the Laminaria life cycle is false?

  1. 1 n zoospores form in the sporangia.
  2. The sporophyte is the 2n plant.
  3. The gametophyte is diploid.
  4. Both the gametophyte and sporophyte stages are multicellular.

[link] C

Questions & Answers

so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Difference between extinct and extici spicies
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Source:  OpenStax, Bmcc 102 - concepts of biology. OpenStax CNX. Aug 11, 2015 Download for free at https://legacy.cnx.org/content/col11856/1.3
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