Euglena: Classification, Structure, Nutrition and Reproduction

Euglena is a fascinating organism belonging to the group of euglenoids. These are unicellular creatures known for their unique flexible bodies. They exhibit characteristics of both plant and animal life. During the day, Euglena uses its plastids to photosynthesize, much like a plant. However, at night, it behaves more like an animal, using its flagellum to move around in search of food. Euglena species are incredibly diverse, with around 1000 species documented. They inhabit a variety of environments, including freshwater, saltwater, marshy areas, and even damp soil.

The Classification of Euglena

Euglena is a genus within the group of euglenoids. The classification of Euglena is a topic of ongoing debate among scientists. Some place Euglena in the phylum Euglenozoa, while others place them in the phylum Euglenophyta, alongside algae, due to their ability to photosynthesize. However, not all Euglena species contain chloroplasts, which complicates their categorization. The class Kinetoplasteae, part of the phylum Euglenozoa, contains non-photosynthetic flagellates known as Trypanosomes. These organisms are parasitic and can cause serious diseases in humans, including African sleeping sickness and leishmaniasis.

The Diagram and Characteristics of Euglena

The Morphology and Anatomy of Euglena

Euglena has a unique, elongated cell structure that measures between 15-500 micrometres.

The organism is primarily green due to the presence of chlorophyll pigment.

Some Euglena species contain carotenoid pigments, which give them a distinct color, such as red.

Euglena is a unicellular organism with a single nucleus.

Unlike plant cells, Euglena does not have a cellulose cell wall.

It possesses a flexible outer membrane known as a pellicle, which supports the plasma membrane. This pellicle is composed of proteinaceous strips and supporting microtubules, giving the cell the ability to contract and change shape.

A thin plasma membrane encloses the cytoplasm and cell organelles.

Euglena contains a contractile vacuole for the removal of excess water.

There is an inward pocket near the base of the flagella, known as a reservoir, where the contractile vacuole expels excess water.

Various cell organelles such as mitochondria, endoplasmic reticulum, and Golgi bodies are present.

The Nutrition of Euglena

Euglena contains chloroplasts that contain chlorophyll. These chloroplasts are believed to have originated from green algae due to an endosymbiotic relationship.

While Euglena performs photosynthesis, it also requires other organic nutrients and vitamins, such as vitamin B12.

Some photosynthetic Euglena lose their chlorophyll when they grow in the dark and obtain nutrients heterotrophically from organic matter.

Some Euglena species are heterotrophic.

Heterotrophic Euglena species either absorb organic compounds from the surrounding water or engulf bacteria and protists through phagocytosis within their food vacuoles.

The chloroplasts in Euglena contain pyrenoids, which are used to synthesize paramylon, a β-1,3 polymer of glucose.

Food is stored in the form of paramylon, providing energy when light is not available.

Some Euglena species produce an alkaloid known as euglenophycin, which has been found to be lethal to fish.

Euglena is cultivated on a large scale in some countries, such as Japan, for the commercial production of paramylon. Some Euglena species have been found to contain vitamin E (α-tocopherol) and a high content of astaxanthin.

Locomotion and Phototaxis Movement

Euglena has an eyespot, also known as a stigma, which contains photoreceptors for the detection of light and is involved in phototaxis.

Light detected by the eyespot is focused on the paraflagellar body.

Euglena has one or two flagella that aid in locomotion.

Most Euglena have two flagella that originate from a small reservoir inside the cell.

One of the flagella is short and does not protrude out of the cell, while the longer flagellum is used for swimming.

The Reproduction of Euglena

Euglena reproduces asexually through binary fission, dividing longitudinally.

The lifecycle of Euglena consists of a free-swimming stage and a non-motile stage.

During unfavorable conditions, Euglena produces a thick-walled protective cyst.

Some Euglena form reproductive cysts under unfavorable conditions. These cysts produce daughter cells through binary fission, which become flagellated and exit the mass under favorable conditions. This is known as the palmelloid stage of the lifecycle.

Frequently Asked Questions

Are Euglena a plant or animal?

Euglena is a genus of unicellular, flagellated microorganisms. They possess characteristics of both plants and animals but are neither placed in the kingdom Plantae nor Animalia. They belong to the kingdom Protista.

Are Euglena prokaryotic or eukaryotic?

Euglena is a genus of eukaryotic, unicellular and flagellated microorganisms. They contain a well-defined nucleus and other cellular organelles such as mitochondria, endoplasmic reticulum, chloroplasts and Golgi bodies, etc.

Where is Euglena found?

They are found in freshwater, saltwater, marshes and also in moist soil.

Why Euglena is known as mixotrophs?

Euglena has chloroplasts and performs photosynthesis in light, but moves around in search of food using its flagellum at night. Some of the photosynthetic euglenoids lose their chlorophyll when they grow in the dark and obtain nutrients heterotrophically from organic matter. The heterotrophic species of Euglena either absorb organic compounds from the surrounding water or engulf bacteria and protists by phagocytosis within the food vacuoles. Since they show both autotrophic and heterotrophic mode of nutrition, they are known as mixotrophic.

What are euglenoids?

Euglenoids are the best-known flagellates of the phylum Euglenozoa. Euglenoids have an outer protein layer called the pellicle. They are unicellular and biflagellate. Examples of euglenoids are Euglena, Trachelomonas, etc.