It can live singly or in a colony. It can swim around with flagella. Is it a plant, an animal, an algae, a protist? You make the call. Most species of Euglena have photosynthesizing chloroplasts within the body of the cell, which enable them to feed by autotrophy making energy-containing organic molecules from inorganic raw material through the use of an energy source such as sunlight , like plants.
However, they can also take nourishment heterotrophically making use of food that comes from other organisms in the form of fats, carbohydrates, and proteins , like animals. Since Euglena have features of both animals and plants, early taxonomists, working within the old two-kingdom system of biological classification, found them difficult to classify - not because they had features different from an animal and different from a plant, but because they had some features that were animal-like and some features that were plant-like.
So could they be both? It was decided that they could not, and in fact other species that had both animal and plant-like characteristics were discovered and so in Ernst Haeckel added a third kingdom to the Animale and Vegetabile of the old taxonomic system: the Kingdom Protis. Plants are multicellular organisms with cellulose cell walls.
Depending on the definition, plants may or may not need also to enclose the developing new plant in an embryo if this definition holds, then green algae are not plants; otherwise, they are. Euglena is single-celled, and the cell is enclosed in a semi-rigid protein sheath, not a true cell wall but not a simple cell membrane. Outside the cell membrane is a flexible, protein-based structure called a pellicle. Although not generally considered a cell wall, it has similar functions in providing some rigidity and strength that the membrane cannot provide.
However the pellicle is much more flexible than most cell walls and allows for the change in form that is often seen in Euglena motion.
Euglena reproduces asexually when cells divide. No sexual reproduction has been found within the group. Sometimes Euglena are a typical photoautotroph s , using the energy of sunlight to synthesize carbohydrates from carbon dioxide and then using the carbohydrates as an energy source in cellular respiration and as building materials to synthesize a variety of biomolecules. Euglenoids store carbohydrates in a different glucose polymer than typical starch — the glucose units are combined in a 1,3 linkage, rather than the 1,4 linkage found in normal starch.
Euglenoids may also behave like heterotrophs and acquire material by ingestion phagocytosis or by absorption of solutes from its aquatic environment.
Some forms of Euglena lack chloroplasts and are solely heterotrophic. It feeds in animal fashion, but it also produces sugar like a plant does. It has a light-sensitive area called an eyespot. Because it resembles both animals and plants, scientists have resisted categorizing euglena as either one.
Was a final decision made? Well yes there was. What decision do you think they made? Nearly sixty years later has modern science confidently relegated the euglena to an appropriate place in the scheme of things? Yet scientists have conveniently added another kingdom. The new kingdom classification is Protista. Other single celled organisms have been assigned to that kingdom. Among them are the ameba and the paramecium.
In the opinion of this scientist, there are only two valid kingdoms to choose from, the animal kingdom and the plant kingdom.
Of the two, the choice should be: euglena is an animal. One final thing: even if assignment to another kingdom possesses validity, even if… Is there reason to say a member of that kingdom can change kingdoms , say to become a plant or an animal? It is part of the Protist kingdom 5 kingdoms. Thank you for your approved comment, Anika. They copped out by inventing another category.
The euglena is neither a plant nor an animal [because] in the absence of sunlight it kills and eats its victims by wrapping around them, spraying them with gastric juice and sucking them up, and a euglena, in the presence of sunlight, uses its chloroplast to manufacture food.
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