Locomotion in Protozoa: We can see different creatures worldwide, but some creatures are so small that we cannot see from our naked eyes. These creatures are so small that they are even present in a drop. If we put a drop of pond water under a microscope, it can be magnified, and those non-visible creatures become visible to the eyes. Some of these can be single-celled eukaryotes that show different movements. Also, there are different types of locomotion in protozoa.

Protozoans need to move in search of food, avoid predators, get into or out of sunlight, move towards chemicals they need, or away from chemicals that poison them. Single-celled eukaryotes all move around in three or four different ways with all the diversity of microscopic life. Protozoans are loosely classified by their style of movement. We will further know how many types of locomotion occurs in protozoa. Read on to know!

Characteristics of Protozoan

i. Protozoans refer to single-celled eukaryotes.
ii. These are also called “one-celled animals”.
iii. They show animal-like behaviour like locomotion and predation.
iv. They lack a cell wall, but it is surrounded by an elastic structure called the pellicle in some protozoans.
v. E.g. Amoeba, Paramecium, and Trypanosoma.
vi. Its size ranges from \(1\mu \) to several MMS.
vii. Some protozoans are-living, common and found in fresh and marine water bodies and other moist environments.
viii. Protozoans are generally parasitic and show heterotrophic modes of nutrition.
ix. They reproduce by asexual reproduction like binary fission or multiple fission.
x. Sexually, they can reproduce by conjugation or formation of gametes.

Types of Locomotion in Protozoa

How many types of locomotion occur in protozoa? We have the answer here. Five modes of locomotion that can be seen in protozoa are:-

1. Locomotion by pseudopodia

I. This type of locomotion is seen in animals that do not have a set structure for mobility and are amorphous. This type of locomotion is seen in Amoeba, etc.
II. It has a finger-shaped protoplasmic extension called pseudopodia or false feet. With these, they can creep over the substratum.
III. These are temporary structures formed by the streaming flow of the cytoplasm.
IV. Finger-like pseudopodia are formed in those protozoans whose body is asymmetric or irregular, capable of changing their shape due to their formation and withdrawal.
V. This type of movement is called amoeboid, which brings about locomotion and change in the body’s shape. This helps in food capture too.
VI. Locomotion is brought about by alternate changes in the colloidal state of the cytoplasm affected by sol-gel-sol transformations and the cytoplasmic streaming of plasmas into the pseudopodia.
VII. Pseudopodia are of four types:-
a. Lobopodia: They are lobe-like with broad and blunt ends. This type of pseudopodia is seen in Amoeba.
b. Filopodia: They are fine thread-like, often with rounded ends, and slender, unsupported, and independent. Found in Euglypha.
c. Axopodia: They are long and stiff with hard axial filament. Example: Actinophrys.
d. Reticulopodia: They are slender, long and branched, forming a reticulate network. Example: Globigerina.

2. Locomotion by flagella

I. These are found in flagellated protists.
II. Flagella are thread-like projections on the cell surface and show whip-like movement.
III. The external long whip-like part of the flagellum is called the shaft.
IV. Its length is about \(2\mu \) to \(3\;{\rm{mm}}\), and its diameter is about \(0.2\mu \).
V. The internal structure of the flagellum consists of a \(9+2\) fibrillar arrangement.
VI. Undulating movement, i.e. movement of organisms in the opposite direction of the beat, is exhibited by most flagella.
VII. In some protozoans, there is one flagellum like in Euglena, while in some, more than one flagella are present, e.g. Giardia lamblia.
VIII. Flagella is used for propulsion. It also helps bring food in by creating a current in the body.

3. Locomotion by cilia

I. Cilia are short, fine, hair-like structures present all over the body surface. Cilia bearing protozoans are called ciliates, and the movement produced by them is called ciliary movements.
II. Cilia help in locomotion and food capture.
III. They perform oar-like movements in a coordinated manner. It produces a progressive wave by beating in succession.
IV. Coordinated movement of cilia creates a vertex that allows the movement of the food into the cavity called the gullet.
V. Example- Paramecium shows ciliary movement that moves at the rate of \(2\,{\rm{mm}}\) per second.

Difference between flagella and cilia

Flagella	Cilia
Larger in size	Smaller in size
Commonly found at one end of the cell	Found throughout the body
They beat whip-like	They beat oar-like
Helps in locomotion	Helps in locomotion, aeration, feeding and circulation
Few flagella are present in each cell, generally \(1\) to \(4\).	Numerous cilia, \(300\) to \(1400\), are present in the cell.

Fig: Locomotory Organs in Protozoans

4. Wriggling locomotion or Sporozoan movement

I. This type of movement is slow and worm-like.
II. Seen in non-flagellated protozoans performed with the help of waves of contraction and expansion of the body. E.g., Sporozoans.
III. They do not possess organelles of locomotion (i.e. flagella, pseudopodia, cilia, etc.) and ingestion of food due to parasitic life.

Summary

In this article, we learned about the protozoans and the different types of locomotion in protozoa. Organisms belonging to protists are microscopic, unicellular eukaryotes. Protozoans have different kinds of locomotory organs. These are pseudopodia, flagella, cilia, etc. Locomotion by pseudopodia is seen in Amoeba, flagella in Euglena, and cilia in Paramecium. Some protozoans lack locomotory organelles due to parasitic life, like sporozoans. Flagella is long, and few are present in a cell, while numerous cilia are present in a single cell.

FAQs on Locomotion in Protozoa

Q.1. How many types of locomotion occur in protozoa?
Ans: Following are the types of locomotion in protozoa-
1. Locomotion by pseudopodia
2. Locomotion by flagella
3. Locomotion by cilia

Q.2. What are the locomotory organelles in protozoa?
Ans: Locomotory organelles in protozoa are cilia, flagella, or pseudopodia.

Q.3. Which type of protozoa shows ciliary locomotion?
Ans: Ciliates like Paramecium show ciliary movement.

Q.4. What is the difference between cilia and flagella?
Ans: a. Flagella is more prominent in size while cilia are smaller in size.
b. Number of flagella is fewer than the number of cilia present in an organism.
c. Flagella beat whip-like while cilia beat oar-like.

Q.5. Which type of protozoans locomotion is explained by sol-gel theory?
Ans: Organisms like Amoeba, which have amorphous structures, show locomotion by sol-gel theory.

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