Ward's World Working with Guides

Page 2 Working with Algae and Cyanobacteria Diatoms Bacillariophytes, which occur in fresh water, salt water, and terrestrially, date back to the Cretaceous Period. They are single-celled algae with shells constructed of two overlapping valves composed of pectin and impregnated with silica; these shells can be quite ornate. Although the diatoms are single- celled organisms, they can form colonies and filaments. The group comprises two main types: centric and pennate. Centric diatoms are radially symmetrical and contain numerous plasmids, while pennate diatoms are bilaterally symmetrical and contain fewer plasmids. Many diatoms have conspicuous oil droplets within the cell, which is the photosynthetic food reserve, chrysolaminarin. The plastids of diatoms contain the pigments chlorophyll a and b, alpha and beta carotene, and several xanthophylls. Dinoflagellates Dinoflagellates are mostly marine organisms and they compose nearly all marine plankton. They occur as free-living flagellates, sessile unicells, colonies, and filamentous forms. The fossil record of the dinoflagellates can be dated back to the Cambrian period, with some evidence suggesting they existed even earlier. The term dinoflagellate actually refers to the twirling motion exhibited by the pair of whip-like undulipodia (flagella). These flagella originate in the sulcus, or groove, of the organism. Some dinoflagellates have thecal plates embedded in their cytoplasmic membrane and are called armored, others lack these plates and are called naked. Food is stored in the form of true starch and oils. Dinoflagellates contain the pigments chlorophyll a and c, beta carotene, and several xanthophylls that often give these organisms a brownish color. Some dinoflagellates produce powerful toxins with potentially dangerous results. When "blooms" occur, the water can take on a pinkish or red hue known as a red tide. This often causes massive fish kills and can be dangerous to humans as well. Some, such as Noctiluca, are bioluminescent, and can cause ocean waves to glow at night. This is the only example of bioluminescence in the Algae kingdom. Euglenoids Typically green and unicellular, euglenoid flagellates live in fresh water. They have characteristics of both plants and animals yet are distinct in many ways. Most are photosynthetic, but many, lacking chloroplasts, are heterotrophs. Most do not reproduce sexually. Euglenoids lack a cellulose cell wall; in- stead, they have a proteinaceous pellicle just inside the plasmalemma. The plastids contain chlorophyll a and b, beta carotene, and xanthophylls. If placed in the dark over the course of several divisions, the chloroplasts of Euglena gracilis will become colorless. When returned to the light, the plastid structure is reformed and the green color returns. Brown Algae Multicellular and structurally complex, with no colonies or simple, unbranched filaments, the Phaeo- phytes, or brown seaweed, are primarily marine algae; less than one percent occur in fresh water. They are most abundant, and reach their maximum development in the colder water of the oceans. While some species of Sargassum are found floating in enormous numbers in the Atlantic, the algae are usu- ally firmly attached to a substrate by means of elaborate holdfast structures. Food is stored as soluble carbohydrates such as lamarin, fats and the alcohol mannitol. The plastids of the brown algae contain pigments chlorophyll a and c, c-carotene, and xanthins; an accessory pigment, fucoxanthin, gives the algae their characteristic dark brown or olive green color. The Phaeophytes are an economically impor- tant resource, used for alginic acid, fertilizer, and food. Basic Types of Algae

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