How do unicellular ‘EUKARYOTES’ move?
In this article, we shall discuss how do unicellular eukaryotes move?
Most animals have different ways to move through their ecosystem to get food, for reproduction, or escape in order to save a life from their enemies. Sessile animals have to move their surrounding water or air in order to catch food, by utilizing their tentacles or by beating cilia to produce water current to capture small food particles. On the other hand, locomotion requires energy, and most animals consumed a considerable amount of energy to overcome the force of friction and gravity that tend to keep them stationary.
At the cellular level, the movement of all animal-based on two systems of cell motility, i.e. microtubules and microfilaments. Microtubules are responsible for the beating of cilia and undulation of flagella, while microfilaments help in the contraction of muscle cells.
Skeleton supports and protects the animal body and very important for movement. Usually, there are three types of skeleton, (a) exoskeleton (b) endoskeleton (c) hydrostatic skeleton. Mostly cnidarians, flatworms, nematodes, and annelids contain a hydrostatic skeleton that is consists of fluid held under pressure in a closed body compartment. These animals have the ability to control their body shape and move by using muscles to change the shape of fluid-filled compartments. Hydrostatic skeletons are ideal in the aquatic ecosystem and they are responsible for the protection of internal organs of the animal from shocks and provide support for crawling and burrowing but they cannot support any terrestrial locomotion in which an animal’s body held off the ground.
The exoskeleton is a hard encasement deposited on the body of the animal. Most mollusks are enclosed in calcium carbonate shells secreted by a sheet-like extension of the body wall, the mantle. By the addition of calcium carbonate in their outer layer animals become able to increase the diameter of their shell. Arthropods have a joint exoskeleton, the cuticle. As the animal grows in size the exoskeleton of the arthropod must be periodically molted replaced by the larger one.
On the other hand, sponges are reinforced by either hard spicules or consisting of an inorganic material or soft fibers made of protein.
Now we discuss locomotion in eukaryotes. Here are four examples including locomotion in Chlamydomonas, Amoeba, Paramecium, and Euglena.
- Locomotion in Chlamydomonas
Flagellum), extends from one end, and their wipe-like lashings pull the Chlamydomonas through the water and rotate it at the same time. Chlamydomonas reinhardtii provides an experimental system for the study of ciliary and flagellar kinetics. The Chlamydomonas flagellum and human cilium share a common 9+2 axonemal structure, in which dynein motors act as co-ordination to create asymmetric, propulsive waveforms. This alga can be manipulated genetically to produce mutations analogous to those seen in human disease. In chlamydomonas, flagella were aided by the uni 1 mutant strain. This mutant strain assembles only one flagellum and its cells that use the breast-stroke or forward movement mode rotate about in place. In early work, Brokaw and Luck photographed uni 1 flagella using darkfield optics with flash illumination at 300 Hz. This method provided 4 to 8 images per beat, which were analyzed in detail to characterize the flagellar waveform.
- Locomotion in Amoeba
In Amoeba locomotion takes place by means of finger-like projections called pseudopodia. These projections are thrown in the direction of movement in which the cytoplasm flows and thus body moves in that direction. The actual process of production of pseudopodia is still debatable.
- Locomotion in Paramecium
This microscopic propels it-self by whiplash movements of cilia, which are arranged in a tightly spaced row around the outside of the body. In paramecium all the cilia move simultaneously, a bunch of cilia moves in a progressive wave-like pattern at a time. Basically, the wave starts at the anterior end and progresses backward. The beating of each cilium has two phases (1) a fast “effective stroke” during which the cilium is relatively stiff, followed by a slow “recovery stroke” during which the cilium curls loosely to one side and sweeps forward in a counter-clockwise fashion. The densely arranged cilia move in a coordinated fashion, with waves of activity moving among across the “ciliary carpet”, producing sometimes an effect linked to that of the wind blowing across the field of grains.
A cilium consists of nine peripheral double fibrils giving the appearance of 8 shape figure and two central smaller fibrils. All these fibrils run longitudinally through the cilium. These are covered with the extensions of the membrane.
The actual process of movement of cilia is not known. However, in 1955 Bradford demonstrated that movement of all cilia is due to simultaneous contraction or sliding of double fibrils in two groups one after the other.
- Five out of nine (5/9) double fibrils contract or slide simultaneously cilium bend or shorten. It is called an effective stroke.
- The four out of nine (4/9) double fibril contract and cilium become, straight. This is called recovery stroke.
As a result of bending and recovery strokes, the paramecium swims against water, the energy for the movement of cilia is provided from the ATP. In the cilia of paramecium, some enzymes break up ATP to release energy.
The action of the cilia is co-ordinated and all the cilia beat together in a fashion to propel the animal in one direction.
- Locomotion in Euglena
This unicellular organism moves with the help of flagellum. As the flagellum is whipped backward the organism moves forward. However, when the flagellum moves forward the Euglena does not move backward. The locomotive flagellum is at its anterior end of the body and pulls the organism forward. A wave of activity generated by itself, and they pass in a spiral fashion from its base to its tip. They increase amplitude and velocity. The activity note of the flagellum caused the body of Euglena to rotate forward about its axis. Euglena has the ability to change its direction by the active contractile myonemes which run along the length of its body. When they contract the shape of the body is changed as well as its direction. First, the body becomes short and wider at the anterior end than in the middle and later at the posterior end. This feature of the movement is actually known as euglenoid movement.