pujalte - exercise 4

8/6/2019 Pujalte - Exercise 4

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Plant-like Algae

Species: Chara spp., muskgrass, stonewort, muskwort

Family: Characeae

Although these common lake inhabitants look similar to many underwater plants, they are actually algae. Muskgrasses are gr

or gray-green colored algae that grow completely submersed in shallow (4 cm) to deep (20 m) water. Individuals can vary

greatly in size, ranging from 5 cm to 1 m in length. The main "stem" of muskgrasses bear whorls of branchlets, clustered at

regularly spaced joints. When growing in hard water, muskgrasses sometimes become coated with lime, giving them a roug

gritty feel. These algae are identifiable by their strong skunk-like or garlic odor, especially evident when crushed.

Leaf:Algae lack true leaves. Six to 16 leaf-like branchlets of equal length grow in whorls around the stem, aare never divided. These branchlets often bear tiny thorn-like projections, which give the plant a rough or pric

appearance when magnified.

Stem:Algae lack true stems. The round, stem-like structure varies from 5 cm to over 1 m in length.

Flower:Algae do not produce flowers. Instead, microscopic one-celled sex organs called oogonia are formeThese tiny organs and patterns in the cases that surround them are used to distinguish between species.

Fruit:Algae do not produce fruits. Tiny spores are produced in fruiting bodies. In some species the fruitingbodies are orange and very conspicuous.

Root: Muskgrasses may be attached to the bottom by root-like structures called holdfasts.

Propagation:Spores carried by water and waterfowl; plant fragments.

Importance of plant: An important food source for waterfowl, particularly ducks. Provides valuableprotection for young fish and invertebrates. Muskgrasses grow quickly and occasionally cover the entire botto

of ponds, however its low growth rarely causes it to be considered a nuisance in Washington.

Distribution:Worldwide. More than 30 species in the U.S.

Habitat:Fresh to brackish water, inland and coastal, in both shallow and deep water. Some species found ialkaline lakes and slow-moving streams. Muskgrassses will often grow in deeper water than vascular aquatic

plants.

May be confused with:Other plant-like algae: Nitella (Nitellaspp.), which have symmetrically forkesmooth branchlets, do not have lime coatings, and lack the odor of muskgrasses; and Tolypella spp., which ha

unsymmetrically forked branches. Slender water-nymph (Najas flexilus) and coontail (Ceratophyllum demersu

are vascular plants which have a different leaf structure and do not produce an odor when crushed.

Algae (singular alga) are a large and diverse group ofphotosynthetic, eukaryotic, plant-likeorganisms that use chlorophyll in capturing light energy, but lack characteristic plantstructures such as leaves, roots, flowers, vascular tissue, and seeds. The designation algaeincludes diverse phyla, including diatoms (golden algae), green algae, euglenoids(flagellates), brown algae, and red algae, and range from single-celled organisms to giantseaweeds. The name alga (plural algae) comes from the Latin word for seaweed. The studyof algae is called phycology or algology.


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Algae range from single-celled organisms to multi-cellular organisms, some with fairlycomplex differentiated form and, if marine, called seaweeds. Some of the single-celledorganisms may be as small as one micrometer. Multicellular algae may consist of a row ofcells, appearing as a filament, or as a thin plate of cells, or even some larger ones may havebodies with a rudimentary division of labor. The multicellular giant kelp reaches 60 metersin length. Seaweeds themselves have many forms, including those that appear as if

terrestrial plants with leaves and stems, looking like moss, mushrooms, leaf lettuce, or evenpalm trees.

The various types of algae play significant roles in ecology. Algae are the base of the aquaticfood chain. Microscopic forms that live suspended in the water columncalledphytoplanktonprovide the food base for most marine food chains. The photosynthetic workdone by algae is believed to produce more than three-quarters of the oxygen in the earth'satmosphere; far more than that produced by terrestrial plants.

In very high densities (so-called algal blooms), algae may discolor the water and outlast orpoison other life forms.

General characteristics and ecology

Algae are usually found in damp places or bodies of water and thus are common in aquaticenvironments, but they are also found in terrestrial locales. Most unicellular and colonialalgae are aquatic, and float near the surface of the water. The seaweeds grow mostly inshallow marine waters, but some, such as the red algae, can grow quite deep in the ocean.Terrestrial algae are usually rather inconspicuous and far more common in moist, tropicalregions than dry ones, because algae lack vascular tissues and other adaptations to live onland. Algae can endure dryness and other conditions in symbiosis with a fungus as lichen.

All algae have photosynthetic machinery that is considered to derive from thecyanobacteria, and so produce oxygen as a by-product ofphotosynthesis, unlike the non-

cyanobacterial photosynthetic bacteria. It is believed that more than three-quarters of theoxygen in the atmosphere comes from algae and cyanobacteria, rather than from plants.Although all algae utilize chlorophyll, at times other pigments mask the green color,resulting in organisms with red and brown colors.

In temperate zones, the photosynthesis of algae may be the sole source of oxygen in ice-covered lakes and ponds. If the ice remains thin and clear, such photosynthesis can helpkeep oxygen levels high enough to prevent fish kills by compensating for oxygen lostthrough respiration and decomposition. When sunlight is reduced through snow cover orthick ice, algal photosynthesis may be reduced to the point of threatening fish survival.

Some algae reproduce both sexually and asexually, such as the green algae (for example,

Chlamydomonas, a unicellular green algae). The presence ofsexual reproduction in someform is a nearly universal trait among living organisms, as seen even at this simple level.

Taxonomy of algae

The term algae is mainly used for convenience, rather than taxonomic purposes, as thereappears little relationship between the various phyla. Although they have historically beenregarded as simple plants, algae are generally classified in the kingdom Protista, rather than


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Plantae. Algae sometimes are defined as "photosynthetic protists"; however, sometaxonomic schemes do not limit them to this kingdom.

Algae are distinguished from the other main protists, the protozoa, in that they arephotoautotrophic (deriving energy from photosynthesis only), although this is not a hardand fast distinction as some groups contain members that are mixotrophic, deriving energy

both from photosynthesis and uptake of organic carbon by such means as osmotrophy (byosmosis) or phagotrophy (enveloping by the cell membrane). Some scientists include asalgae the prokaryotic (simple cell structure lacking a nucleus or organelles)cyanobacteria,which are aquatic, photosynthetic, and commonly known as "blue-green algae." However, ingeneral, the designation of algae is limited to eukaryotic (cell structure with a differentiatednucleus and organelles), photosynthetic organisms.

Prokaryotic "algae"

Sometimes the prokaryoticcyanobacteria, given their aquatic and photosyntheticcharacteristic, have been included among the algae, and have been referred to as thecyanophytes or blue-green algae. Recent treatises on algae often exclude them, and

consider as algae only eukaryotic organisms. Cyanobacteria are some of the oldestorganisms to appear in the fossil record, dating back about 3.8 billion years (Precambrian).Ancient cyanobacteria likely produced much of the oxygen in the Earth's atmosphere.

Cyanobacteria can be unicellular, colonial, or filamentous. They have a prokaryotic cellstructure typical of bacteria and conduct photosynthesis directly within the cytoplasm,rather than in specialized organelles. Some filamentous blue-green algae have specializedcells, termed heterocysts, in which nitrogen fixation occurs.

Eukaryotic algae

As commonly defined, algae are eukaryotes and conduct photosynthesis within membrane-

bound structures (organelles) called chloroplasts. Chloroplasts contain DNA and are similarin structure to cyanobacteria, with the speculation that they represent reducedcyanobacterial endosymbionts. The exact nature of the chloroplasts is different among thedifferent lines of algae, possibly reflecting different endosymbiotic events.

There are three groups that haveprimarychloroplasts:

y Green algae (together with higher plants)

y Red algae

y Glaucophytes

In these groups, two membranes surround the chloroplast. The chloroplasts of red algaehave a more or less typical cyanobacterial pigmentation, while the green algae and higherplants have chloroplasts with chlorophyll a and b, the latter found in some cyanobacteriabut not most. There is support for the view that these three groups originated from acommon pigmented ancestor; i.e., chloroplasts developed in a single endosymbiotic event.

Red and green algae have an "alternation of generations" life cycle. This is the same lifecycle as the mosses, suggesting that green algae were ancestral to mosses. Green aquatic,the most diverse algae with over seven thousand identified species, are generally aquatic,


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and the majority are freshwater organisms. They range from unicellular organisms tomarine species of large, multicellular seaweeds. Most of the seaweeds of the warm oceansare red algae. They absorb the deep penetrating blue light, allowing them to exist deeperthan other algae.

Two other groups have green chloroplasts containing chlorophyll b:

y euglenids and

y chlorarachniophytes.

Three and four membranes surround these, respectively, and it is speculated that they wereretained from an ingested green alga. Those of the chlorarchniophytes contain a smallnucleomorph, which is the remnant of the alga's nucleus.

The remaining algae all have chloroplasts containing chlorophylls a and c. The latterchlorophyll type is not known from any prokaryotes or primary chloroplasts, but geneticsimilarities with the red algae suggest a relationship there. These groups include:

y Heterokonts (e.g., golden algae, diatoms, brown algae)

y Haptophytes (e.g., coccolithophores)

y Cryptomonads

y Dinoflagellates

In the first three of these groups (put together in the supergroup Chromista, along withvarious colorless forms), the chloroplast has four membranes, retaining a nucleomorph incryptomonads, and it is speculated that they share a common pigmented ancestor. Thetypical dinoflagellate chloroplast has three membranes, but there is considerable diversityamong chloroplasts in the group. The Apicomplexa, a group of closely related parasites, alsohave plastids, though not actual chloroplasts, which share similarities with that of thedinoflagellates. The brown algae include the major seaweeds found on the shores in the

temperate zones and the large, offshore beds of kelps.

Note many of these groups contain some members that are not photosynthetic, but areconsidered to have once been photosynthetic. Some retain plastids, but not chloroplasts,while others are considered to have lost them entirely.

Forms of algae

Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and non-motile forms have developed independently among several of the groups. Some of the morecommon organizational levels, more than one of which may occur in the life cycle of a

species, are:

y Colonial- small, regular groups of motile cells

y Capsoid- individual non-motile cells embedded in mucilage (thick, gluey, sugary substance)

y Coccoid- individual non-motile cells with cell walls

y Palmelloid- non-motile cells embedded in mucilage

y Filamentous - a string of non-motile cells connected together, sometimes branching

y Parenchymatous - cells forming a thallus with partial differentiation of tissues


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In three lines, even higher levels of organization have been reached, leading to organismswith full tissue differentiation. These are the brown algaesome of which may reach 60meters in length (kelps)the red algae, and the green algae. The most complex forms arefound among the green algae, in a lineage that is considered to have eventually led to thehigher land plants. The point where these non-algal plants begin and algae stop is usuallytaken to be the presence of reproductive organs with protective cell layers, a characteristic

not found in the other algal groups.

Algae and symbioses

Algae frequently form part of a symbiosis with other organisms. In a symbiotic relationship,the alga photosynthesises and supplies photosynthates to its host. The host organism isthen capable of deriving some or all of its energy requirements from the alga. Examplesinclude:

y lichens - a fungus is the host, usually with a green alga or a cyanobacterium as the symbiont.

Both fungi and algae found in lichens are capable of living independently.

y

corals - several algae form symbioses (zooxanthellae) with corals. Notable among these is thedinoflagellate Symbiodinium, found in many hard corals. The loss ofSymbiodinium, or other

zooxanthellae, from the host leads to coral bleaching.

Uses of algae

Algae are helpful in reducing pollutants. They assist in capturing the runoff fertilizers thatenter lakes and streams from nearby farms. Algae are used in many wastewater treatmentfacilities, reducing the need for harmful chemicals, and are used in some power plants toreduce carbon dioxide emissions. The carbon dioxide is pumped into a pond, or some kindof tank, on which the algae feed. The natural pigments produced by algae can be used as analternative to chemical dyes and coloring agents.

Algae is commercially cultivated as a nutritional supplement. Among algal species cultivatedfor their nutritional value include chlorella (a green algae) and dunaliella (Dunaliella salina),which is high in beta-carotene and is used in vitamin C supplements.

One of the most popular microalgal species is spirulina (Arthrospira platensis), which is acyanobacteria, and has been hailed by some as a superfood. Algae is used in the Chinese"vegetable" known as fatchoy(which is actually a cyanobacterium).

Many common products, such as hand lotion, lipstick, paint, and ice cream, containderivatives from algae.

Algae can be used to produce biodiesel fuel, and by estimates can potentially producesuperior amounts of oil compared to land-based crops. Because algae grown to producebiodiesel do not need to meet the requirements of a food crop, it is much cheaper toproduce. Also, it does not need fresh water or fertilizer (both of which are quite expensive ).Currently, most research into efficient algal-oil production is being done in the privatesector, but if predictions from small-scale production experiments bear out, then usingalgae to produce biodiesel may be the most viable method by which to produce enoughautomotive fuel to replace current world gasoline usage. The per unit area yield of oil fromalgae is at least 15 times greater than the next best crop, palm oil. The difficulties in


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It is in these environments that the diversity of structurally complex algae (calledseaweeds) reaches its pinnacle.

As a grouping, the algae cut across even the prokaryote/eukaryote divide: the so-called"Blue-green algae" are cyanobacteria. All other algae are eukaryotes. Green Algae (differentfrom Blue-green algae) are considered to be the ancestors of green plants. Other kinds ofalgae on the other hand are distinct from green plants and from each other in having

different and unrelated accessory pigments. These pigments are responsible for the waysdifferent algae absorb light, providing advantage to each individual type of alga to competebest at a water depth where its prefered wavelength is perhaps strongest.

y Read Phycology(article not developed yet)

y Read Algae

[edit] Cyanobacteria

The cyanobacteria comprise the structurally simplest algae, and presumably are closelyrelated to the oldest photosynthetic organisms on the planet. Although capable of extracting

energy from sunlight through photosynthesis, these algae are related to bacteria asevidenced by their prokaryotic cell structure. Yet, some Blue-greens have developed multi-cellular thalli that approach eukaryotic algal forms, and thus their traditional inclusion withinthe "algae."

Algae

From Wikipedia, the free encyclopedia

Jump to: navigation, search

For other uses, seeAlgae (disambiguation) andAlga (disambiguation).

Algae


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Laurencia, a marine genus ofRed Algae from Hawaii.

Scientificclassification

Domain: Eukaryota

Included groups

y Archaeplastida

o Chlorophyta (Green algae)

o Rhodophyta (Red algae)

o Glaucophyta

y Rhizaria, Excavata

o Chlorarachniophytes

o Euglenidsy Chromista, Alveolata

o Heterokonts

Bacillariophyceae (Diatoms)

Axodine

Bolidomonas

Eustigmatophyceae

Phaeophyceae (Brown algae)

Chrysophyceae (Golden algae)

Raphidophyceae

Synurophyceae

Xanthophyceae (Yellow-green algae)

o Cryptophyta

o Dinoflagellates

o Haptophyta

Excluded groups

y Cyanobacteria


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y Plantae

The lineage of algae according to Thomas Cavalier-Smith. The exact number and placement of

endosymbiotic events is not yet clear, so this diagram can be taken only as a general guide[1][2]

It

represents the most parsimonious way of explaining the three types of endosymbiotic origins of

plastids. These types include the endosymbiotic events ofcyanobacteria, red algae and green algae,

leading to the hypothesis of the supergroups Archaeplastida, Chromalveolata and Cabozoa respectively.

However, the monophyly ofCabozoa has been refuted and the monophylies of Archaeplastida and

Chromalveolata are currently strongly challenged. Endosymbiotic events are noted by dotted lines.

Algae (pronounced /ldi/ or /li/; singular alga/l/, Latin for "seaweed") are a

large and diverse group of simple, typically autotrophic organisms, ranging from unicellularto multicellular forms. The largest and most complex marine forms are called seaweeds.They are photosynthetic, like plants, and "simple" because they lack the many distinctorgans found in land plants.

Though the prokaryoticCyanobacteria (commonly referred to as blue-green algae) weretraditionally included as "algae" in older textbooks, many modern sources regard this asoutdated[3] as they are now considered to be closely related to bacteria. [4] The term algae isnow restricted to eukaryotic organisms.[5]All true algae therefore have a nucleus enclosedwithin a membrane and plastids bound in one or more membranes.[3][6]Algae constitute aparaphyletic and polyphyletic group,[3] as they do not include all the descendants of the lastuniversal ancestor nor do they all descend from a common algal ancestor, although theirplastids seem to have a single origin.[1]Diatoms are also examples of algae.

Algae lack the various structures that characterize land plants, such as phyllids (leaves) andrhizoids in nonvascular plants, or leaves, roots, and other organs that are found intracheophytes (vascular plants). Many are photoautotrophic, although some groups contain


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members that are mixotrophic, deriving energy both from photosynthesis and uptake oforganic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellularspecies rely entirely on external energy sources and have limited or no photosyntheticapparatus.

Nearly all algae have photosynthetic machinery ultimately derived from the Cyanobacteria,

and so produce oxygen as a by-product of photosynthesis, unlike other photosyntheticbacteria such as purple and green sulfur bacteria. Fossilized filamentous algae from theVindhya basin have been dated back to 1.6 to 1.7 billion years ago.[7]

The first alga to have its genome sequenced was Cyanidioschyzon merolae.

Contents

[hide]

y 1Etymology and study

y 2Classification

y 3Relationship to higher plants

y 4Morphology

y 5Symbiotic algae

o 5.1Lichens

o 5.2Coral reefs

o 5.3Sea sponges

y 6Life-cycle

y 7Numbers

y 8Distribution

y 9Locations

y 10Useso 10.1Agar

o 10.2Alginates

o 10.3Energy source

o 10.4Fertilizer

o 10.5Nutrition

o 10.6Pollution control

o 10.7Pigments

o 10.8Stabilizing substances

y 11See also

y 12Notes

y 13Bibliography

o 13.1General

o 13.2Regional

y 14External links

[edit] Etymology and study


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Title page ofSamuel Gottlieb Gmelin, Historia Fucorum, dated 1768.

The singular alga is the Latin word for a particular seaweed and retains that meaning inEnglish.[8] The etymology is obscure. Although some speculate that it is related to Latinalgre, "be cold",[9] there is no known reason to associate seaweed with temperature. Amore likely source is alliga, "binding, entwining."[10] Since Algae has become a biologicalclassification, alga can also mean one classification under Algae, parallel to a fungus being aspecies of fungi, a plant being a species of plant, and so on.

The ancient Greek word for seaweed was (fkos or phykos), which could mean either

the seaweed, probably Red Algae, or a red dye derived from it. The Latinization, fcus,meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate haslong been some word related to the Biblical (pk), "paint" (if not that word itself), a

cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the easternMediterranean. It could be any color: black, red, green, blue.[11]

Accordingly the modern study of marine and freshwater algae is called either phycology oralgology. The name Fucus appears in a number oftaxa.

[edit] Classification


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Higher plants (Embryophyta)Chlorarachniophytes

Supergroup

affiliationMembers Endosymbiont Summary

Primoplantae/

Archaeplastida

y Chlorophyta

y Rhodophyta

y GlaucophytaCyanobacteria

These Algae haveprimarychloroplasts,i.e. the chloroplasts are surrounded by

two membranes and probably

developed through a single

endosymbiotic event. The chloroplasts

ofRed Algae have chlorophyllsa and c

(often), and phycobilins, while those of

Green Algae have chloroplasts with

chlorophyll a and b. Higher plants are

pigmented similarly to Green Algae and

probably developed from them, andthus Chlorophyta is a sister taxon to the

plants; sometimes they are grouped as

Viridiplantae.

Excavata and

Rhizaria

y Chlorarachniophytes

y EuglenidsGreen Algae

These groups have greenchloroplasts containingchlorophylls a and b.[12] Theirchloroplasts are surrounded byfour and three membranes,respectively, and were probablyretained from ingested GreenAlgae.

Chlorarachniophytes, whichbelong to the phylum Cercozoa,contain a small nucleomorph,which is a relict of the algae'snucleus.

Euglenids, which belong to thephylum Euglenozoa, live primarilyin freshwater and havechloroplasts with only three

membranes. It has beensuggested that the endosymbioticGreen Algae were acquiredthrough myzocytosis rather thanphagocytosis.

Chromista and

Alveolata

y Heterokonts

y Haptophyta

y Cryptomonads

Red AlgaeThese groups have chloroplastscontaining chlorophylls a and d,and phycobilins. The latter


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y Dinoflagellates chlorophyll type is not known fromany prokaryotes or primarychloroplasts, but geneticsimilarities with the Red Algaesuggest a relationship there.

In the first three of these groups(Chromista), the chloroplast hasfour membranes, retaining anucleomorph in Cryptomonads,and they likely share a commonpigmented ancestor, althoughother evidence casts doubt onwhether the Heterokonts,Haptophyta, and Cryptomonadsare in fact more closely related toeach other than to othergroups.[2][15]

The typical dinoflagellatechloroplast has three membranes,but there is considerable diversityin chloroplasts within the group,and it appears there were anumber of endosymbioticevents.[1] The Apicomplexa, agroup of closely related parasites,also have plastids calledapicoplasts. Apicoplasts are notphotosynthetic but appear to havea common origin with

Dinoflagellate chloroplasts.[1]

W.H.Harvey (18111866) was the first to divide the Algae into four divisions based on theirpigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey'sfour divisions are: Red Algae (Rhodophyta), Brown Algae (Heteromontophyta), Green Algae(Chlorophyta) and Diatomaceae.[16]

[edit] Relationship to higher plants

The first plants on earth evolved from shallow freshwater algae much like Chara some 400million years ago. These probably had an isomorphic alternation of generations and were

probably filamentous. Fossils of isolated land plant spores suggest land plants may havebeen around as long as 475 million years ago.[17][18]

[edit] Morphology


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The kelp forest exhibit at the Monterey Bay Aquarium. A three-dimensional, multicellular thallus.

A range of algal morphologies are exhibited, and convergence of features in unrelatedgroups is common. The only groups to exhibit three dimensional multicellular thalli are the

reds and browns, and some chlorophytes.[19]

Apical growth is constrained to subsets ofthese groups: the florideophyte reds, various browns, and the charophytes.[19] The form ofcharophytes is quite different to those of reds and browns, because have distinct nodes,separated by internode 'stems'; whorls of branches reminiscent of the horsetails occur atthe nodes.[19]Conceptacles are another polyphyletic trait; they appear in the coralline algaeand the Hildenbrandiales, as well as the browns.[19]

Most of the simpler algae are unicellularflagellates or amoeboids, but colonial and non-motile forms have developed independently among several of the groups. Some of the morecommon organizational levels, more than one of which may occur in the life cycle of aspecies, are

y

Colonial: small, regular groups of motile cellsy Capsoid: individual non-motile cells embedded in mucilage

y Coccoid: individual non-motile cells with cell walls

y Palmelloid: non-motile cells embedded in mucilage

y Filamentous: a string of non-motile cells connected together, sometimes branching

y Parenchymatous: cells forming a thallus with partial differentiation of tissues

In three lines even higher levels of organization have been reached, with full tissuedifferentiation. These are the brown algae,[20]some of which may reach 50 m in length


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(kelps)[21]the red algae,[22] and the green algae.[23] The most complex forms are foundamong the green algae (see Charales and Charophyta), in a lineage that eventually led tothe higher land plants. The point where these non-algal plants begin and algae stop isusually taken to be the presence of reproductive organs with protective cell layers, acharacteristic not found in the other alga groups.

[edit] Symbiotic algae

Some species of algae form symbiotic relationships with other organisms. In thesesymbioses, the algae supply photosynthates (organic substances) to the host organismproviding protection to the algal cells. The host organism derives some or all of its energyrequirements from the algae. Examples are as follows.

[edit] Lichens

Main article: Lichens

Rock lichens in Ireland.

Lichens are defined by the International Association for Lichenology to be "an association ofa fungus and a photosynthetic symbiont resulting in a stable vegetative body having aspecific structure."[24] The fungi, or mycobionts, are from the Ascomycota with a few fromthe Basidiomycota. They are not found alone in nature but when they began to associate isnot known.[25] One mycobiont associates with the same phycobiont species, rarely two, fromthe Green Algae, except that alternatively the mycobiont may associate with the samespecies ofCyanobacteria (hence "photobiont" is the more accurate term). A photobiont maybe associated with many specific mycobionts or live independently; accordingly, lichens arenamed and classified as fungal species.[26] The association is termed a morphogenesis

because the lichen has a form and capabilities not possessed by the symbiont species alone(they can be experimentally isolated). It is possible that the photobiont triggers otherwiselatent genes in the mycobiont.[27]

[edit] Coral reefs

Main articles: Coral, Coral reef, andZooxanthella


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Floridian coral reef

Coral reefs are accumulated from the calcareousexoskeletons ofmarine invertebrates ofthe Scleractinia order; i.e., the Stony Corals. As animals they metabolizesugar and oxygento obtain energy for their cell-building processes, including secretion of the exoskeleton,with water and carbon dioxide as byproducts. As the reef is the result of a favorable

equilibrium between construction by the corals and destruction by marine erosion, the rateat which metabolism can proceed determines the growth or deterioration of the reef.

Algae of the Dinoflagellate phylum are often endosymbionts in the cells of marineinvertebrates, where they accelerate host-cell metabolism by generating immediatelyavailable sugar and oxygen through photosynthesis using incident light and the carbondioxide produced in the host. Endosymbiont algae in the Stony Corals are described by theterm zooxanthellae, with the host Stony Corals called on that account hermatypic corals,which although not a taxon are not in healthy condition without their endosymbionts.Zooxanthellae belong almost entirely to the genus Symbiodinium.[28] The loss ofSymbiodinium from the host is known as coral bleaching, a condition which unless correctedleads to the deterioration and loss of the reef.

[edit] Sea sponges

Main article: Sea sponge

Green Algae live close to the surface of some sponges, for example, breadcrumb sponge(Halichondria panicea). The alga is thus protected from predators; the sponge is providedwith oxygen and sugars which can account for 50 to 80% of sponge growth in somespecies.[29]

[edit] Life-cycle

Rhodophyta, Chlorophyta and Heterokontophyta, the three main algal Phyla, have life-cycles which show tremendous variation with considerable complexity. In general there isan asexual phase where the seaweed's cells are diploid, a sexual phase where the cells arehaploid followed by fusion of the male and female gametes. Asexual reproduction isadvantageous in that it permits efficient population increases, but less variation is possible.Sexual reproduction allows more variation, but is more costly. Often there is no strictalternation between the sporophyte and also because there is often an asexual phase, whichcould include the fragmentation of the thallus.[21][30][31]


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For more details on this topic, see Conceptacle.

[edit] Numbers

Algae on coastal rocks at Shihtiping in Taiwan

TheAlgalCollection of the U.S. NationalHerbarium (located in the National Museum ofNatural History) consists of approximately 320500 dried specimens, which, although notexhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of thenumber of algal species (that number remains unknown).[32] Estimates vary widely. Forexample, according to one standard textbook,[33] in the British Isles the UK BiodiversitySteering Group Reportestimated there to be 20000 algal species in the UK. Anotherchecklist reports only about 5000 species. Regarding the difference of about 15000 species,the text concludes: "It will require many detailed field surveys before it is possible toprovide a reliable estimate of the total number of species ...."

Regional and group estimates have been made as well: 50005500 species of Red Algae

worldwide, "some 1300 in Australian Seas,"[34] 400 seaweed species for the westerncoastline of South Africa,[35] 669 marine species from California (U.S.A.),[36] 642 in thecheck-list of Britain and Ireland,[37] and so on, but lacking any scientific basis or reliablesources, these numbers have no more credibility than the British ones mentioned above.Most estimates also omit the microscopic Algae, such as the phytoplankta, entirely.

[edit] Distribution

The topic of distribution of algal species has been fairly well studied since the founding ofphytogeography in the mid-19th century AD.[38]Algae spread mainly by the dispersal ofspores analogously to the dispersal of Plantae by seeds and spores. Spores are everywhere

in all parts of the Earth: the waters fresh and marine, the atmosphere, free-floating and inprecipitation or mixed with dust, the humus and in other organisms, such as humans.Whether a spore is to grow into an organism depends on the combination of the species andthe environmental conditions.

The spores of fresh-water Algae are dispersed mainly by running water and wind, as well asby living carriers.[39] The bodies of water into which they are transported are chemicallyselective. Marine spores are spread by currents. Ocean water is temperature selective,resulting in phytogeographic zones, regions and provinces.[40]


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To some degree the distribution ofAlgae is subject to floristic discontinuities caused bygeographical features, such as Antarctica, long distances of ocean or general land masses.It is therefore possible to identify species occurring by locality, such as "Pacific Algae" or"North Sea Algae". When they occur out of their localities, it is usually possible tohypothesize a transport mechanism, such as the hulls of ships. For example, Ulva reticulataand Ulva fasciata travelled from the mainland to Hawaii in this manner.

Mapping is possible for select species only: "there are many valid examples of confineddistribution patterns."[41] For example, Clathromorphum is an arctic genus and is notmapped far south of there.[42] On the other hand, scientists regard the overall data asinsufficient due to the "difficulties of undertaking such studies."[43]

[edit] Locations

Phytoplankton, Lake Chuzenji

Algae are prominent in bodies of water, common in terrestrial environments and are found

in unusual environments, such as on snow and on ice. Seaweeds grow mostly in shallowmarine waters, under 100 metres (330 ft); however some have been recorded to a depth of360 metres (1,180 ft)[44]

The various sorts of algae play significant roles in aquatic ecology. Microscopic forms thatlive suspended in the water column (phytoplankton) provide the food base for most marinefood chains. In very high densities (algal blooms) these algae may discolor the water andoutcompete, poison, or asphyxiate other life forms.

Algae are variously sensitive to different factors, which has made them useful as biologicalindicators in the Ballantine Scale and its modification.

[edit] Uses


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Harvesting Algae

[edit] Agar

Agar, an Algae derivative, has a number of commercial uses.[45]

[edit] Alginates

Between 100,000 and 170,000 wet tons ofMacrocystis are harvested annually in Californiafor alginate extraction and abalone feed.[46][47]

[edit] Energy source

To be competitive and independent from fluctuating support from (local) policy on the longrun, biofuels should equal or beat the cost level of fossil fuels. Here, algae based fuels hold

great promise, directly related to the potential to produce more biomass per unit area in ayear than any other form of biomass. The break-even point for algae-based biofuels shouldbe within reach in about ten years.[citation needed]

Main articles:Algae fuel, Biological hydrogen production, Biohydrogen, Biodiesel, Ethanol fuel, Butanol

fuel, andVegetable fats and oils

[edit] Fertilizer


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Seaweed is used as a fertilizer.

For more details on this topic, see Seaweed fertiliser.

For centuries seaweed has been used as a fertilizer; George Owen of Henllys writing in the16th century referring to drift weed in South Wales:[48]

This kind of ore they often gather and lay on great heapes, where it heteth and rotteth, andwill have a strong and loathsome smell; when being so rotten they cast on the land, as theydo their muck, and thereof springeth good corn, especially barley ... After spring-tydes orgreat rigs of the sea, they fetch it in sacks on horse backes, and carie the same three, four,or five miles, and cast it on the lande, which doth very much better the ground for corn andgrass.

Today Algae are used by humans in many ways; for example, as fertilizers, soil conditionersand livestock feed.[49]Aquatic and microscopic species are cultured in clear tanks or ponds

and are either harvested or used to treat effluents pumped through the ponds. Algacultureon a large scale is an important type ofaquaculture in some places. Maerl is commonly usedas a soil conditioner.

[edit] Nutrition

Seaweed gardens on Inisheer.

See also: Edible seaweed

Naturally growing seaweeds are an important source of food, especially in Asia. Theyprovide many vitamins including: A, B1, B2, B6, niacin and C, and are rich in iodine,potassium, iron, magnesium and calcium.[50] In addition commercially cultivated microalgae,including both Algae and Cyanobacteria, are marketed as nutritional supplements, such asSpirulina,[51]Chlorella and the Vitamin-C supplement, Dunaliella, high in beta-carotene.

Algae are national foods of many nations: China consumes more than 70 species, includingfatchoy, a cyanobacterium considered a vegetable; Japan, over 20 species;[52]Ireland,dulse; Chile, cochayuyo.[53]Laver is used to make "laver bread" in Wales where it is known


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as bara lawr; in Korea, gim; in Japan, nori and aonori. It is also used along the west coastof North America from California to British Columbia, in Hawaii and by the Mori ofNewZealand. Sea lettuce and badderlocks are a salad ingredient in Scotland, Ireland, Greenlandand Iceland.

Dulse, a food.

The oils from some Algae have high levels ofunsaturated fatty acids. For example,Parietochloris incisa is very high in arachidonic acid, where it reaches up to 47% of thetriglyceride pool.[54] Some varieties ofAlgae favored by vegetarianism and veganism containthe long-chain, essential omega-3 fatty acids, Docosahexaenoic acid (DHA) andEicosapentaenoic acid (EPA), in addition to vitamin B12.

[citation needed] The vitamin B12 in algaeis not biologically active. Fish oil contains the omega-3 fatty acids, but the original source isalgae (microalgae in particular), which are eaten by marine life such as copepods and arepassed up the food chain.[55]Algae has emerged in recent years as a popular source of

omega-3 fatty acids for vegetarians who cannot get long-chain EPA and DHA from othervegetarian sources such as flaxseed oil, which only contains the short-chain Alpha-Linolenicacid (ALA).

[edit] Pollution control

y Sewage can be treated with algae, reducing the need for greater amounts of toxic chemicals

than are already used.

y Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the

enriched algae itself can be used as fertilizer.

[edit]P

igments

The natural pigments produced by algae can be used as an alternative to chemical dyes andcoloring agents.[56]

[edit] Stabilizing substances

Carrageenan, from the red alga Chondrus crispus, is used as a stabiliser in milk products.


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Main articles: Carrageenan andChondrus crispus

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The plant-like protists, or algae, are all photosynthetic autotrophs. These organisms form the

base of many food chains. Other creatures depend on these protists either directly for food or

indirectly for the oxygen they produce. Algae are responsible for over half of the oxygen

produced by photosynthesizing organisms. Many forms of algae look like plants, but they differin many ways. Algae do not have roots, stems, or leaves. They do not have the waxy cuticle

plants have to prevent water loss. As a result, algae must live in areas where water is readily

available. Algae do not have multicellular gametangia as the plants do. They contain

chlorophyll, but also contain other photosynthetic pigments. These pigments give the algae


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characteristic colors and are used to classify algae into various phyla. Other characteristics used

to classify algae are energyreserve storage and cell wall composition.

Members of the phylum Euglenophyta are known as euglenoids. These organisms are both

autotrophic as well as heterotrophic. There are hundreds of species of euglenoids. Euglenoids

are unicellular and share properties of both plants and animals. They are plant-like in that they

contain chlorophyll and are capable ofphotosynthesis. They do not have a cell wall of

cellulose, as do plants; instead, they have a pellicle made of protein. Euglenoids are like

animals in that they are motile and responsive to outside stimuli. One particular species,

Euglena, has a structure called an eyespot. This is an area of red pigments that is sensitive to

light. AnEuglena can respond to its environment by moving towards areas of bright light,

where photosynthesis best occurs. In conditions where light is not available for photosynthesis,euglenoids can be heterotrophic and ingest their food. Euglenoids store their energy as

paramylon, a type of polysaccharide.

Members of the phylum Bacillariophyta are called diatoms. Diatoms are unicellular organisms

with silica shells. They are autotrophs and can live in marine or freshwater environments. They

contain chlorophyll as well as pigments called carotenoids, which give them an orange-yellow

color. Their shells resemble small boxes with lids. These shells are covered with grooves and

pores, giving them a decorated appearance. Diatoms can be either radially or bilaterally

symmetrical. Diatoms reproduce asexually in a very unique manner. The two halves of the shell

separate, each producing a new shell that fits inside the original half. Each new generation,

therefore, produces offspring that are smaller than the parent. As each generation gets smaller

and smaller, a lower limit is reached, approximately one quarter the original size. At this point,

the diatom produces gametes that fuse with gametes from other diatoms to produce zygotes.

The zygotes develop into full sized diatoms that can begin asexual reproduction once more.

When diatoms die, their shells fall to the bottom of the ocean and form deposits called

diatomaceous earth. These deposits can be collected and used as abrasives, or used as an

additive to give certain paints their sparkle. Diatoms store their energy as oils or carbohydrates.

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The dinoflagellates are members of the phylum Dinoflagellata. These organisms are unicellular

autotrophs. Their cell walls contain cellulose, creating thick, protective plates. These platescontain two grooves at right angles to each other, each groove containing one flagellum. When

the two flagella beat together, they cause the organism to spin through the water. Most

dinoflagellates are marine organisms, although some have been found in freshwater

environments. Dinoflagellates contain chlorophyll as well as carotenoids and red pigments. They

can be free-living, or live in symbiotic relationships withjellyfish or corals. Some of the free-

living dinoflagellates are bioluminescent. Many dinoflagellates produce strong toxins. One

species in particular, Gonyaulax catanella, produces a lethal nerve toxin. These organisms

sometimes reproduce in huge amounts in the summertime, causing a red tide. There are so

many of these organisms present during a red tide that the ocean actually appears red. When

this occurs, the toxins that are released reach such high concentrations in the ocean that many

fish are killed. Dinoflagellates store their energy as oils or polysaccharides.


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The phylum Rhodophyta consists of the red algae. All of the 4,000 species in this phylum are

multicellular (with the exception of a few unicellular species) and live in marine environments.

Red algae are typically found in tropical waters and sometimes along the coasts in cooler areas.

They live attached to rocks by a structure called a holdfast. Their cell walls contain thick

polysaccharides. Some species incorporate calcium carbonate from the ocean into their cell walls

as well. Red algae contain chlorophyll as well as phycobilins, red and blue pigments involved in

photosynthesis. The red pigment is called phycoerythrin and the blue pigment is called

phycocyanin. Phycobilins absorb the green, violet, and blue light waves that can penetrate deep

water. These pigments allow the red algae to photosynthesize in deep water with little light

available. Reproduction in these organisms is a complex alternation between sexual and asexual

phases. Red algae store their energy as floridean starch.

The 1,500 species of brown algae are the members of the phylum Phaeophyta. The majority of

the brown algae live in marine environments, on rocks in cool waters. They contain chlorophyll

as well as a yellow-brown carotenoid called fucoxanthin. The largest of the brown algae are the

kelp. The kelp use holdfasts to attach to rocks. The body of a kelp is called a thallus, which can

grow as long as 180 ft (60 m). The thallus is composed of three sections, the holdfast, the stipe,

and the blade. Some species of brown algae have an air bladder to keep the thallus floating at the

surface of the water, where more light is available for photosynthesis. Brown algae store their

energy as laminarin, a carbohydrate.

The phylum Chlorophyta is known as the green algae. This phylum is the most diverse of all the

algae, with greater than 7,000 species. The green algae contain chlorophyll as their main

pigment. Most live in fresh water, although some marine species exist. Their cell walls are

composed of cellulose, which indicates the green algae may be the ancestors of modern plants.

Green algae can be unicellular, colonial, or multicellular. An example of a unicellular green alga

is Chlamydomonas. An example of a colonial algae is Volvox. AVolvoxcolony is a hollow

sphere of thousands of individual cells. Each cell has a single flagellum that faces the exterior of

the sphere. The individual cells beat their flagella in a coordinated fashion, allowing the colony

to move. Daughter colonies form inside the sphere, growing until they reach a certain size and

are released when the parent colony breaks open. Spirogyra and Ulva are both examples of


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multicellular green algae. Reproduction in the green algae can be both sexual and asexual. Green

algae store their energy as starch.

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