“Plant-Like” Protists: 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 Nucleus EyespotFlagella 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