external image paramecium1.gif

-Jesse Landy
Kingdom Protista
The kingdom protista is one that is open to much debate. Many systematists would like to split this one kingdom into many different ones. As of right now, it consists of single celled eukaryotes, cells with a nucleus and organelles that are enclosed in membranes and are present in protists, fungi, plants, and animals, and some simple multicellular forms, that seem related. The kingdom protista became the place where many systematists put the rest of the organisms that did not quite fit the description of the other kingdoms. There are some protists that are less related than plants are to animals. They vary in structure and function more than any other kingdom. There are about 60,000 known unicellular protists. These cells are the most complex of any other cell and are actually analogous to any cell in a human or any other multicellular organism. The cell in a protist is about as complete an organism than an entire plant of animal. [Some protists are considered colonial, meaning that they have more than one cell, but these cells are similar in appearance and in function. Colonial protists differ from actually defined multicellular organisms because their cells do not perform different functions associated with specific types of cells. According to the Colonial Theory developed by Haekel in 1874, colonial cells work together (symbiosis) to form a multicellular organism. (BY)] [A theory suggests that the organelles of protists descended from earlier bacteria that symbiotically lived within other bacteria cells.This theory would help explain the evolutionary shift from prokaryotic cells to early eukaryotic cells. (APS)]
[Protists are usually classified by how they acquire energy. They are grouped in one of the following classifications:
- Photosynthetic Autotroph (make their own food by using light energy to create glucose)
- Chemosynthetic Autotroph (make their own food by obtaining energy from the breakdown of chemicals)
- Heterotroph by ingestion (eat by consuming food; food is digested by enzymes and released throughout the body)
- Heterotroph by absorption (eat by secreting digestive enzymes outside of their bodies, then absorbing the nutrients into their bodies) (SW)]


Anatomy of a Protista (Ali Kirsch)protista.jpg

Common Forms of Protists

àDiplomonadida and Parabasala
These protists are placed on the phylogenic branch that branched the earliest in eukaryotic history. These protists don’t have mitochondria, which many biologists claim they lost during evolution. Instead they rely upon endosymbiotic bacteria for respiration. Diplomonads are organisms are relatively simple, with few organelles (no plastids or mitochondria). They do have multiple flagella, for movement, and two separate nuclei. Parabasala is a type of protist designed for movement, having both flagella and an undulating body, designed for movement, usually along mucus covered skin. Both of these protists have species that are famous parasites like Giardai lamblia (diplomonads) and Trcichomonas vaginalis (parabasalid).

This clade of protists is comprised of two groups, euglenoids and kinetoplastids. Euglenoids are easily distinguished by a pocket in the front that house one or more flagella. They are also known for their use of paramylon, a glucose polymer whose main function is storage. Most euglenoids are autotrophic, but there are a few that are mixotrophic or heterotrophic. Kinetoplastids contain an extra large mitochondria, along with an organelle called a kinetoplast. The kinetoplast holds extra DNA, allowing this symbiotic organism to cloak itself, preventing immunity from forming. Euglenoids have a stigma, which is a photoreceptor otherwise known as an "eye spot." It is not a
Euglena (LS)
Euglena (LS)
real eye, but it enables the organism to react to light in the environment. (KTD)

Alveolata is comprised of three different groups of protists: dinoflagellates, apicomplexans, and ciliates. Alveolata gets its name from the small membrane bound cavities under its surface, called alveoli. Dinoflagellates are flagellates, which helps them move in their usually aquatic environments. They are major parts of phytoplankton population in the ocean, which supports most of the marine food-web. They are especially important to the food-web in reef communities because they live in mutualistic cymbiosus with the cnidarians and provide most of the primary production. They are not all autotrophic though; there are a few species that are heterotrophs. They are also not always unicellular, some live in colonial forms. Each species has a special shape, which is often reinforced by plates of cellulose. Two flagella come from the perpendicular-creases in the cellulose, propelling it. Dinoflagellates are known to cause red tides because of the xanthophylls pigment in their plastids. These red tides are dangerous to all other life in the water because of the toxins released at this time. Some dinoflagellates are even bioluminescent, using an ATP reaction to give off light and bring in the predators of their predators.
Apicomplexans are all parasites of animals, circulating small cells called sporozoites. The sporozoite contains intricate organelles on one end, whose only job is to burrow into the host cell. They rely on both sexual and asexual means of reproduction and require two or more host species for completion.
Ciliophora are aptly named because of their reliance on cilia to move and feed. They use a submembrane system of microtubules to coordinate the movement of thousands of cilia. Some are completely covered by cilia, while other are have just clusters or rows of them. They are among the most complex of cells. They have two types of nuclei; a large macronucleus that controls the day-to-day, and 1-80 micronuclei that are only involved in the sexual process that is required for genetic variation. The macronucleus takes care of the actual reproduction, using binary fission, where it elongates and splits (no mitosis), while the micronucleus is responsible for conjugation, the sexual shuffling of genes.

Stramenopila contains both heterotrophic and photosynthetic protists. Stramenopila refers to the hairy flagella that is characteristic of many of these organisms. These organisms are only reproductive in their flagellated state.
Oomycota is a group of protists including water molds, white rust, and downy mildews. Most of them are unicellular, but they do have hyphae, which are branching filaments (analogous to fungi) that are multinucleated. Oomycota shares many traits with fungi, though it is not one; for instance, they both have a filamentous body structure with a large surface area, allowing for greater absorption of nutrients. This trait evolved through convergent evolution with fungi. Most oomycota live in groups on dead algae and animals in fresh water, but some are parasites that live in the gills and on the flesh of injured fish. White rust and downy mildews are terrestrial, living on land as plant parasites. They reproduce through wind-blown spores. Oomycota is also referred to as “egg-fungi” because when it reproduces, a large egg is fertilized by a small sperm nucleus, forming relatively strong zygotes.
Heterokont Algae is the most photosynthetic taxa, containing three subgroups: Bacillariophyta, Chrysophyta, and Phaeophyta. Bacillariophyta (a.k.a. diatoms) is a yellow/brown organism that is housed by glass-like walls made of hydrated silica. Diatoms usually reproduce by mitotic cell division, where each daughter cell gets half of the wall; sexual reproduction is pretty rare. Diatoms can be found in both fresh and ocean water, and are found in incredibly high numbers, though they are microscopic. Chrysophyta (a.k.a. Golden Algae) is a biflagellated cell found in freshwater and marine plankton. It is usually an autotroph, but there are some mixotrophs that perform phagocytosis near the end of their flagella. They are mostly unicellular; however, there are some colonial ones. Phaeophyta (a.k.a. Brown Algae) is entirely multicellular and usually found in the cool waters along temperate coasts. Most seaweed is brown algae, and it is the most complex protisit.

Rodophyta also know as red algae is unique for not have any flagella. Red algae draws its names from pigments called phycobilins, which allow some species to receive the little light that penetrates down to deep water. Their color does change though, according to water depth. They are most often found in warm coastal waters in tropical oceans. Some seaweed is also considered red algae, though it is far more branched and
Common types of rhodophyta
Common types of rhodophyta
considerably smaller. Red algae relies upon ocean currents to bring gametes together, and alternation of generation is very common in Red algae. [Red algae are important builders of limestone reefs. The earliest such coralline reefs are known from the Cambrian period. There are alos calcite crusts which have been identified asthe remains of coralline red algae dating back to the terminal Proteozoic. RS]

à Chlorphyta
Chlorophyta or “green algae” is named for the chloroplast in the cells, giving it a green color. It is considered very similar to plants, and some systematists are considering moving some species into the plant kingdom. Almost always found in water, usually fresh water, but also marine ecosystems, snow, damp soil, and even in other eukaryotes.
Snow Algae are a type of photosynthetic protist that grow in deep and consistant snow banks. There are about 350 species of snow algae, which color the snow around them green, red, or orange. Snow algae is a source of speculation because it is able to grow in very cold, "sunblasted" environments with little access to nutrients.(DRM) Scientists have discovered that because snow algae can adapt so well to acidic environments, the amount of snow algae present can be used to measure the presence of acid rain in an area.(JAS)
Chlorphyta can live in lichens, or groups that live symbiotically with fungi. They can be filamentous and can be found in “pond scum” and some are also considered seaweed. They have both sexual and asexual reproductive stages and produce biflagellated gametes, though some conjugate.
This green algae is chock full of chlorophylls a and b (KNS).

àProtists that use Pseudopodia
Protists that use pseudopodia are of much debate. Little is know of their evolution and they are not listed in the phylogenetic tree.Some eukaryotes move and feed themselves using pseudopodia. They are usually heterotrophs who eat bacteria, other protists, and detritus. Rhizopoda is also known as Amoebas they are unicellular and use microtubules and microfilaments to aid their movement. They are usually free living and are found in both fresh and marine environments. Some secrete shells around themselves, while others do not. None of them have flagella, cilia, or meiosis. (JJF) Actinopoda are organisms that use a smaller pseudopodia called axopodia, which uses a bundle of microtubules and thing layer of cytoplasm. Most of them are panktonic and their large surface area helps them float and feed. There are two kinds of actinopoda, heliozoans, with a glassy skeleton, and radiolarian with a skeleton that is fused into one delicate piece. Forminifer, the third and final protist that uses pseudopodia, is a marine organism with a multi-chambered shell that attaches itself to rocks and algae. It has strands of cytoplasm that go through the pores in its shell that let it swim and feed.

Mycetozoa is taxa that one day may become its own kingdom. It has an analogous resemblance to fungi, and uses pseudopodia for movement. It is very close to fungi and animalia in the eukaryotic tree. The two main types of Mycetozoa are myxogastrida and dictuostelida. Myxogastrida is also known as plasmodial slime mold. It is heterotrophid, feeding during its plasmodium stage. It becomes a massive cell, performing mitosis over and over without ever performing cytokenisis. Dictostelida is also known as cellular slime mold. It is a solitary cell when feeding, but when the food is used up; a community of cells gets together and functions as one unit together. The produce asexually and are haploids, with no flagellated stage.

A plasmodial slime mold (JM)
A plasmodial slime mold (JM)

Protists move by either one of three modes of transportation. Most organisms use either flagella or cilia at one point in their lives, but there are some organisms that use pseudopodia. Flagella and cilia are pretty similar; both are attached to the cell surface and are extensions of the cytoplasm via microtubules. The major difference between the two is that cilia tend to be smaller and more numerous. Pseudopodia is a form of cellular extension that is used for both movement and feeding. Organisms that use pseudopodia are usually heterotrophs, and their definition as protists is often questioned.

Flagella - most often involved in locomotion

1. Whiplash - without appendages
2. Tinsel - has appendages (barbs)
3. Vary in number, size and/or position, e.g. anterior, posterior, lateral. Flagella may be present only in reproductive cells or not at all. {RS}

Protists are the most nutritionally diverse of all eukaryotes. Protists can be autotrophs, using chloroplast for photosynthesis, heterotrophs, or even mixotrophs, organisms that combine photosynthesis and predation. Heterotrophic protists are called protozoa while photosynthetic protists are called algae, a combination of aquatic plants and protists. Because of the difference in diet, nutrition is not a reliable means of determining taxa. [The process by which predacious protists ingest their food is by phagocytosis (shown in the video below). This means that they surround thier prey until they form a vacuole around their prey and can begin to eat it. Some protists use psuedopodia in their mouth like structures to aid in surrounding their prey. (DG)]

Watch as amoeba cell engulfs a small flagellate chilomona:

Life Cycle and Reproduction
Almost all protists undergo some for of mitosis at one point in their lifespan. Some produce only asexually, while others sexually reproduce, and others use conjugation, genetic shuffling, followed by asexual reproduction. The ones that reproduce asexually use binary fission, which is when the cell body is basically pinched into two halves and seperate, forming two new "daughter" cells. (LD)Conjugation allows for genetic diversity, and can most obviously be seen in Ciliophora. Protists also practice alternation of generation, which is when each generation trades off being haploid and diploid. The diploid generation is called the sporophyte, because it produces spores for reproduction, and the haploid generation is called gameophyte. Spores develop into gameophytes, which in turn produce gametes, which join together (syngamy) and form a diploid zygote. Some of the generations are Heteromorphic, where each generation looks different, while others are Isomorphic, when each generation looks the same, only has a different number of chromosomes. At some point in its life, many protists will form cysts, or resistant cells that can survive harsh conditions.
Most protists live in aquatic ecosystems, but can be found almost anywhere there is water, like in damp soil, leaf litter, and anything else moist. They are also known to be found in bodily fluids, tissues, or cell hosts.They are usually bottom dwellers and attach themselves to rock and the ground. Are members of the phytoplankton community, made up eukaryotic algae and prokaryotic cynobacteria, which accounts for one half of the primary production of organic material.
Review Questions:
Explain the role of the flagellum and cilia in protists' locomotion(Walker K.).
Describe the differences among protists that cause scientists to question the continued use of the kingdom, including examples of locomotion, reproduction, and diet. (SF)
Describe conjugation and explain how it contributes to genetic variation among protists. (AZ)
What is the advantage of reproducing through conjugation? (AS) (KTD) [BY] (DG) [BY]
(APS) (AG) (Liz Daley) (Ali Kirsch) (KNS) (Sara Waugh) Schwartz)
(Jake Schwartz) (JAF) (Jackson Murphy) (JJF) (Donna McDermott)