Most protists are unicellular, microscopic organisms, but a few are complex and multicellular. These are the most diverse (different) organisms according to life cycles, since they reproduce asexually and sexually. This kingdom contains ancestral life-forms that gave rise to three kingdoms of multicellular organisms--the fungi, the plants and animals.
As we talked about the theory of endosymbiosis, we should now be able to understand that early in the development of our planet, scientist feel that prokaryotic organisms were the only forms of life on our planet. As time went on, these organisms were invaded by parasites which eventually lost their ability to live outside the host cell and became organelles of the host. This brought about the Eukaryotic cells. Protist organisms exibit the most basic characteristics of these eukaryotic cells as well as some complex characteristics involved in organisms within the fungi, plant and animal kingdoms. Several features evolved as did the eukaryotic cell. These characteristics that evolved in protist organisms are;
1) Multicellularity- The prokaryotic bacteria are the only groups of organisms which are soley unicellular. Most protist are unicellular but there quit a few groups of multicellular organisms in this kingdom as well.
2) Sexual Reproduction- All prokaryotic organism asexually reproduced which meant that they reproduced an exact copy of the parent organism unless a mutation occured in the offspring. With protist organisms sexual reproduction came about as a form of necessity due to environmental stresses ( ie. lack of nutrition, temp. change, predation. etc.) Sexual reproduction brings about genetic variation without mutation needing to occur due to there being two parent organisms producing offspring.
3) Complex development of the Cilia and Flagella- is another characteristic which evolved in the protist group. In bacteria the flagella were just a single protein filament (basically solid in structure) but in the protist, they had cilia and flagella develop with the 9 & 2 principle. 9 pairs of microtubules surrounding 2 microtubules. A microtubule is a hollow protein filament. These hollow filaments allowed for easier movement and lighter weight, which allowed them greater range of motion in the movement of these structures.
Differences between Cilia and Flagella
a) cilia are short hairlike projections which are used for movement of
either the organism or materials around or through an organism. There are
usually hundreds of these per cell.
b) Flagella are long whiplike structures used primarily for movement (
locomotion). There are usually one or two pair.
4) Eyespots- another characteristic to emerge in
this group is the eyespot which is sensative to the quantity or quality
of light. Some protist are heterotrophic but must reside in a moist
environment. With light comes heat and desication( drying out) so they
must stay away from the light. Others are photosynthetic and aquatic and
need the sun to maintain photosynthesis, so they need to go toward light
sources.
Environments we find protists in.
a) Aquatic - means any place we find water
1) Marine- Saltwater , oceans
2) Freshwater- Lakes, Ponds, & streams
b) Leaf litter or damp places
c) Moist Sand or Soil
d) Body fluids of tissues of organisms
e) Blood streams of organism.
Why do these organisms need to be located in moist
environments?
The reason or answer to this question, is due to the fact that these
organisms do not have any ability to keep moisture in their structure,
like plants which have a cell wall to help retain moisture, and humans
who have skin to keep moisture in so therefore they have to live in a moist
environment.
Reproduction in Protist.
Most protist organisms reproduce asexually as a general
rule. Environmental Stress will cause the organisms to reproduce Sexually.
The 3 basic types of environmental stress that effects all living organisms
is temperature, moisture, and nutrition. Either the lack of or too much
of each of these environmental factors will bring about sexual reproduction
in the protist organisms.
The 3 types of Sexual reproduction are:
1) Conjugation- This process happens between many types of filamentous algae, in which two filamentous algae, while aligned next to each other, will form a conjugation tube between each filament. The tube will extend from one cell in the filament to a cell in the other filament. The haploid nuclei from each cell will travel through the conjugation tube and fuse together, forming a diploid zygote. This diploid zygote will then undergo meiosis to produce 4 haploid cells again which will develop into new filaments and mature.
2) Gamet Production- Here again this usually occurs with filamentous algae, but now there are specialized cells in each filament which produce and hold egg and sperm structures. The sperm are released from one cell in a filament and go through the water to fertilize the egg in a different filament. This will bring about offspring with characteristics from each of the different filaments.
3) Alternation of Generations- IN this reproductive process, there are
two phases to the reproductive life cycle in these algae.
1) Asexually the organism
goes through mitosis to produce diploid or exact replicas of the parent
cells.
2) Sexually the organism
goes through in another phase of its life cycle meiosis which produces
haploid cells.
Protista the Catch All Kingdom
This kingdom is called the catch all kingdom because these organism lack the specific characteristics that would put them into the other three kingdoms, fungi, plant, and animal.
Animals- Are all heterotrophic, multicellular, sexually reproducing organism which only have a cell membrane and no cell wall present.
Plants- Are all autotrophic, multicellular, mostly sexually reproducing( few asexual forms) which have a cell wall made of cellulose and a cell membrane.
Fungi- Are mostly multicellular ( few are unicellular),
heterotrophic, sexually and asexually reproducing organism, with a cell
wall of chitin instead of cellulose like plants
Types of Movement
Protist
Ameboes & Forams
These organisms move by using a process called pseudopodia (false foot).
Pseudopodia are cytoplasmic extension of the cell cytoplasm. The cell membrane of these organisms allows them to change shape. Pseudopodia are formed by a process called cytoplasmic streaming which is the cytoplasm constantly moving, the rest of the cell will follow the pseudopod.
Flagellates- are protist which use flagellas to move. There are 3 major phyla of flagellates.
Dinoflatellates- unicellular, photosynthetic protist, usually with 2 flagella, usually in marine environments, but we do find some in freshwater. Some dinoflagellates produce toxins (poisons). Red Tide is a phenomena that occurs when there is a rapid population increase in these protists and as aquatic organisms or humans consume them, they too become poisoned with the toxin. Some are bioluminescent which means they produce a light as they live that is given off.(Like Fireflys) Introduction to the Dinoflagellata
Zoomastigotes- unicellular, heterotrophic, protist with at least one flagellum. Trychonympha is a zoomastigote that live in the gut of termites where they provide the enzymes that digest wood. Trypanosomes are zoomastigotes are dangerous pathogens in humans and domestic animals.
Euglenoids- are freshwater
protist with 2 flagella. 1/3 of these are photosynthetic, the rest are
heterotrophic, the euglena is the common example we use in study in biology.
Ciliates- are protists that have cilia for swimming. The paramecium is the common example used in study of biology and have large numbers of rows of cilia surrounding their cell surface.
Protist Diversity
We have already talked about the amoebas which are unicelluar and very
simply constructed organisms.There are several others we need to mention
to show how different various protist are.
Diatoms- Are more commonly found in Lakes & Oceans. These organisms have a shell composed of Silica. Silica is a material that is made into many products, such as glass and other materials. As diatoms reproduce asexually their shell continues to get progressively smaller. Eventually they outgrow their shell and discard it. As discarded shells setttle to the bottom of the aquatic floor, they form a layer of earth called diatomaceous earth, which is mined for the silica. This material is used commercially as an abrasive in cleaners like toothpaste and also used as the reflecting material found in roadway marking paint.
The Algae- are a group of photosynthetic organisms and are seperated into three groups. Red, Green and Brown Algae
Phylum Chlorophyta- Green Algae, the phylum name comes from the pigment they have which traps the suns energy called chlorophyll. There are several types of chlorophyll, but green algae have Chlorophyll A & B which is the same pigment that plants have, which is why scientist feel that green algae is the direct descendant of plants.This type of algae is found in shallow waters.
Phylum Rhodophyta- Red Algae, contains the pigment phycobilins, which traps the green, violet, and blue light waves of sunlight. These light waves penetrate the deeper waters, so we find red algae in deeper waters.
Phylum Pheophyta- Brown Algae- these are all multicellular and
mostly marine, Kelp is the common example used when discussing this group,
since this is a commonly noticed algae, even though many mistake it as
a plant. Kelp have a unique air bladder system in their stems which will
cause the plant to grow toward the surface so as much light can be absorbed
as possible.
Protist Diseases
The Disease
African Trypanosomiasis
Control
Lishmaniasis Control
Chagas Disease Elimination