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‘Seaweeds’ - protists too

•  Brown Algae/Heterokont algae (Stramenopila) - Phaeophyta

•  Red Algae: Rhodophyta

•  Green Algae: Chlorophyta

•  Leading to ‘land plants’…from green algae - Charophyceans

Figure 28.8 A tentative phylogeny of eukaryotes.

Alga = photosynthetic protist

“Heterokont” algae are the algae in Stramenopila (browns, goldens, and diatoms)

Stramenopila = hairy flagellum

Diatoms:

Prelude to plants: Green Algae, including Chlorophytes and Charophyceans (the closest relatives of plants)

Phylum (Division) Phaeophyta:brown algae •  Location –mostly marine, largest and most structurally complex,

therefore found in temperate (cool) waters mainly and areas with high nutrients.

•  Photoautotrophs •  Multicellular •  Alternation of generations •  Cellulose cell walls •  Pigments – olive green to brown color comes from fucoxanthin, a

yellow pigment (also a carotenoid). Chlorophyll a & c •  Form– Diverse in form and structure, the browns contain the largest

individuals. Kelps – are a group of large brown algae, usually subtidal, make "forests"

and provide both energy/food and structure to kelp forest ecosystems •  Habitat – intertidal to mid–subtidal •  Heavily used for commercial purposes

Figure 28.20x1 Brown algae (Phaeophyta): another heterokont alga. Brown algae are the largest and most complex algae. All are multicellular, and most are marine (i.e., oceanic). Many exist as “seaweeds” (large oceanic algae) in cool ocean waters.

Figure 28.18 Brown algae (Phaeophyta): another heterokont alga. Brown algae are the largest and most complex algae. All are multicellular, and most are marine (i.e., oceanic). Many exist as “seaweeds” (large oceanic algae) in cool ocean waters.

Pneumatocyst

Floats (air-filled bladders) on Sargassum

pneumatocyst

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Sieve tubes in kelps are analogous to phloem in plants.

Would kelp have something analogous to xylem?

Figure 28.21 The life cycle of Laminaria: an example of “alternation of generations” Many of the large multicellular algae (“kelps”), including many brown, red, and green algae, exhibit this kind of life cycle, which is like the life cycle of plants.

Laminaria are heteromorphic - the gametophyte and sporophyte differ in appearance.

Other algae can be isomorphic - both the haploid and diploid forms look the same.

Red and Green Algae are the closest relatives to land plants…

Figure 28.25 A hypothetical history of plastids in the photosynthetic eukaryotes

Figure 28.4 A tentative phylogeny of eukaryotes.

Red algae have chloroplasts with a double membrane.

(Like green algae, plants)

Primary endosymbiosis only.

Red algae: Rhodophyta •  Primarily found in warm ocean waters •  May have alternation of generations •  Chloroplasts have double membranes •  mostly marine, most abundant in species •  Cell walls: cellulose and sometimes CaCO3 •  Pigments – chl a and (d), phycobilins, a wide

variety of carotenoids •  Form – ranges from thin film, to upright, foliose.

Some forms secrete CaCO3 in the skeleton – tropical

•  Habitat – intertidal to deepest subtidal (to 250m) •  No flagellated stages - rely on water to bring

gametes together

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Figure 28.28 Red algae (Rhodophyta): unique algae, closely related to the Green algae. Do not have flagellated stages. Plastids evolved by primary endosymbiosis of cyanobacteria. Dominant large algae in warm ocean waters, though also found abundantly in cool ocean waters. Diverse life cycles, but many exhibit “alternation of generations.”

Polysiphonia Life Cycle: a red alga with heteromorphic alternation of generations

Figure 28.20 Brown and red algae provide food and other useful materials.

Gel-forming substances In cell walls:

algin in brown algae

agar and carrageenan In red algae

Green algae •  Includes two groups:

chlorophytes and charophyceans •  Closest relatives of the land

plants (esp. the charophyceans) •  Bright green chloroplasts and

complex life cycles (both asexual and sexual, with gametes biflagellated)

•  Like red algae, plastids evolved via primary endosymbiosis of cyanobacteria

Green algae: Chlorophyta

•  Location – mainly fresh water, some marine •  Cell walls: cellulose or silica •  Pigments – chl a and b, and carotenoids, same as

terrestrial plants. Chlorophyll not masked by other pigments and therefore bright "grass" green. •  Habitat – upper portion of the photic zone, intertidal

mainly. Some are associated with eutrophic areas (rich in nutrients)

•  Mostly freshwater, but some marine •  Some unicellular, some colonial, some truly

multicellular (with “alternation of generations” life cycle)

•  Some symbiotic (e.g. as part of a lichen)

Ulva Life Cycle: Alternation of isomorphic generations

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Calcareous Chlorophyta: Halimeda

Figure 28.23 Colonial and multicellular chlorophytes: Volvox: colonial (top left), Caulerpa: multinucleate filaments (top right), Ulva: truly multicellular (“sea lettuce,” bot. right)

Figure 28.24 The life cycle of Chlamydomonas, a unicellular chlorophyte

Gametes via mitosis

Resistant zygote

Mature cell with multiple “daughter” cells forming

Figure 28.25 A hypothetical history of plastids in the photosynthetic eukaryotes

Spirogyra

http://www.olympusbioscapes.com/gallery/2009/3.html

• Helical arrangements of chloroplasts

• Conjugation as well as asexual reproduction

• Asexual reproduction through fragmentation

“Protists” II 1)  Overview of sexual life cycles: review

2)  Modern diversity of protists, Part 2: Diatoms, Brown Algae, Red Algae, Green Algae

3)   The evolution of “Plants” or “Land Plants” from Green Algae

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Figure 29.1 Some highlights of plant evolution Figure 29.2 Charophyceans: Chara (top), Coleochaete orbicularis (bottom)

Figure 29.2x Chara Traits shared by charophyceans and

land plants •  Very similar plastids (structurally similar, but

especially similar chloroplast DNA) •  Very similar cellulose cell walls (cellulose is

even produced by a similar rose-shaped structures)

•  Anti-photorespiration enzymes packaged in peroxisomes

•  Similar structure of flagellated sperm •  Similar structures during cell division

(phragmoplasts)