Chapter 28: the Protists Even a low-power microscope can reveal a great variety of organisms in a drop of pond water These amazing organisms belong to.

Chapter 28: the Protists Even a low-power microscope can reveal a great variety of organisms in a drop of pond water These amazing organisms belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists Advances in eukaryotic systematics have caused the classification of protists to change significantly

Kingdom Protista?? now part of the Domain Eukaryota
eukaryotes = true nucleus evolution of a nucleus for the genetic information evolution of membrane-bound organelles diverse group of single and colonial forms informally known as The Protists but Kingdom Protista really doesn’t exist anymore – too polyphyletic probably arose from more than one prokaryotic group 7 to 45 species recognized depending on zoologist

Protists include groups that are photoautotrophs, heterotrophs and mixotrophs mixotrophs = combine photosynthesis and heterotrophic nutrition divide the protists into three categories: 1. Photosynthetic – plant-like or algae 2. Ingestive – animal-like or protozoans amoeba 3. Absorptive – fungus-like

Cellular Anatomy most are unicellular
but the cellular composition is extremely complex unicellular protists carry out similar functions to multi-cellular eukaryotes with their organ systems do so using subcellular organelles many of these organelles are seen in higher organisms other organelles are not found in the typical multicellular eukaryote contractile vacuoles for osmoregulation

Protist Evolution diversity of protists has its origins in endosymbiosis process where a unicellular organism engulfs another cell become endosymbionts and eventually a new organelle e.g. acquisition of mitochondria – ingestion by alpha-proteobacteria by an ancestral cell

Endosymbiosis early cellular evolution – ingestion of a photosynthetic cyanobacteria through primary endosymbiosis by a primitive eukaryote eventual development into the plastids of the photosynthetic red and green algae Red and green algae then underwent secondary endosymbiosis they themselves were ingested by another primitive eukaryotic cell to eventually become the plastids of the protists listed below in the figure Cyanobacterium Primary endosymbiosis Secondary Heterotrophic eukaryote Red algae Green algae Dinoflagellates Plastid Apicomplexans Stramenopiles Euglenids Chlorarachniophytes

The 5 Supergroups of Eukaryotes
Phylogenetic classification of eukaryotes produces five Clades: 1. Excavata 2. Chromalveolata common ancestors – the alveolates and stramenophiles 3. Rhizaria 4. Archaeplastida contains green algae and land plants 5. Unikonta slime molds, entamoebas, fungi and animals

Eukaryotic Phylogenetic Tree
Alveolata Diplomonadida Parabasala Euglenozoa Ancestral eukaryote Stramenopila Amoebozoa (Opisthokonta) (Viridiplantae) Cercozoa Radiolaria Rhodophyta Plants Chlorophytes Charophyceans Red algae Metazoans Fungi Choanoflagellates Cellular slime molds Plasmodial slime molds Gymnamoebas Entamoebas Radiolarians Chlorarachniophytes Foraminiferans Brown algae Golden algae Oomycetes Diatoms Ciliates Apicomplexans Euglenids Dinoflagellates Kinetoplastids Diplomonads Parabasalids Excavata Chromalveolata Unikonta Rhizaria Archaeplastida Animalia Chlorophyta Plantae Charophyta Clade:

Clade: Excavata A. Diplomonads B. Parabasalids C. Euglenozoans

Clade: Excavata Diplomonads & Parabasilids
protists in these two groups lack plastids (no photosynthesis) mitochondria do not have DNA or the enzymes for the citric acid cycle or proteins for the electron transport chain anaerobic environments

Clade: Excavata A. Diplomonads
giardia intestinalis Clade: Excavata A. Diplomonads two equal-sized nuclei and multiple flagella flagella is very different from prokaryotic flagella have modified mitochondria = mitosomes many are parasites

B. Parabasalids also have reduced/modified mitochondria
include the protists called trichomonads – Trichomonas vaginalis mobility through an undulating membrane in addition to flagella LE 28-5b Flagella Trichomonas vaginalis, a parabasalid (colorized SEM) Undulating membrane 5 µm

C. Euglenozoans belong to a diverse clade – includes heterotrophs, photosynthetic autotrophs and parasites considered a photosynthetic protist similar to algae like algae – the photosynthetic protists have chlorophyll a and b in chloroplasts distinguishing feature – a rod with either a spiral or crystalline structure inside each of their flagella divided into the groups: 1. the Kinetoplastids 2. the Euglenoids Crystalline rod Flagella (9+2 arrangement) Cross-section of a Euglenozoan

1. Kinetoplastids - Trypanosomes
defined by a single, large mitochondrion that contains an organized mass of DNA = kinetoplast free-living forms in freshwater, marine and soil – feed on the prokaryotes in these ecosystems some are parasites of animals, plants and other protists Trypanosoma gambienese – sleeping sickness (neurological disease) & Chagas’ disease (congestive heart failure) in humans

Kinetoplastids: Trypanosoma
Life cycle -cycles between the tse tse fly and the human -different forms of the trypanosome depending on what host (fly vs. human) and where it is in the host fly injects the trypanosome multiplication in the human host – e.g. in the blood bit by fly and transfer back to fly multiplication in the fly’s gut and then in the salivary gland

2. Euglenoids – The Euglena
unicellular protist most are autotrophic several chloroplasts with chlorophyll a and b and carotenoid pigments main characteristic - two flagella that emerge from a “pocket” structure at the pocket is a large contractile vacuole that connects to the outside continuously collects water from the cell and returns it to the outside – regulates osmotic pressure two flagella arise at this reservoir the long one emerges from the canal and actively beats for locomotion used to be classified as the Class Phytomastigophorea

2. Euglenoids inside the plasma membrane is a structure called the pellicle articulated strips of protein lying side by side that enable turning and flexing of the protist eyespot (stigma) - near the flagella allows only certain wavelengths of light to strike the light detector light detector (photoreceptor) – detects the filtered light and results in movement toward the light direction

Clade: Chromalveolata
originated more than a billion years ago when their ancestor ingested a photosynthetic red algae (via secondary endosymbiosis) plastids within these protists have red algae origins (DNA analysis) divided into two major groups: 1. Alveolates 2. Stramenophiles

Clade: Chromalveolata
A. Alveolates: 1. Dinoflagellates 2. Apicomplexans 3. Ciliates B. Stramenophiles 1. Diatoms 2. Golden Algae 3. Brown Algae 4. Oomycetes

Chromalveolata - A. Alveolates
characterized by membrane-bound sacs called alveoli just under the plasma membrane function unknown 1. Dinoflagellates – move through flagellar action 2. Apicomplexans - parasites 3. Ciliates – move through ciliary action

Alveolates: 1. Dinoflagellates
several thousand species “dinos” = whirling surrounded by a cell wall encrusted with silica - act as “armor” most are autotrophic with well-formed plastids for photosynthesis possess mitochondria with tubular cristae (similar to animals) two flagellae – located in grooves one groove is transverse (around the protist) = cingulum – its flagella propels the dinoflagellate forward and causes it to spin other groove is perpendicular to that = sulcus – the flagella acts as the rudder LE 28-10 3 µm Flagella

capable of proliferating explosively – “blooms”
“red tide” (carotenoid pigments found in the plastids) dinoflagellates produce a toxin that kills off invertebrates some can be bioluminescent – ATP driven reaction that creates a glow at night

Alveolates: 2. Apicomplexans
nearly all are animal parasites spread through the formation of tiny infectious cells = sporozoites named because one end (apex) contains a complex of organelles specialized for penetrating host tissues and cells have a non-photosynthetic plastid = apicoplast which has many functions including the synthesis of fatty acids for its membranes life cycle – includes sexual and asexual stages requires more than one host to complete

Alveolates: 2. Apicomplexans
best known is the Plasmodium – causes malaria rivals tuberculosis as the leading cause of human death by infectious disease can be reduced by insecticides that kill the Anopheles mosquito (DDT) and by drugs that kill the Plasmodium (quinine based drugs) vaccines hard to develop – Plasmodium lives inside the RBC (hidden) carriers of sickle cell anemia gene – resistant to malaria trophozoites gametocyte

Plasmodium Life Cycle 1. infected Anopheles mosquito bites a person injecting its sporozoites (n) 2. sporozoites enter the liver and undergo division to become merozoites (n) 3. the merozoites infect RBCs via their apical complex 4. merozoites develop into gametocytes which break out of the RBCs fevers and chills 5. gametocytes picked up by a new mosquito 6. gametes form and fertilization takes place in the mosquito’s digestive tract  zygote 7. an oocyst develops and produces more sporozoites which are delivered to the human when bitten again LE 28-11 Sporozoites (n) Inside mosquito Oocyst Zygote (2n) MEIOSIS Merozoite Liver cell FERTILIZATION Gametes Gametocytes Red blood cells Inside human Apex 0.5 µm Haploid (n) Key Diploid (2n)

Alveolates: 3. Ciliates - Paramecium
use of cilia to move and feed cilia may completely cover the protist or may cluster in a few rows or tufts distinguished by the presence of two types of nuclei: macronucleus (large) and micronucleus (small) may have one or more of each type macronucleus – contains dozens of copies of the genome control the everyday functions of the ciliate micronucleus – function in reproduction exchanged between two ciliates during conjugation

FEEDING, WASTE REMOVAL, AND WATER BALANCE
LE 28-12 Paramecium FEEDING, WASTE REMOVAL, AND WATER BALANCE Contractile vacuole Oral groove Cell mouth Micronucleus Macronucleus 50 µm Thousands of cilia cover the surface of Paramecium. Paramecium, like other freshwater protists, constantly takes in water by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane. Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis. Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell. The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore. freshwater protist – constantly takes on water from its hypotonic environment they contain contractile vacuoles for the regulation of osmotic pressure – accumulate excess water and then expel it through the plasma membrane back into the environment

FEEDING, WASTE REMOVAL, AND WATER BALANCE
Paramecium cilia participate in movement but also gather food and move it toward the oral groove which holds the cell mouth at the bottom food is then engulfed into a food vacuole via phagocytosis food vacuoles combine with lysosomes containing digestive enzymes FEEDING, WASTE REMOVAL, AND WATER BALANCE Contractile vacuole Oral groove Cell mouth Micronucleus Macronucleus 50 µm Thousands of cilia cover the surface of Paramecium. Paramecium, like other freshwater protists, constantly takes in water by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane. Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis. Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell. The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore.

CONJUGATION AND REPRODUCTION
Paramecium CONJUGATION AND REPRODUCTION MEIOSIS MICRONUCLEAR FUSION Haploid micronucleus Diploid Compatible mates Two cells of compatible mating strains align side by side and partially fuse. Macronucleus Meiosis of micronuclei produces four haploid micronuclei in each cell. Three micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis. The cells swap one micronucleus. The cells separate. Key Micronuclei fuse, forming a diploid micronucleus. Conjugation Reproduction Two rounds of cytokinesis partition one maccronucleus and one macronucleus into each of four daughter cells. The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. Three rounds of mitosis without cytokinesis produce eight micronuclei. asexual reproduction – through binary fission sexual reproduction involves conjugation 1. two compatible mating strains align side by side and partially fuse 2. meiosis of their micronuclei produces a total of 4 haploid micronuclei in each cell 3. three micronuclei in each disintegrate & the remaining micronuclei in each divides by mitosis- resulting in 2 micronuclei in each paramecium 4. the cells swap one of their micronuclei – genetic recombination 5. the cells separate

Paramecium CONJUGATION AND REPRODUCTION MEIOSIS MICRONUCLEAR FUSION Haploid micronucleus Diploid Compatible mates Two cells of compatible mating strains align side by side and partially fuse. Macronucleus Meiosis of micronuclei produces four haploid micronuclei in each cell. Three micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis. The cells swap one micronucleus. The cells separate. Key Micronuclei fuse, forming a diploid micronucleus. Conjugation Reproduction Two rounds of cytokinesis partition one maccronucleus and one macronucleus into each of four daughter cells. The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. Three rounds of mitosis without cytokinesis produce eight micronuclei. 6. the two micronuclei in each cell fuse to produce a diploid nuclei 7. three round of mitosis without fission results in 8 micronuclei in each paramecium 8. the original macronuclei disintegrates and 4 micronuclei become 4 macronuclei to replace it – leaves 4 micronuclei 9. two rounds of binary fission now happen results in 4 daughter cells 10. the micronuclei (4) and macronuclei (4) then partition into the four daughter cells – each paramecium ends up with 1 micronuclei and 1 macronuclei

Got all that?? CONJUGATION AND REPRODUCTION MEIOSIS MICRONUCLEAR FUSION Haploid micronucleus Diploid Compatible mates Two cells of compatible mating strains align side by side and partially fuse. Macronucleus Meiosis of micronuclei produces four haploid micronuclei in each cell. Three micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis. The cells swap one micronucleus. The cells separate. Key Micronuclei fuse, forming a diploid micronucleus. Conjugation Reproduction Two rounds of cytokinesis partition one macronucleus and one macronucleus into each of four daughter cells. The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. Three rounds of mitosis without cytokinesis produce eight micronuclei. -partially fuse -1 micronucleus becomes 4 via meiosis (haploid) -3 disappear -1 micronuclei becomes 2 via mitosis -paramecia “swap” 1 micronuclei and separate -fuse 2 micronuclei into 1 (diploid) -micronucleus becomes 8 (mitosis/no cytokinesis) -macronucleus disappears -so 4 of the 8 micronuclei develop into 4 macronuclei -4 of the micronuclei stay micronuclei -2 rounds binary fission  4 daughter paramecia -each daughter cell gets a macronuclei and a micronuclei

Chromalveolata - B. Stramenophiles
stramen = “straw”; pilos – “hair” contains several groups of phototrophs (considered to be algae) flagella are said to be “hairy” this hairy flagellum is paired with a smooth flagellum 1. oomycetes – water molds 2. bacillariophytes - diatoms 3. chrysophytes – golden algae 4. phyophyceans – brown algae Smooth flagellum Hairy 5 µm

First of All - What is Algae??
photosynthetic protists algae = eukaryotic organism with chlorophyll a pigments that carry out oxygen-producing photosynthesis study of algae = phycology no longer any formal classification schemes algae are scattered across many phyla = polyphyletic BUT they differ from plants – lack a well-organized vascular system and they have a simple reproductive system occur most often in water fresh and marine – may be suspended as planktonic organisms or attached to the bottom (benthic)

Algae: Photosynthetic Protists
algae frequently confused with plankton plankton = free-floating microscopic aquatic organisms phytoplankton – made up of algae and small plants zooplankton – non-photosynthetic protists and animals classical algae are now grouped together with the plants - Phylum Chlorophyta some are a separate lineage - known as red algae Phylum Rhodophyta some are grouped with the stramenophiles - yellow and brown algae Phyla Chrysophyta and Phaeophyta

Algae: Photosynthetic Protists
important properties that classify them: 1. cell wall composition – rigid cell wall of cellulose 2. the form in which food is stored 3. chlorophyll molecules and accessory pigments (carotenoids) 4. flagella number and location of their insertion into the cell 5 morphology of the cells and/or body comprised of a vegetative body = thallus 6. habitat: marine or freshwater 7. reproductive structures: reproduction is asexual or sexual 8. mitochondria cristae structure: tubular, disc or plate-like (lamellar)

Stramenophiles: 1. Oomycetes: Water molds
oomycete = “egg fungus” water molds, white rusts and downey mildews used to be considered fungi – have multinucleate filaments called hyphae that resemble those seen in fungi molecular data also cannot confirm fungal origins do not carry out photosynthesis – non-autotrophic acquire nutrients as decomposers – grow as cottony masses on dead animals and algae = heterotrophic water mold

Stramenophiles: 2. Diatoms
100,000 species of unicellular algae surrounded by unique glass-like wall made of silica embedded in an organic matrix two parts that overlap like a shoe box and lid upperlid = epitheca, lowerlid = hypotheca effective protection against extreme crushing forces reproduce asexually via mitosis daughter receives half of the parental cell wall and generates a new half most are photosynthetic – chlorophylls a and c and carotenoids

Stramenophiles: 2. Diatoms
major component of phytoplankton in fresh and marine environments in cooler waters source of food for fish and other marine animals upon death –sink to the bottom = diatomaceous earth active ingredient in detergents, fine abrasive polishes, paint removers, decoloring oils, filtering agents, components of insulation and soundproofing products, reflective paint additive

Stramenophiles: 3. Golden Algae -Phylum Chrysophyta
all species are photosynthetic photosynthetic pigments: chlorophylls a and c + carotenoids found in plastids (like plants) dominant pigment is a carotenoid called fucoxanthin  golden-brown color most are unicellular but some are colonial most are biflagellated – both attached near one end of the cell Dinobryon

Stramenophiles: 4. Brown algae - Phylum Phaeophyta
brown algae – most complex algae all are multicellular and all are marine have the most complex multicellular anatomy of all algae some have specialized tissues like animals and plants include the seaweeds giant seaweeds in intertidal zones – kelps

4. Brown algae: Phaeophyta
composed of a thallus = algal body that is plant-like thallus has a rootlike hold-fast which anchors the seaweed and a stem-like stipe that supports leaf-like blades BUT there are no true roots, stems and leaves! blades – surface for photosynthesis blades can come equipped with floats to keep them near the surface 4. Brown algae: Phaeophyta LE 28-18 Blade Stipe Holdfast Brown algae Thallus

Brown algae: Life cycle
e.g. Laminaria Developing sporophyte Zygote (2n) FERTILIZATION Mature female gametophyte (n) Egg Sperm MEIOSIS Haploid (n) Key Diploid (2n) Sporangia Sporophyte Zoospores Female Gametophytes Male brown algae exhibit alternation of generations alternate between haploid and diploid multicellular forms only applies to multicellular stages in the life cycle two forms seen that are structurally different: A. diploid sporophyte – for the production of haploid spores via meiosis B. haploid gametophytes – for the production of haploid gametes via mitosis An overview of Alternation of Generations the spores develop into gametophytes (n) the gametophytes make gametes (n) the gametes fuse and regenerate the diploid sporophyte (2n)

Brown algae: Life cycle
life cycle starts with the diploid sporophyte (adult algae thallus) 1. on the blade of the sporophyte – development of a sporangium 2. the diploid sporangium develops haploid zoospores by meiosis 3. 50% of zoospores develop into male gametophytes and 50% into female gametophytes (small but multicellular) 4. the haploid gametophytes produce haploid gametes via mitosis 5. gametes are released and fuse to form the diploid zygote 6. zygote develops into a new sporophyte which grows via mitosis to form a new adult algae Developing sporophyte Zygote (2n) FERTILIZATION Mature female gametophyte (n) Egg Sperm MEIOSIS Haploid (n) Key Diploid (2n) Sporangia Sporophyte Zoospores Female Gametophytes Male e.g. Laminaria

Clade Rhizaria characterized by the presence of threadlike pseudopodia = extensions of the cytoplasm that bulge anywhere along the cell’s surface “false –feet” used in locomotion and prey capture extend and contract pseudopodium by assembly and disassembly of actin subunits into microfilaments locomotion: anchor a tip to the surface – stream cytoplasm into the pseudopodium prey capture: pseudopodia senses the prey through physical contact and surrounds it members of this clade: A. Radiolarins B. Forams C. Cercozoans

Clade Rhizaria A. Radiolarians: delicate, intricately symmetrical internal skeletons made of silica axiopodia which “radiate” out from a central body – reinforced by microtubultes pseudopodia are also capable of phagocytosing food – cytoplasmic streaming then carries the food into the central body LE 28-23 200 µm Pseudopodia Radiolarins

Clade Rhizaria B. Forams: formerly called foraminiferans
named for their porous shells holes in the shells are called foramina shell is called a test = single piece of organic material hardened with calcium carbonate pseudopodia extend through the holes – function in swimming, in making the test and feeding Forams

C. Cercozoans: The Amoeba
contain the organisms called amoebae amoeba species are also found in other clades most are heterotrophs – many are parasites of plants and animals some can be predators! predators of bacteria

A word about amoebas no longer one specific clade too polyphyletic
find amoebas in several clades – 2 major ones: Cercozoa Amoebozoa amoeba = protist that does not have a definitive shape eat via phagocytosis have an outer ectoplasm and an inner endoplasm move by pseudopodia that form through cytoplasmic streaming of their ectoplasm and endoplasm

Clade Archaeplastida more than a billion years ago – heterotrophic protist acquired a cynanobacterial endosymbiont gave rise to red algae and green algae these cyanobacteria evolved into plastids numerous functions: photosynthesis and storage 475 million years ago – green algae ancestors evolved into land plants red algae, green algae and land plants are now placed into the same clade based on molecular data – Archaeplastida Cyanobacterium Primary endosymbiosis Heterotrophic eukaryote Red algae Green algae Plastid

Clade Archaeplastida Archaeplastida can be divided into:
A. Red algae – Phylum Rhodophyta B. Green algae – Phylum Chlorophyta C. Charophytes – includes Plants; Phylum Charophyta

Archaeplastida - A. Red Algae: Phylum Rhodophyta
red algae – 6000 species multicellular algae most are autotrophic – plastids for photosynthesis red pigment = phycoerythritin and blue pigment = phycocyanin (phycobilins) pigments allow for the absorption of green and blue light which have long wavelengths and can penetrate the deeper waters where the red algae are found

Archaeplastida - A. Red Algae: Phylum Rhodophyta
red algae – 6000 species sugar storage form = floridean cell wall includes a matrix of proteins and sugars this matrix is also called agar = polymers of galactose largest red algae are included in a group called seaweeds (e.g. nori) life cycle does not include a flagellated step – must rely on ocean currents to deliver gametes for fertilization

Archaeplastida - B. Green algae: Phylum Chlorophyta
named for the green chloroplasts contain chlorophyll pigments that are very similar to plants chloroplasts also have a similar structure to plants thylakoid membranes divide into two groups: 1. Charophytes – most closely related to plants 2. Chlorophytes – 7000 species of green algae

Archaeplastida - B. Green algae: Phylum Chlorophyta
2. Chlorophytes – 7000 species chloro = “green” mostly freshwater chlorophylls a and b + carotenoid pigments sugar storage form = starch cell walls made of cellulose most are unicellular some are colonial some are also multicellular - filamentous (pond scum) and sheet-like forms can also live symbiotically with fungus – as lichens

Unicellular Green Algae
e.g. Chlamydomonas – example of a unicellular algae two flagella of equal length at the anterior end one conspicuous pyrenoid organelle found in or beside the chloroplasts of algae involved in carbohydrate synthesis eyespot or stigma movement towards light two small contractile vacuoles at the base of the flagella – function as osmoregulatory organs asexual reproduction sexual reproduction is also possible – cell division produces gametes of each “sex”

Green algae: Life Cycle
life cycle: sexual and asexual stages mature green algae cells are haploid and have 2 flagellae asexual reproduction: the algae reabsorbs its flagellae and divides by mitosis to form four identical haploid cells (zoospores) - held within a capsule zoospores are released  new mature green algae MEIOSIS Haploid (n) Key Diploid (2n) SYNGAMY SEXUAL REPRODUCTION Zoospores ASEXUAL Mature cell (n) Zygote (2n) Regions of single chloroplast Nucleus Flagella Cell wall 1 µm

Green algae: Life Cycle
sexual reproduction: happens upon shortage of nutrients haploid algae develops into male and female gametes fusion  zygote (diploid + 4 flagella) zygote loses its flagellae and surrounds itself by a coat to protect itself meiosis in the zygote results in 4 haploid cells – two from each mating type these released haploid cells become new mature algal cells MEIOSIS Haploid (n) Key Diploid (2n) SYNGAMY SEXUAL REPRODUCTION Zoospores ASEXUAL Mature cell (n) Zygote (2n) Regions of single chloroplast Nucleus Flagella Cell wall 1 µm

Colonial Green Algae not really multicellular
colony of unicellular algae e.g. Volvox colony or 500 to 60,000 cells – mostly small vegetative cells individual cells resemble Chlamydomonas – bi-flagellated cells have eyespots – will orient toward the light some cells are reproductive - develop from the cells at the equator = called gonads  gametes for fertilization zygote undergoes mitosis to form a small daughter colony the daughter colony remains in the parental colony until it bursts free Volvox, a colonial freshwater chlorophyte. The colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm; if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “daughter” colonies within them.

Clade Unikonta recently proposed clade
supergroup of eukaryotes that includes animals, fungi and some protists means “one flagella” two major clades: A. Amoebozoans: the amoebas & slime molds B. Opisthokonts: fungi and animals

Unikonta: A. Amoebozoans
three types of Amoebozoans: 1. Gymnamoebas unicellular, one flagella soil, freshwater and marine most are heterotrophic – consume bacteria and other protists plus detritus (decomposers)

Unikonta: A. Amoebozoans
2. Entamoebas parasitic amoebae infect all classes of vertebrates and some invertebrates humans are host to at least 6 species Entamoeba histolytica – amoebic dysentery third leading cause of death in the world due to parasites – 100,000 deaths each year 3. Mycetezoans = Slime molds cellular slime molds plasmodial slime molds

Plasmodial slime molds
brightly pigmented – orange or yellow named for the formation of a feeding stage = plasmodium in the life cycle capable of moving over a substrate plasmodium – very large but still is unicellular single cell undergoes mitosis but fails to divide through cytokinesis – “super-cell” feeding plasmodium lives on organic matter – takes in nutrients through phagocytosis 1 mm MEIOSIS Haploid (n) Key Diploid (2n) Zygote (2n) SYNGAMY Feeding plasmodium Mature (preparing to fruit) Young sporangium Spores (n) Stalk Amoeboid cells Germinating spore Flagellated cells

Plasmodial slime molds
mature plasmodium undergoes sexual reproduction when conditions become harsh plasmodium develops sporangia via meiosis which release haploid spores (n) germination of the spores takes place in the presence of adequate moisture results in the production of either amoeboid cells or flagellated cells – both are haploid fertilization (syngamy) requires the fusion of the same type of cell – i.e. swarm with swarm production of the zygote (2n) and development of a new plasmodium forms 1 mm MEIOSIS Haploid (n) Key Diploid (2n) Zygote (2n) SYNGAMY Feeding plasmodium Mature (preparing to fruit) Young sporangium Spores (n) Stalk Amoeboid cells Germinating spore Flagellated cells

Cellular slime molds MEIOSIS Haploid (n) Key Diploid (2n) Zygote (2n) SYNGAMY Migrating aggregate Emerging amoeba SEXUAL REPRODUCTION Amoebas Spores (n) Solitary amoebas (feeding stage) ASEXUAL Fruiting bodies Aggregated amoebas 200 µm feeding stage is a solitary amoeboid form – feeding stage engulfs bacteria and yeasts by phagocytosis can undergo asexual or sexual reproduction determined by food supply sexual reproduction: takes place in presence of abundant food two haploid amoebas fuse and form the zygote (2n) the zygote engulfs more haploid amoebae to grow larger – forms an aggregate aggregate develops fruiting sporangia - releases haploid spores  new amoeba cells 600 µm

Chapter 28: the Protists Even a low-power microscope can reveal a great variety of organisms in a drop of pond water These amazing organisms belong to.

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Chapter 28: the Protists Even a low-power microscope can reveal a great variety of organisms in a drop of pond water These amazing organisms belong to.

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