I have this new project on Euglena that I’m handling for a guy doing life sciences but there seem not to be enough information on the web about the organism, a little touch on the following headings will be of great help.
- euglena viridis classification,
- euglena viridis habitat,
- euglena characteristics
- euglena viridis diagram
- euglena reproduction
- euglena movement
- euglena viridis common name
Euglena viridis is a favorable animal to represent the class MASTlOOPHORA. It is found in fresh-water ponds and may appear in cultures prepared for amrebre. It is green in color, and, though a single animal cannot be seen with the naked eye, when a great many are massed together they impart a green tint to the water.
Cytology – Euglena is a single elongated cell pointed at the posterior, and blunt at the anterior end. Two kinds of cytoplasm may be distinguished in Euglena as in Amoeba and Paramecium, a dense outer layer, the ectoplasm, and a central mass, endoplasm, which is more fluid. A thin cuticle is present, as in Paramecium, covering the entire surface of the body.
Parallel thickenings of this cuticle run obliquely around the animal, making it appear striated. A little to one side of the center of the anterior blunt end of the body is a funnel-shaped depression known as the cytostome. At the bottom of this depression is an opening which leads into a short duct” called the gullet. This in turn enters a large spherical vesicle, the reservoir, into which several minute contractile vacuoles discharge their contents. ir contents. The mouth and gullet are not used for the ingestion of food but as a canal for the escape of fluid from the reservoir.
A conspicuous structure in Euglena is the red eye spot or stigma. This is placed near the inner end of the gullet close to the reservoir. It consists of protoplasm in which are embedded a number of granules of haematochrome. The anterior end of the body of Euglena is said to be more sensitive to light than any other part, and it is supposed by some that the stigma functions as a rather primitive visual organ. This view is made probable by the presence of lens-like paramylum grains just anterior to it. The haemotochrome also has many of the characteristics of the pigments
in the eyes of higher organisms. If kept in the dark, Euglena soon loses its red pigment. A recent view is that the haematochrome shades a sensitive particle of protoplasm.
Euglena contains a single oval nucleus lying in a definite position a little posterior to the center of the body. It has a distinct membrane, and contains a central body which is called an endosome; this body functions as a division center during mitosis.
Euglena derives its green color from a number of oval disks suspended in the protoplasm. These are known as chromatophores. They are arranged about a collection of granules situated in the center of the body, and contain chlorophyll, which is diffused throughout their protoplasmic
contents. They manufacture food by a process common in green plants but rare in animals, called photosynthesis.
When properly fixed and stained a number of bodies appear within Euglena that are not visible in the animal when alive or when prepared for study by the usual methods. They include the chondriome, pseudochondriome, plastidome, and Golgi bodies. The relations
of these protoplasmic inclusions to the functions of the Euglena are more or less problematical.
Nutrition: Although Euglena has mouth and gullet, it is very doubtful, as noted above, if any food is ingested. Food is manufactured as in green plants, by the aid of the chlorophyll in the chromatophores. This mode of nutrition is known as holophytic. The chlorophyll is able, in the presence of light, to break down the carbonic acid (C02 ), thus setting free the oxygen, and to unite the carbon with water forming a substance allied to starch called paramylum.
If specimens are kept in good light continually, a large amount of paramylum will be stored up for future use, being laid down around some granules of protein substance near the center of the body. These granules are called pyrenoids.
Both the pyrenoids and chromatophores are permanent cell structures and increase in number by division and not· by the origin of new ones from the other parts of the· body. That all the food necessary for the life of Euglena is not procured by photosynthesis is shown by the fact that the animal is able to live in the dark for over a month, whereas chlorophyll demands light before the production of paramylum is possible. This seems to indicate that organic substances in solution are absorbed through the surface of the body, that is, saprophytic nutrition supplements the holophytic.’ The nutrition of Euglena differs from that of the majority of animals, since the latter live by ingesting solid particles of food and are said to be holozoic. By some authorities Euglena is regarded as a plant and placed in the plant series among the unicellular algre since it contains chlorophyll, a substance characteristically present in plants. Others regard Euglena as an animal that has acquired a plant-like type of nutrition.
Locomotion: Euglena changes its shape frequently, becoming shorter and thicker, and shows certain squirming movements. These prove that it possesses considerable elasticity, since the normal shape is regained if enough water is present. Often in a favorable specimen,a thread-like structure may be seen projecting from the anterior end of the body and bending to and fro, drawing the animal after it. This is the flagellum. It is more or less cylindrical and possesses a central rod-like elastic core and a much more fluid protoplasmic sheath. If the flagellum cannot be seen in the living animal, a little iodine placed under the cover glass will help to bring it out.
Behavior: Euglena swims through the water in a spiral path. The effect of this is the production of a perfectly straight course through the trackless water. When stimulated by a change in the intensity of the light, Euglena, in the majority of cases, stops or moves backward, turns strongly toward the dorsal side, but continues to revolve on its long axis. The posterior end then acts as a pivot while the anterior end traces a circle of wide diameter in the water. The animal may swim forward in a new direction from any point in this Circle. This is the avoiding reaction.
Euglena is very sensitive to light. It swims toward an ordinary light such as that from a window and if a culture containing euglenae is examined, most of the animals will be found on the side toward the brightest light. This is of distinct advantage to the animal, since light is necessary for the assimilation of carbon dioxide by means of its chlorophyll. Euglena will swim away from the direct rays of the sun. Direct sunlight will kill the organism if allowed to act for a long time. If a drop of water containing euglenae is placed in the direct sunlight and then one half of it is shaded, the animals will avoid the shady part and also the direct sunlight, both of which are unfavorable to them, and will remain in a small band between the two in the light best suited for them, that is, their optimum. By shading various portions of the body of a Euglena it has been found that the region in front of the eye spot is more sensitive than any other part. It should be noted that when Euglena is swimming through the water it is this anterior end which first reaches an injurious environment; the animals give the avoiding reaction at once, and are thus carried out of danger.
Reproduction: Reproduction in Euglena takes place by binary longitudinal division. Nuclear division takes place within the nuclear membrane. The chromatin, which is in the form of paired strands of chromomeres in the vegetative stage, form pairs of chromosomes each of which divides longitudinally into two. The endosome becomes constricted into two approximately equal parts. The intranuclear body also divides into two and these give rise to the blepharoplasts. The body begins to divide at the anterior end. the old flagellum is retained by one half, while a new flagellum is developed by the other. Often, division takes place while the animals are in encysted condition. Occassionally, euglenae are found which have become almost spherical and are surrounded by a rather thick gelatinous covering which they have secreted. such an animal is said to be encysted. in this condition, periods of drought are successfully passed, the animal becoming active when water is again encountered. Usually in cultures brought into the laboratory, many cysts are found on the sides of the dish. Encystment frequently takes place without any apparent cause. The animal resting in this condition for a time and again re-emerging into its free-swimming habit. Before encystment, the flagellum is thrown off, a new one being produced when activity is again resumed. One cyst usually produces two euglenae although these may divide while still within the old cyst wall, making four in all, while certain observers nave recorded as many as thirty-two young flagellated euglenae which escaped from a single cyst.
SOURCE:
INVERTEBRATE ZOOLOGY BY ROBERT W. HEGNER, PH.D.
0 Comments
Comment