Ch. 12 Algae

Question 1

Algae characteristics

Answer 1

• simple eukaryotic photoautotrophs
• some are unicellular
• some form chains of cells (are filamentous)
• few have thalli
• historically considered plants but lack the embryos of true plants. They also lack roots and stems.
• mostly aquatic, but some found in soil and trees when there is sufficient moisture
• can even be found on sloths or polar bears
• need water for physical support, reproduction, and diffusion of nutrients
• mostly found in cool temperature waters

Question 2

vegetative structure

Answer 2

-thalli of multicellular alga (seaweeds) consist of:
-branched holdfasts that anchor alga to rock,
-stem-like and often hollow stipes (unsupportive stems)
-leaflike blades
-some have hollow gas-filled bladders for floating
called pneumatocyst (like a lung)
-cells covering thallus can carry out photosynthesis

Question 3

life cycle

Answer 3

• all can reproduce asexually
• multicellular algae with thalli and filamentous forms can fragment–each piece is capable of forming a new thallus or filament
• unicellular algae divides, it undergoes mitosis (nucleus divides) and cytokinesis
• algae can also reproduce sexually
• some species can do both and alternate their method of reproduction from generation to generation (i.e. asexual–asexual–asexual–sexual–sexual–asexual–sexual)

Question 4

Nutrition

Answer 4

• most algae are photosynthetic; oomycotes (fungal-like algae) are chemoheterotrophs
• photosynthetic algae are found in photic (light) zone of bodies of water
• Chlorophyll a (a light trapping pigment) and accessory pigments involved in photosynthesis are responsible for the distinctive colors of many algae

Question 5

Brown Algae (kelp)

Answer 5

• macroscopic (BIG)–can reach 50m lengths
• mostly found in costal waters
• grow really fast–can grow 20+ cm per day! so can be harvested regularly
• ALGIN–can be extracted from cell walls–used as a thickener in many foods (ice cream, cake decorations) and other goods (rubber tires and hand lotion)
• LAMINARiA JAPONICA–used to induce vaginal dilation before surgical entrance into the uterus through the vagina

Question 6

Red Algae

Answer 6

• most have delicate branched thalli
• can live at greater ocean depths than other algae
• some thalli form crust-like coatings on rocks and shells
• red pigments enable blue light absorption that penetrates deepest into ocean
• agar used in microbio media is extracted from red algae
• carrageenan–another gelatinous material–used as a thickening agent in evaporated milk, ice cream, and pharmaceutical agents
• GRACILARIA species are used as food by humans–some produce a lethal toxin (pacific ocean)

Question 7

Green Algae

Answer 7

• have cellulose cell walls
• contain chlorophyll a and b
• store starch
• believed to be precursor to terrestrial plants
• most are microscopic (tiny)
• can be unicellular or multicellular
• some filamentous kinds form grass green scum in ponds

Question 8

Diatoms

Answer 8

• kingdom Stramenopila
• unicellular or filamentous algae with complex cell walls made of pectin and silica–2 pieces
• distinct cell wall useful in identifying diatoms
• store energy captured through photosynthesis in the form of oil.
• produce domoic acid–often concentrated in mussels–TOXIC–diarrhea and memory loss. brain damage can be permanent. domoic acid toxicosis

Question 9

Dinoflagellates (plankton)

Answer 9

• unicellular algae called plankton/free floating organisms
• rigid structure–due to cellulose in plasma membrane
• some produce neurotoxins
• KARENIA BREVIS–gets trapped in gills of fish and produces a neurotoxin that stops fish from breathing
• ALEXANDRIUM–produce a neurotoxin (saxitoxins) that cause paralytic shellfish poisoning (PSP)
• concentrated when large numbers of dinoflagellates are eaten by mollusks
• if humans eat these mollusks, can also get PSP
• large concentrations of Alexandrium give ocean a deep red color–RED TIDE
• PFIESTERIA –causes massive fish deaths along atlantic coast

Question 10

water molds (oomycota)

Answer 10

• most are decomposers
• cellulose cell walls
• form cottony masses on dead algae and animals, usually in fresh water
• asexually resemble the zygomycete fungi–produce spores in sporangium (spore sac)
• oomycote spores called zoospores–have two flagella (fungi do not have flagella)
• previously classified as fungi
• many terrestrial oomycotes are plant parasites
• PHYTOPHTHORA INFESTANS–caused the great potato famine/blight
• phytophthora kills many plants

Question 11

roles in nature

Answer 11

• fix carbon into organic molecules (like molecular O2) for chemoheterotrophs–important for aquatic food chain
• indicate water pollution from their blooms–like red tide
• responsible for petroleum and natural gas production–from decomposition of algae millions of years ago.
• symbionts for animals

ex. giant clam Tridacna–algae proliferates in the clams and give the clam glycerol; and essential proteins from phagocytizing old algae