ULTRASTRUCTURE OF CILIATED PROTOZOA

ULTRASTRUCTURE OF CILIATED PROTOZOA

Pellicle 

·       Pellicle is the outer cell membrane present in Ciliated Protozoa.

·       Ciliated Protozoa have fixed shape due to covering of thick and rigid Pellicle.

·     Although all Protozoa contain a cell membrane, some of them have compound coverings of membranes transformed for protection, support, and movement. Such combinations of membranes are known as a Pellicle.

·       The simplest form of pellicle is known as Plasmalema, for example, Amoebas are covered by a Plasmalemma only.

·       In some Protozoa and additional protective covering region has been evolved around the Pellicle. These coverings are known variously Asthecae, Shells, Tests, or Loricae and occur in almost all major groups of Protozoa.

Plasmalema

·    The Cytoplasm is separated from the external environment by a Semipermeable membrane known as Plasmalema or Cell membrane or Plasma membrane.

·     This Plasmalema protects the cytoplasm, helps in the exchange of various substances, and also helps in attachment with other cells.

·    In some Protozoa, a diffuse layer of Mucopolysaccharides is surrounded the Plasmalema. This layer helps in Pinocytosis (Cell drinking) or in the Adhesion of the cell to the substratum. 

Cytoplasm

·      Cytoplasm is a homogenous substance, which is consists of Globular protein molecules. These proteins are linked together and create a three-dimensional molecular framework.

·    The cytoplasm contains different sub-microscopic protein fibrils such as Fibrillar bundles, Myonemes and Microtubules. All of these are responsible for Contractility in Protozoa.

·      The pigments are diffused throughout the Cytoplasm of Protozoa, these are responsible for the different colors of Protozoa such as green, brown, blue, purple, or pink.

·      The cytoplasm of protozoa is divided into two categories such as the Ectoplasm and the Endoplasm. The ectoplasm is a more gel-like structure while the Endoplasm are more voluminous and fluid. Different organelles are mainly found in Endoplasm.

·       The cytoplasm is surrounded by a membrane.

·  It contains different organelles such as Ribosomes, Golgi complexes or Dictyosomes (piles of membranous sacs), Mitochondria, Kinetosomes or Blepharoplasts (Intracytoplasmic basal bodies of cilia or flagella), Food vacuoles, Contractile vacuoles, and Nuclei.

Nucleus

·       The protozoan nucleus contains the following components

ü  Chromosomes

ü  Nucleolar substance

ü  Nuclear membrane

ü  Karyoplasm (Nucleoplasm).

·    Protozoa contain one eucaryotic nucleus, even some of them contain multiple nuclei (e.g., almost all ciliates) throughout the greater part of the life cycle.

·      The ciliates contain 2 dissimilar nuclei one of them is larger known as Macronucleus and the second one is small known as Micronucleus.

ü  Macronucleus helps to maintain the metabolic activities and regeneration processes.

ü  Micronucleus is helped with reproductive activity.

·  The number of Chromosome in Nucleus vary based on the types of protozoa. For example, Spirotrichonympha polygyra has 2 haploid chromosomes; Spirotrichosoma magnum has 60 chromosomes. 

Oral Groove (or) Vestibulum

·     Vestibulum, also known as the Oral groove, is a flattened, funnel-shaped indentation that is the opening to the mouth region of the Ciliates like Paramecium.

·    Oral groove push the food particle through the Cytopharynx (acting as the gullet) and into the food vacuole where the substrate is broken down.

·       However, some Ciliated Protozoa lack an Oral groove and use absorption to feed/obtain nutrients.

·       The Vestibulum has its own pellicle and cilia. This groove leads into the Buccal overture.

Buccal Overture

·    The Buccal overture is an opening that leads to an “S” shaped cylindrical structure called the Buccal cavity.

·       The Buccal cavity contains four structures called the

a)     Endoral kinety

b)     Dorsal peniculus

c)     Ventral peniculus

d)     Dorsal quadrulus

Cytostome

·       The Cytostome is the “Cell mouth” of the Paramecium and it resembles a Tear drop shape.

·       The Cytostome transfers the Paramecium prey into the Food vacuole.

Food Vacuoles

·       Food vacuoles accumulate food gathered by Paramecium through the Cytostome.

·       Once the Food vacuole becomes a certain size it will break off and will travel through the cell.

·       The food will be digested by Digestive enzymes.

·     The useful material will remain in the cytoplasm and the remaining material will be expelled from the cell through the Cytoproct. 

Cytoprotect

·       The Cytoproct, also known as the “Anal pore” where waste is expelled from the cell.

Radiating canals

·      Radiating canals absorb wastewater and materials from the surrounding cytoplasm which eventually will get transported out of the cell by the Contractile vacuole.

Contractile vacuole

·      Two types of Contractile vacuoles are present on a Paramecium. One type is a Canal-fed vacuole and a Vesicle-fed vacuole.

·       The Contractile vacuole is used to transport waste liquid out of the cell.

·       It also helps to maintain proper water and salt concentrations within the organism (Osmoregulation).  

Trichocysts

·       Trichocysts are used in the defense of the Paramecium.

·     Trichocyst has a spindle shaped body and at the wider end and looks similar to a golf tee turned upside down.

·      Trichocysts are located at specialized cortical sites and there are typically about one thousand per cell.

·    When the Paramecium is attacked these little filaments are fired at the attacker to try and thwart the attack.

Cilia

·       Cilia are little hair like projections that are just a continuation of the cell surface membrane.

·       The two main functions of the cilia are for

a)     Movement

b)     Ingesting food.

·     The Cilia responsible for ingesting food are located in a funnel shaped depressed region of the cell called the Gullet.

·     All other cilia on the Paramecium are thought to be used for movement except for the Caudal cilia which are longer Cilia.

·       During the Mating process, Cilia are used to initiate the mating process also known as Conjugation.