The Eukaryotes: Fungi, Algae, Protozoa, and Helminths
Algae are unicellular, filamentous, or multicellular (thallic).
Most algae live in aquatic environments.
All algae are eukaryotic photoautotrophs that produce oxygen (except for the water molds, which are fungus-like chemoheteroptrophs).
The thallus (body) of multicellular algae usually consists of a stipe, a holdfast, and blades.
Algae reproduce asexually by cell division and fragmentation.
Many algae reproduce sexually.
Algae are classified according to their structures and pigments.
Brown algae (kelp) may be harvested for algin.
Red algae grow deeper in the ocean than other algae because their red pigments can absorb the blue light that penetrates to deeper levels.
Irish moss (Chondrus crispus) produces carrageenan, used as a food thickener.
Gracilaria can be used for food but some species are toxic.
Green algae have cellulose and chlorophyll a and b and store starch.
Diatoms are unicellular and have pectin and silica cell walls: some produce a neurotoxin, domoic acid, that causes a rare syndrome known as amnesic shellfish poisoning (ASP). The toxin concentrates in shellfish, primarily in mussels.
Symptoms start with gastrointestinal distress within 24 hours and may include dizziness, headache, disorientation, and permanent short-term memory loss. In severe cases, seizures, focal weakness, paralysis, and death may occur.
Water molds - decomposers, resemble fungi, produce asexual spores in a sac but their spores have flagella and fungi don't.
Usually seen as a white fuzzy mass on dead algae or animals in fresh water. Terrestrial forms are often plant pathogens.
Phytophthora infestans – caused the Irish potato famine, infects soybeans and cocoa also.
Algae are the primary producers in aquatic food chains.
Planktonic algae produce most of the molecular oxygen in the earth’s atmosphere.
Most petroleum is the fossilized remains of planktonic algae.
Unicellular algae are symbionts in such animals as Tridacna (giant clam).