How does Euglena respond to the environment? – (Behaviour of Euglena)

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Introduction to the behaviour of Euglena

Euglena reacts to a variety of stimuli in the same manner as the protozoans do. They respond to light, mechanical stimuli, thermal and chemical stimuli with a wide variety of orientations and movements.

Several experiments done so far includes the study of microorganisms like Euglena viridisEuglena gracilis, etc. by chemotaxis, viability (mostly based on photosynthesis process), and overall coexistence.

Euglena plays a critical role in the various biogeochemical cycles, as they live in moist soil and aquatic ecosystems. They live in fresh and brackish water and moist soils that are rich in organic matter.

They have adapted themselves to the various stimuli and have learned new behavioural patterns that are mostly dedicated to their type of ecosystem.

In doing so, Euglena performs a complex set of responses to stimuli which is called their behaviour. Behavioural responses refer to how Euglena cope with changes in their environments.

It has been seen that Euglena shows a diversity of cell characteristics and behaviours that are involved in chemotaxis and phototaxis that is originating from differences in the metabolic status of the cells.

How does Euglena respond to the environment?

There are 3 ways of how euglena responds to the environment through various behavioural patterns. These are:


  1. Reaction To Light: This type of reaction occurs when the Euglena moves towards the direction of light.
  2. Shock Reaction: This type of reaction occurs when the direction of light suddenly changes, causing a shock to the Euglena that was gradually moving in the previous direction of light.
  3. Avoiding Reaction: This type of reaction occurs when the Euglena moves away from the obstacles that come its way due to the various mechanical, or thermal, or chemical stimuli that are present in water.

Let’s know about each of these types of response in detail…

1. Phototaxis: Reaction To Light

It is seen that Euglena grows and moves towards or away from light depending on their needs. This process is known as phototaxis.

It has also been seen that Euglena avoids direct light and no-light regions but remains concentrated in the region of moderate light intensity.

This means that if you conduct an experiment on a petridish with Euglena in it and keep one half of the petridish to direct sunlight and the other half of it in shade, then you will eventually find that the Euglena will move from the region of direct sunlight and no sunlight (shady region) to the intermediate region between the two forming a small band.

This intermediate region is characterized by that region where there is no direct sunlight and no shade, but its a moderately intense lighted region between the sunlight and the shady region.

So, it can be clearly stated that the Euglena avoids strong lights as well as shady areas, but in fact, it stays and reacts positively to a moderately intense light such as that coming from a window or ventilator.

It is also seen that Euglena orients itself parallel to a beam of light coming towards it and swims towards the source of illumination for performing photosynthesis.

We know that Euglena is both autotrophic (make its own food) and heterotrophic (consume food).

In doing so, it has been seen that when sunlight is not available they become heterotrophic, and start to absorb nutrients across their cell membrane.

When the sunlight is available, they can detect the light using their eyespot and eventually moves toward the light by phototaxis (reaction to light). The sunlight is trapped by chloroplasts within the euglena for photosynthesis purposes.

2. Shock Reaction

Now, we have learned that the Euglena will move towards the light which is detected by its eyespot (stigma). This is actually a great advantage to Euglena for performing its photosynthetic nutrition.

But, what happens if the direction of the light suddenly changes? This will cause shock reactions in Euglena.

A swimming Euglena moves in a spiral manner rotating and gyrating around its own axis but it shows a shock reaction whenever the direction of light is changed.

This means that the Euglena will be shocked for a while and will not get the proper stimulus of its direction of movement, and so with trial and error, it will soon detect the new direction of light and will flow towards the new direction.

The process of shock reaction is explained below in easy to understand way:

It has been seen that the Euglena is well to go and do when the beam of light is not changing and is falling in one particular direction only. As a result to which, Euglena moves in one direction and is properly oriented.

As long as the Euglena moves in one particular direction, the eyespot and the photoreceptor cells are properly illuminated in each and every rotation, and so everything goes well.

Now, if that direct beam of light changes its direction and falls laterally (from the side), the eyespot and the photoreceptor cells will be partly shaded and partly be illuminated in its each and every rotation, and so will cause phobic responses (shock reactions).

Each darkening of the eyespot and the photoreceptor cells with its each and every rotation will excite its body to produce a minor shock reaction.

This affects the flagellar action in such a way, with various trails and errors after many successive minor shock reactions, that the body of the Euglena will bend at right angles, thus turning the flagellar-end gradually towards the new light source respectively.

This type of phobic response (shock reaction) is indeed a great advantage to Euglena as it brings the animal into the light which is of distinct advantage to its photosynthetic nutrition.

3. Avoiding Reaction

Euglena also responds to mechanical, thermal, and chemical stimuli showing an avoiding reaction on a trial and error pattern. This is known as phobotaxis.

Avoiding reaction is actually a random behavioural response that causes strong dislike or disinclination towards aversive stimuli.

In positive phobic response, the activity of the Euglena is increased and the organism moves toward the stimulus.

While in a negative phobic response, the activity of the Euglena is decreased and the organism moves away from the stimulus.

This avoiding reaction helps the Euglena to avoid obstacles due to the various unwanted aversive stimuli. Euglena does this by reversing the direction in which it’s moving forward.

This results in stopping, spinning, or turning at right angles, after which point Euglena resumes swimming forward.

This reaction usually occurs when the organism hits an obstruction, that causing a mechanical or thermal, or chemical stimulus.

The organism will then reverse, by stopping and then rotating itself with various trials and errors. This will now make it face a new direction, and to move off in that particular direction.

This process will continue until the organism is able to negotiate its way around the obstruction.

Mechanical stimuli can result from water currents, sound, body movements, pressure, or gravity. Thermal stimuli can result from rising in warmth, or the sensations of coldness in water. Chemical stimuli can result from the release of various chemicals from external sources or from other microorganisms.

Each of these types of stimulation is available in water and may be involved in migration and orientation.

How does euglena help the environment?

The way Euglena responds to the environment is actually very beneficial to the environment. The way it reacts to the various stimuli by creating various movements, orientations, and reactions makes it beneficial to the environment.

Due to its ability to perform phototaxis (reaction to light), makes it a very important organism within the environment as it is able to photosynthesize. And, in doing so, it takes in carbon dioxide and releases oxygen into the atmosphere so that other organisms can better survive.

They have the ability to recycle the primary elements that make up all living systems, especially carbon (C), oxygen (O), and nitrogen (N) in the aquatic ecosystem. These elements occur in different molecular forms that must be shared among all types of life.

It’s shocking and avoiding reactions better help to do its regular beneficial activities like helping it to better photosynthesize, moving towards the light source, avoiding mechanical or chemical or thermal stimuli, thus supporting its own lifeform and so in an overall supporting all the lifeforms in its surrounding.

Avoiding the harmful Euglenas, the helpful ones are very helpful. Some researchers have found that Euglena could possibly be a solution to global warming.

However, toxic Euglenas can be harmful as these are causative agents of various human and animal diseases such as Chagas’ disease, African sleeping sickness, kala-azar, and various forms of leishmaniasis.

Euglena has various powerful benefits, ranging from health, cosmetics to sustainability. And, in many countries like Japan, Korea, etc. it is taken as a drink.

Euglena can also be used as a food supplement for our day-to-day needs. Euglena cells contain bio-compounds like Paramylon (β-glucan) which enhances the immune system, helps remove undesirable substances like fats and cholesterol, and also reduces the level of uric acid in the blood.

Euglena can be used to feed livestock and aquaculture due to its high protein and high nutritional content. As Euglena is rich in protein and nutritional value, it is often utilized to prepare food for livestock and aquafarm fishes.

Moreover, in the very near future, Euglena-based biofuels can soon replace fossil fuels to power aircraft and automobiles, creating a sustainable low carbon environment.

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