Observing Algae

 Objectives:

• Prepare wet mounts of algae for microscopic examination.
• Locate and identify chloroplast, holdfast, and pyrenoids of various species of algae.
• Distinguish among unicellular, filamentous, and colonial forms of organization.

Process Skills:

• Observing
• classifying
• recognizing
• spatial relationships
• using numbers.

Time Allotment:  2 class periods

Materials: 

• microscopes
• microscope slides
• coverslips
• droppers
• iodine solution
• paper towels
• laboratory aprons
• living specimens of 
• Closterium
• Oedogonium
• Scenedesmus
• Synedra
• Ulothrix
• Volvox

Preparation: 

• Be sure to order algae cultures to arrive prior to your lab day.  Some biological supply houses sell algae sets. Check the catalog to see if the specimens required for this Exploration are more economically obtained as part of a set.
• Prepare iodine solution according to directions. 

Test for Carbohydrates (Test for Starch)

1. Put on goggles and an apron.  Label three test tubes 1, 2, and 3.  Place them in a test-tube rack.

2.  Using a separate dropper for each solution, add 10 drops of soluble starch solution to test tube 1, 10 drops of glucose solution to test tubes 2, 1, and 10 drops of water to test tube 3. Record the color of each tube's contents in Table 1.

3.  Add 3 drops of iodine solution to each test tube.  Caution: If iodine is spilled, rinse with water and call your teacher immediately.

4. Record in Table 1 the color of each tube's contents after the addition of the iodine.  A blue-black color indicates the presence of starch.

5. Discard the contents of the test tubes according to your teacher's directions.  Gently use a test-tube brush and soapy water to clean the three test tubes and rinse with clean water.

 Teaching the lab:

• If sufficient microscopes are availables, have students work individually.
• Set up algae specimens with individually labeled droppera.  This will  prevent contamination. 

Data and Observations

Analysis

1. Synedra and Closterium
2. Usually 4, most colonies have 2 to 6 cells.
3. The individual cells of Volvoz are very small and they are very numerous.  Two flagella on each individual cell allow the colony to move.
4. Closeterium, Oedogonium, and Ulonthrix contain pyrenoids.
5. Pyrenoids produce and store starch.
6. Iodine Stains starch blue-black.  Pyrenoids contain starch, so they are stained by iodine.