Ch 28 Protists Flashcards
protists
Protists are a polyphyletic assortment of mostly unicellular (or they are multicellular without specialized tissues; this simple cellular organization distinguishes the protists from other eukaryotes, such as fungi, animals and plants, although some fungi and animals are also unicellular) organisms that account for the bulk of eukaryotic diversity. Much of this diversity is unseen, evident only from small subunit ribosomal RNA gene sequences extracted from environmental samples, used to redefine this group in modern taxonomy as diverse and often distantly related phyla. Furthermore, novel species and unexpected diversity from every major protist group continue to be identified from diverse environments. In current views of eukaryotic phylogeny, these protist groups are combined, together with metazoans and fungi, into six major eukaryotic clades that are thought to be descended from an ancestral diversification and radiation of the earliest eukaryotic organism(s) around 1–1.5 Ga years ago. There have been attempts to remove the kingdom from modern taxonomy but it is still very much in use. The group of protists is now considered to mean diverse phyla that are not closely related through evolution and have different life cycles, trophic levels, modes of locomotion and cellular structures. Besides their relatively simple levels of organization, the protists do not have much in common.
how close are the evolutionary ties amongst varying protist?
Genetic and morphological studies have also shown that some protists are more closely related to plants, fungi, or animals than they are to other protists. As a result, the kingdom in which all protists once were classified, Protista, has been abandoned, and various protist lineages are now recognized as kingdoms in their own right. Most biologists still use the term protist, but only as a convenient way to refer to eukaryotes that are not plants, animals, or fungi.
what is generally meant by the modern definition of protists
The kingdom in which all protists once were classified, Protista, has been abandoned, and various protist lineages are now recognized as kingdoms in their own right. Most biologists still use the term protist, but only as a convenient way to refer to eukaryotes that are not plants, animals, or fungi.
Aside from compartmentalisation and a nucleus, what is a major difference between prokaryotes and eukaryotes?
Eukaryotic cells have a well-developed cytoskeleton that extends throughout the cell. The cytoskeleton provides the structural support that enables eukaryotic cells to have asymmetric (irregular) forms, as well as to change in shape as they feed, move, or grow. In contrast, prokaryotic cells lack a well-developed cytoskeleton, thus limiting the extent to which they can maintain asymmetric forms or change shape over time.
(Shown: green for microtubules and reddish orange for microfilaments. A third component of the cytoskeleton, intermediate filaments, is not evident here. Blue color tags the DNA in the nucleus.)
how many eukaryortes are considered protists?
the organisms in most eukaryotic lineages are protists, and most protists are unicellular.
describe the difference between a protist and a metazoan
Many protists are very complex—the most elaborate of all cells. In multicellular organisms, essential biological functions are carried out by organs. Unicellular protists carry out the same essential functions, but they do so using subcellular organelles, not multicellular organs. The organelles that protists use include the nucleus, endoplasmic reticulum, Golgi apparatus, and lysosomes. Certain protists also rely on organelles not found in most other eukaryotic cells, such as contractile vacuoles that pump excess water from the protistan cell.
describe protistian nutrition
Some protists are photoautotrophs and contain chloroplasts. Some are heterotrophs, absorbing organic molecules or ingesting larger food particles. Still other protists, called mixotrophs, combine photosynthesis and heterotrophic nutrition. Photoautotrophy, heterotrophy, and mixotrophy have all arisen independently in many different protist lineages.
what does nutrition say about the evolutionary lineage of a protistan?
nothing, photoautotrophy, heterotrophy, and mixotrophy have all arisen independently in many different protist lineages
what types of sexual cycles can protists complete?
All three basic types of sexual life cycles are represented among protists, along with some variations that do not quite fit any of these types. The common feature of all three cycles is the alternation of meiosis and fertilization, key events that contribute to genetic variation among offspring. The cycles differ in the timing of these two key events.
are more eukaryotes unicellular or multicelluar?
the organisms in most eukaryotic lineages are protists, and most protists are unicellular.
mixotroph
a combination of photoautotrophic and heterotrophic nutrition
do all protists reproduce sexually?
No, some protists are only known to reproduce asexually; others can also reproduce sexually or at least employ the sexual processes of meiosis and fertilization. All three basic types of sexual life cycles are represented among protists, along with some variations that do not quite fit any of these types.
list two common examples of endosymbiosis
mitochondria, plastids (other answers possible)
plastid
The plastid (pl. plastids) is a major double-membrane organelle found, among others, in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell. They often contain pigments used in photosynthesis, and the types of pigments present can change or determine the cell’s color. They have a common origin and possess a double-stranded DNA molecule, which is circular, like that of prokaryotes.
In normal intraspecific crossings (resulting in normal hybrids of one species), the inheritance of plastid DNA appears to be quite strictly 100% uniparental. In interspecific hybridisations, however, the inheritance of plastids appears to be more erratic. Although plastids inherit mainly maternally in interspecific hybridisations, there are many reports of hybrids of flowering plants that contain plastids of the father.
Plastids are thought to have originated from endosymbiotic cyanobacteria. The symbiosis evolved around 1.5 billion years ago and enabled eukaryotes to carry out oxygenic photosynthesis. Three evolutionary lineages have since emerged in which the plastids are named differently: chloroplasts in green algae and plants, rhodoplasts in red algae and muroplasts in the glaucophytes. The plastids differ both in their pigmentation and in their ultrastructure.
which evolved first, mitochondrial or plastidic eukaryotic endosymbiosis?
evidence suggests that mitochondrial endosymbiosis evolved before plastidic endosymbiosis, thus a defining moment in the origin of eukaryotes occurred when a host cell (likely an archea or archeal divergent “protoeukaryote”) engulfed a bacterium that would later become an organelle found in all eukaryotes—the mitochondrion
where did mitochondria originate from and how many times did this occur?
Mitochondria arose from an alpha proteobacterium. Results from mtDNA sequence analyses also indicate that the mitochondria of protists, animals, fungi and plants descended from a single common ancestor, thus suggesting that mitochondria arose only once over the course of evolution. Similar analyses show that plastids arose once from an engulfed cyanobacterium.
where did plastids originate from and how many times did this occur?
Studies of plastid-bearing eukaryotes suggest that plastids evolved from a single gram-negative cyanobacterium that was engulfed by an ancestral heterotrophic eukaryote (primary endosymbiosis). That ancestor then diversified into red algae and green algae, some of which were subsequently engulfed by other eukaryotes (secondary endosymbiosis). Primary endosymbiosis occurred once, secondary endosybiosis occurred multiple times.
explain the diversity of plastids produced by endosymbiosis
Studies of plastid-bearing eukaryotes suggest that plastids evolved from a single gram-negative cyanobacterium that was engulfed by an ancestral heterotrophic eukaryote (primary endosymbiosis). That ancestor then diversified into red algae and green algae, some of which were subsequently engulfed by other eukaryotes (secondary endosymbiosis). Primary endosymbiosis occurred once, secondary endosybiosis occurred multiple times.
how many times did secondary endosymbiosis of plastids occur?
multiple times
how many times did primary endosymbiosis of plastids occur?
once
chlorarachniophytes
[archaeplastidia>chloarachniophytes] have a single, large plastid (seconary endosymbiont) that contains a nucelomorph, the vestigial nucleous of a green algae (primary endosymbiont).
nucleomorph
Protists known as [archaeplastidia>chlorarachniophytes] likely evolved when a heterotrophic eukaryote engulfed a green alga. Evidence for this process can be found within the engulfed cell, which contains a tiny vestigial nucleus, called a nucleomorph. Genes from the nucleomorph are still transcribed, and their DNA sequences indicate that the engulfed cell was a green alga.
excavata
Originally proposed based on morphological studies of the cytoskeleton, some members of this diverse group have an “excavated” feeding groove on one side of the cell body. The supergroup and its three subgroups are all individually monophyletic:
[Excavata>Diplomonads]
[Excavata>Parabasalids]
[Excavata>euglenozoans>kinetoplastids]** /** [Excavata>euglenozoans>euglenids]
categorise the phylogeny of kinetoplastids
[Excavata>euglenozoans>kinetoplastids]
categorise the phylogeny of euglenids
[Excavata>euglenozoans>euglenids]
diplomonads
[Excavata>diplomonads] : monophyletic subgroup of the supergroup excavata, lack plastids and have reduced mitochondria that lack functional electron transport chains and hence cannot use oxygen to help extract energy from carbohydrates and other organic molecules, termed mitosomes. Most diplomonads are found in anaerobic environments. Best known example is Giardia intestinalis, parasitic to intestine of mammals.
parabasalids
kinetoplastids
euglenozoans
(shown a flagellum cross section: the rod lies alongside the 9 + 2 ring of microtubules found in all eukaryotic flagella)
euglenids
[Excavata>euglenozoans>euglenids], a monophyletic clade within subgroup euglenozoans (which are excavates that have a special spiral or crystalline rod of unknown function inside their flagella) have a pocket at one end of the cell from which one or two flagella emerge, many are mixotrophs, others use phagocytosis.
what does the SAR clade stand for?
stramenophiles, alveolates, rhizarians
what does the “s” group in the SAR supergroup stand for, and what are its subgroups?
[SAR clade>stramenopiles] (from the Latin stramen, straw, and pilos, hair) (have a “hairy” flagellum paired with a “smooth” flagellum. An alternative name they are known by is Heterokonts – meaning two different flagella)
Subgroups include diatoms, golden algae, and brown algae.
diatoms
[SAR clade>stramenopiles>diatoms] are mostly unicellular with shells containing silica. These outer shells have a box-within-box structure. They are classified as an algae because they do photosynthesis which use Chlorophyll a & c as well as accessory pigments carotenoids. They store their food as a chrysolaminarin. The only evidence of flagella are seen in the gametes.
golden algae
[SAR clade>stramenopiles>golden algae] are mostly unicellular, biflagellate algae that can be found in both freshwater and marine environments. They have chlorophyll a & c as well as an accessory pigment: fucoxanthin (carotenoid). They store their food as oil. Golden algae are a type of stramenophile, from the SAR supergroup.
brown algae
[SAR clade>stramenopiles>brown algae] (Phaeophytes): multicellular seaweed commonly referred to as kelp and are ecologically important in cooler ocean waters. Like most members, they have chlorophyll a & c with an accessory pigment – fucoxanthin (carotenoid). They store their food as a laminarin (starch). The only evidence of flagella are seen in their gametes. Brown algae cell walls contain: alginic acid, a colloidal product used for thickening, suspending, stabilizing, emulsifying and gel-forming. It can be found in dairy products, adhesives, digestive aids and textiles.
compare and contrast bown algae, golden algae, and diatoms
All are [SAR clade>stramenophiles], have chlorophyll a & c and carotenoids, mostly found in marine environments.
Diatoms and brown algae are only flagellate in gametes, golden algae are biflagellate.
Diatoms and golden algae are mostly unicellular, while brown algae is multicellular.
Diatoms store food as chrysolaminarin, golden algae store food as oil, brown algae store their food as laminarin (starch).
alternation of generations is also called what?
In sporic meiosis (also known as alteration of generations), the zygote divides mitotically to produce a multicellular diploid sporophyte (2n). The sporophyte creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes. The gametophytes (n) produce gametes via mitosis. In some plants the gametophyte is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the “dominant” stage of the life cycle.
- Isomorphic generations* refer to organisms in which the sporophytes (2n) and gametophytes (n) look similar to each other, although they differ in chromosome number.
- Heteromorphic generations* refer to organisms in which the sporophytes (2n) and gametophytes (n) are structurally different.
This type of life cycle is called a haplodiplontic life cycle. It differs from our own diplontic life cycle, in which only the gametes are in the haploid state.
(brown algae Laminaria shown)
sporic meiosis
In sporic meiosis (also known as alteration of generations), the zygote divides mitotically to produce a multicellular diploid sporophyte (2n). The sporophyte creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes. The gametophytes (n) produce gametes via mitosis. In some plants the gametophyte is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the “dominant” stage of the life cycle.
- Isomorphic generations* refer to organisms in which the sporophytes (2n) and gametophytes (n) look similar to each other, although they differ in chromosome number.
- Heteromorphic generations* refer to organisms in which the sporophytes (2n) and gametophytes (n) are structurally different.
This type of life cycle is called a haplodiplontic life cycle. It differs from our own diplontic life cycle, in which only the gametes are in the haploid state.
alternation of generations
In sporic meiosis (also known as alteration of generations), the zygote divides mitotically to produce a multicellular diploid sporophyte (2n). The sporophyte creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes. The gametophytes (n) produce gametes via mitosis. In some plants the gametophyte is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the “dominant” stage of the life cycle.
- Isomorphic generations* refer to organisms in which the sporophytes (2n) and gametophytes (n) look similar to each other, although they differ in chromosome number.
- Heteromorphic generations* refer to organisms in which the sporophytes (2n) and gametophytes (n) are structurally different.
This type of life cycle is called a haplodiplontic life cycle. It differs from our own diplontic life cycle, in which only the gametes are in the haploid state.
sporophyte
In sporic meiosis (also known as alteration of generations), the sporophyte (2n) creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes (n). The gametophytes (n) produce gametes (n) via mitosism which fuse (during fertilisation) to form the zygote (2n). The zygote divides mitotically to produce a multicellular diploid sporophyte (2n). In some plants the gametophyte (n) is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the “dominant” stage of the life cycle.
gametophyte
In sporic meiosis (also known as alteration of generations), the gametophytes (n) produce gametes (n) via mitosism which fuse (during fertilisation) to form the zygote (2n). The zygote divides mitotically to produce a multicellular diploid sporophyte (2n). The sporophyte (2n) creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes (n). In some plants the gametophyte (n) is not only small-sized but also short-lived; in other plants and many algae, the gametophyte is the “dominant” stage of the life cycle.
(brown algae Laminaria shown)
list some haplodiplonts
Haplodiplonts are:
- Land plants
- Some green algae, e.g. Ulva
- Red algae (which have two sporophyte generations)
- Brown algae (except the Fucales)
- Haptophytes
- Some rhizaria, e.g. many foraminiferans and Plasmodiophora
- Some fungi
alveolates
[SAR clade>alveolates] have membrane-enclosed sacs (alveoli) just under the plasma membrane. Alveolates are abundant in many habitats and include a wide range of photosynthetic and heterotrophic protists. We discuss three alveolate clades: a group of flagellates [SAR clade>alveolates>dinoflagellates], a group of parasites [SAR clade>alveolates>apicomplexans], and a group of protists that move using cilia [SAR clade>alveolates>ciliates].
alveoli
These sacs under the plasma membrane are a characteristic that distinguishes [SAR clade>alveolates] from other eukaryotes (TEM image shown).
dinoflagellates
[SAR clade>alveolates>dinoflagellates] are reinforced by cellulose plates. Two flagella located in grooves in this “armour” make [SAR clade>alveolates>dinoflagellates] (from the Greek dinos, whirling) spin as they move through the waters of their marine and freshwater communities.
Although the group is thought to have originated by secondary endosymbiosis, roughly half of all dinoflagellates are now purely heterotrophic. Others are important species of phytoplankton (photosynthetic plankton, which include photosynthetic bacteria as well as algae); many photosynthetic dinoflagellates are mixotrophic. Mixotrophic dinoflagellates have both chlorophyll a and c and accessory carotenoids.
Some are known to create red tides (coloured by carotenoids) produced by population explosion of dinoflagellates possibly due to coastal pollution. These can also produce a toxin that leads to massive fish kills.
More than 18 genera of dinoflagellates are bioluminescent, and the majority of them emit a blue-green light.
name two lineages that evolved through secondary endosymbiosis of red algae
[SAR clade>alveolates>dinoflagellates] and [SAR clade>stramenophiles]
apicomplexans
[SAR clade>alveolates>apicomplexans] are non-motile parasites using their host’s fluid to move them through complex multi-stage life cycles. They are named for their apical complex which allows entry of host cells. The stages can be readily identified in blood samples. Plasmodium (two-host life cycle shown) is of the genus that causes malaria where it shares both the mosquito and human hosts to complete its life cycle.
what does the “a” group in the SAR supergroup stand for, and what are its subgroups?
[SAR clade>alveolates] have membrane-enclosed sacs (alveoli) just under the plasma membrane. Alveolates are abundant in many habitats and include a wide range of photosynthetic and heterotrophic protists. We discuss three alveolate clades: a group of flagellates (the dinoflagellates), a group of parasites (the apicomplexans), and a group of protists that move using cilia (the ciliates).
ciliates
[SAR clade>alveolates>ciliates] move by hair-like cilia using them to create currents that also allow them to trap food in an oral groove. Also have contractile vacuoles. Paramecium (shown) has micronuclei for sexual reproduction and macronuclei control metabolism. They reproduce sexually by conjugation and asexually by binary fission.
Describe reproduction in ciliates
A distinctive feature of [SAR clade>alveolates>ciliates] is the presence of two types of nuclei: tiny micronuclei and large macronuclei. A cell has one or more nuclei of each type. Genetic variation results from conjugation, a sexual process in which two individuals exchange haploid micronuclei but do not reproduce (shown in Paramecium). Ciliates generally reproduce asexually by binary fission, during which the existing macronucleus disintegrates and a new one is formed from the cell’s micronuclei. Each macronucleus typically contains multiple copies of the ciliate’s genome. Genes in the macronucleus control the everyday functions of the cell, such as feeding, waste removal, and maintaining water balance.
rhizarians
The [SAR clade>rhizarian] subgroup includes many species of amoebas, most of which have pseudopodia that are threadlike in shape. Pseudopodia are extensions that can bulge from any portion of the cell; they are used in movement and in the capture of prey. We cover two groups of rhizarians: [SAR clade>rhizarian>radiolarians] and [SAR clade>rhizarian>forams] (also called foraminiferans).
(shown: Globigerina, a [SAR clade>rhizarian>foraminiferans]. This species is a foram, a group whose members have threadlike pseudopodia that extend through pores in the shell, or test (LM). The inset shows a foram test, which is hardened by calcium carbonate (SEM).
radiolarians
[SAR clade>rhizarians>radiolarians] are mostly marine plankton with silica tests. They extend axopodia which are very thin extension of microtubules covered with a cytoplasmic sheath, which engulfs smaller microorganisms that become attached to the pseudopodia.
foraminiferans
[SAR clade>rhizarians>foraminiferans] (from the Latin foramen, little hole, and ferre, to bear), or forams have many-chambered calcium-carbonate (CaCO3) tests with pores. Over 10,000 species are recognized, both living (8,708) and fossil (1,837). Along with the calcium-containing remains of other protists, the fossilized tests of forams are part of marine sediments, including sedimentary rocks that are now land formations. They are usually less than 1 mm in size, but some are up to 20 cm. They have reticulopodia which are cytoplasmic extensions to move and obtain food. Some derive nutrients from photosynthesis with symbiotic algae.
how do rhizarians move and feed?
Many species in [SAR clade>rhizarians] are amoebas, protists that move and feed by means of pseudopodia, extensions that may bulge from almost anywhere on the cell surface. As it moves, an amoeba extends a pseudopodium and anchors the tip; more cytoplasm then streams into the pseudopodium. Amoebas do not constitute a monophyletic group; instead, they are dispersed across many distantly related eukaryotic taxa. Most amoebas that are rhizarians differ morphologically from other amoebas by having threadlike pseudopodia. Rhizarians also include flagellated (non-amoeboid) protists that feed using threadlike pseudopodia.
