(C) Flagella

Locomotion in algae is largely based on the action of flagella. The figure below illustrates the wide variety of flagella present in the algae. The primary distinctions used for classification are the number of flagella, their location on the cell, and their morphology. Two major types of flagella are recognized: the smooth, or acronematic, and the hairy, or pleuronematic, types. The smooth flagella generally moves by whiplash motion and the hairy flagella moves by a pulling motion.

(1) Live Mounts

Chlamydomonas is a unicellular green alga with two equal flagella. Observe how they move in a whiplash fashion.Gonium is a colonial alga with 8 to 16 Chlamydomonas-type cells united together. Is there any coordination to the movement of the flagella? Describe how this colony moves through the water?

(b) Volvox

It is difficult to observe the flagella on the individual cells in Volvox, but you should be able to see the slow movement of the colony if you haven't squashed it too hard under your coverslip. There is great deal of specialization in the Volvox colony, unlike the Gonium colony. Cells towards the anterior are smaller and vegetative, while the posterior cells are larger and contribute to the sexual reproduction of the colony. You might also notice some small colonies in the center or the large sphere. In the material we typically get for the laboratory exercise, these are daughter colonies formed as a result of asexual reproduction. It is interesting to note that the number of cells of the colony remains the same from the initial daughter colony to the large mature colony. Expansion in the size of the cells and the distance between them contributes to the increase in colony size.

(c) Euglena

Euglena has two flagella, though only one is readily visible. The other flagellum is short and does not extend beyond the cell body. How do the flagella in Euglena move? Euglena can lose its flagella under certain environmental conditions and will move through the substrate by an amoeboid-like action called metaboly. Can you observe such motion in your material? If you have difficulty observing flagella in your live preparations, observe the prepared slides that have been specially stained for flagella. Unfortunately, you will miss seeing them in action.

(d) Diatoms

Not all algae have flagellar stages in their life history. For example, red algae do not have flagella and the reproductive spores are distributed solely by wave and currents. Diatoms are another group of algae that lack flagella, yet are able to move over substrates by secreting mucilage through pores in their cell wall. Make a preparation of pennate diatoms, if available. Do not place too much water on the slide and you may want to include some fine mud as a substrate on which these diatoms can move. The diatoms are noticeable by their golden-brown color. Observe their movement. On intertidal mud flats, diatoms often move to the surface of the mud at low tide turning a brown mud flat a bright golden color.