Some members of Kingdom
are unicellular, others are colonial, and yet others are multicellular. Note that in the colonial forms, all the cells are similar with similar, generalized functions, whereas in the truly
multicellular species, the body of the organism consists of a variety of types of cells, each type with its own specialized function. These organisms are all eukaryotes (they have a true nucleus). They all need some kind of a
water-based environment--which can be fresh or marine water, snow, damp soil, polar bear hairs--in which to live. All are aerobic and have mitochondria to do cellular respiration, and some have chloroplasts and can do photosynthesis. Most
of them reproduce or grow by mitosis, and some reproduce by meiosis and fertilization. Many can form cysts in adverse conditions. Protists are a major component of
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.
These protists are animal-like, especially in their nutrition. They ingest their food by
Some have mouth-like structures into which the prey is put while others use
to move and to engulf prey. Typical prey include bacteria and other smaller one-celled organisms.
An example of a member of this Division is genus
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.
form that causes
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.
- These are all parasites and form tiny, infectious spores. All have complex life cycles. An example is
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 persons liver, and the next stage invades the persons 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.
This Division contains some organisms which are free-living, others which are
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
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 persons cerebrospinal fluid.
An example of an organism in this Division is
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.
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.
- 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
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.
Probably the best-known example of this Division is genus
Each of these organisms has a
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
near their anterior ends. This is not a true eye, in that it
cannot do any image formation, but rather it is a
which senses the light level in the organisms environment.
- 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).
are unicellular and contain an eyespot (stigma), a chloroplast, two flagella, and a nucleus.|
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.|
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).|
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
In living Closterium, each end of the cell bears a small vacuole containing several gypsum grains which dance by Brownian motion.|
are colonial, being organized into long filaments. Each cell contains a spiral chloroplast with pyrenoids (used to store starch) and a nucleus.
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
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
because they produce the gametes (eggs and sperm), which are still 1n. An egg and sperm unite by
increasing the chromosome number from 1n to 2n, and
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.
- 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 doesnt 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 doesnt do any good because what its lacking is the iodine needed to make the hormone). This enlarged thyroid is called a goiter.
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 womans 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.
- 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.
- 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).
Copyright © 1997 by J. Stein Carter. All rights reserved.
This page has been accessed times since 15 Mar 2001.