Protists are grouped into three major, unofficial categories based on means by which they obtain nutrition. These are the Protozoa, the Algae, and the Fungus-like Protists. For some reason, botanists use the word “Division” to mean the same taxonomic level as “Phylum”, and since, way back everything was lumped in as either a plant or an animal, taxonomists who study Kingdom Protista (and those who study Kingdom Fungi) also still use the word “Division” to mean “Phylum”, so for example, when “Division Rhizopoda” is listed below, that means the same thing as saying “Phylum Rhizopoda”.
Protozoa:
These protists are animal-like, especially in their nutrition. They ingest their food by phagocytosis. Some have mouth-like structures into which the prey is put while others use pseudopodia to move and to engulf prey. Typical prey include bacteria and other smaller one-celled organisms.- Division Rhizopoda:
An example of a member of this Division is genus
Amoeba,
a fresh-water dweller. Protists in this group are unicellular and have pseudopodia.
Some secrete shells around themselves, while others do not. None of them have flagella, cilia, or meiosis.
Entamoeba histolytica
is a
parasitic
form that causes
amoebic dysentery.
These colonize the colon and feed on bacteria, causing symptoms that
range from mild diarrhea to dysentery.
Typically periods of watery diarrhea, often containing blood, may
alternate with constipation, and often there is flatulence and abdominal
cramping. Entamoeba can be directly spread (anal sex), or
indirectly spread (by drinking
contaminated water). Fresh fruits and vegetables may be unsafe if
fertilized with human feces, watered with contaminated water, or
prepared by a person with it on his/her hands.- Division Apicomplexa:
- These are all parasites and form tiny, infectious spores. All have complex life cycles. An example is Plasmodium vivax, which causes malaria, for which certain species of mosquitoes are the secondary host. It is also possible to become infected with Plasmodium parasites from a transfusion from an infected person or if a drug addict shares a syringe with an infected person. One stage in this complicated life cycle grows in the mosquito, the next stage in the newly-infected person’s liver, and the next stage invades the person’s red blood cells, rupturing the RBCs as the parasites leave to invade other cells. Symptoms include cyclical alternating chills, fever, and sweating which at first, can be mistaken for flu. While usually less than 1% of the RBCs are infected, often malaria causes anemia due to the smaller number of RBCs. Often the spleen and liver become enlarged as they try to deal with the dying RBCs. Malaria is treated with extract from the quinine tree. Remember that people with sickle-cell are more resistant because when a malaria parasite enters a RBC, the RBC sickles, killing the parasite, thereby preventing it from multiplying and spreading.
- Division Zoomastigophora:
This Division contains some organisms which are free-living, others which are
symbionts,
and yet others which are parasites. An example of a symbiotic member
of this Division is the protozoans which live in the gut of termites and
digest
cellulose in the wood the termites eat. An example of a parasitic form
would be
Trypanosoma gambiense,
which causes African sleeping sickness and is spread by the bite
of the tsetse fly. Symptoms include irregular fever, general
swelling of the lymph nodes, skin eruptions, and areas of painful local
swelling. Eventually CNS symptoms like tremors, headache, apathy, and
convulsions appear and become worse, leading to eventual coma and death.
Early on, the parasites are
found in blood and lymph, but later only in the person’s cerebrospinal
fluid.- Division Ciliophora:
An example of an organism in this Division is
Paramecium.
These protozoans are solitary, fresh water organisms and use cilia to move. They have
probably the most complex structure and organization of all cells. Rather than one nucleus, they have a larger macronucleus and several smaller micronuclei. They use a form of sexual reproduction called conjugation in which
some of the micronuclei are exchanged between the two individuals involved.
Algal Protists
These protists are photosynthetic; their nutrition is plant-like. Almost all of them have chlorophyll A, most have chlorophyll C, but only a few have chlorophyll B. They also have a variety of carotenoids and other pigments, and frequently they are grouped into Divisions based on similarities in pigments.- Division Dinoflagellata:
- These are abundant in plankton, occasionally occurring in large numbers. They can occasionally become so numerous that the water looks red, thus this algal bloom (meaning there are large numbers of them, having nothing to do with flowers, which they do not have) is called Red Tide. Because Dinoflagellates are toxic to humans, it is not safe to eat “shellfish” (clams, etc.) collected where Red Tide is occurring (the Protists get inside the clam shell and cannot be easily removed). Dinoflagellates are bioluminescent, that is, they are able to produce light like lightening bugs, and at night during Red Tide, the crests of the ocean waves appear to glow in the dark.
- Division Euglenophyta:
Probably the best-known example of this Division is genus
Euglena.
Each of these organisms has a
flagellum
on its
anterior
end, and this is used to propel the organism. They have chloroplast
and, when in the light, do photosynthesis. If they are not in the
light, they can also obtain
nutrition by phagocytosis. To help them sense light (which they then
move toward), Euglena have a light-sensitive “eyespot” or
stigma
near their anterior ends. This is not a true eye, in that it
cannot do any image formation, but rather it is a
photoreceptor
which senses the light level in the organism’s environment.- Division Chlorophyta:
- These protists are also known as the “green algae.” Their
chloroplasts and the pigments therein are similar to plants (this is
about the only group of algae with chlorophyll
B), thus it is thought that the green algae may be the evolutionary
ancestors of plants. Various species of green algae may be found in a
variety of environments including both fresh and salt water, damp soil,
the surface of snow, and within other
organisms (lichens, hydra, polar bear hair).
Chlamydomonas are unicellular and contain an eyespot (stigma), a chloroplast, two flagella, and a nucleus. 
Volvox are colonial and often contain darker green daughter colonies inside. Each cell posesses two flagella, enabling the colony to be mobile. There is an intercellular matrix holding the colony of cells together. Ulva is called Sea Lettuce. This is truely multicellular, with a division of labor among the various cells, and is macroscopic. The “body” is two cells thick, and there is a specially-modified “holdfast” to anchor the organism to the ocean floor. Its life cycle includes both 1n and 2n stages (see below). 
Closterium is a member of the sub-group called the Desmids. Some desmids form colonies, but Closterium is solitary. Its nucleus is in the center with a cone-shaped chloroplast on each side. Each chloroplast contains a series of starch-storage organelles called pyrenoids In living Closterium, each end of the cell bears a small vacuole containing several gypsum grains which “dance” by Brownian motion. 
Spirogyra are colonial, being organized into long filaments. Each cell contains a spiral chloroplast with pyrenoids (used to store starch) and a nucleus. They have conjugation--a type of sexual reproduction in which the contents of the male gamete cell go over into the female cell.
Many green algae, especially the multicellular ones, have both sexual
and asexual stages in their life cycles, thus we must re-introduce the
idea of Alternation of Generations we discussed along with
meiosis. When we first discussed Alternation
of Generations, we looked at a very simple diagram in which adults
produced 1n gametes by meiosis, and those gametes joined by syngamy to
form a new 2n generation. In reality in algae and plants, there are a
few more stages in the process, thus we
now need to re-visit this cycle. The 2n generation, which in humans is
called an “adult,” in algae and plants is called a
sporophyte
because it produces spores. Within specialized reproductive structures
in/on
the bodies of the sporophyte, meiosis occurs to reduce the chromosome
number from 2n to 1n, thus the spores which are produced are 1n. Each
spore germinates and grows into a new, independent, 1n organism (which
often looks totally different than the
2n generation). These 1n organisms are called
gametophytes
because they produce the gametes (eggs and sperm), which are still 1n. An egg and sperm unite by
syngamy
increasing the chromosome number from 1n to 2n, and
forming a
zygote
which is 2n. The zygote grows into the sporophyte, and the cycle
starts over. Various of the green algae go through this cycle as do
members of the next two groups, the brown and red algae. Plants also
go through this same cycle with some interesting modifications we will
discuss later. - Division Phaeophyta:
- These organisms are commonly known as the “brown algae.” They are multicellular and live in marine, temperate zone, costal areas. They all have a form of sexual reproduction with alternation of generations. One member of this Division with which you may be familiar is Kelp, which actually can be any of several species of seaweed in the genera Fucus and/or Laminaria. Brown algae are used in many cultures as human food, and are good sources of iodine. We need iodine for our thyroid glands, and if a person doesn’t enough iodine in his/her diet (most commonly in inland areas where iodine is not added to salt), the thyroid gland enlarges in an attempt to keep making enough thyroid hormone (which doesn’t do any good because what it’s lacking is the iodine needed to make the hormone). This enlarged thyroid is called a goiter. Laminaria also has an interesting gynecological use. If a woman is scheduled for some medical procedure for which the doctor needs access to the inside of her uterus, often a day or so beforehand, rolled-up, dried pieces of Laminaria are inserted into the opening of the woman’s cervix. As the seaweed absorbs water from her body fluids, it gently and slowly expands, gradually stretching the cervix. Thus, by the time her surgery is scheduled, her cervix has been dilated slowly and gently rather than the doctor having to forcibly and quickly (thus painfully) stretch the cervix open minutes beforehand.
- Division Rhodophyta:
- These are called the “red algae.” They also are multicellular and marine-dwelling, but are more typically found in tropical zones and deeper in the ocean. They also go through alternation of generations, Many of these (such as the Nori used in sushi) are used by humans as food, and are also good sources of iodine.
Fungus-like Protists
- Division Myxomycota:
- These organisms are called “slime molds.” They are fungus-like in their nutrition in that they absorb nutrients from their environment. Their “body” structure is unusual in that the nuclei undergo mitosis, but there is no cytokinesis--there are no individual cells with one nucleus each. Rather, the “body” is a giant, multinucleate mass of cytoplasm. Slime molds are mobile: they move by amoeboid movement, in other words, like a giant Amoeba with giant pseudopodia. They live in decayed wood and move around in between the fibers, ingesting bacteria, etc. by phagocytosis. Slime molds are often brightly-colored (yellow or orange).
- http://biology.clc.uc.edu/courses/bio106/protista.htm
