Protists

What is the difference between mitosis and meiosis?

Mitosis is an organized stepwise nuclear division observed in eukaryotes that results in two genetically identical nuclei via separation of a previously duplicated set of chromosomes in a cell; it usually precedes the process of cytokinesis. Meiosis is an organized process of two nuclear divisions also preceded by duplication of all chromosomes in a cell; a diploid nucleus gives rise to four haploid nuclei of differing genetic composition.

On what criteria are the five supergroups of protista supported?

Various morphologies and DNA data

Oomycetes features

decomposers, parasites, e.g. Phytopthera infestans (potato late blight) (Stramenophile/Chromalveolate)

zygote

diploid cell formed when the nucleus of a haploid sperm cell fuses with the nucleus of a haploid egg cell

Excavata subgroups

diplomonads: 2 nuclei (di), mitosomes e.g. Giardia parabasalids: hydrogenosomes, undulating membrane e.g. Trichomonas euglenozoans: flagella with microtubules/crystalline rods, pellicle, contractile vacuoles e.g. euglena

Protist supergroups

excavata, chromalveolatra, rhizaria, archaeplastida, unikonta

Excavata features

feeding grooves, cytoskeletons homologies, modified mitochondra, unique flagella

zygotic life cycle

haploid cells transform into gametes

Foraminiferans feautres

have tests, mixotroph (Rhizarian )

gametophyte

in organisms that have alternation of generations, muliticellular haploid form that produces haploid gametes by MITOSIS. The haploid gametes unite and develop into sporophytes.

sporophyte

in organisms that have alternation of generations, multicellular diploid form that results from the union of gametes. Sporophytes produce haploid spores by MEIOSIS that develop into gametophytes

gametic life cycle

in this type of life cycle, all cells except the gametes are diploid and gametes are produced by meiosis

Radiolarians features

internal silican skeleton, microtubules in pseudopodia that radiate (Rhizarian)

heteromorphic alternation of generations

when the haploid and diploid multicellular generations differ in morphology

isomorphic alternation of generations

when the haploid and diploid multicellular generations look similar morphologically.

sygamy

when two pronuclei fuse in the zygote

Ciliate features

cilia, feeding structures, contractile vacuole, macronuclei (everyday) and micronuclei (conjugation); e.g. Paramecium (Alveolate/Chromalveolate)

accessory pigment

compound other than chlorophyll that absorbs light at different wavelengths than chlorophyll

mitosome

1) An organelle found in certain protists that lack mitochondria or hydrogenosomes. However, evidence shows that these protists may have once had mitochondria. 2) eukaryotic organelle derived from degenerate mitochondria, found in trichomonas and giardia

What biochemical feature of the photosynthetic protists links them to higher plants, and what features help define their separate clades within the protist supergroups?

All photosynthetic eukaryotes, whether they are unicellular, multicellular algae, or land plants, possess chlorophyll a. The features that help define them as separate clades are their accessory photosynthetic pigments, cell wall components, and storage carbohydrates.

All sexual life cycles alternate between which two states and which two processes?

All sexual life cycles alternate between diploid and haploid states and meiosis and fertilization.

pellicle

A firm, flexible coating outside the plasma membrane.

alternation of generations

A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte

What is the fundamental difference between the sporic life cycle and the other two sexual life cycles (gametic & zygotic)?

A sporic life cycle features multicellular haploid and diploid states, where as the other two life cycle types feature only one multicellular state (diploid in gametic life cycles and haploid in zygotic life cycles).

pseudopod

A temporary, foot-like extension of a cell, used for locomotion or engulfing food

Which organisms are included in the protist grouping?

All eukaryotic unicellular and multicellular organisms that are not included in Kingdom Planta, Kingdom Animalia, Kingdom Fungi; the protist grouping of course excludes Domains Archaea and Bacteria.

Chromalveolata subgroups

Alveolates and Stramenophiles

Rhizaria subgroups

Chlorarachniophytes, Forams, Radiolarians

What is the difference between conjugation in bacteria and in ciliates?

Conjugation in bacteria involves the formation of a sex pilus between two bacteria usually directed by the bacterium possessing a plasmid(s). The pilus draws the bacteria close together facilitating the update of plasmid DNA by one bacterium after its release by the other bacterium. Conjugation in ciliates involves the close association of two ciliates of different mating strains and swapping of haploid micronuclei.

Stramenophiles groups

Diatoms, Golden algae, brown algae, oomycetes

Alveolate groups

Dinoflagellates, Apicomplexans, Ciliates

What kind of cells featured in sexual life cycles can germinate to produce multicellular individuals or phases?

Haploid sexual spores can germinate, grow and develop into multicellular phases or generations via mitotic divisions; this is characteristic of sporic and zygotic life cycles.

Plants and fungi produce gametes via which nuclear division process?

Plants and fungi produce gametes (eggs and sperm or their equivalents) via mitosis.

What are the main differences between prokaryotic and eukaryotic cells?

Prokaryotes lack a membrane bound nucleus & membrane bound organelles, possess a single circular chromosome, smaller ribosomes, and flagella composed of flagellin not surrounded by the plasma membrane.

Why is "Kingdom Protista" no longer a valid taxonomic grouping?

Protists include all eukaryotes except the clades Planta, Animalia and Fungi. Since all of these organisms are presumed to share a common ancestor, protists as a group would not include all of its descendents thereby making the grouping paraphyletic. Also, some protists are more closely related to members of the clades Planta, Animalia and Fungi than they are to other protists (e.g., green algae and Planta).

Archaeplastidas subgroups

Red algae, chlorophytes, charophytes, land plants

Unikonta subgroups

Slime molds, gymnamoebas, plants, animals, etc.

Explain how the body form of some brown algae (Figs. 28.15 & 28.16) and the body form of the oomycetes are analogous to that of land plants and fungi respectively, via convergent evolution.

The body form of some brown algae includes a holdfast, stipe and blade which are structures analogous to the root, stem and leaves of members of Kingdom Planta. The filamentous structure of the oomycetes is analogous to the typical fungal body form which is also filamentous; this body form provides a high surface area to volume ratio for these organisms thus maximizing their absorptive abilities. The similarities of body structures in very different organisms are not explained by close common ancestry but rather by natural selection of similar traits via similar selection pressures (convergent evolution).

What is the purpose of the contractile vacuole?

The contractile vacuole allows unwalled unicellular eukaryotes that live in hypotonic environments to excrete excess water so they do not explode.

What is the endosymbiotic theory of the origin of mitochondria and chloroplasts? From which prokaryotic groups did each of these organelles descend?

The endosymbiotic theory states that an ancestral eukaryote or host cell engulfed an aerobic prokaryote (alpha proteobacterium) thus giving rise to mitochondria. It also states that at a later time in evolution an ancestral organism with mitochondria engulfed a photosynthetic prokaryote (cyanobacterium) giving rise to chloroplasts.

spore

a haploid reproductive cell that grows into a new plant

gamete

a haploid reproductive cell that unites with another haploid reproductive cell to form a zygote

kinetoplast

a mass of DNA present in the single large mitochondrion

amoeba

a protist characterized by the presence of pseudopodia

Apicomplexan features

apex structure with complex organelles for penetrating host cells and tissues; e.g. Plasmodiums (malaria) (Alveolate/Chromalveolate)

Brown algae features

cell wall is cellulose, laminarin (storage polysaccharide), e.g. Kelps (Stramenophile/Chromalveolate)

Red algae features

cell wall is cellulose, storage polysaccharide (Archeaplastida)

Green algae features

cell wall is cellulose, storage polysaccharide, e.g. Chlamydomonas (Archeaplastida)

Diatom features

cell wall is hydrated silica, laminarin (storage polysaccharide) (Stramenophile/Chromalveolate)

Dinoflagellate features

marine and freshwater; autrophic, heterotrophic, mixotrophic; ridge on cell wall and two flagella; cause red tide (Alveolate/Chromalveolate)

storage polysaccharide

polysaccharides that are stored in cells as a glucose energy reserve; examples include starch in plants and glycogen in animals.

contractile vacuole

sac-like organelles that expand to collect excess water and contract to squeeze the water out of the cell

cilia

short, hair-like structures made of microtubules that enable movement of cells or movement of materials outside a cell

sporic life cycle

the phenomenom that occurs in plants (and some protists) in which the life cycle alternates between multicellular diploid organisms, called sporophytes, and multicellular haploid organisms called gametophytes

tests

the porous shells of foraminiferans