Euglena movement, characteristics, and structure

What is Euglena?

Euglena is a genus classification of organisms that exhibit characteristics of both plants and animals. The euglena movement and structure are unique. These organisms’ movement is based on the structural possession of a flagellum and pellicle. Euglena can be found inhabiting fresh and brackish water habitats as well as moist soils. There are more than 1000 species in this genus such examples include Euglena gracilis, Euglena viridis, Euglena sanguinea, etc.

Definition

Euglena can be defined as a known genus consisting of species of unicellular flagellates that exhibit both plant and animal characteristics. Even though, euglena share some characteristics of both plants and animals, they are not seen as plants or animals but as protists. They may be plant-like in that they can manufacture their own food, which is a typical characteristic of a plant. But, they also exhibit animal-like features by being capable of locomotion. Apart from being able to move, they can also consume food (heterotrophic), which are typical characteristics of animals.

Pictures of euglena
Picture of a euglena

Euglena as a unicellular organism is too small to be seen with naked eyes, hence, in order to observe and study them, they are viewed under a compound microscope. These organisms divide their cell longitudinally for reproduction. They reproduce asexually through cell division by dividing down their length. Many species even produce dormant cysts that can withstand drying.

What does euglena eat?

Euglena eats autotrophically and heterotrophically. The majority of the species of euglena within their cell have chloroplasts that are used for photosynthesis. This organelle is what is responsible for their autotrophic feeding nature like plants.

Even though, these organisms are photosynthetic some of them absorb food directly through the cell surface. They feed heterotrophically through the process of phagocytosis, whereby the cell membrane entraps the food in a vacuole for digestion.

Is euglena a plant or animal?

Euglena is not a plant or an animal but a protist. Protists are single-celled organisms that are not plants, animals, or fungi. Even though, euglena share some characteristics of both plants and animals, they are not seen as plants or animals.

They may be plant-like in that they can manufacture their own food, which is a typical characteristic of a plant. On the other hand, they still exhibit animal-like features by being capable of locomotion. They can also consume food (heterotrophic), which are typical characteristics of animals.

In the past, both zoologists and botanists claimed this small group of organisms. Botanists sometimes referred to them as Euglenophyta while zoologists sometimes call them Euglenozoa. ‘Phyta’ refers to plants and ‘zoa’ refers to animals. Even though these organisms have been grouped in the protist kingdom, there are recent phylogenetic studies that have been diverging them from other eukaryotes into very small groups of unfamiliar unicellular organisms. The organism, Trypanosoma cruzi that cause sleeping sickness and Chagas disease are some of the close relatives of euglena.

Where does euglena live?

Euglena lives in fresh and saltwater bodies, as well as moist soils. They are known to live in water rich in organic matter. Being part of certain aquatic habitats, euglena functions as a primary producer. In the aquatic ecosystem food web, as primary producers, these organisms are eaten by other organisms. Also, they can be decomposers that consume and break down other organisms or dead organic matter in the food chain.

In euglena habitats such as lakes or ponds with high nitrogen content, some species like the Euglena sanguinea and Euglena viridis, in particular, inhabit such waters and form large toxic populations of red or green blooms. In abundance, E.sanguinea color the surface of ponds and ditches red while Euglena viridis color the water surface green. These euglena species can produce toxins in the water body that kill fish.

Is euglena unicellular or multicellular?

Euglena is unicellular. Euglena is a genus of many unicellular flagellated microorganisms with both plant and animal features. Hence, they are not multicellular; and as unicellular organisms, they are too small to be seen with naked eyes. Therefore, in order to observe and study them, a compound microscope must be used.

Euglena Classification

Domain: Eukaryota

Kingdom: Protista

Super phylum: Discoba

Phylum: Euglenozoa

Class: Euglenoidea

Order: Euglenales

Family: Euglenaceae

Genus: Euglena

Initially, in the past, euglena has been classified as protozoans because they lack a cell wall, have a pellicle, and are motile. Nevertheless, euglena as single-celled protists that are photosynthetic, are placed either in the algal phylum Euglenophyta or in the phylum Euglenozoa since they can also feed heterotrophically like animals.

Since euglena species are not plants or animals, the characteristics of euglena being plant-like and animal-like classify them under the kingdom Protista. Like many other similar unicellular organisms, they are grouped under this kingdom because they cannot be grouped under the plant or animal kingdom. The recognized euglena phylum is Euglenozoa, even though some put them under the phylum Euglenophyta.

Hence, the euglena kingdom being Protista makes them protists which are eukaryotic organisms that are not fungi, plants, or animals. The majority of protists are single-celled except algae that are multicellular. Other examples of organisms that belong to this euglena kingdom are amoeba and paramecium.

The genus Euglena are eukaryotes and are therefore the best known and most widely studied member of the class Euglenoidea. Euglena class- Euglenoidea, is a diverse class group that has about 54 genera and at least 800 species.

Structure of Euglena

The euglena cell structure is tear-drop shaped with one end pointed and the other end, blunt (head). Organelles that are common in the animal cell and plant cell and are also found in the euglena cell structure include the Golgi apparatus, ribosomes, nucleus, endoplasmic reticulum, contractile vacuole, mitochondria, and lysosomes. The other unique structure of the euglena cell includes an eyespot, flagella, pellicle, paramylon, and a paraflagellar body.

What does euglena look like?

Euglena looks like teardrop-shaped cells under the microscope. The size of euglena ranges between 0.0006-0.02 inches with a complex internal structure. It is characterized by an elongated cell with one nucleus. This euglena nucleus makes these organisms eukaryotic. The anatomy of the euglena cell contains a contractile vacuole that can expel water and regulate the cytoplasm.

They have a red eyespot and numerous chlorophyll-containing chloroplasts for photosynthesis. These euglenoids possess two flagella for locomotion. One of the flagella is long while the other is short. The euglena flagella are responsible for movement. Also, these organisms can move by means of changing their shape.

Certain species like the E. rubra contain a large number of carotenoid pigments and thus appear red in the sunlight. The structure of the euglena lacks a rigid cellulose cell wall and possesses flexible pellicles that enable them to change shape.

Euglena diagram

Euglena Diagram Labeled
A labeled euglena diagram showing the structural features visible in living and stained preparations of the euglena cell.

Let’s discuss some of the parts of the euglena seen under the microscope, labeled in the diagram above.

Parts and features

Euglena Size

The euglena size varies between 15–500 micrometers or 0.0006–0.02 inches.

Tear-drop Shape

The euglena structure, as viewed under the light microscope appear as an elongated unicellular organism. They are seen rapidly moving across the field surface. One distinct feature that is noticed about the euglena shape is its blunt (rounded) end portion and a pointed end that gives it a tear-drop shape. The blunt rounded end is usually regarded as the head of the organism. Nevertheless, it is important to note that this is not the shape of all euglena species even though the tear-drop shape is the most common appearance of the species.

Flagella

A whip-like structure known as the flagellum (plural: flagella) is attached to the blunt rounded end of the euglena. It is because of the possession of a flagellum that euglenoids are classified as flagellates. These organisms have two flagella, even though it is one that is usually seen. This is because the other one is usually hidden in a part of the euglenoid known as a reservoir.

The longer visible flagellum of the euglenoid is located at the anterior end of the organism and is visible under a light microscope whereas the hidden one is very short and doesn’t protrude from euglena cells. In some species, the two flagella are non-emergent and are entirely hidden in the cell’s reservoir, thus, they cannot be seen using the light microscope e.g E. mutabilis. There are about 30, 000 fine filaments known as mastigonemes that coat the surface of the flagellum.

These organisms are able to move and swim across water surfaces due to the longer visible flagellum. Flagella and cilia are similar in structure as they both have a central bundle of microtubules known as axoneme. Each axoneme has nine pairs of microtubules (doublet) that form the outside of a ring as well as two central microtubules. This structure is referred to as 9+2. These microtubules are bound together by cross-linking proteins with each doublet connected by nexin protein.

Paraflagellar body or photoreceptor

At the base of the flagellum is a swelling structure known as the paraflagellar body or photoreceptor. This structure is photosensitive as it senses light. Since the paraflagellar body and the euglena eyespot are located close to the flagella, their proximity enhances light-guided directional movement.

Pellicle

Euglena possesses a flexible tough pellicle rather than a rigid cellulose cell wall as in plants. This pellicle structure of euglena is flexible and tough, thereby facilitating the flexible and contractible movement of the organism. The toughness of the pellicle structure maintains the shape of the euglena cells. Its flexibility also allows changes in the body shape, referred to as metaboly movement or euglenoid movement.

The pellicle lies under the plasma membrane and covers the euglenoid body. It is made up of a layer of fibrous elastic proteins and microtubules. The protein layer is supported by microtubule structures and the microtubules are arranged in strips in a way that they spiral around the cell. The flexibility and contractility of the euglenoid to change shape is a result of the pellicle strips sliding over one another. As these strips slide over each other, the membrane flexibility and contractility are enhanced. This is why euglenoids are able to squeeze and pass through tiny spaces.

Membrane

As earlier said, euglena species do not have cell walls. Hence, the organisms’ organelles and cytoplasm are bound by a plasma (cell) membrane that allows for easier movement. The flexible, protein-based structure known as a pellicle is then located outside the cell membrane. The presence of this thin protein layer under the plasma membrane protects the plasma membrane and helps in maintaining the cell’s shape.

Although the pellicle of the euglena is not generally considered a cell wall, it has similar functions to a cell wall. It provides some rigidity and strength that the cell membrane of the organism cannot give. However, in contrast to most cell walls, the pellicle is much more flexible and allows for a change in the form that is usually seen in euglenoid movement. It is the flexible nature of the ornamented pellicle that facilitates movement.

Eyespot

At the anterior part of the Euglenoid, there is a bright red eyespot, also called stigma. This organelle is made up of carotenoid pigment granules. The function of the eyespot in euglena is not as an actual eye, rather it helps to filter the wavelength of light that reaches the photoreceptor at the base of the flagellum.

Therefore, the euglena stigma serves as sunglass for the photoreceptors also called paraflagellar body. This means the function of the eyespot in euglena is to tell the organism where the light source comes from. In response to this, the euglenoid moves towards the light source for photosynthesis. This bodily movement of the euglena towards the light source is commonly known as positive phototaxis.

Chloroplast

Apart from the red eyespot, there are dark (greenish) spots around the body of euglenoids. Some of these spots are the euglena chloroplasts. These chloroplasts contain chlorophyll to produce sugar through photosynthesis. There are two types of chlorophyll- chlorophyll A produces the green hue responsible for photosynthesis and chlorophyll B produces a bluish-green color that enhances the light absorption needed for photosynthesis. Some organisms have chlorophyll A whereas some have both chlorophyll A and B.

The chloroplasts in euglena main function are to trap sunlight that is used to produce food through photosynthesis. This organelle has a subcellular compartment known as pyrenoids that function to generate an environment rich in carbon dioxide for ribulose diphosphate carboxylase. Ribulose diphosphate carboxylase is one of the enzymes for carbon fixation in photosynthesis. As a result of photosynthesis, a starch-like carbohydrate, paramylon is produced which serves as food storage, so that when light is not available the euglenoids can survive.

Since these organisms in the presence of sunlight are capable of manufacturing their own food, they are said to be autotrophic organisms. Therefore, euglenoids can survive with light even without eating heterotrophically. It is also important to note that even though they are autotrophic they can also be heterotrophic by consuming food through phagocytosis.

Vacuole

Even though, euglenoids are photosynthetic some of them absorb food directly through the cell surface. They feed heterotrophically through the process of phagocytosis, whereby the cell membrane entraps the food in a vacuole for digestion.

As the euglena engulfs the food particle in a vacuole for digestion, enzymes are then released in the vacuole to digest the food particle. Also, the euglena structure consists of a contractile vacuole that helps collect and remove excess fluids from the cell. This organelle helps the cell from taking in too much water which could lead to the rupture of the cell.

Paramylon

Food is stored in the euglena as paramylon, a specialized complex carbohydrate. This stored carbohydrate enables them to survive in low-light conditions.

Microscopy

At 40X, euglena under the microscope appears as tiny particles moving in the water. As magnification increases to 100X and 400X, the whiplike tail and other features become more visible. The appearance of the euglena under a microscope at 400x will be green/ light green in color with visible dark spots inside. Higher magnification power will also show the colored granules known as the eyespot.

These organisms are easily collected from ponds, shallow water surfaces, etc and prepared for viewing. Euglena gracilis is one species that is commonly used in laboratory studies as model organisms. They are used to study cell metabolism and growth in several environmental conditions.

How do euglena move?

The euglena move by either turning and twisting the flagella or by using its pellicle for peristaltic movement.

Types of Euglena Movement

  1. Flagellar movement
  2. Euglenoid movement

Flagellar movement

In this type of euglena movement, the euglena turns and twists the flagella to move. The whipping and turning of the flagella make the euglenoid move like a propeller. Two motions are created from the beating of the flagella. One of the motions is the transitional motion whereby the euglena moves forward. The other motion is the rotational motion whereby the euglenoid body rotates.

Below is a video illustration of a flagellar movement of the euglena as viewed under a microscope.

A video showing the flagellar movement of the euglena under a microscope

Euglenoid movement

In this type of movement, the euglena uses the pellicle for peristaltic movement. As explained earlier, these organisms can alter their shape due to the presence of a flexible pellicle. The process at which they alter their shape and return back to their initial shape like an elastic band is called metaboly movement or euglenoid movement. This euglena locomotion is a result of peristaltic waves.

As peristaltic waves travel through the euglena body, the body is triggered to become much shorter and wider at the anterior end first, then the middle body follows suit, and lastly the posterior end. This smooth movement is only possible because of one of the unique parts of a euglena called the pellicle. The pellicle is a unique structure that aids the euglena movement.

Below is a video illustrating the euglenoid movement of the euglena.

A video showing the metaboly movement of the euglena under a microscope

How do euglena reproduce?

Euglena reproduction is asexual; how they reproduce is through a form of cell division called binary fission. Reproduction in euglena starts with the mitosis of the cell nucleus, which is followed by the cell dividing itself. This division is longitudinal, beginning at the front end of the cell.

These organisms divide their cell longitudinally for reproduction. They reproduce asexually through cell division by dividing down their length. Flagellar processes, gullet, and the euglena stigma (eyespot) are duplicated in the process. During the process of reproduction in euglena, a cleavage forms in the anterior part of the euglena, and a V-shaped bifurcation moves gradually towards the posterior, until the two halves are entirely separated.

The lifecycle of the euglena involves a free-swimming stage and a non-motile stage. They become dormant and form a protective cyst around themselves when environmental conditions are unfavorable. Low moisture or scarcity of food makes it difficult for them to survive, thus, they form a thick-walled protective cyst and go dormant till when the conditions are favorable. The forming of the protective cyst is a characteristic of the non-motile stage.

Many Euglenoids leave their flagella, gather together forming a mass that gets enclosed in a gelatinous substance. Individual Euglena forms a reproductive cyst, that produces daughter cells by binary fission. In the palmelloid stage of the lifecycle, these daughter cells under favorable conditions become flagellated and come out of the mass.

Characteristics of euglena

  • These organisms have two flagella- one long flagellum and a short one.
  • The longer visible flagellum is located at the anterior end of the organism and is visible under a light microscope whereas the hidden one is very short and doesn’t protrude from the euglena cell.
  • They are unicellular flagellated microorganisms with both plant and animal features.
  • One of the major characteristics of euglena is that it lacks a cell wall but possesses a cell membrane and pellicle.
  • Euglenoids can take in nutrients by osmotrophy.
  • They can survive without light by feeding heterotrophically, which involves feeding on a diet of organic matter e.g peptone, beef extract, carbohydrate, or ethanol.
  • One of the major characteristics of euglena is that in the presence of sunlight, they feed via phototrophy by making use of their chloroplasts that contains chlorophyll to produce sugars through photosynthesis.
  • As compared to the chloroplasts of plants and the green alga that is surrounded by only 2 membranes, the euglena’s chloroplast is surrounded by 3 membranes.
  • The euglena turns and twists the flagella to move or uses the pellicle for movement.
  • A unique euglena characteristics include the presence of pyrenoids in the euglena’s chloroplasts that distinguishes the genus from other euglenoids like Lepocinclis and Phacus.
  • These organisms reproduce asexually via binary fission.
  • The exceptional flexibility and contractility characteristics of euglena are due to the pellicle structure under the cell membrane.
  • Euglenoid possesses a photosensitive swelling structure known as the paraflagellar body or photoreceptor which is located at the base of the flagellum.
  • They have a bright red eyespot that is made up of carotenoid pigment granules which help to filter the wavelength of light that reaches the photoreceptor at the base of the flagellum.
  • Euglena characteristics include their tear-drop shape where one end is blunt (rounded) and the other end is pointed.
  • In unfavorable conditions, euglena forms a protective wall around itself and lies dormant until the environmental conditions become favorable.
  • Euglena inhabits freshwater, saltwater, and moist soils. They are known to live in water rich in organic matter.
  • The lifecycle of the euglenoid involves a free-swimming stage and a non-motile stage.

Ecological role

One major euglena ecological role is to take in carbon dioxide and give out oxygen during the process of photosynthesis. The oxygen released into the atmosphere is used by other organisms in the ecosystem. Also, another ecological role of the euglena is to consume and break down other organisms or dead organic matter in the food chain.

FAQs

Does euglena have a nucleus?

Yes

How does euglena eat?

They eat autotrophically and heterotrophically. With the possession of chloroplasts, they carry out photosynthesis like plants. Even though they are photosynthetic some of them still feed heterotrophically through the process of phagocytosis, whereby the cell membrane entraps the food in a vacuole for digestion.

Is euglena autotrophic or heterotrophic?

Euglena can be autotroph or heterotroph. As autotrophic organisms, they get energy from the sunlight and use this energy to synthesize carbohydrates from carbon dioxide. This carbohydrate is then used as an energy source in cellular respiration and serves as a building material to synthesize a variety of biomolecules.

These organisms store carbohydrates in a different glucose polymer than typical starch. The glucose units combine in a 1,3 linkage instead of the 1,4 linkage seen in typical starch. However, euglenoids can also be heterotrophic and get energy from the ingestion of food through phagocytosis or by absorbing solutes from their aquatic environment. Some euglenoids lack chloroplasts generally and are only heterotrophic.

What is Euglena gracilis kingdom?

Kingdom Protista

How does euglena obtain energy?

Euglena is sometimes phototrophic, so they get energy from the sunlight. They use this energy to synthesize carbohydrates from carbon dioxide. This carbohydrate is then used as an energy source in cellular respiration and serves as a building material to synthesize a variety of biomolecules.

These organisms store carbohydrates in a different glucose polymer than typical starch. The glucose units combine in a 1,3 linkage instead of the 1,4 linkage seen in typical starch. However, euglenoids can also be heterotrophic and get energy from the ingestion of food through phagocytosis or by absorbing solutes from their aquatic environment. Some euglenoids lack chloroplasts generally and are only heterotrophic.

What is Euglena gracilis phylum?

Euglenozoa

What are the euglena species?

E.gracilis, E. viridis, E. deses, E. sanguinea, E. acus, E. anabaena, E. oxyuris, E. sociabilis, E. proxima, E. rubra, E. oblonga, E. convoluta, E. stellata, E. sabulosa etc.

Where is euglena found?

They are found in fresh and saltwater bodies, as well as moist soils

Does euglena have a cell wall?

No, they don’t have a cell wall. They possess a flexible tough pellicle rather than a cell wall. This pellicle of euglena facilitates the flexible and contractible movement of the organism. Also, the toughness of the pellicle structure maintains the shape of the euglena cells.

Which of the organelles enables the euglena to be photoautotrophic?

The chloroplast. These chloroplasts contain chlorophyll to produce sugar through photosynthesis. They trap the sunlight that is used to produce food through photosynthesis.

Is euglena prokaryotic or eukaryotic?

They are eukaryotic because they have a nucleus.

How does euglena obtain food?

They obtain their own food through the process of photosynthesis or through the process of phagocytosis whereby the cell membrane entraps the food in a vacuole for digestion.

What are the reasons why euglena have in the past been classified as protozoans?

Euglena has in the past been classified as protozoans because they lack a cell wall, have a pellicle, and are motile.

Why is euglena green?

Not all euglena species are green in appearance. Most of them such as Euglena viridis, Euglena gracilis, etc. are green while others like Euglena sanguine, etc. appear red in color.

The species that appear green have photosynthesizing chloroplasts with chlorophyll pigments in their cell that give them plant-like features. Also, through a process of phagocytosis, euglena feed on green algae, amoebas, paramecium, and rotifer. Hence, their green color is not only a result of the green chloroplasts as the green algae they consume contributes.

What is the eyespot used for in euglena?

The function of the eyespot of euglena is to filter the wavelength of light that reaches the photoreceptor at the base of the flagellum. Therefore,
the significance of an eyespot in the cell of euglena is to serve as a sunglass for the photoreceptors.

Euglena uses which structure for movement?

The structure the euglena use for movement is the flagella or pellicle. These organism turns and twists the flagella to move or use the pellicle for peristaltic movement. Hence, it makes use of flagellar movement or euglenoid movement.

The flagellum is a whip-like structure attached to the blunt rounded end of the euglena. It is because of the possession of this flagellum that the genus euglena is classified as flagellates. These organisms have two flagella and move and swim across water surfaces by beating the longer flagellum. This is the flagellar movement.

The euglena possesses a flexible tough pellicle rather than a rigid cellulose cell wall as in plants. This pellicle structure of euglena is flexible and tough, thereby facilitating the flexible and contractible movement of the organism. Its flexibility allows changes in the body shape, referred to as the metaboly movement or euglenoid movement.

What phylum does euglena belong to?

Euglenozoa.

How many flagella do euglena have?

They have two flagella, even though it is one that is usually seen. This is because the other one is usually hidden in a part of the euglena known as a reservoir.
The longer visible flagellum of the euglena is located at the anterior end of the organism and is visible under a light microscope whereas the hidden one is very short and doesn’t protrude from the euglena cell.

What type of organism is euglena?

They are unicellular protists.

What is the function of the nucleus in the euglena cells?

The nucleus is the center of the cell and contains the DNA of the cell. Also, it controls the activities of the cell.

Which group of protists to euglena belong to?

Euglenoids

What is euglena classified as?

A protist

What do euglena and paramecium have in common?

They are both photosynthetic aquatic organisms that possess chloroplasts. However, they can both be heterotrophic. Euglena and paramecium are both sensitive to light.

How does euglena get rid of waste?

They get rid of waste through a contractile vacuole that helps collect and remove excess fluids from the cell. This organelle helps the cell from taking in too much water which could lead to the rupture of the cell.

What kingdom does euglena belong to?

The kingdom the euglena is classified into is the Protista kingdom. The characteristics of euglena being plant-like and animal-like made it difficult for the early taxonomists to classify them. It was these unclassifiable organisms that prompted Ernst Haeckel to add another kingdom known as the kingdom Protista which the euglena currently belongs to.

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