The algae are an extremely diverse group of plant-like organisms belonging to the kingdom Protista (Campbell 6th Ed. Fig. 28.8; 7th Ed. Fig. 28.8). The levels of cellular organization exhibited by the algae include unicells and multicellular filaments. Some algae, notably members of the divisions (phyla) Phaeophyta, Rhodophyta and certain representatives of the division Chlorophyta, exhibit the more complex multicellular thalloid level of organization (see Lab. 7). The biology of the thalloid algae will not be represented in this course. The algae are autotrophs and the majority live in an aquatic environment.
Cosmarium is a non-motile, freshwater member of division Chlorophyta (green algae). Cosmarium is a relatively large unicell characterized by a constriction in the middle of the cell (termed the isthmus) which divides it into two symmetrical halves or semicells. A single haploid nucleus occupies the isthmus.Each semicell is partly filled by a large green chloroplast containing two pyrenoids composed of proteinaceous material. Surrounding the pryenoid are numerous starch granules. A large portion of the protoplast of each semicell is occupied by a clear vacuole. The cell wall is relatively rigid and composed of cellulose, a polysaccharide found in the cell walls of most members of the division Chlorophyta and all members of the more highly evolved plant groups.
Click to view a prepared slide of Cosmarium
Click to view a fresh mount of Cosmarium
Click to view a fresh mount of Cosmarium stained with IKI
(Note: IKI has stained the starch)
II - Euglena
(Campbell 6th Ed. 555-556; 7th Ed. 553-554)
Euglena is a motile unicellular freshwater organism traditionally classified as a plant-like member of the kingdom protista. Euglena is an elongate unicell containing a large haploid nucleus and several green disc shaped chloroplasts. A long, very fine, hair-like flagellum emerges from the anterior end of the cell. A small clear contractile vacuole is also found within the anterior region of the cell. This non- pigmented organelle is very difficult to locate using a standard student compound microscope. Like Cosmarium, the chloroplasts of Euglena also contain pyrenoids; however, the glucose storage polymer in Euglena is the polysaccharide paramylum rather than starch. Paramylum is unique to the Euglenoids.
Click to view Euglena at 40x power
Click to view Euglena with 100x power
III - Chlamydomonas
(Campbell 6th Ed. 565-567; 7th Ed. 567-569)
Chlamydomonas is a motile unicellular member of the division Chlorophyta. The organism is commonly found in small pools and other bodies of fresh water and in soils. With the 10X objective in place, the organism is visible as a small green sphere. A thin cell wall composed of glycoproteins surrounds the cell. The majority of the cell protoplast is occupied by a single cup shaped chloroplast making the centrally located haploid nucleus difficult to see. The region of the protoplast between the top of the chloroplast and the anterior end of the cell is more or less clear. Within this region are two contractile vacuoles. They are usually very difficult to locate.
Click to view Chlamydomonas
