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Lecture #3 Protists.

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1 Lecture #3 Protists

2 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

3 Kingdom Protista?? now part of the superkingdom 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 include the algae and slime molds first observed in pond water by Antoni van Leeuwenhoek 300 years ago 7 to 45 species recognized depending on zoologist some as small as prokaryotes molecular analysis has discovered many commonalities that make them Protists

4 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

5 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 endoplasmic reticulum Golgi apparatus lysosomes other organelles are not found in the typical multicellular eukaryote contractile vacuoles for osmoregulation

6 Protists and Eukaryotic Evolution
Many components of the eukaryotic animal and plant cell were derived from protists 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 early evolution – ingestion of a photosynthetic cyanobacteria through primary endosymbiosis by a heterotrophic eukaryote eventual development into the plastids of the photosynthetic red and green algae DNA of red and green algae is very similar to that of cyanobacteria plastid membrane is dual layered – similar to the inner and outer membranes of the cyanobacteria Red and green algae also underwent secondary endosymbiosis – they were ingested by a heterotrophic eukaryotic cell to become endosymbionts and eventual 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

7 The 5 Supergroups of Eukaryotes
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

8 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 Fungi Plantae Charophyta

9 Clade: Excavata A. Diplomonads B. Parabasilids C. Euglenozoans
Diplomonads & Parabasilids protists in these two clades lack plastids (no photosynthesis) mitochondria do not have DNA or the enzymes for the citric acid cycle or proteins for the electron transport chain cannot use O2 to help extract energy from carbohydrates therefore they are found in anaerobic environments two equal-sized nuclei and multiple flagella flagella is very different from prokaryotic flagella eukaryotic flagella is an extension of the cytoplasm and are made of microtubules composed of tubulin in a distinct 9+2 array pattern have modified mitochondria = mitosomes many are parasites e.g. giardia intestinalis – intestinal protist in contaminated drinking water – severe diarrhea

10 B. Parabasalids also have reduced/modified mitochondria = hydrogenosomes generate some energy anaerobically – releasing H2 gas as a by-product include the protists called trichomonads – Trichomonas vaginalis disturbance in the normal pH of the vagina allows this protist to outcompete beneficial microbes and infect the vaginal lining – sexually transmitted to males also probable acquisition of parasitic behavior through genetic recombination (conjugation) with a parasitic bacteria also within the vagina mobility through an undulating membrane in addition to flagella LE 28-5b Flagella Trichomonas vaginalis, a parabasalid (colorized SEM) Undulating membrane 5 µm

11 C. Euglenozoans belong to a diverse clade – includes heterotrophs, photosynthetic autotrophs and parasites 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 unknown function divided into the groups: 1. the Kinetoplastids 2. the Euglenoids

12 1. Kinetoplastids used to be called the zoomastigophores
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 Coated with millions of copies of a single protein Evade detection by the host using a “bait and switch” mechanism which allows the trypanosome to change the composition of theis surface protein to a different molecular structure about 1/3 of the trypanosomes genome is devoted to making these surface proteins!

13 Kinetoplastids: Trypanosoma

14 unicellular protist with 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 only one emerges from the canal and actively beats for locomotion most are autotrophic several chloroplasts with chlorophyll a and b and carotenoid pigments some can also be mixotrophic – photosynthetic in sunlight, engulfs prey in absence of sunlight inside the plasma membrane is a structure called the pellicle articulated strips of protein lying side by side elastic enough to enable turning and flexing of the cell but rigid enough to prevent major changes in shape eyespot (stigma) - near the flagella functions as a pigment shield allowing 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 probably developed in order to maximize its photosynthetic potential 2. Euglenoids used to be classified as the Class Phytomastigophorea

15 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: Alveolates & Stremenophiles A. Alveolates: 1. Dinoflagellates 2. Apicomplexans 3. Ciliates B. Stramenophiles 1. Diatoms 2. Golden Algae 3. Brown Algae 4. Oomycetes

16 A. Alveolates characterized by membrane-bound sacs called alveoli
just under the plasma membrane function unknown – may be involved in the stabilization of the cell membrane or may regulate the entrance and exit of ions and water (osmolarity) 1. Dinoflagellates – move through flagellar action 2. Apicomplexans - parasites 3. Ciliates – move through ciliary action

17 1. Dinoflagellates Dinoflagellates – several thousand species
“dinos” = whirling components of both marine and freshwater phytoplankton some can be heterotrophic (phagocytic) most are autotrophic with well-formed plastids for photosynthesis chlorophylls a and c + carotenoids and xanthophylls – yellowish green color possess mitochondria with tubular cristae (similar to animals) characteristic shapes – reinforced by internal plates of cellulose that become encrusted with silica - act as “armor” LE 28-10 3 µm Flagella

18 two flagellae – located in perpendicular grooves in these plates
one groove is transverse = cingulum – propels the dinoflagellate forward and causes it to spin other groove is longitudinal = sulcus – acts as the rudder capable of proliferating explosively – “blooms” “red tide” (carotenoid pigments found in the plastids) can result from blooms of certain dinoflagellates – produce a toxin that kills off invertebrates some can be bioluminescent – ATP driven reaction that creates a glow at night may be a defense mechanism if the water is lit-up by predators that eat dinoflagellates – it may attract fish to eat those predators

19 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 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 plasmodium killed by the “leakiness” of the affected RBCs

20 Sexual and asexual reproduction that requires more than one host to complete
1. infected Anopheles mosquito bites a person injecting its sporozoites (n) 2. sporozoites enter the liver and undergo division to become merozoites (n) merozoites enter RBCs by using their apical complex 3. the merozoites asexually divide into more merozoites every 48 to 72 hrs – merozoites will break out of some RBCs – fever and chills some will go on to infect more RBCs and multiply 4. other merozoites develop into gametocytes 5. gametocytes picked up by a new mosquito 6. gametes form and fertilization takes place in the mosquito’s digestive tract the fertilized cell = zygote 7. an oocyst develops from the zygote and adheres to the wall of the mosquito’s gut produces more sporozoites Plasmodium 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)

21 3. Ciliates 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 not organized as chromosomes packed into smaller units each bearing duplicates of just a few genes control the everyday functions of the ciliate micronucleus – function in reproduction exchanged between two ciliates during conjugation

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 via radial canals and then expel it through the plasma membrane back into the environment

23 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 undigested food particles are carried to the opposite end of the cell as the cell mouth fuse with the plasma membrane in a specific region – acts as an “anal pore”

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 involving 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 of these in each disintegrate & the remaining micronuclei in each divides by mitosis- resulting in 2 micronuclei in each 4. the cells swap one of their micronuclei – genetic recombination 5. the cells separate 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 ends up with 1 micronuclei and 1 macronuclei -partially fuse -1 micronuclei becomes 4 haploid micronuclei (meiosis) -3 disappear -1 micronuclei becomes 2 (mitosis) -“swap” 1 micronuclei and separate -fuse 2 micronuclei into 1 (diploid) -2 micronuclei become 8 (mitosis/no division) -macronuclei disappears -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

25 B. Stramenophiles stramen = “straw”; pilos – “hair”
comprised of several groups of heterotrophs and several groups of phototrophs (algae) flagella are said to be “hairy” – have numerous hair-like projections along the length this hairy flagellum is paired with a smooth flagellum 1. oomycetes – water molds 2. bacillariophytes - diatoms 3. chrysophytes – golden algae 4. charophyceans – brown algae Smooth flagellum Hairy 5 µm

26 Algae: Photosynthetic Protists
study of algae = phycology no longer any formal classification schemes scattered across many phyla = polyphyletic algae = eukaryotic organisms with chlorophyll a pigments that carry out oxygen-producing photosynthesis differ from the plants – lack a well-organized vascular system and they have a simple reproductive system reproduce sexually and asexually occur most often in water fresh and marine – may be suspended as planktonic organisms or attached to the bottom (benthic) plankton = free-floating microscopic aquatic organisms phytoplankton – made up of algae and small plants zooplankton – non-photosynthetic protists and animals some classical algae are now grouped together with the plants (green algae), some are a separate lineage (red algae), some are grouped with the stremenophiles (yellow and brown algae, diatoms), some are grouped with the alveolates (diatoms) and some with the protozoans (euglenoids)

27 Algae: Photosynthetic Protists
important properties that classify them: 1. cell wall composition – rigid cell wall some have an outer membrane outside the wall – similar to the bacterial capsule 2. form in which food is stored 3. chlorophyll molecules and accessory pigments (carotenoids) chloroplasts have membrane-bound sacs (thylakoids) for the light-reactions of photosynthesis 4. flagella number and location of their insertion into the cell flagella are used for locomotion 5 morphology of the cells and/or body comprised of a vegetative body = thallus 6. habitat: marine or freshwater unicellular, colonial, filamentous, membranous, blade-like or tubular 7. reproductive structures: reproduction is asexual or sexual asexual – seen in unicellular forms three forms: 1. fragmentation, 2. spores and 3. binary fission sexual – generation of eggs within modified vegetative cells (oogonia) or sperm by antheridia 8. mitochondria cristae structure: tubular, disc or plate-like (lamellar) chlorophyta, charophyta, euglenophyta, chrysophyta, phaeophyta, rhodophyta, pyrrophyta

28 1. Oomycetes: Water molds
Water mold oogonium 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 but the oomycetes have cell walls made of cellulose (fungus – chitin) and the diploid condition predominates (reduced in fungi) molecular data also cannot confirm fungal origins similarities are an example of convergent evolution derived from a plastid containing ancestor - no longer have plastids and do not carry out photosynthesis – non-autotrophic acquire nutrients as decomposers – grow as cottony masses on dead animals and algae = heterotrophic white rusts and downey mildews live as parasites on land plants Phytophthora infestans – potato blight contributed to the Irish famine of the 19th century today still leads to crop losses of close to 15% (North America) and as high as 70% (Russia) molecular engineers have transferred blight-resistant genes into domestic potato crops to protect them water mold

29 Egg nucleus (n) MEIOSIS FERTILIZATION Haploid (n) Key Diploid (2n) Oogonium Antheridial hypha with sperm nuclei (n) SEXUAL REPRODUCTION Zygote germination Zygotes (2n) Zoosporangium Zoospore Cyst Germ tube ASEXUAL life cycle: can alternate between asexual and sexual forms asexual cell called a zoospore develops via mitosis into a hyphae the zoospore is biflagellated with one smooth flagella and the other “hairy” this hyphae develops sexual structures that produce gametes or alternatively can form zoospores asexually in the sexual life cycle - one region of the hyphae undergoes meiosis to produce egg nuclei (n) within a structure called an oogonium other branches can develop sperm nuclei (n) via meiosis – contained within an antitheridial hyphae these antitheridial hyphae grow and “hook” around the oogonium and deposit their nuclei through fertilization tubes = fertilization the hyphae then becomes dormant – wall of the oogonium breaks apart and releases the zygotes these zygotes germinate to regenerate hyphae which then develops into a new sexual structure – completes the sexual life cycle however some zygotes will form a zoosporangium which produces zoospores asexually germination of these zoospores starts the asexual life cycle Water mold zoospores

30 2. Diatoms 100,000 species of unicellular algae
with a 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 wall is a lacework of holes and grooves reproduce asexually via mitosis daughter receives half of the parental cell wall and generates a new half sexual reproduction is not common photosynthetic – chlorophylls a and c and carotenoids some are heterotrophic – absorb carbon-containing molecules through holes in their walls 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 not broken down by decomposers – carbon remains on the sea floor and is not released as CO2 may be able to decrease global warming – by taking CO2 out of the environment active ingredient in detergents, fine abrasive polishes, paint removers, decoloring oils, filtering agents, components of insulation and soundproofing products, reflective paint additive store their food reserves in the form of a glucose polymer = laminarin modern uses in nanotechnology – mechanism of assembly of their cell walls is being used as a model for miniature models and lasers

31 3. Golden Algae: Chrysophyta
all species are photosynthetic but some can be mixotrophic by absorbed dissolved organic compounds or ingesting good particles by phagocytosis major photosynthetic pigments: chlorophylls a and c + carotenoids (fucoxanthin) dominant pigment is fucoxanthin – golden-brown color major carbohydrate reserve = chrysolaminarin some have cell walls some have intricate external coverings = scales, walls and plates most are unicellular but some are colonial most are biflagellated – both attached near one end of the cell Dinobryon

32 4. Brown algae: Phaeophyta
brown algae – most complex algae all are multicellular and marine some have the most complex multicellular anatomy of all algae some have specialized tissues like animals and plant include the seaweeds giant seaweeds in intertidal zones – kelps carotenoid pigments located in plastids also found in the golden algae and diatoms sugar storage form = laminarin 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 Brown algae Thallus LE 28-18 Blade Stipe Holdfast

33 Brown algae: Life cycle
brown algae exhibit alternation of generations alternation between haploid and diploid multicellular forms only applies to multicellular stages in the life cycle if the two multicellular forms are structurally different = heteromorphic 1. diploid multicellular individual = sporophyte – adult algae with hold-fast, stipe and blades 2. on the blade – development of sporangia from the sporophyte 3. sporangia develop haploid zoospores by meiosis 4. 50% of zoospores develop into male gametophytes and 50% into female gametophytes – these are multicellualr 5. the gametophytes produce and release the gametes that will fuse and form the zygote eggs remain attached to the female gametophyte eggs can release a chemical that will attract sperm 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

34 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 by reversible assembly of actin subunits into microfilaments contraction requires interaction between actin and myosin first formed through the projection of a lamellipodium – actin assembles in the leading edge until it forms a microfilament network cytoplasm flows in forming the pseudopodium locomotion: anchor a tip to the surface – stream cytoplasm into the pseudopodium prey capture: pseudopodia senses the prey through physical contact and surrounds it types of pseudopodia: 1. Lobopodia – blunt shaped possess forms of cytoplasm called ectoplasm and endoplasm locomotion and feeding 2. Filopodia – football shaped ectoplasm only, two-way streaming to move food like a conveyor belt 3. Reticulopodia – branching filopodia complex and bear individual pseudopodia that form an irregular net used for primarily ingestion, can be used for locomotion 4. Axiopodia – long and thin reinforced by microtubule arrays enveloped by cytoplasm responsible for phagocytosis NOT locomotion

35 Clade Rhizaria A. Radiolarians: delicate, intricately symmetrical internal skeletons made of silica pseudopodia which “radiate” out from a central body – reinforced by microtubultes pseudopodia are also capable of phagocytosing food – cytoplasmic streaming then carries the food inro the central body B. Forams: formerly called foraminiferans named for their porous shells – holes are called foramen 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 marine and freshwater – in sand or attached to rocks or algae C. Cercozoans – the amoebas LE 28-23 200 µm Axopodia Forams Radilarins

36 C. Cercozoans contain the organisms called amoebas
amoeba species are also found in other clades most are heterotrophs – many are parasites of plants and animals; many are predators predators species include the most important predators of bacteria in many ecosystems

37 Clade Archaeplastida more than a billion years ago – heterotrophic protist acquired a cynanobacterial endosymbiont gave rise to red algae and green algae 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 divided into: A. Red algae B. Green algae C. Charophytes – includes Plants Cyanobacterium Primary endosymbiosis Secondary Heterotrophic eukaryote Red algae Green algae Dinoflagellates Plastid Apicomplexans Stramenopiles Euglenids Chlorarachniophytes

38 A. Red Algae: Rhodophyta
red algae – 6000 species multicellular most are autotrophic – photosynthesis possess plastids that contain numerous pigments red pigment = phycoerythritin and blue pigment = phycocyanin (phycobilins) masks the green of the chlorophyll in the plastids 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 blue and red wavelengths are absorbed by the phycobilins and the light energy is then transferred to the chlorophylls for photosynthesis shallow water algae may not have as much phycoerythritin and may be more green sugar storage form = floridean some can be parasitic on other red algae – lack pigmentation for photosynthesis cell wall includes a rigid inner part of microfibrils and a matrix of proteins and sugars this matrix is also called agar = sulfated polymers of galactose largest red aldae 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

39 B. Green algae: Chlorophyta
named for the green chloroplasts –pigments and structure are very similar to plants divide into two groups: 1. Charophytes – most closely related to plants 2. Chlorophytes – 7000 species chloro = “green” unicellular forms unicellular forms live symbiotically with other eukaryotes – contributing to photosynthetic output also live symbiotically with fungus – as lichens some are also multicellular - colonial, filamentous and sheetlike forms mostly freshwater chlorophylls a and b + carotenoid pigments sugar storage form = starch cell walls made of cellulose

40 Chlorophytes 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 from CO2 eyespot or stigma movement towards light two small contractile vacuoles at the base of the flagella – function as osmoregulatory organs sexual reproduction is also possible – cell division produces gametes of each “sex”

41 Chlorophytes size and complexity of green algae has evolved one of three ways: 1. formation of colonies of individual cells – e.g. Volvox colony or 500 to 60,000 cells – mostly smaller vegetative cells individual cells resemble Chlamydomonas - biflagellated cells are connected by thin strands of cytoplasm flagella all beat in a coordinated fashion – rotates the colony in a clock-wise fashion cells have eyespots – will orient toward the light some cells reproduce asexually other cells are reproductive - develop from the cells at the equator = called gonads zygote undergo mitosis until they form a sphere – flagella are on the inside!! therefore it must invert before leaving the daughter colony remains in the parental colony until it ruptures 2. repeated division of nuclei with no cytoplasmic division – multinucleate filaments (pond scum) 3. formation of true multicellular forms by mitosis and cytokinesis 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.

42 Green algae: Reproduction
life cycle: sexual and asexual stages mature cells are haploid – single cell with a cup-like chloroplast and 2 flagellae asexual reproduction: the cell reabsorbs its 2 flagellae and divides by mitosis to form four identical cells (zoospores) within a capsule cells are released as swimming zoospores sexual reproduction: upon shortage of nutrients haploid zoospore develops into gametes – male and female gametes of opposite mating types fuse to form the 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 develop into biflagellated mature cells that can continue the sexual life cycle or reproduce asexually 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: Reproduction

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

44 A. Amoebozoans lobe or tube-shaped pseudopodia rather than threadlike
1. Gymnamoebas unicellular soil, freshwater and marine most are heterotrophic – consume bacteria and other protists plus detritus (decomposers) some can possess shells = tests particle feeders – use their pseudopodia to capture food 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 plasmodial

45 3. Mycetozoans: Plasmodial slime molds
brightly pigmented – orange or yellow named for the formation of a feeding stage = plasmodium in the life cycle many similarities to fungus – including the formation of fruiting bodies & spores plasmodium – very large but still is unicellular cell undergoes mitosis but fails to divide through cytokinesis – “super-cell” lives on organic matter takes up food via phagocytosis then undergoes cytoplasmic streaming – cytoplasm streams first one way then the next – distribution of nutrients and O2 takes on a web-like form and undergoes sexual reproduction when conditions become harsh these bodies develop into fruiting bodies or sporangium via meiosis which are released as haploid spores (n) germination of the spores takes place in the presence of adequate moisture results in the production of either amoeboid cells (myxoamoebae) or flagellated cells (swarm cells) - 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 – mitosis without cytokinesis 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 3. Mycetozoans: Plasmodial slime molds

46 3. Mycetozoans: 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 3. Mycetozoans: Cellular slime molds feeding stage is a solitary amoeboid form = myxoameoba 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 halpoid amoebae fuse and form the zygote the zygote engulfs more haploid amoebae to form a giant cell (2n) forms a cell wall and begins to divide into numerous haploid amoebae via meiosis then mitosis the newly formed amoebae are release when the cell wall bursts asexual reproduction: occurs upon food depletion aggregation of hundreds of amoebae and their migration = multicellular organism called a pseudoplasmodium myxoameobae secrete cAMP upon the decrease in food supply cAMP attracts other myxoameobae – secrete more cAMP etc…. (positive feedback) the pseudoplasmodium is capable of migration once it stops moving – some amoebae differentiate into a stalk others differentiate into an asexual fruiting body and form spores (n) = sorus or the sorocap formation of the stalk requires the death and dessication of many of amoebae in the aggregation genetic information that directs formation of a stalk cell and a spore-forming cell??? spores are released – in the presence of food – haploid myxoamoebae emerge from spores 600 µm

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