Multicellular Algae

Kingdom Protista

Developed by Adam F Sprague& Dave Werner

Characteristics of Algae:• Plantlike members of the kingdom Protista • Eukaryotes • Most unicellular, but some multicellular • Autotrophic – contain chlorophyll & make food by

photosynthesis • Planktonic• Produce oxygen• microscopic to seaweeds hundreds of feet in length • Do not have true roots, stems, nor leaves • Form gametes (eggs & sperm) in single-celled gametangia

(chambers) instead of multicellular gametangia like true plants • Found in freshwater, marine, and moist soil habitats • Most have flagella at some time in life cycle • Algae cells contain organelles called pyrenoids organelles that

make & store starch

 Structure of Algal Cells:

• The body of algae is called the thallus  • Algae may  be unicellular, colonial,

filamentous, or multicellular • Unicellular algae are single-celled & make up

phytoplankton (a population of photosynthetic organisms that begins many aquatic food chains)

• Phytoplankton make much world's carbohydrates & are the major producers of oxygen

Structure of Seaweeds

• Filamentous algae have slender, rod-shaped thallus arranged in rows joined end-to-end

• Holdfasts are specialized structures in some filamentous algae that attaches the algae so it can grow toward sunlight at the surface

Structure of Seaweeds:

• Multicellular algae often have a large, complex leaf-like thallus & may have stem-like sections and air bladders called pneumatocysts

•  Macrocystis is among the largest multicellular algae

Structure of algae vs. seagrass

Filamentous algae Enteromorpha

Multicellular algae Macrocystis

Classification:

• Algae are classified into 3 phyla, based on color, type of chlorophyll, form of food-storage substance, and cell wall composition

• All phyla contain chlorophyll a • Many species of algae reproduce

sexually and asexually • Sexual reproduction in algae is often

triggered by environmental stress

Chlorophyta (green Algae): 7000 species

• May be unicellular, multicellular, or colonial • Include Spirogyra, Ulva, & Chlamydomonas • Contain chlorophyll a & chlorophyll b and

carotenoids (orange & yellow pigments) as accessory pigments

• Store food as starch • Cell = cellulose, some add CaCO3 • Habitat -freshwater, moist surfaces, or marine

environments • Some have whip-like flagella for movement • May live symbiotically as lichens • Thought to have given rise to terrestrial plants

Phaeophyta (brown algae): 1500 species

• Contain chlorophyll a & chlorophyll c and fucoxanthin (brown pigment) as accessory pigments

• Most multicellular- growing in cooler marine habitats • Includes kelps & seaweeds • Largest protists • Specialized rootlike holdfasts • Specialized air bladders• Stemlike structures are called the stipe • Store food as a carbohydrate called laminarin • Include Laminaria & Fucus

Rhodophyta (red algae): 4000 species

• Multicellular algae that mainly grow deep in warm marine waters

• Some freshwater species exist • Highly branched thallus • Contain chlorophyll a & phycobilins (red pigments)

to trap sunlight• Store food as starch • Cell walls contain cellulose and agar (used as a base

in culture dishes to grow microbes) • Some species contain carageenan in their cell walls

used for gelatin capsules & in some cheeses

Common Marine algae of Barnegat Bay

Enteromorpha

Ulva lactuca(Sea Lettuce)

Agardhiella

Fucus(rockweed)

spongomorpha

Sargassum

A closeup of a small mass of sargassum weed. The numerous small round spheres are floats filled with carbon dioxide. These provide buoyancy to the algae.

There are numerous types of marine algae found throughout our back bay areas, this has just been

a sample of what you will find.

Diatom Reproductionfig. 5.6

Asexual = Cell Division into Auxospores

• Produces Blooms

Sexual = Egg & Sperm

Reproduction in Unicellular Algae

Bio book p.528Asexual Phase• Algae absorbs its flagellum • Haploid algal cell then divides

mitotically from 2 to 3 times • From 4 - 8  haploid flagellated cells

called zoospores develop in this parent cell

• Zoospores break out of the parent cell & eventually grow to full size

Sexual Phase

• Haploid cells dividing mitotically to produce either “plus” or “minus” gametes

• A plus gamete and a minus gamete come into contact with one another, shed their cell walls, and fuse to form a diploid zygote

• This resting stage of a zygote is called a zygospore & can withstand bad environmental conditions

• When conditions are bad, the thick wall opens and the living zoospore emerges

Chlamydomonas

Reproduction in Multicellular Algae:

• Oedogonium is a multicellular, filamentous green algae with specialized cells called gametangia that form gametes

• The male gametangia or antheridium makes sperm, & the female gametangia or oogonium makes eggs

• Sperm are released into the water & swim to the egg to fertilize them

• The fertilized egg or zygote is released from the oogonium & forms thick-walled zoospores

• Zoospores undergo meiosis so one cell attaches to the bottom & develops a holdfast while the other zoospores divide & form a filament

Spirogyra, another filamentous green algae, reproduces by

conjugation

Two filaments align side by side, their adjacent cell walls dissolve, & a conjugation tube forms between them

Fertilization occurs when a + gamete cell moves through the tube & fuses to the - gamete cell 

Zygote forms a thick walled spore (sporangium) that breaks away from the parent & forms a new filament

Conjugation Tube between Spirogyra

Ulva fig.6.11

• The leaflike algae Ulva has a sexual reproductive cycle characterized by a pattern called alternation of generations

•  Alternation of generations has two distinct multicellular phases- a haploid, gamete-producing phase called a gametophyte and a diploid, spore-producing phase called a sporophyte

• Alternation of Generation also occurs in more complex land plants, but the gametophyte & sporophyte do not resemble each other