<< Chapter < Page Chapter >> Page >

Alveolates: dinoflagellates, apicomplexians, and ciliates

A large body of data supports that the alveolates are derived from a shared common ancestor. The alveolates are named for the presence of an alveolus, or membrane-enclosed sac, beneath the cell membrane. The exact function of the alveolus is unknown, but it may be involved in osmoregulation. The alveolates are further categorized into some of the better-known protists: the dinoflagellates, the apicomplexans, and the ciliates.

Dinoflagellates exhibit extensive morphological diversity and can be photosynthetic, heterotrophic, or mixotrophic. Many dinoflagellates are encased in interlocking plates of cellulose. Two perpendicular flagella fit into the grooves between the cellulose plates, with one flagellum extending longitudinally and a second encircling the dinoflagellate ( [link] ). Together, the flagella contribute to the characteristic spinning motion of dinoflagellates. These protists exist in freshwater and marine habitats, and are a component of plankton    , the typically microscopic organisms that drift through the water and serve as a crucial food source for larger aquatic organisms.

The illustration shows two dinoflagellates. The first is walnut-shaped, with a groove around the middle and another perpendicular groove that starts at the middle and extends back. Flagella fit in each groove. The second dinoflagellate is horseshoe-shaped, with the body extending from the wide part of the horseshoe toward the narrow end. Like the first dinoflagellate, this one has two perpendicular grooves, each containing a flagellum.
The dinoflagellates exhibit great diversity in shape. Many are encased in cellulose armor and have two flagella that fit in grooves between the plates. Movement of these two perpendicular flagella causes a spinning motion.

Some dinoflagellates generate light, called bioluminescence    , when they are jarred or stressed. Large numbers of marine dinoflagellates (billions or trillions of cells per wave) can emit light and cause an entire breaking wave to twinkle or take on a brilliant blue color ( [link] ). For approximately 20 species of marine dinoflagellates, population explosions (also called blooms) during the summer months can tint the ocean with a muddy red color. This phenomenon is called a red tide, and it results from the abundant red pigments present in dinoflagellate plastids. In large quantities, these dinoflagellate species secrete an asphyxiating toxin that can kill fish, birds, and marine mammals. Red tides can be massively detrimental to commercial fisheries, and humans who consume these protists may become poisoned.

The breaking wave in this photo is an iridescent blue color.
Bioluminescence is emitted from dinoflagellates in a breaking wave, as seen from the New Jersey coast. (credit: “catalano82”/Flickr)

The apicomplexan protists are so named because their microtubules, fibrin, and vacuoles are asymmetrically distributed at one end of the cell in a structure called an apical complex ( [link] ). The apical complex is specialized for entry and infection of host cells. Indeed, all apicomplexans are parasitic. This group includes the genus Plasmodium , which causes malaria in humans. Apicomplexan life cycles are complex, involving multiple hosts and stages of sexual and asexual reproduction.

Illustration A shows an oval cell that has a narrow end and a wide end. The apical complex is located at the narrow end. The three branches of this complex narrow and join at the apical, or narrow, end of the cell. Illustration b shows the life cycle of Plasmodium, which causes malaria. The plasmodium life cycle begins when a mosquito takes a blood meal and injects Plasmodium into the bloodstream. The Plasmodium enters the liver where it multiplies, and eventually reenters the blood. In the blood it enters the ring stage, so called because the cell is curled into a ring shape. The Ring stage may multiply by mitosis or it may undergo meiosis, forming new 1n gametes of male or female sex types. When a mosquito takes a blood meal from an infected host the gametes are ingested. A smaller gamete sex type, called a microgamete, fertilizes a larger sex type, called a macrogamete, producting a 2n zygote. The zygote undergoes mitosis and differentiation. It enters the saliva where it can be injected into another host, completing the cycle.
(a) Apicomplexans are parasitic protists. They have a characteristic apical complex that enables them to infect host cells. (b) Plasmodium , the causative agent of malaria, has a complex life cycle typical of apicomplexans. (credit b: modification of work by CDC)

Questions & Answers

in genetics which disease is also termed as the queen disease
Phinihas Reply
what are the types of cell
Teye Reply
prokaryote ,eukaryote, akaryotes
bonney
biology is the study of living organisms
bonney Reply
what are the important of cells in the body
Nharnhar Reply
what is biology
Saidu Reply
Is the study of living things
Nharnhar
what is biology
Emmanuel Reply
what is diffusion
Lenox Reply
what are the important of ecology?
Lenox
what are the importance of ecology
Foday Reply
double stranded DNA is found in which viruses?
Deborah Reply
Virusws usually dont hsve double strnaded DNA they have a single strand RNA. U should probably check them in gpogle just to be sure
Danisha
what would happen if humans were not multicellular
Grace Reply
ettr
Grace
sorry but no
Grace
i haven't any things
mascuud
what is biology
Emmanuel
study of life
Dads
what are types of photosynthesis
Dads
Is there any other type of a eukaryotic cell.
Grace Reply
what is bionomial nomenclature
Rachaelda Reply
state the role of mitochondria
Rachaelda
mitochondria ia power House of the cell. it provides energy and as ATP. Cells energy currency.
Haider
The scientific method of giving short names on the basis of genius and species.
Haider
it is introduce by carlous Lennieus
Haider
it is naming of living organism where by they are given two names one generic and the other specific name
Kenneth
what is element
Kofi Reply
Structure of water molecule and it's biological significance. .....help guys
Ashly
what is the formula for chemical equetion
Justo Reply
Why mitochondria is called the power house of the congo the bahamas cell
Farrukh Reply

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask