Locomotion in Protozoa -Theory by Dr. Vidhin Kamble

LOCOMOTION IN PROTOZOANS

“Movement of the animal from place to place is called locomotion.”

Animals are capable to move place to place in search of food, shelter, and reproduction. Locomotion in animals is influenced by so internal and external stimuli. For locomotion specials kinds of organs are developed in animals are called locomotory organs. In higher animals, limbs, wings, fins, etc. are present.

The chief locomotory organelles found in  protozoa are - Pseudopodia, Flagella, Cilia and Myonemes.

Kind of locomotory organelle	Type of locomotion	Examples
Pseudopodia	Amoeboid locomotion	Amoeba
Cilia	Swimming locomotion	Paramecium
Flagella                      :	Swimming locomotion	Euglena
Myonemes	Gliding movement	Sporozoans

Pseudopodia-

Pseudopodia are nothing but the temporary outgrowths of the cell formed on the surface of the body.  In amoeba, many pseudopodia are present at a time called Polypodial  organisms. In Entamoeba only one pseudopodium is presently called as monopodial organism.

On the basis of their form and structure, four types of pseudopodia  are as  follows.   

1.                                                                   1.      Lobopodia, 

2.      Filopodia, 

3.      Reticulopodia 

                                 4.Axopodia or Actinopodia

Lobopodia – these types of pseudopodia are blunt and finger-like projection with a rounded tip arise from body containing ectoplasm and endoplasm Eg: Amoeba, Entamoeba.

Filopoda – These types of pseudopodia are filamentous and slender with pointed tips. Eg : Euglypha, Lecithium.

Reticulopodia  –These type of pseudopodia are also called myxopodia filamentous branched and net like meant for food collection found in foraminifers. 

Axopodia or Actinopodia – These types of pseudopodia are meant for food collection.  These pseudopodia are found in Helozoans (Actinosphaerium) and Radiolarians (Collozoum).

 

Formation of Pseudopodia in Amoeba. (Amoeboid Movement in Amoeba.)

Amoeba is a microscopic unicellular animal that belongs to phylum protozoa. The shape of amoeba is irregular in which locomotion is carried out by pseudopodia. The movement of amoeba is called amoeboid movement.

The pseudopodia are nothing but the formation of temporary outgrowth of the body of amoeba. The number of pseudopodia is varying with species to species of amoeba. The individual with many pseudopodia is called Polypodial organisms,eg. Amoeba proteus.  Organism with only one pseudopod is called Monopodial organisms, eg. Entamoeba hystolytica.

Sole-gel  Theory or Change in Viscosity Theory

During the formation of pseudopodia, cytoplasm in Amoeba undergoes a series of biochemical changes by altering viscosity or thickness at different regions of the body.

Pseudopodia in amoeba develop at any point in the body. The mechanism of the formation of pseudopodia is taken place by the Solation and Gelation process of endoplasm.  This theory is called “Sol-Gel Theory”.  This theory was the first time was proposed by Miss L.H. Hyman (1917).   This theory also called as “Change in Viscosity Theory”.

The body of amoeba encloses the protoplasm or cytoplasm surrounded by a membrane.   The protoplasm is of two types.

1.      Outer ectoplasm.

2.      Inner endoplasm.

Ectoplasm is thick, viscous, transparent and non-granular whereas, endoplasm is watery, less-viscous, opaque, and granular. In these to protoplasm physic-chemical changes take place during pseudopodia formation.

The membrane of  amoeba enclose protoplasm which is of two types i.e. outer thick, transparent, non-granular and contractile called Ectoplasm. The inner protoplasm is more in quantity, opaque, less viscous, granular and watery fluid called Endoplasm.

In an endoplasm, physic-chemical changes take place in which, Sole change into Gel and Gel into Sol. Conversion of plasma gel into plasma sol by taking water is called Solation. Conversion of plasma sol into plasma get by losing water is called Gelation.

During pseudopodia formation, the first stage is the formation of a Hyaline cap at the advancing end. The hyaline cap is clear ectoplasmic region between the plasma membrane and plasma gel called hyaline fluid.  At this region elasticity of plasma gel becomes weak below the hyaline cap. 

The conversion of Sol into Gel is taken place at the advancing end (Smooth rounded end) called the Gelation zone and the conversion of Gel into Sol is taking place near the uroid end called as Solation zone. The conversion of a sol into gel and gel into sol is taken place at the same rate.

During pseudopodia formation, a plasma gel tube develops at the advancing end which exerts hydraulic pressure resulted in the flow of plasma sol into the plasma gel tube leads to formation of pseudopodia. It helps Amoeba to move towards the chosen direction.  

During pseudopodia formation actin and myosin protein present in cytoplasm involved in amoeboid locomotion.  When protein molecules are in the relaxed condition the endoplasm remains in Sol state.

When protein molecules are in contracted state the endoplasm is in Gel state. For the conversion of Sol to Gel and Gel to Sol require energy is available from ATP by the action ATPase enzyme.

FLAGELLA.

“Flagellae are nothing but threadlike or whip-like extremely fine, vibratile structure are locomotory organelles.

The presence of flagellum is the characteristic of mastigophore protozoans. The flagellum is a long stiff axial filament or axoneme.  It arises from basal granules also known as kinetosomes.  Structurally, the flagellum shows the presence of 11 microtubules of micro-filaments lies in two groups, i.e. 9 –peripheral and 2 are central filaments.  Peripheral filaments are a doublet. The doublets are held in position by radial spokes. The central filaments are a singlet. The peripheral filaments are surrounded by a protoplasmic sheath. The microfilament at the base shows the presence of basal granules. Minute hair-like structures running along the length of some flagella are called  Mastigonemes  or  Flimmers.

On the basis of mastigonemes following are the kinds of flagellum

On the basis of the presence and absence of mastogonemes, there are various kinds of flagellum found in flagellates. The number of flagella varies with species to species.

For e.g.,

In Ceratium                    -        02  flagella,

In Trichomonas    -        04 .

In Giardia             -        08

In Trichonympa   -        Many.

1.      Anematic:

If Flagella are without mastigonemes are called as animatic flagellum

e.g., Noctiluca.

 

1.     Stichonematic:

If there is the presence of a single row of Flagella with a single row of mastigonemes on one side of the flagellum are called stichonematic flagellum. e.g., Euglena.

3. Pantonematic:

If there is the presence of two or more rows of mastogonemes on flagellum is called pantonematic flagellum. e.g., Peranema, Monas socialis.

4. Acronematic:

In this type, flagellum does not bear any arrangement of mastigonemes but a terminal filament is present, e.g., Polytoma.

Pentacronematic:

The flagellum bears two rows of mastigonemeson the sides and the flagellum ends in a terminal filament without mastigonemes, e.g., Urcoclus.

 Locomotion in flagellate protozoan.

In flagellates, movement is occurred by two methods as follows.

1.     Flagellar movement

2.     Undulation movement

1.     Flagellar movement:  The flagellar movement is caused by the bending of the long whip-like flagellum. The doublets are responsible for bending as they are held in position to the center with the help of spokes.

The sidewise movement of the flagellum is consisting of two strokes.

a. Effective stroke

b. Recovery stroke

2.     Undulation Movement:

In flagellates, flagellum shows undulation movement and sidewise beating of the flagellum. If undulation of the body from the tip of the body toward the base, causing forward movement.  If undulation of the body from the base of body toward the tip of the body causing backward movement. Due to spiral undulation, a body of animal rotates itself.

Ciliary movement:

Cilia are nothing but the hair-like structure present all over the body surface. The cilia act as locomotory organs in ciliate protozoan and also helpful for the collection of food.
Ultrastructure of cilium shows the presence of 11 microscopic axial filaments called as axoneme or microfibrils.  The axoneme are surrounded by a protoplasmic sheath. The microfibrils arranged into two groups. Nine are peripheral and two are central fibrils. Central fibrils are singlet whereas peripheral nine are a doublet. Central filaments are surrounded by central sheath and peripheral filaments are surrounded by peripheral sheath.

Types of cilia.

On the basis of location following are the types of cilia.

a.     In some ciliate cilia are present all over the body, such cilia are called as holotrichs Eg: Paramecium.

b.     In some ciliate cilia are present only in a peristomal region called Peritricha, Eg. Vorticella

c.      In this type, cilia are present only in young stage which are further replaced by sucking tentacles in adult called suctorians,  Eg. Acineta.

Ciliary   movement :

The cilia are chief locomotory organelle found in ciliata. 

The movement of each cilium is studied into two strokes as follows.

1.     Effective stroke

2.     Recovery stroke.

1.     Effective stroke: During locomotion each cilium become straight, stiffen rod like structure and moves backward, become parallel to the body surface and beats water.   During this stroke, the body of paramecium push forward.

2.     Recovery stroke: During recovery stroke, each cilium bends itself to reduce resistance of water and again brought to its original position.

By repeating an effective stroke and recovery stroke locomotion or movement is achieved in paramecium.

During forward movement,  the body of paramecium rotates itself. It is because of two reasons.

1.     The cilia do not beat directly backward but beat obliquely backward.

2.     The vestibular cilia beat faster than body cilia leads to central force.

Metachronous movement of cilia:

During movement, not all the cilia beats at once but beats alternately one after another. It  leads to characteristic wave-like movement of cilia, this movement of cilia is called metachronous movement.

MYONEMES (PELLICULAR CONTRACTILE EXTENSIONS)

Many protozoans have contractile structures in the pellicle or ectoplasm called as myonemes. These may be in the form of,

1.     Ridges or grooves                    -        Eg: Euglena

2.     Contractile myofibrils    -        Eg: Larger ciliates

3.      Microtubules                 -        Eg: Trypanosoma