The Algae Study of algae= Phycology Morphology, size and shape Eukaryotic, motile or non motile Unicellular, filamentous, or multicellular (thallic) Wide range of sizes and shapes Single cell- spherical, rod, club or spindle shaped Multicellular-branched and unbranched Cell wall- thin and rigid but diatoms have silica in their wall making them thick and very rigid Discrete nucleus. Other inclusions are starch grains, oil droplets and vacuoles Algal pigments- chlorophylls, carotenoids, phycobilins

Vegetative structure Relatively simple eukaryotes lacking the tissues (roots, stem, leaves) of plants Body of a multicellular alga is called a thallus Larger algae (sea weeds) contain branched holdfasts which anchor them to rock, stem like hollow stipes and leaf like blades. Cells covering the thallus carry out photosynthesis Thallus lacks conductive tissue (xylem/phloem) characteristics of vascular plants

Unicellular alga

Comparison between unicellular algal, fungal and protozoal cell

Habitat and Nutrition Mostly live in aquatic environment, also thrive as terrestrial algae Ocean, salt lake, fresh water, damp soil, rocks, stones, tree bark etc. They are found in places where there are sufficient light, moisture and simple nutrients to sustain them Majority are photoautotrophs, contain chlorophyll and other pigments Algae absorb nutrients from the water over their entire surface Red Tide/Algal Bloom

Figure 12.11a

Reproduction Both sexual and asexual Differ from plants in having simple reproductive structures for sexual reproduction Unicellular algae may function as gametes Asexual reproduction carried out by producing flagellated spores and/or nonmotile spores in sporangia

Figure 12.12b

Algae Table 12.1

Selected phyla of algae Brown algae (Phaeophyta) Red algae (Rhodophyta) Green algae (Chlorophyta) Diatoms (Bacillariophyta) Dinoflagellates (dinoflagellata)

Phaeophyta Brown algae (kelp) Cellulose + alginic acid cell walls Multicellular Chlorophyll a and c, xanthophylls Store carbohydrates Harvested for algin Figure 12.11b

Rhodophyta Red algae Cellulose cell walls Most multicellular Chlorophyll a and d, phycobiliproteins Store glucose polymer Harvested for agar and carrageenan Figure 12.11c

Chlorophyta Green algae Cellulose cell walls Unicellular or multicellular Chlorophyll a and b Store glucose polymer Figure 12.12a

Bacillariophyta Diatoms Pectin and silica cell walls Unicellular Chlorophyll a and c, carotene, xanthophylls Store oil Fossilized diatoms formed oil Produce domoic acid Figure 12.13

Dinoflagellata Dinoflagellates Cellulose in plasma membrane Unicellular Chlorophyll a and c, carotene, xanthins Store starch Some are symbionts in marine animals Neurotoxins cause paralytic shellfish poisoning Figure 12.14

Biological and Economic Importance Primary producer- they form the base of most aquatic food chains because of their photosynthetic activities Water algae increase the O2 conc through photosynthesis, help to reduce hardness of water and removes salts Produce undesirable taste and odor in water supplies, heavy growth (mat) prevent oxygen and light penetration into water, cause suffocation to fish and marine animals

Commercial products from algae From cell wall- agar, alginic acid and carrageenan are obtained Agar, carrageenan- polymer of galactose, used to make gel or viscous materials, as stabilizer/emulsifier in food products (icecream), as binder in toothpaste or pharmaceutical products, ulcer therapy, finishing compound in textile and paper industry, thickening agent in shaving cream, lotoin, in soap industry agar used as solidifying agent in microbiological media. Obtained from red alga Gelidium and Gracilaria. Alginic acid obtained from brown algae eg. Laminaria, Fucus etc. Used in icecream, cheese industry, bakery, dentistry.

Algae as food Mostly red and brown algae are used as food in the Far East Porphyra is used as food in Japan, where it is called ‘Nori’ Other red algae Chondrus, Nemalion etc are used as vegetables or in soups or prepared as sweetened jellies. Gracilaria used in China as food Chlorella as food/source of protein for human and domestic animal

Algae and Disease Prototheca- probable pathogen of Human causes systemic or subcutaneous infections/ inflammation of joints Parasitic on higher plants. e.g. Cephaleuros attacks leaves of tea, coffee, pepper etc. (Irish potato blight) Toxin produced by aquatic algae which are lethal to fish and animals. e.g. dinoflagellate release neurotoxin cause death of aquatic shellfish. Domoic acid intoxication due to diatoms in shellfish, diarrhea & memory loss Poisoning of human occurs after ingesting shilfish, scallops or mussels infected with dinoflagellate.

Red tide A phenomenon known as an algal bloom- an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water Red tides are caused by increase in nutrients that algae need, usually due to farm runoff, causing an overpopulation Their occurrence in some locations appear to be entirely natural, a seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents while, in others they appear to be a result of human activities It is usually found in coastal areas The growth of marine phytoplankton is generally limited by the availability of nitrates and phosphates, which can be abundant in agricultural run-off as well as coastal upwelling zones Coastal water pollution produced by humans and systematic increase in sea water temperature have also been implicated as contributing factors in red tides

When the algae are present in high concentrations, the water appears to be discolored or murky, normally being red or green. Some red tides are associated with the production of natural toxins, depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms The most conspicuous effects of red tides are the associated wildlife mortalities among marine and coastal species of fish, birds, marine mammals, and other organisms. In the case of Florida red tides, these mortalities are caused by exposure to a potent neurotoxin called brevetoxin which is produced naturally by the marine algae Karenia brevis.

Figure: Red Tide

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