Students of botany as well as those of zoology often are required to study the organisms of Euglenophyta because these organisms possess both animal and plant characteristics. These organisms are currently (if temporarily) considered part of the Protista kingdom. Yet, they are still called algae. The number of Euglenophyta species is estimated to range from 450 to 800.
* Notes * A classic example of the group is Euglena, a single-celled, flagellated, gen erally green (although several forms are colorless, and one form is red) organism lacking a rigid cell wall. The pigments are chlorophyll a, chlorophyll b (as in green algae and flowering plants), and carotenes. They store not starch but a starchlike product, paramylum, and oil droplets. Rather than a cell wall, there is a plasma membrane, just beneath which are fine, parallel strips that spiral around the cell. These structures are collectively referred to as the pellicle. Cellulose is not produced.
At the anterior end is a gullet leading to a reservoir. Near the reservoir is an eye spot; at the base of the reservoir is a contractile vacuole. Arising from the base of the reservoir are two flagella, one of which is so short that it remains within the reservoir (and long escaped detection). The other flagel-lum is long and has numerous tiny hairs along one side. It is used in
propulsion. When Euglena divides, the process is by longitudinal fission; no # Notes # sexual process occurs.
Euglena possesses several chloroplasts and a centrally placed nucleus. These organisms are plantlike in that they carry on photosynthesis. They are also, however, able to thrive in the dark, if suitable nutrients are provided in the water. A good recipe for a medium in which to grow Euglena in the laboratory calls for boiling an extract of horse manure. In certain conditions, Euglena is observed to divide more rapidly than do its chloroplasts and, thus, it becomes colorless. Such colorless forms are able to survive and reproduce if provided with suitable nutrients. Dr. Knut Norstog1 notes that photosynthetic forms of
'Norstog, Knut, and Robert Long. 1976. Plant Biology. Philadelphia: W.B. Saunders Co.
Figure 16-4 Euglena divides by longitudinal fission.
# Notes # Euglena can be converted to colorless forms by treatment with streptomycin, ultraviolet light, or heat. Dr. Arthur Cronquist2 asserts that Euglena manufactures the essential amino acid lysine using the same pathway as is noted in fungi.
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