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By the end of this section, you will be able to:
  • Describe the cell structure characteristics of protists
  • Describe the metabolic diversity of protists
  • Describe the life cycle diversity of protists

There are over 100,000 described living species of protists, and it is unclear how many undescribed species may exist. Since many protists live as commensals or parasites in other organisms and these relationships are often species-specific, there is a huge potential for protist diversity that matches the diversity of hosts. As the catchall term for eukaryotic organisms that are not animal, plant, or fungi, it is not surprising that very few characteristics are common to all protists.

Cell structure

The cells of protists are among the most elaborate of all cells. Most protists are microscopic and unicellular, but some true multicellular forms exist. A few protists live as colonies that behave in some ways as a group of free-living cells and in other ways as a multicellular organism. Still other protists are composed of enormous, multinucleate, single cells that look like amorphous blobs of slime, or in other cases, like ferns. In fact, many protist cells are multinucleated; in some species, the nuclei are different sizes and have distinct roles in protist cell function.

Single protist cells range in size from less than a micrometer to three meters in length to hectares. Protist cells may be enveloped by animal-like cell membranes or plant-like cell walls. Others are encased in glassy silica-based shells or wound with pellicles of interlocking protein strips. The pellicle functions like a flexible coat of armor, preventing the protist from being torn or pierced without compromising its range of motion.


Protists exhibit many forms of nutrition and may be aerobic or anaerobic. Protists that store energy by photosynthesis belong to a group of photoautotrophs and are characterized by the presence of chloroplasts. Other protists are heterotrophic and consume organic materials (such as other organisms) to obtain nutrition. Amoebas and some other heterotrophic protist species ingest particles by a process called phagocytosis, in which the cell membrane engulfs a food particle and brings it inward, pinching off an intracellular membranous sac, or vesicle, called a food vacuole ( [link] ). The vesicle containing the ingested particle, the phagosome, then fuses with a lysosome containing hydrolytic enzymes to produce a phagolysosome    , and the food particle is broken down into small molecules that can diffuse into the cytoplasm and be used in cellular metabolism. Undigested remains ultimately are expelled from the cell via exocytosis.

In this illustration, a eukaryotic cell is shown consuming a food particle. As the food particle is consumed, it is encapsulated in a vesicle. The vesicle fuses with a lysosome, and proteins inside the lysosome digest the food particle. Indigestible waste material is ejected from the cell when an exocytic vesicle fuses with the plasma membrane.
The stages of phagocytosis include the engulfment of a food particle, the digestion of the particle using hydrolytic enzymes contained within a lysosome, and the expulsion of undigested materials from the cell.

Subtypes of heterotrophs, called saprobes, absorb nutrients from dead organisms or their organic wastes. Some protists can function as mixotrophs , obtaining nutrition by photoautotrophic or heterotrophic routes, depending on whether sunlight or organic nutrients are available.

Questions & Answers

what is cell
Saleh Reply
the cell wall is targeted
Rebel Reply
what is rispiration
Liaquat Reply
transpiration in organism
what is biology mean?
Nickey Reply
bio means life logy means study . study about life . physiology. morphology . anatomy and others organisms related topics is termed as biology
Biology is the study life. that the study about living organism
Biology is derived from two Greek words "Bio" "Logos" Bio means life, Logos means study.... So Biology is the study of life
means the study of life
what do you mean by cocervates ?
what is oxidation?
Rose Reply
 the state or result of being oxidized
hahahaha thanks, but my teachers requires a thorough meaning about that
Is the process of oxidizing ,the addition of oxygen to a compound with a loss of electrons, always accompanied by reduction
loss of electron....
thank you. 😊
thank you. 😊
thank you. 😊
what is oxidized
the process or result of oxidizing or being oxidized.
my pleasure
Google itttt.....if need explanation
to rose...
oxidation is the removal of oxygen addition of hydrogen
what is genetic
Chibawa Reply
genetic is the study of inheritance and variation
Nice one genetic is the scientific study of heredity and variation in living organism
Genetic : generally is the scientific study of heredity and variation in living thing .
is the basic structural of inheritance
name the enzymes that i found in the saliva
Valuables Reply
salivary amylase
draw a bacterium cell and label
Kadijah Reply
What are the osmoregulatory functions of the kidney?
bisi Reply
What is ecology
Hebert Reply
it is the study of interaction of living organisms with their environment.
what is cell
Etama Reply
cell is the basic unit of life
cell is the basic structural and functional unit of an living organism
a cell is the smallest and most basic unit of a living thing
cell is the basic unit of life. we are made up of 60,000 billions of cells.Each cell carry out a specific function in the body.
A cell is the smallest basic functioning unit of life.
where is the pectoral gridle located?
Tiania Reply
What is hypotonic
Bright Reply
what is hypotonic
Hypotonic means weak solution
the difference between the two cells
Obeng Reply
explain the courses and the correction of lon term sightedness and short term sightedness
Isaac Reply
long sightedness is said to be like someone that can see far object clearly why short sightedness is someone that only can see near obect

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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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