Biological classification is a scientific plan that consists of arranging organisms into taxonomic groups and subgroups based on their similarities and dissimilarities. The word Biology was first coined by Lamarck and Treviranus in 1802. It is mandatory to classify organisms for numerous reasons. Aristotle was the first scientist to take a step toward the classification of organisms.
Cells are one of the most crucial features of living organisms, as they are the building blocks of life. They perform particular functions. All of these cells join to form a tissue. There are plenty of living organisms present in this world. Mega biodiversity regions are those which are humid and warm because they provide the optimum temperature and nutrients for the development of species. Two kingdom system was proposed by Linnaeus, which includes Plantae and Animalia kingdoms. The five-kingdom system was proposed by R.H Whittaker in 1969 which included Monera, Protista, Fungi, Plantae, and Animalia kingdoms.
- They have a protein-rich layer called a pellicle in place of a cell wall.
- Euglenoids have two flagella, i.e, short and long.
- It is important to note that the pigments of euglenoids are similar to those present in higher plants.
- Euglenoids belong to the class Euglenophyceae
Characteristics of Euglenoid
Some characteristics of Euglenoid as Structure, Habitat and Habits, Reserve Food, and Reproduction are as follows:
- Unicellular Euglena and its comparative have both animal and plant characteristics.
- Euglenoids are more advanced than blue-green algae from an evolutionary point of view, for they have a definite easily stained nucleus, and the chlorophyll is not scattered in granules but is localized in chloroplasts as in higher plants. The nuclear envelope persists during division.
- Euglena is very much like protozoans, but it bears chloroplast.
- They are free-living and found in freshwater ponds and ditches or in damp soil.
- Euglena is a more easily available protist for laboratory work.
- Euglenoids are distinguished by the absence of a cell wall, but they do contain flexible pellicles made up of protein.
- All the euglenoids have one or two flagella, by means of which they can swim easily.
- Euglena bears a flagellum put at the anterior end of a cavity.
- They bear a red-pigmented eye spot and a gullet near the base of the flagellum. The pigment in the eye spot is astaxanthin.
- Some euglenoids are green and holophytic (photoautotrophic) like other plants. Few are non-green and saprobic, like fungi and bacteria. Some capture and ingest the organisms like animals (holotropic).
- Green forms have a saprobic mode in addition to holophytic (i.e. mixotrophic).
- Photosynthetic forms bear many, radiating chloroplasts. The chloroplasts contain pigments like chlorophyll a, chlorophyll b, and xanthophyll.
- Holotropic or phagotrophic nutrition is absent in Euglena.
- Euglenoids reserve carbohydrates in the form of paramylum chemically distinct from starch and glycogen.
- Reproduction is usually asexual by cell division, but sexual reproduction has been reported in one genus.
- Under favorable conditions, euglenoids reproduce by simple, longitudinal binary fission.
- The flagellum disappears prior to division.
- Most of the species produce cysts having thick stratified membranes with deep red coloration due to the synthesis of haematochrome.
- Besides cyst formation, many non-flagellate cells may get embedded in a common gelatinous sheath resembling a palmella stage.
Examples: Euglena, Phacus, Peranema, Astasia, Trachelomonas.
Euglena – The spindle Organism
Classification of Euglena
- Euglena is a large genus having 152 species.
- Euglena is a flagellated organism with no cell wall.
- In contrast to the lack of cell walls in which they resemble animals, euglenas usually have well-defined chloroplasts and store a carbohydrate only slightly different from the starches of higher plants.
- In absence of sunlight and in presence of organic matter they ingest the food like other protozoans. That is why Euglena has been considered a plant by botanists and an animal by zoologists.
- The Euglena, when treated with antibiotic streptomycin or with heat loses its chlorophyll in other words, it can be converted from a plant to an animal.
- It needs special attention when one is searching for an organism that may represent the ancestral type from which plants and animals have evolved.
Euglena is studied as a plant as well as an animal. It is called plant-animal.
Plant Characters of Euglena
- Presence of chloroplasts with chlorophyll.
- Holophytic (photosynthetic) nutrition.
Animal Characters of Euglena
- Presence of pellicle which is composed of proteins and not of cellulose.
- Presence of stigma and paraflagellar body (photosensitive structures).
- Presence of contractile vacuole (not found in plants).
- Presence of longitudinal binary fission.
- Holozoic (animal-like), Holophytic (plant-like), and saprophytic nutrition can be seen in Euglena.
- Photoautotrophic nutrition.
- Euglena acquires its carbohydrate food by photosynthesis and nitrogenous food by absorption from the environment.
- Flagella plays a vital role in the movement of euglena.
- It also shows euglenoid movement or metabolic in which it betrays a slow worm-like movement by alternate contraction and expansion of the body.
- It shows phototaxis movement, i.e, responds to light or stimulus of light.
Euglena shows two types of reproduction, i.e, binary and multiple fission. No Sexual reproduction.
- Euglena secretes a protective wall around it and makes itself encysted under unfavorable conditions.
- After the encysted stage, two solitary daughters are formed when the organism splits longitudinally.
- The splitting starts from the former end and moves backward. The nucleus elongates and divides into two.
- Finally, the individual is split into two, each half receiving one daughter nucleus.
- In the encysted stage, the nucleus splits often and a huge number of minute daughter nuclei are generated.
- The cytoplasm smashes up and a small amount surrounds each daughter nucleus and various minute animals called flagellate are generated.
- Under favorable conditions, the flagellate comes out of the cyst and passes a short period through the amoeboid stage, develop into adult Euglena.
Why Euglena is known as Mixotrophs?
- Mixotrophs are those organisms that reveal more than one mode of nutrition.
- Eugena is a mixotroph because it shows the saprotrophic and autotrophic modes of nutrition.
- Autotrophic in the sense means it makes its own food just like plants, and saprophytic in the sense means it feeds on other organisms to obtain carbon.
FAQs on Euglenoid
Question 1: Are Euglenoids Photosynthetic?
Euglenoids are freshwater protists. In presence of sunlight, they are photosynthetic and behave like heterotrophs by predating other smaller organisms in the absence of sunlight.
Question 2: How many flagella does Euglena have?
Euglena has two flagella i.e., one short and one long.
Question 3: What is the life cycle of Euglena?
Most Euglena has a life cycle consisting of a free-swimming stage and a non-motile stage.
Question 4: Why Euglena is called a plant-animal?
Euglena is called to be a plant by botanists because it possesses chloroplasts and obtains its food through photosynthesis.
Question 5: What is the shape of Euglena cells?
The cells are cylindrical with a rounded anterior and tapered posterior.
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