Euglena

Table of Contents :

Euglena is a unicellular eukaryote. Euglena has characteristics of both plants and animals. Euglena is flagellated. Euglena has plastids and performs photosynthesis in light but moves around in search of food using its flagellum at night. There are around 1000 species of Euglena found. They are found in freshwater, saltwater, marshes and also in moist soil.

Euglena Classification

Classification of Euglena is contentious. They are kept in the phylum Euglenozoa or in the phylum Euglenophyta with algae due to the presence of chlorophyll. Since all the species of Euglena do not contain chloroplasts, they are kept in the phylum Euglenozoa. The class Kinetoplasteae in the phylum Euglenozoa contains non-photosynthetic flagellates known as Trypanosomes, which are parasitic and cause serious diseases in humans such as African sleeping sickness, leishmaniasis

Euglena Classification

Euglena Structure with Diagram and Characteristics

Morphology and Anatomy

  • Euglena has an elongated cell measuring 15-500 x 10-6 m
  • Mostly green in colour due to the presence of chlorophyll pigment
  • Some of the species of euglena contain carotenoid pigments, which give it distinct colour like red
  • Euglena is unicellular having one nucleus
  • Euglena lacks the cellulose cell wall present in a plant cell
  • There is a presence of a flexible outer membrane known as a pellicle, which supports the plasma membrane. The pellicle is composed of a proteinaceous strip and supporting microtubules. The pellicle gives flexibility to the cell and an ability to contract and change its shape
  • A thin plasma membrane is present which encloses the cytoplasm and cell organelles
  • It contains a contractile vacuole which removes excess water
  • There is inward pocket near the base of flagella called a reservoir, where contractile vacuole dispels excess water
  • Various cell organelles such as mitochondria, endoplasmic reticulum and Golgi bodies are present

Nutrition

  • Euglena contains chloroplast having chlorophyll. These chloroplasts have the green algal origin and seemed to have acquired due to endosymbiotic relationship
  • They perform photosynthesis but also require other organic nutrients and vitamins such as vitamin B12
  • Some of the photosynthetic euglenoids lose their chlorophyll when they grow in the dark and obtain nutrients heterotrophically from organic matter
  • Some species of Euglena are also heterotrophs
  • The heterotrophic species of Euglena either absorb organic compounds from the surrounding water or engulf bacteria and protists by phagocytosis within the food vacuoles
  • The chloroplast of Euglena contains pyrenoids, which is used to synthesise paramylon, a ꞵ-1,3 polymer of glucose
  • Food is stored in the form of paramylon, which provides energy when there is no light
  • Some species of Euglena produce an alkaloid known as euglenophycin, which is found to kill fishes
  • Euglena is cultivated for large scale production in some countries like Japan for commercial production of paramylon. Some species of Euglena have shown to contain vitamin E (⍺-tocopherol) and high content of astaxanthin

Locomotion and Phototaxis movement

  • It has an eyespot also known as stigma, that contains photoreceptors for detection of light and involves in phototaxis
  • Light detected by the eyespot is focused on paraflagellar body
  • One or two flagella are present, which help in locomotion
  • Mostly two flagella are present, that originates from a small reservoir inside the cell
  • One short flagellum is present, which does not protrude out of the cell, the long flagellum is used for swimming

Reproduction

  • Euglena reproduces asexually by binary fission, they divide longitudinally
  • Their lifecycle consists of a free-swimming and a non-motile stage
  • It produces thick-walled protective cyst that can withstand unfavourable conditions, this is characteristic of a non-motile stage
  • Some euglenoids make reproductive cyst under unfavourable conditions. Many Euglenoids gather together, leave their flagella and get enclosed in a gelatinous substance. Individual Euglena produces reproductive cyst, which produces daughter cells by binary fission. Under favourable conditions, these daughter cells become flagellated and come out of the mass. This is known as the palmelloid stage of the lifecycle

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