Identify this alga. The key is provided below. PRACTICE WITH MICROSCOPIC IDENTIFICATION In this activity you will observe a variety of algae types. You will find that there will be a great diversity in the cell shape and the arrangement of the organelles between different species of algae. Additionally, you will find that some live as single cells, colonially or in long multicellular filaments. Algae are extraordinarily important primary producers that form the basis of aquatic food chains and supply the majority of our atmospheric oxygen. In this activity you will use a dichotomous key to identify the algal cultures that are in jars. Please do not use the same Pasteur pipette for different cultures as contamination will result. Keep the pipette in the container that you found it with. Keys can very useful to biologists for identifying specimens. In this exercise, you will be expected to read each statement and select from the pair of lettered choices associated with each number (#2-either a or b for example). You may find that the choices lead to a number-go to that number and follow the key and decide between a or b again until you have identified the alga. You must decide which of the paired statements best describe the organism that you are observing. When you have identified your algae check with your instructor to see whether or not you are correct. Keys can be great tools, but they can also be imprecise, as organisms do not always fit the description perfectly. You may also misinterpret the key and have to start again. DICHOTOMOUS KEY: 1. (a) cells arranged in a colony or forming a long filament: 2 (b)singular arrangement of cells: 3 2. (a) cells are joined end to end in a long filament: 4 (b)cells are not joined in a filamentous colony: 5 3. (a) cells are tiny (less than 24 micrometers) rounded and motile: CHLAMYDOMONAS (b)cells singular in an elongated shape: 6 4. (a) cells rectangular with green chloroplasts:7 (b) no chloroplasts present in cells; distinct nucleus lacking; blue-green in color: 8 5. (a) colony flat: 9 (b) colony spherical: 10 6. (a) round vacuoles located at the tip of long crescent shaped cells: bright green; oval pyrenoid bodies which contain starch run from tip to central clear region: CLOSTERIUM (b) cells elongated but not crescent shaped; usually motile: 11 7. (a) chloroplast spiral shaped with pyrenoid bodies: SPIROGYRA (b) chloroplast not spiral shaped: 12 8. (a) filament interrupted by large thick-walled spherical structures (heterocysts) : ANABAENA (b) heterocysts are not present; filaments may appear to move:OSCILLATORIA 9. (a) colony of four spindle-shaped cells: tip of cells often have spines: SCENDESMUS (b) rounded colony that is flat in appearance; 5-25 cells together: PEDIASTRUM 10. (a) ball-shaped colony of tiny cells swimming with a tumble-weed movement; color green : VOLVOX (b) cluster of several motile large cells; may observe a gelatinous sheath around colony: PANDORINA 11. (a) Long golden-brown cells that are narrow with rounded ends and fine lines etched in the cell wall: SYNDEDRA (b) flagellated cells that are green in color; definite swimming motion: EUGLENA 12. (a) filament contains occasional large rounded cell (female component); chloroplasts fill cells: OEDOGONIUM (b) cells contain two star-shaped chloroplasts: ZYGONEMA