“Plant-Like” Protists:

Unicellular Algae

Unicellular Algae– Algae are

• photosynthetic protists whose chloroplasts support food chains in

– freshwater and– marine ecosystems.

– Many unicellular algae are components of plankton, the communities of mostly microscopic organisms that drift or swim weakly in aquatic environments.

• Chlorophyll and accessory pigments allow algae to harvest and use energy from sunlight.

– Both give algae a wide range of colors

Unicellular Algae• Unicellular algae include:

– dinoflagellates, with

– two beating flagella and

– external plates made of cellulose,

– diatoms, with glassy cell walls containing silica, and

– green algae, which are

– unicellular in most freshwater lakes and ponds,

– sometimes flagellated, such as Chlamydomonas, and

– sometimes colonial, forming a hollow ball of flagellated cells as seen in Volvox.

Phylum Pyrrophyta - Dinoflagellates

• Half are photosynthetic, half are heterotrophs

• Two flagella• Reproduce asexually by

binary fission• Some luminescent/give off

light• Only eukaryote with no

histones to help store DNA• Can cause red tides

Phylum Bacillariophyta – Diatoms

• Most abundant organisms on Earth• Thin, silicon cell walls used to make glass

Phylum Euglenophyta - Euglena • “Plant-like” protists that have two

flagella but no cell wall• Red eye-spot – helps organism find

sunlight to power photosynthesis• Phototrophic autotroph or

heterotroph (absorb nutrients in decayed organic material)

• Pellicle – cell membrane• Reproduce asexually by binary

fission

Euglena Anatomy

Gullet

Chloroplast

NucleusEyespotFlagella

Carbohydrate storage bodies

Pellicle

Contractile vacuole

Phylum Chrysophyta • Mostly solitary• Yellow-green and golden-

brown algae• Gold-colored chloroplasts• Cell walls contain pectin

rather than cellulose; others can have both pectin and cellulose

• Reproduce asexually and sexually

• Store oil, not starch

Ecology of Unicellular Algae

• Helpful:– Phytoplankton – diatoms and dinoflagellates– 70% of photosynthesis occurs in ocean– Symbiosis – corals and dinoflagellates –

Tridacha gigas (clam) and dinoflagellates• In both cases, algae provide food to the animal

Ecology of Unicellular Algae• Harmful:

– Algae “blooms” – dangerous toxin produced by algae – shellfish eat the algae and eat the toxin = people can’t eat it

– Dinoflagellate Gonyaulx – red tide

“Fungus-like” Protists

• Heterotrophs that absorb nutrients from dead or decaying matter. Unlike true fungi, “fungus-like” protists have centrioles and lack chitin in cell walls

• Recyclers of dead organisms

Slime Molds

– Slime molds • resemble fungi in appearance and lifestyle, but• are more closely related to amoebas.

– The two main groups of these protists are• plasmodial slime molds (aka acellular slime molds)

and• cellular slime molds.

Slime Molds

• Play key roles in recycling organic material• 3 Phyla of slime molds

– Phylum Myxomycota (plasmodial)– Phylum Acrasiomycota (cellular)– Phylum Oomycota

Phylum Myxomycota• Plasmodial slime molds

(aka acellular slime molds)– Begin life as amoeba-like

cell, called plasmodia, that contain thousands of nuclei but only one cell membrane

– Plasmodia may reach several meters in diameter

– Form fruiting bodies – Produce haploid spores

which germinate into flagellate cells which fuse to produce the diploid “amoeba”

Phylum Acrasiomycota

• Cellular slime molds – Begin life as amoeba-like cells– When food begins to run out, then form colonies and

produce a fruiting body which produces spores– Spores “hatch” into amoeba-like cells

Phylum Oomycota• Water molds

– Thrive on dead or decaying organic matter in water and are plant parasites on land

– Hyphae – thin filaments– A water mold caused the potato famine in Ireland in

1840s