Diversity Lab: Protists

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Protist diversity of habitat

protists are found almost everywhere there is water, including oceans, freshwater, damp soils, in the moisture of the atmostphwere, and in the tissues of other organisms

Protist diversity of form

most protists are unicellular, but there are also many examples of colonial, filamentous, and multicellular forms; multicellular forms include the "seaweeds"; some protists have bizarre "coenocytic" form that consists of a single large cell with numerous nuclei

Protist diversity of nutrition

protists are often grouped based on their modes of nutrition; "algae" represent the "plant-like" protists that are photosynthetic autotrophs; "seaweeds" are the large, multicellular marine algae; "protozoa" are the "animal-like" protists, because they are heterotrophs that ingest their food or use food vacuoles; there are also "fungus-like" heterotrophic protists that are important decomposers; many protists are parasites; there are even protists that can be either "plant-like" or "animal-like" depending on the conditions

Protist diversity of motility

some protists lack motility, and are either attached to a substrate with holdfast (ex: seaweeds), or float in water currents (and are part of the plankton); others do have specialized structures for movement, including flagella, cilia, and pseudopodia (extensions of the cytoplasm)

Protist diversity of life cycles

in addition to asexual reproduction, which is very common among protists, a variety of sexual life-cycles are represented; all sexual life-cycles include meiosis and fertilization; life-cycles vary as to the timing of these events and the extent of the haploid and diploid phases within the life cycle; sexual life-cycles can be broadly grouped into the following types: haploid dominant with zygotic meiosis, diploid dominant with gametic meiosis, and alternation of generations with sporic meiosis

Haploid dominant, with zygotic meiosis (protists)

the dominant phase of the life cycle is haploid; the zygote is the only diploid stage of the life-cycle; it undergoes meiosis to produce haploid cells

Diploid dominant, with gametic meiosis (protists)

this is the life cycle found in humans; the dominant phase is diploid; gametes are produced by meiosis, and represent the only haploid phase of the life-cycle

Alternation of generation, with sporic meiosis (protists)

a life cycle with an alternation between a multicellular haploid phase (gametophyte) and a multicellular diploid phase (sporophyte); meiosis produces haploid spores; this is the life cycle found in plants; when teh gametophyte and sporophyte are alike in appearance, we say there is an isomorphic alternation of generations; a heteromorphic alternation of generations is when teh two multicellular stages differ in apperance


the animal-like protists, because they are heterotrophs that ingest their food or use food vacuoles

Isomorphic alternation of generations

when teh gametophyte and sporophyte are alike in apperance

Heteromorphic alternation of generations

when the two multicellular stages differ in apperance

The life cycle of the brown alga Laminaria: an example of alternation of generations

the sporophytes are usually found in water just below the line of the lowest tides, attached to rocks by branching holdfasts; cells on the surface of the blade develop into sporangia; sporangia produce zoospores by meiosis; the zoospores are all structurally alike, but about half of them develop into male gametophytes and half into female gametophytes; the gametophytes are short, branched filaments that growon subtidal rocks; male gametophytes release sperm, and female gametophytes produce eggs, which remain attached to the female gametophyte; eggs secrete a chemical signal that attracts sperm of the same species, thereby increasing the probability of fertilization in the ocean; sperm fertilize the eggs; the zygotes grow into new sporophytes while attached to the remains of the female gametophyte; the cycle restarts


in organisms (plants and some algae) that have alternation of generations, the multicellular diploid form that results from teh union of gametes; the sporophyte produces haploid spores by meiosis that develop into gametophytes


a multicellular organ in fungi and plants in which meiosis occurs and haploid cells develop


flagellated spore found in chytrid fungi and some protists


in organisms (plants and some algae) that have alternation of generations, the multicellular haploid form that produces haploid gametes by mitosis; the haploid gametes unite and develop into sporophytes


is part of the gymnamoeba group; they have rather thick, lobed psudopodia; they do not reproduce sexually, and do not undergo meiotic divisions; the gymnamoebas are free-living unicellular protists in marine and freshwater, or even in damp soils

Brown algae

most are large, complex, multicellular "seaweeds"; they are common in temperate and colder waters, including those off california; they exibit a variety of life-cycles, including alternation of generations that may be heteromorphic or isomorphic;

Brown algae importance

they can form large kelp forests that provide habitat and food for a number of other species, including fish and sea lions; the cell walls are composed of cellulose and algin, a gelatinous material that makes them feel slippery and slimy; algin is used commercially as a thickening agent in puddings, ice creams, and even cosmetics; includes a holdfast, stipe, flotation bladders, and blades


a rootlike structure that anchors a seaweed


a stemlike structure for seaweed; support the blades


a leaflike structure of a seaweed that provides most of the surface area for photosynthesis


they are sometimes refereed to as little "glass houses" because of the silica cell walls, which fit together like a lid and a box; when diatoms die, their silica skeletons can form large deposits of diatomaceous earth, which is mined for various uses including for swimming pool filters; many resemble beautiful jewelry

Importance of diatoms

the most important component of phytoplankton, and as such contribute substantially to the primary productivity of the oceans; in other words they form the base of many food chains ("plankton" refers to small organisms that drift in the water currents; phytoplankton refers to the photosynthetic members of plankton, as opposed to the heterophic zooplankton)


heterotrophic or photosynthetic organisms that obtained thier chloroplasts through secondary and even tertiary endosymbiosis; some release toxins, and when present in large quantities, as in the so-called "red tides", they can cause massive fish and invertebrate kills; they are characterized by cellulose plates of "armor" and by two flagella oriented in perpendicular grooves, one of which forms a girdle around the cell; they often spin when they swim

Dinoflagellates importance

these primarily marine organisms are an important component of phytoplankton; they also form symbiotic relationships with the corals of coral reefs


these unicellular organisms can move and carry on photosynthesis; many are capable of both autotrophic and heterotrophic nutrition, and would thus be considered mixotrophs; they move quickly with their flagella; you should be able to see their chloroplasts, and a red eyespot used to detect light


these mostly marine organisms have porous shells made of calcium carbonate, so they are chalky rather than glassy in appearance; like radiolarians, they are a type of amoeba with thin, thread-like cytoplasmic extensions used to capture prey; because foram fossils are quite abundant, they are commonly used as index fossils; often teh shells of forams have a helical, snail-like shape

Green algae

includes chlorophytes, and charophyceans; they are thought to be the group from which the plants evolved; they have chlorophyll a, chlorophyll b and carotenoids as their photosynthetic pigments, just like plants; they also store carbohydrates as starch and have cell walls composed of cellulose, just like plants; most live in fresh water, but there are also marine species, including some "seaweeds"; the group includes unicellular forms, filamentous forms, colonial forms such as volvox, coenocytic forms, and multicellular members; a familiar multicellular form found in california coastal waters is ulva, or sea lettuce


a member of the "ciliates" group, which moves by means of cilia; this is probably the most familiar representative of this group; these are "animal-like" heterotrophs that ingest food into food vacuoles; many members of this group achieves an astonishing degree of complexity within the limits of unicellularity


all members of the apicomplexan group to which plasmodium belongs are parasites and have complex life cycles, often involving several hosts; by far the most important ones to humans are in teh genus plasmodium, which includees species which cause malaria

The two-host life of Plasmodium, the apicomplexan that causes malaria

an infected anopheles mosquito bites a person, injecting plasmodium sporozoites in its saliva; the sporozoites enter the person's liver cells; after several days, the sporozoites undergo multiple divisions and become merozoites, which use their apical complex to penetrade red blood cells; the merozoites divide asexually inside the red blood cells; at intervals of 48 or 72 hours (depending on the species), large numbers of merozoites break out of the blood cells, causing periodic chills and fever; some of hte merozoites infect other red blood cells; some merozoites form gametocytes; another anopheles mosquito bites the infected person and picks up plasmodium gametocytes along with blood; gametes form from gametocytes; each male gametocyte produces several slender male gametes; fertilization occurs in teh mosquito's digestive tract, and a zygote forms; an oocyst develops from the zygote in the wall of the mosquito's gut; the oocyst releases thousands of sporozoites, which migrate to teh mosquito's salivary gland; the cycle continues


"amoebas" are organisms that move by extending their cytoplasm outward in structures called pseudopodia; the group of organisms we used to refer to as amoebas turns out to be polyphyletic; radiolarians and foraminefera are types of amoebas that are closely related to each other, but not to other types of amoebas; the pseudopodia of radiolarians are thin, thread-like cytoplasmic extensions called axopodia; axopodia, which are reinforced by microtubules, are used to capture and ingest prey by phagocytosis; when you observe radiolarians under the microscope, their beautiful silica shells look like fine pieces of crystal

Red algae

another group of "seaweeds"; they can be large, but not as large as the giant brown algal kelps; some can live at great depths because their non-chlorophyll, accessory pigments (called phycobilins) can use the blue light which is the only light that penetrates to those depths; their cell walls contain the slimy compounds agar and carageenan in addition to cellulose; these products are used as thickeining agents (as are the cell wall components of brown algae); agar is also used in microbiology and molecular labs to grow bacteria; red algae are more characteristic of tropical waters than are the brown algae

Slime molds

were traditonally placed in kingdom fungi, but this classification causes difficulties because, whereas slime molds are phagocytic like protozoa, fungi are never phagocytic but obtain their nutrition by absorption; characteristics other than feeding mode, including cellular ultrastructure, cell wall chemistry, and molecular studies, suggest that slime molds fit better with the amoebozan protists than with fungi; slime molds play an important role as decomposers, as do fungi; there are two tipes of slime molds, plasmodial slime molds and cellular slime molds

Cellular slime molds

they spend part of their life cycle as unicellular organisms, but when food is scarce these unicells congregate to form a multicellular fruiting body for reproduction; this structure is at that blurry boundary between being a colony and being a multicellular organism

Plasmodial slime molds

(usually brightly colored, often yellow or orange) the vegetative stat is called plasmodium, and consists of a multinucleate mass of protoplasm totally devoid of cell walls (coenocytic); this mass feeds on bacteria as it creeps along the surface of moist logs or dead leaves; when conditions are right, it is converted into one or more reproductive structures, called fruiting bodies, that produces spores;


like paramecium, this genus is a member of the "ciliates" group, which move by means of cilia, and ingest food with food vacuoles; stentor individuals have a pretty blue color; individuals may be compactly coilded, or may stretch out into a bugle-like shape


(flagellated protozoans) parasitic creatures that cause sleeping sickness in humans; they move with an undulating membrane and flagellum; is part of a group that also includes the cellulose-digesting endosymbionts in termite guts


a genus of filamentous green algae, named for the helical or spiral arrangement of the chloroplasts that is diagnostic of the genus


(green algae) a thin flat green alga growing from a discoid holdfast. The margin is somewhat ruffled and often torn


is one of the best-known chlorophytes and is the most developed in a series of genera that form spherical colonies. Each mature Volvox colony is composed of numerous flagellate cells similar to Chlamydomonas, up to 50,000 in total, and embedded in the surface of a hollow sphere or coenobium containing an extracellular matrix made of a gelatinous glycoprotein.

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