May 4, 2018 | Author: mailtosiba | Category: Eukaryotes, Chloroplast, Algae, Cyanobacteria, Chromosome
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Chapter 19

Life began about 3.5 billion years ago in the oceans with the appearance of prokaryotes. The oldest reliable date for the appearance of the eukaryotes is about 1.9 billion years ago, when the first members of a group of unicellular organisms organisms called acritarchs appear in the fossil record in China. critarchs ! re probably the remains of a group of ancient eukaryotes • "ere plankton • #ome resemble dinoflagellates while others resemble green algae • Their relationship among li$ing organisms is uncertain • http%&&'eol#ciµpal&acritarch.htm http%&&'eol#ci µpal&acritarch.htmll http%&&www.geo.ari( http%&&www .geo.ari( lynology&ppacrtrc.html ppacrtrc.html )ukaryotic cells came into e*istence probably by a process called endosymiosis. +itochondria arose first, as an early eukaryotic cell engulfed but did not digest a bacterium capable of aerobic respiration. The two organisms li$ed together, one inside the other, and both benefited. F!n"i# $%ants and anima%s are all probably deri$ed from protists.

ungi and animals are eukaryotes organisms that lack plastids. nother line of e$olution, one that had mitochondria, entered another endosymbiosis with a  photosynthetic  photosynthetic cyanobacterium, which later later e$ol$ed into a chloroplast. chloroplast. This line ga$e rise to algae including green algae, which in turn produced true plants, the emryo$hytes. #e$eral clades e*ist that still ha$e some e*tant members whose plastids ha$e numerous prokaryotic prokaryotic characters. Chloroplasts of red algae especially resemble cyanobacteria. The kingdom -rotista contains eukaryotes that cannot be assigned with certainty to other kingdoms The kingdom -rotista is an artificial grouping and classification does not represent e$olutionary relationships. This kingdom is also known as &rotoctista. -rotists co$ered in this course are those photosynthetic organisms that function like plants in ecosystems. •

They are the grass of the ocean.

-rotists to be studied include% 1. lgae% lgae% photosynt photosynthetic hetic organism organismss studied studied by $hyco%o"ists.

/. #lime #lime molds and oomycetes% oomycetes% heterotr heterotrophi ophicc organisms organisms that are traditi traditional onally ly studied studied by myco%o"ists, although these organisms are not fungi. nother group of protists not included in this course are the ciliates, flagellates, and other heterotrophs. The phylogenetic relationship among the different groups of protists is contro$ersial, e.g. the relationship  between the green and brown brown algae.


0n prokaryotes, proteins do not surround the 2. 0ts numerous negati$e charges are neutrali(ed by calcium ions. 0n eukaryotes, the 2 is packaged with histones forming nucleosomes. The 2 condenses into chromosomes. The genome is a short circle of 2 containing containing about 3, genes, and lack introns. 0n eukaryotes, the 2 molecule molecule carries thousands of genes. The chromosomes of eukaryotes ha$e a homologous and ne$er  occur as a single chromosome in normal circumstances. )ukaryotic )ukaryotic genes ha$e introns, which do not code for any type of 42. N!c%ear str!ct!re and di'ision

-rokaryotic cells lack nucleus. The 2 circle is attached to the plasma membrane. s the cell grows and the plasma membrane e*pands, the two daughter 2 molecules are separated. The nuclei of plants, animals and fungi are $ery similar in structure, metabolism, mitosis and meiosis. pparently these three clades di$erged after the nucleus had achie$ed a high le$el of comple*ity. 0n eukaryotes, most of the 2 is found in the nucleus. The nucleus is surround by two doublelayered membranes with nuclear pores.  nucleolus is present. The nuclei are typically haploid or diploid. +itosis assures that each daughter cell recei$es one of each type of chromosome to maintain the species number of chromosomes. +eiosis usually occurs as part of se*ual reproduction. The pairing of paternal and maternal homologous chromosomes, followed by crossing o$er and genetic recombination assures genetic di$ersity. di$ersity. #ome groups of organisms ha$e a uni6ue mitotic process that may represent an earlier di$ergence in the history of eukaryotes. Or"ane%%es

-rokaryotes lack membrane bound organelles. They ha$e ribosomes and storage granules, which are not membrane bound organelles. -hotosynthetic -hotosynthetic prokaryotes ha$e folded plasma membrane that pro7ects into the cytoplasm.

)ukaryotes ha$e membrane bound organelles that compartmentali(e the cell and perform different functions simultaneously. 4ibosomes of prokaryotes are 8#, being smaller and denser than the # ribosomes of eukaryotes. lagella and cilia are uniform in eukaryotes ha$ing a 9 : / arrangement of microtubules.  few  prokaryotes ha$e flagella, flagella, and ne$er ha$e the 9:/ arrangement. arrangement. They are not composed composed of microtubules or tubulin. Endosymiotic Theory.

This hypothesis attempts to e*plain the origin of eukaryotic organelles, mitochondria and chloroplasts. 0n 195, ;. C. +ereschkowsky had speculated that plastids were prokaryotes prokaryotes li$ing inside eukaryotic cells. 0n the 19ne chloroplast with a red photosensiti$e eyespot, or stigma, aids in the detection of light. Chloroplast has a pyrenoid, which is typically surrounded by a shell of starch. The cell wall is made of a carbohydrate and protein comple* inside which is the plasma membraneB there is no cellulose in the cell wall. 4eproduction is both se*ually and ase*ually. #ee the Life Cycle diagram on page 331 in 4a$el et al.

*o%'o. is a motile colony. 

The colony consists of a hollow sphere called the spheroid, made up of a single layer of 5 to edogonium, #tigeoclonium, and ritschiella. C%ass U%'o$hyceae •

+ostly marine algae with a few representati$es in fresh water.

ilamentous septate, filamentous coenocytic ?siphonous@ or thalloid   

ilamentous species ha$e large multinucleate cells separated by septaB some may be netlike others straight chains. They ha$e a netlike chloroplast. #iphonous algae are characteri(ed by $ery large, branched, coenocytic cells Thalloid species ha$e a single nucleus and chloroplast.

+a7ority has one plane of di$ision, unlike the 'lva with 'lva with three planes

#pindle and nuclear en$elope persist through mitosis.

lagellated cells may ha$e two, four or many flagella directed forward

lternation of generations with a haploid gametophyte and diploid sporophyte.

They ha$e sporic meiosis or a diploid, dominant life history in$ol$ing gametic meiosis.

C%ado$hora is a filamentous septate ul$ophyte.

   

0t forms large blooms in fresh water. There are both marine and fresh water species of (ladophora. (ladophora. )ach cell is multinucleated and has one single, peripheral, netlike chloroplast with many  pyrenoids. +arine species species ha$e an alternation of isomorphic isomorphic generations. generations. +ost of the fresh water species do not ha$e an alternation of generations.

U%'a consists of a twocell thick flat thallus that may grow up to a meter in length.  0t is known as sea lettuce. 'lva is anchored to the substrate by a holdfast produced by e*tensions of the cells at its base.  'lva is  The cells of the thallus are uninucleate and ha$e one chloroplast. 'lva is anisogamous and has an alternation of isomorphic generations. generations.  'lva is 'lva on page ==8.  #ee the Life Cycle of 'lva on Codi!m and Ha%imeda  are e*amples of siphonous marine algae.    

Fery Fery large, coenocytic cells that are rarely septate characteri(e siphonous algae. Cell walls are only produced during reproduction. #iphonous green algae are diploid, with gametes being the only haploid stage. Aalimeda has calcified cell walls.

)*amples to study% Thalloid% El$a. #iphonous% cetabularia, Codium, Fentricaria, Aalimeda. ilamentous septate% Cladophora. C%ass Charo$hyceae •

'rowth habit may be unicellular, filamentous, filamentous, colonial or thalloid ?parenchymatous@.

Considered closely related to plants due to structural, biochemical and genetic similarities.

The orders Coleochaetales and Charales ha$e plantlike characteristics. These include%     

symmetrical flagellated cells always ha$e two flagella. reakdown of the nuclear en$elope at mitosis -ersistent spindles or phragmoplast at cytokinesis. -resence of phytochrome, fla$onoids and chemical precursors of the cuticle. >ther molecular features.

filamentous charophyte. S$iro"yra is an unbranched, filamentous      

ound in fresh water, often forming blooms. Cells uninucleate. ilaments are surround by a watery sheath. Chloroplasts one or more, flat ribbonlike with numerous pyrenoids. se*ual reproduction occurs by fragmentation. There are no flagellated cells at any stage of its life c ycle.

   

#e*ual reproduction takes place through the formation of a con7ugation tube. The cytoplasm of one cells migrates to the other cell and function as isogametes.  thick wall of sporopollenin surrounds the (ygote. +eiosis is (ygotic.

Desmids are a large group of fresh water charophytes.   

Lack flagellated cells. esmid cells consist of two sections of semicells 7oined by a narrow constriction. #e*ual reproduction is similar to #pirogyra.

Two Two orders of Charophyceae, the Co%eochaeta%es and the Chara%es, resemble bryophytes and $ascular  plants.  

They ha$e plantlike microtubular phragmoplast operating during cytokinesis. They are oogamous and their sperm are ultrastructurally similar similar to those of bryophytes. bryophytes.

+orphological and molecular studies indicate that an early basal split in the green algae ga$e rise to a ch%oro$hyte c%ade containing most of the green algae, and a stre$to$hyte c%ade that includes the Coleochaetales and Charales, (ygnematalean green algae, and land plants ?bryophytes and $ascular  plants@. Co%eochaeta%es • •

• • •

0nclude branched filamentous and discoid genera. 'rowth occurs at the ape* or peripheral cells, and the plant is anchored in mud or silt by translucent rhi(oids. Coleochaete has uninucleate $egetati$e cells that each contains one large chloroplast with an embedded pyrenoid. 0t reproduces ase*ually by (oospores that are formed singly within cells. #e*ual reproduction is oogamous. The (ygotes remain attached to the parental thallus, which stimulate the growth of a layer of cells that co$ers the (ygotes. These parental cells ha$e wall ingrowths are belie$ed to function in nutrient transport between gametophyte and sporophyte.

Chara%es •

• • • • • • •

The thallus in some stoneworts is encrusted with white lime, gi$ing a crusty te*ture ?hence the name brittlewort@. The Charales e*hibit apical growth. The thallus is differentiated into nodal and internodal regions. The nodal regions ha$e plasmodesmata. #perms are produced in multicellular antheridia. )ggs are produced in oogonia enclosed by se$eral long, tubular, twisted dells. #perms are the only flagellated cells in their life cycles. Gygotes are surround by sporopollenin. sporopollenin.

)*amples to study% ilamentous% #pirogyra, desmids. Thalloid% Coleochaete. ranched filamentous% Chara

Di'ision Rhodo$hyta •

4ed algae are mostly marine organisms found in tropical and warm waters. ewer than 1 species occur in fresh water. #ome occur in cooler regions of the world.

+any species are found in $ery deep water.

There are =1 to 3 in their walls. 

Coralline algae play an important role in coral reef building.

+any produce to*ic terpenoids that deter herbi$ores.

ood reser$es are stored as )%oridean starch in granules. 

loridean starch resembles glycogen.

Chloroplasts are reddish ?rhodoplasts@ and contain chlorophyll a, H and Icarotene, accessory watersoluble watersoluble pigments called $hycoi%ins ?phycocyanin, ?phycocyanin, phycoerythrin, allophycocyanin@. allophycocyanin@. 

These pigments absorb well green and bluegreen wa$elengths that penetrate deep into the water.

Chloroplast chemicals resemble those found in cyanobacteria and may ha$e originated from this group by endosymbiosis.

Com$%icated Li)e Histories

See fig. 19.2) on page 4)*. •

+any reproduce ase*ually by discharging spores, called monos$ores , into the water.

ll red algae ha$e comple* life cycles, reproduce se*ually and ha$e no flagellated stages. 

The simplest form of se*ual reproduction in$ol$es the alternation of a haploid gametophyte and a diploid sporophyte.      

The gametophyte produces s$ermatan"ia ?sing. s$ermatan"i!m@ that release nonmotile The female gamete or egg is produced in the car$o"oni!m, on a same gametophyte. The carpogonium de$elops a protuberance called the tricho"yne for the reception of the spermatia. The spermatium fuses with the trichogyne and the nucleus tra$els to the female nucleus and fuses with it. The resultant diploid (ygote then produces a few diploid car$os$ores, which are release into the water. Carpospores produce sporophytes sporophytes that form haploid spores, which in turn produce new gametophytes.

0n some red algae, the (ygote produces a car$os$oro$hyte generation, which remains attached to the parent gametophyte.  

'ametophyte, 'ametophyte, carposporophyte, carposporophyte, tetrasporophyte. tetrasporophyte.

The carposporophyte di$ides mitotically and e$entually produces carpospores. The carpospores are released and settle onto a substrate, and grow into separate diploid sporophytes.

0n many red algae, the diploid (ygote is transferred to another cell of the gametophyte gametophyte called the a!.i%iary ce%% where it proliferates into many carpospores.   

The carpospores produce a new generation called the tetrasporophyte. tetrasporophyte. +eiosis occurs 0 in speciali(ed cells of the tetras$oro$hyte, called the tetras$oran"ia. )ach tetras$ore germinates into a gametophyte.

Di'ision &haeo$hyta -haeophytes are also known as brown algae •

0t is an entirely marine group especially abundant in temperate and cold waters.

Common in the intertidal and subtidal (onesB dominant alga of rocky shores.

bout 1,5 species.

The Tha%%!s •

#i(e  few are microscopic, most much larger  up to f great economic importance% fertili(er, food especially in Kapan, source of algin  stabili(er  moisture retainer in many products such as ice cream, cake frosting, paint, pharmaceuticals,  processing of natural natural and synthetic rubber. rubber.

Li)e Cyc%e

See fig. 19.2! on page 4)2. •

Their life cycle in$ol$es an alternation of generation, and meiosis occurs during spore formation ?s$oric meiosis @.

The ends of the branches are called rece$tac%es and are swollen with large deposits of hydrophilic compounds. compounds. #cattered o$er the surface of the receptacles are small openings that lead to ca$ities called conce$tac%es0 Gametan"ia de$elop in the conceptacles.

The gametophytes of the primiti$e brown algae produce reproducti$e structures called $%!ri%oc!%ar "ametan"ia. They may function as male or female gametangia or produce flagellated haploid spores that gi$e rise to new gametophytes.

The diploid sporophyte produces both plurilocular and unilocular sporangia.  The plurilocular sporangia produce diploid (oospores that produce diploid sporophytes.  +eiosis takes place in the unilocular sporangia producing haploid (oospores that germinate to  produce haploid gametophytes. gametophytes.

Goospores ha$e tinsel and whip flagella.

#ome groups ?e.g. -ucus ?e.g. -ucus@@ do not form spores and ha$e a gametic life cycle without alternation of generations.

&hy%!m +aci%%ario$hyta •

n ancient group that appeared in the fossil record about /5 million years ago, and became abundant in the fossil record about 1 million years ago during the Cretaceous. iatoms are unicellular or colonial organisms that form an important component of the  phytoplankton.  phytoplankton. They may count for as much as /5M of the primary production of the earth.

There may be as many as 1, species, some of the most di$erse and abundant algae on earth.

iatoms are the primary source of food for many marine animalsB they pro$ide essential carbohydrates, fatty acids, sterols, and $itamins to the consumers.

iatoms li$e in both freshwater and marine habitats, but are especially abundant in cold marine waters.

iatoms can also inhabit terrestrial habitats such as damp cliff faces, moist tree trunks and on the surfaces of buildings.

The 2a%%s O) Diatoms Consist O) T3o Ha%'es •

Cell wall in two parts known as )r!st!%es, are made of polymeri(ed silica ?#i> / A/>, 95M@ and carbohydrates especially pectin ?5M@. The shell is composed of an upper and lower half, with the lower half fitting neatly within the upper, like a -etri dish.

The shell is highly ornamented and perforated with microscopic holes so precisely spaced that they are used commercially to test the resolution of e*pensi$e microscope lenses.

These holes connect the li$ing protoplast with the e*ternal en$ironment.  

reshwater forms are usually cylindrical in shape% $ennate. +arine species are usually spherical or circular% centric.

Chrysophytes Chrysophytes form sometimes Nbrown bloomsO in fresh and salt water.

iatoms ha$e chlorophyll a and c, and the goldenbrown carotenoid )!co.anthin.

Two Two large chloroplasts are present in pennate diatoms, and many discoid chloroplasts in centric species.

ood is stored in the form of oils and chryso%aminarin, a soluble polysaccharide stored in $acuoles.

#ome species are heterotrophic absorbing organic molecules from the en$ironment. >ther heterotrophs li$e symbiotically in foraminiferans.

ossil frustules make the diatomaceous earths mined for use as filters, insulating material and abrasi$e polish.

Re$rod!ction In Diatoms Is ,ain%y Ase.!a% •

4eproduction is usually ase*ual. Changes in the en$ironment or critical small si(e triggers se*ual reproduction.

Ye%%o34"reen a%"ae

#ome phycologists as a di$ision or class consider the yellowgreen algae different from the chrysophytes. >thers include them in the chrysophytes. •

• • • •

They ha$e a $ariety of body shapes% unicellular, filamentous, filamentous, siphonous or large multicellular  body form. They ha$e chlorophyll c. se*ual reproduction occurs by iso"amy  in aucheria  in aucheria.. #e*ual reproduction consists of biflagellated sperms and a multinucleated egg. The (ygote breaks off and after a period of dormancy germinates forming a new NtubeO filled with haploid nuclei.

Di'ision Chryso$hyta lso know as the goldenbrown algae. •

Chrysophytes Chrysophytes are photosynthetic, unicellular colonial organismsB some plasmodia, filamentous and tissuelike forms. bout 1 known species.

bundant in freshwater and marine en$ironments worldwide.

Chrysophytes Chrysophytes contain chlorophylls a and c, and accessory pigment )!co.anthin, a carotenoid.

Cells usually ha$e one or two chloroplasts.

They store food in a $acuole in the form of polysaccharide chrysolaminarin, chrysolaminarin, which is stored in a $acuole usually found in the posterior of the cell.

#ome species are heterotrophic ingesting bacteria, algal cells and organic particles.

#ome species ha$e cell wall containing cellulose and impregnated with minerals. >thers are without walls. >ne group has silica plates on the cell surface.

4eproduction is mostly ase*ual by means of 1oos$ores with une6ual flagella of similar structure.

#ome species can reproduce se*ually.

4esting cysts are formed as a result of se*ual reproduction at the end of the growing season.

0n many ways, golden algae are biochemically and structurally similar similar to brown algae.

Di'ision Dino$hyta The dinophyta are also known as dinoflagellates.

+olecular e$idence indicates that the dinoflagellates are closely related to ciliate proto(oa such as  Para,eciu, and  Para,eciu, and orticella, orticella, and to apicomple*ans, a group of parasitic flagellates whose cells contain a nonpigmented plastid, e.g.  Plas,odiu, that  Plas,odiu, that causes malaria. picomple*ans, dinoflagellates dinoflagellates and others form a group called al$eolates. •

+ost are unicellular biflagellates.

bout = known species, most of which are members of the marine phytoplankton.

Their flagella beat in two groo$es, one encircles the cell and the other e*tends lengthwise.

The nonmotile dinoflagellates produce flagellated cells that beat in groo$es.

Their chromatin is always condensed into chromosomes.

+any are co$ered with cellulose plates forming a theca.

bout half of the dinoflagellates lack photosynthetic apparatus and feed by ingesting food  particles or absorbing dissol$ed organic organic compounds. They ha$e chlorophyll a and c, I and Pcarotenes, a carotenoid called peridinin, peridinin, fuco*anthin, a yellowbrown carotenoid, and other *anthins..

#ome pigmented flagellates carry out photosynthesis and also feed by absorbing carbon compound through a protruded peduncleB this is called ,yxotrophy. ,yxotrophy .

"hen dinoflagellates are symbionts, they lack theca, e.g. (oo*anthellae of giant clams, corals, worms, etc.

inoflagellates store their food as oils and starch. Ender ad$erse periods of low nutrient le$els, dinoflagellates form resting cysts that are carried by currents.

4eproduction is mostly ase*ual but se*ual reproduction has been obser$ed in some species.

#ome species produce bioluminescence and powerful neuroto*ins that are accumulated by fish and mollusks.

They ha$e a characteristic type of nuclear and cell di$ision.

http%&& http%&&'eol#ci http%&&www'eol#ciµpal&dinoflag µpal&dinoflagellate.html ellate.html http%&&$eolates.html http%&&*a.html http%&& http%&&www tany&pro7ects&dinoflag& noflag&

&hy%!m Oomycota •

>omycetes is a distinct heterotrophic group of about 8 species.

Enicellular to highly branched, coenocytic and filamentous forms.

>omycetes are either saprobes or symbionts.

They inhabit a6uatic en$ironments% marine, freshwater or moist terrestrial habitats.

Their cell wall is made of cellulose.

Their food reser$e is in the form of glycogen.

se*ual reproduction is by means of motile 1oos$ores, which ha$e the characteristic two flagella of heterokonts.

#e*ual reproduction is oo"amo!s % one gamete large and nonmotile, the other small and motile.    

)ggs are produced in the oo"onia. The antheridi!m contains many male nuclei. The fertili(ed egg forms a thickwalled (ygote called the oos$ore . The oospore ser$es as a resting stage during stressful conditions.

>omycetes are also called water molds, white rusts and downy mildew. mildew.

2ater ,o%ds Are A/!atic Oomycetes0 •

bundant in fresh water.

+ostly saprophytic and a few parasitic including species that cause diseases to fish and fish eggs.

#pecies may be homotha%%ic or heterotha%%ic.

Saprolegnia  and /chlya  and /chlya are  are common water molds that reproduce se*ually and ase*ually.

Some Terrestria% Oomycetes Are Im$ortant &%ant &atho"ens •

Terrestrial Terrestrial oomycetes produce motile (oospores when water is a$ailable.

Terrestrial Terrestrial oomycetes are important plant pathogensB the genus  Phytophthora is  Phytophthora is particularly destructi$e to plants.

They attack important crops like grapes, pineapples, onions, strawberries, apples, citrus fruits, cacao, etc. 

 Phytophthora cinna,o,i cinna,o,i killed  killed millions of a$ocado trees in southern California, and destroyed thousands of hectares of  "ucalyptus timberland  "ucalyptus timberland in ustralia. ustralia.

  

         

 Phytophthora ra,oru, ra,oru, was the cause of the disease called Nthe sudden oak death.O 0t attacks many species of oaks and also /< other species of plants including firs and coastal redwoods. The great potato famine in 0reland ?1=ne protoplast gets the top half, and the other gets the bottom half. 0n either case, the protoplast then secretes a new bottom to the -etri dish?i.e., a new half fitting inside the old half@. This means that after e$ery mitotic di$ision, one of the resulting diatoms is smaller than the original. This can go on for se$eral generations. )$entually, )$entually, the protoplast inside the tiny shell undergoes meiosis rather than mitosis. our haploid gametes are released from the shell, which is discarded. "hen two gametes meet and fuse, the resulting diploid cell is called an a!.os$ore ?(ygote@. The au*ospore grows into a normal si(e of the species. 0t then secretes a silica case of the original si(e...and the cycle begins anew. #e*ual reproduction in centric diatoms is usually oo"amo!s , and in pennate diatoms non motile iso"amo!s0

Di'ision  E!"%eno$hyta0

+ostly unicellular fresh water organismsB one colonial genus. +olecular e$idence indicates that earlier euglenoids were phagocytic. bout one third of euglenoids contain chloroplastsB their chloroplasts resemble those of the green algae and suggest that they were formed from endosymbiotic green algae. bout two thirds of the genera are colorless heterotrophs that depend on particle feeding and absorption of dissol$ed organic compounds. They are mostly freshwater organisms li$ing in waters rich in organic compounds and particles. Cell structure% • • • • • •

Cell membrane, with pellicle immediately beneath the membrane. Lack cell wallB one genus has a walllike co$ering made of manganese and iron minerals. The $e%%ic%e is made of protein strips arranged arranged in the form of a heli*B it may may be rigid or fle*ible. #ingle )%a"e%%!m for mo$ement coming from the reser'oir , and a second nonemergent flagellum. flagellum. F%a"e%%ar s3e%%in"  and the sti"ma  or eyespot makes the lightsensing system. system. Contracti%e 'ac!o%e used in maintaining water balance.

• •

• • •

&yrenoids are found in ch%oro$%asts. 0t is a region where r!isco is found and $aramy%on, a  polysaccharide is stored. stored. -igments present% chlorophylls a and b, carotenoids and se$eral *anthophylls. )uglenoids grown in absence of light ha$e been known to lose their chloroplasts and become heterotrophic. 4eproduction in euglenoids is ase*ual, by mitotic cell di$ision. #e*ual reproduction is unknown. The nuclear membrane remains intact during mitosis in a way similar to the fungi. bout 9 species are known.

n intact mitotic nuclear en$elope is probably a primiti$e condition. The break down of the nuclear membrane is probably a deri$ed condition that appeared after euglenoids separated from the main stack of   protists. http%&& http%&&botit.botany& botanyQ13&i$ersity&)ugl i$ersity&)uglena&)uglena.html ena&)uglena.html http%&& http%&&www &delwiche&-#life&lectures&)uglenophy ectures&)uglenophyta.html ta.html http%&& http%&&www &R7cclark&classes&bot1/5&resource&su ot1/5&resource&sur$ey&euglenophy r$ey&euglenophyta.html ta.html

ECOLOGY OF THE ALGAE The "cology of the algae is not found in your textboo0. lgae are dominant in salt and fresh water habitat. )$erywhere they grow, they play a role similar to that of plants in terrestrial habitats. long rocky shores, the large and more comple* members of the brown, red and green algae grow forming bands that reflect the ability of the seaweeds to withstand e*posure. #eaweeds in this intertidal (one are e*posed twice a day to large fluctuations of humidity, humidity, salinity and light, in addition to pounding action of the surf and forceful, abrasi$e water motions. -olar seaweeds endure months of darkness under the sea ice. #eaweeds are the food source to a host of herbi$ores and parasites. Large beds of seaweeds pro$ide a safe habitat for many a6uatic organisms, e.g. kelp beds off the coast of California. &%an(ton refers to all suspended drifting organisms organisms found in all bodies of water. •

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-lanktonic algae and cyanobacteria constitute the $hyto$%an(ton found in oceans and fresh water. Aeterotrophic plankton and usually swimming microorganisms are called 1oo$%an(ton. acteria and some heterotrophic protists form the acterio$%an(ton.

-hytoplankton is found at the base of the f ood chain.

Colonial and singlecelled chrysophytes, dinoflagellates, diatoms and green algae are the most important organisms organisms at the base of the food chain in freshwater habitats. Enicellular and colonial haptophytes, dinoflagellates and diatoms are the primary producers of the ocean.

0n both marine and freshwater habitats, phytoplankton populations are kept in check by seasonal climatic changes, nutrient limitation and predation. -hytoplankton is the ma7or producers of o*ygen in the atmosphere. -hytoplankton reduces the amount of C> / in the atmosphere by fi*ing it during photosynthesis. photosynthesis. -hytoplankton is important in the deposition of CaC> 3 deposits on the ocean floor. The C>/ fi*ed by photosynthesis and the calcification process is replaced by atmospheric C>


#e$eral types of multicellular algae are important members of coral reefs and deposit a substantial amount of calcium compound important in coral building. #ome haptophyte protists produce substantial substantial amounts of sulfur o*ides that are added to the atmosphere and reflect sunlight helping to maintain a cooler temperature.

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