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Motility

The majority of protists are motile, but different types of protists have evolved varied modes of movement ( [link] ). Some protists have one or more flagella, which they rotate or whip. Others are covered in rows or tufts of tiny cilia that they coordinately beat to swim. Still others form cytoplasmic extensions called pseudopodia anywhere on the cell, anchor the pseudopodia to a substrate, and pull themselves forward. Some protists can move toward or away from a stimulus, a movement referred to as taxis. Movement toward light, termed phototaxis, is accomplished by coupling their locomotion strategy with a light-sensing organ.

Part a shows a shoe-shaped Paramecium, which is covered with fine, hair-like cilia. Part b shows an Amoeba, which is irregular in shape with long extensions of cytoplasm jutting out from the main body. The extensions are called pseudopods. Part c shows an oval Euglena, which has a narrow front end. A long, whip-like flagellum protrudes from the back end.
Protists use various methods for transportation. (a) Paramecium waves hair-like appendages called cilia to propel itself. (b) Amoeba uses lobe-like pseudopodia to anchor itself to a solid surface and pull itself forward. (c) Euglena uses a whip-like tail called a flagellum to propel itself.

Life cycles

Protists reproduce by a variety of mechanisms. Most undergo some form of asexual reproduction, such as binary fission, to produce two daughter cells. In protists, binary fission can be divided into transverse or longitudinal, depending on the axis of orientation; sometimes Paramecium exhibits this method. Some protists such as the true slime molds exhibit multiple fission and simultaneously divide into many daughter cells. Others produce tiny buds that go on to divide and grow to the size of the parental protist. Sexual reproduction, involving meiosis and fertilization, is common among protists, and many protist species can switch from asexual to sexual reproduction when necessary. Sexual reproduction is often associated with periods when nutrients are depleted or environmental changes occur. Sexual reproduction may allow the protist to recombine genes and produce new variations of progeny that may be better suited to surviving in the new environment. However, sexual reproduction is often associated with resistant cysts that are a protective, resting stage. Depending on their habitat, the cysts may be particularly resistant to temperature extremes, desiccation, or low pH. This strategy also allows certain protists to “wait out” stressors until their environment becomes more favorable for survival or until they are carried (such as by wind, water, or transport on a larger organism) to a different environment, because cysts exhibit virtually no cellular metabolism.

Protist life cycles range from simple to extremely elaborate. Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle. Some protists are unicellular in the haploid form and multicellular in the diploid form, a strategy employed by animals. Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations that is also used by plants.

Habitats

Nearly all protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow. Several protist species are parasites that infect animals or plants. A few protist species live on dead organisms or their wastes, and contribute to their decay.

Section summary

Protists are extremely diverse in terms of their biological and ecological characteristics, partly because they are an artificial assemblage of phylogenetically unrelated groups. Protists display highly varied cell structures, several types of reproductive strategies, virtually every possible type of nutrition, and varied habitats. Most single-celled protists are motile, but these organisms use diverse structures for transportation.

Questions & Answers

why the applied science are deal with problem of world?
John Reply
why do most organisms store lipids instead of carbohydrates
Anthony Reply
Amyloids and prions are all the following EXCEPT:
Malek Reply
who introduced cell
Angel Reply
what is the control system of the nervous system
Milly Reply
is for the passage of blood vasscles
Jabbie
what is cell
Kasu
@Kasu kasu, a cell is the basic unit of all living organisms. it's the structural and functional unit of all organisms.
Leadership
correct
Merub
Which cells causes cancer ?
Merub
what is the main function of the heart
Tessy Reply
the heart pumps blood through out the body
Wakilu
who introduced cell
Angel
How is xylem & phloem adapted to their function
John Reply
What is the importance of biodiversity?
London Reply
histology of the gonads means what
Modesta Reply
Explain the effect of insulin on a named target organ
Blessed Reply
as how
Steve
it increases the rate of glucose consumption
Steve
I think it increases the rate of energy consumed
Steve
glucose ,energy wat shld we take
ama
the effect of insulin on a named organ*** insulin carries out it's effect on an organ called the LIVER.. INSULIN helps to convert excess Glucose in the body to Glycogen (animal fat)..... The inability of the pancreas to produce insulin results in sugar disease called DIABETES MELLITUS....
Emmanuel
hi I wanted to know the difference between hydrotropism and xerotropism
Steve Reply
according to me hydrotropism refers to a condition where living organism such as plants adapts its self to wet conditions for example a water lilly is a Hydrophyte while xerotropism is a condition where living organisms such as cuctus has the ability to adapt itself to dry condition
John
what is fragmentation
Dari Reply
fragmentation simply means scartted
John
la fragmentation est une subdivision d'une particule ou d'une cellule en fragments!!
Louis
so fragmentation means subdivition thanks Louis Sepi
John
yes john !! we can say like that!!
Louis
what is the function of cellulose fibres in a plant cell
John
it is for storing food for plants
Steve
la cellulose est tu forme de stockage des glucides chez les plantes
Louis
Thanks louis but your language can't be easily understood could you please put it in simple terms? please
John
it is because I am mostly written in French!!
Louis
then please try using britain or American English
John
is there a specific number of cells that an organism has to be with
Isaac Reply
how water vapour loss is affected by stomata
Tlotliso Reply
distinguish between archaebacteria and kingdom eubacteria
Anita Reply
what is the name of the sweetest elements on earth
Josiah
how is earth sweet
Olisa

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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