Euglena is a single-celled organism, a type of protist, that inhabits freshwater environments such as ponds and puddles. Its ability to move is fundamental for survival, allowing it to navigate its surroundings and obtain necessary resources.
Movement by Flagella
Euglena primarily moves through water using a specialized appendage called a flagellum. This long, whip-like structure extends from the anterior end of the cell. The flagellum operates by performing a wave-like beating motion, much like a propeller, pulling the organism forward.
Bending waves initiated at its base travel its length, generating propulsion. This creates forces that drive Euglena through water while rotating the cell body, helping it maintain a spiraling path. The flagellum can beat at approximately 40 Hz.
Euglenoid Movement
Beyond flagellar propulsion, Euglena exhibits another distinct method of movement known as euglenoid movement, or metaboly. This process involves significant changes in the organism’s body shape. The flexibility required for this movement is due to the pellicle, a flexible outer layer located just beneath the cell membrane.
The pellicle is composed of proteinaceous strips arranged in spirals around the cell, supported by microtubules. During euglenoid movement, these pellicle strips slide past one another, allowing the Euglena to contract and expand its body. This enables the organism to “squirm” or “crawl” through tight spaces, along surfaces, or to detach from surfaces. While flagellar movement is a swimming motion, euglenoid movement is a shape-changing process, sometimes triggered when flagellar function is impaired.
Why Euglena Moves
Euglena’s distinct modes of movement serve important purposes, allowing it to navigate its environment to support its life processes. Both flagellar and euglenoid movements are employed to respond to external stimuli, helping the organism find optimal conditions for survival. A primary reason for movement is phototaxis, the directed movement toward or away from light.
Euglena contains chloroplasts for photosynthesis, moving towards moderate light intensities to produce its own food. An eyespot (stigma), a red pigmented organelle, assists in detecting light direction. This eyespot shades a light-sensitive photoreceptor at the flagellum’s base, allowing Euglena to orient itself towards suitable light. Movement is also influenced by chemotaxis, the response to chemical stimuli, enabling Euglena to move towards nutrients or away from harmful substances.