CH28 ORIGINS OF EUKARYOTIC DIVERSITY (PART II)

By Stella Lee, Michelle Leu, Jonathan Kim, & Austin Angelidakis

STRAMENOPILA Includes several groups of photosynthetic

autotrophs (algae) and numerous heterotrophs

Stramenopiles are classified in the Kingdom Chromista

Photosynthetic stramenopiles have unusual chloroplasts: two additional membranes outside the usual chloroplast envelope, a small amount of cytoplasm, and a vestigial nucleus

DIATOMS Yellow or brown in color Unique glasslike walls of hydrated silica

embedded in an organic matrix Many glide using physical interactions in

cytoplasm Reproduce asexually by mitotic cell division

most of the year Diatoms store food reserves in the form of

laminarin; some also store food in form of oil

A freshwater diatom

GOLDEN ALGAE Cells typically biflagellated—both flagella

attached near one end of the cell Some species are mixotrophic, absorbing

dissolved organic compounds or extending pseudopodia to ingest food particles and bacteria

Most are unicellular, but some, such as Dinobryon, are colonial

Dinobryon, a colonial type of golden algae

WATER MOLDS AND THEIR RELATIVES Water molds, white rusts, and downy mildews are all

examples of oomycotes which are heterotrophic stramenopiles that lack chloroplasts.

Some of these are unicellular and consist of hyphae but all their cell walls are made of cellulose

Most water molds are decomposers in mainly fresh water and are also parasites

Water mold

WATER MOLDS AND THEIR RELATIVES

White rusts and downy mildews live on land as parasites of plants and are dispersed by windblown spores or form flagellated zoospores

Downy mildews

White rust

SEAWEEDS support many animals and other

heterotrophs and thrive in the intertidal and subtidal zones of coastal waters.

Have the most complex multicellular anatomy of all algae because they can have differentiated tissues and organs that resemble plant anatomy.

Anatomy of a Seaweed: Thallus-seaweed body that is plantlike but lacks true roots, stems, and leaves. A typical seaweed thallus consists of a rootlike holdfast, which anchors the algae, and a stem-like stipe, which supports leaf-like blades. Blades provide most of the surface for photosynthesis.

SEAWEEDS Some seaweed also have biochemical adaptations-

their cell walls are composed of cellulose and gel-forming polysaccharides which help cushion the thalli against the agitation of the waves. Red algae in lower intertidal and subtidal zones incorporate large amounts of calcium carbonate cell walls, making them uneatable to marine invertebrate herbivores.

Seaweeds are an important source of food and other commodities for humans. Laminaria and Porphyra are used in Japanese dishes. Algae are rich in iodine and other minerals. They are used in foods as thickeners and lubricants in oil drilling.

Some algae have life cycles with alternating multicellular haploid and diploid generations. Alternations of generations is the alternations of multicellular haploid forms and multicellular diploid forms.

RED ALGAE (CANDIDATE KINGDOM RHODOPHYTA) LACK FLAGELLA Red algae (Rhodophyta) have no flagellated

stages in their life cycle, unlike other eukaryotic algae

Red algae are reddish because of an accessory pigment called phycoerythrin

Phycoerythrin belongs to a family of pigments known as phycobilins

RED ALGAE (CANDIDATE KINGDOM RHODOPHYTA) LACK FLAGELLA Species adapted to different water depths

differ in their proportions of accessory pigments

Phycobilins allow some species to absorb filtered wavelengths (blue/green) in deep water

The thalli of red algae are filamentous (branched/interwoven in delicate, lacy paterns) and the base of the thallus is a simple holdfast

Red algae lack flagella, so the gametes rely on water currents to get together

GREEN ALGAE AND PLANTS Green algae (Chlorophyta) are named for

their green chloroplasts Some species of green algae live

symbiotically within other eukaryotes, supplying their hosts with portions of their photosynthetic products (ex: Chlorophytes live symbiotically with fungi, known as lichens)

The simplest chlorophytes are biflagellated unicells (ex: Chlamydomonas)

GREEN ALGAE AND PLANTS Larger sized chlorophytes probably evolved by the

formation of colonies of individual cells, the repeated division of nuclei with no cytoplasmic division, and the formation of true multicellular forms

Nearly all green algae reproduce sexually by way of biflagellated gametes having cup-shaped chloroplasts

Conjugating algae produce amoeboid gametes Isogamy means literally a marriage of equals Anisogamy is the fusion of gametes of different

size/shape Oogamy is a type of anisogamy, where a flagellated

sperm fertilizes a nonmotile egg

GREEN ALGAE AND PLANTS

MULTICELLULARITY ORIGINATED INDEPENDENTLY MANY TIMES More variations are possible for complex

structures than simpler ones As cells in colony become interdependent,

some cells may have lost flagella and become specialized

Early form of division of labor involved distinction of sex cells from somatic cells

evolution of the enzyme telomerasemay have occurred during formation of gametes

Evolution of division of labor required additional steps in somatic cell specialization