జంతుశాస్త్రము

కె. శ్రీనివాసులు

Introduction:
 *    This unit covers the methods of locomotion and types of repro- duction in Protozoans. Proto- zoans are unicellular organsisms. Inspite of having single cell they show different activities like locomotion and reproduction.
 *    Voluntary movement of an orga- nism from one place to another is known as locomotion.
 *    Reproduction is a biological process in which an organism gives rise to off springs similar to itself.
 Important Content:
 Locomotion In Protozoa:
 *    Pseudopodia are present in rhizopods. There are four types of pseudopodia namely lobo-podia, filopodia, reticulopodia and axopodia (heliopodia).
 *    Pseudopodium is formed by the conversion of outer gel to inner- sol part and vice versa.
 *    Sol-gel theory is the most acce-pted theory to explain the forma-tion of pseudopodium.
 *    Allen's theory of Front contra- ction or fountain zone theory is considered as the more appro- priate theory.
 *    Amoeboid movement is the most primitive and slowest type of locomotion.
 *    Flagella are the long whip like organelles present in mastigo phoran protozoans.
 *    Typical flagellum consists of axoneme, microtubules, dynein arms, sheaths, radial spokes, lateral appendages etc.,
 *    Axoneme is the central longi tudinal microtubular structure surrounded by a membrane.
 *    Axoneme is made up of  9 + 2 arrangement of microtubules with 2 central singlets and 9 peri pheral doublets. These are formed by the protein known as tubulin.
 *    Peripheral doublets are inter-connected by linkers known as nexins.
 *    'A' tubule of each doublet consists dynein arms. Dynein arms are considered protein motor molecules.
 *    Inner sheath surrounds central singlets while peripheral dou blets are covered by outer sheath.
 *    Radial spokes are elastic fibres that connect the inner sheath with 'A' tubule of each doublet.
 *    Centriole is modified as basal granule or kinetosome which gives rise to cilium or flagellum. It is present in ectoplasm. It is a cylindrical body formed by 9 peripheral triplets arranged in a circle.
 *    Rootlets  are the communication tubules which connect basal granule to plasma membrane and nucleus to pull the flagellum and later its orientation.
 *    Mastigonemes are the lateral appendages present as one or two or many rows of short hair like fibrils for a flagellum.
 *    Number and arrangement of flagella in different flagellates appear in the following manner.
 *    Trypanosoma: single flagellum, arising at the rear end of the body.
 *    Euglena : two flagella parallel to each other.
 *    Trichomonas   : four flagella.
 *    Giardia    : four pairs.
 *    Trichonympha : many flagella.
 
 Types of flagella:
 *    Primitive ciliates like Para mecium has cilia on the entire body ..  holotrichous.
 *    Advanced ciliates like Vorticella has cilia at peristomial region around the mouth only… peritrichous.
 *    Infraciliary system consists of kinetosomes, kinetodesmal fibrils and kinetodesmata.
 *    Infraciliary system connects with motorium present near cyto- pharynx and form neuromotor system which controls and coor dinates the movement of cilia.
 *    Myonemes are contractile fibrils present below the pellicle in ectoplasm in flagellates, apicom- plexans and ciliates.
 *    Flagella and cilia are unduli- podia.
 *    Bending movements are shown by flagella and cilia.
 *    Undulations from base to tip of flagellum provide pushing force while undulations from tip to base provide pulling force.
 *    Sidewise lashing movements include effective stroke and recovery stroke.
 *    Cilia of transverse row show synchronous movement by beating simultaneously.
 *    Cilia of longitudinal row show metachronous movement where the cilia beat one after another like a wave.
 *    Myonemes help in gliding locomotion.
 
 Reproduction In Protozoans
 *    Methods of asexual reproductive methods in protozoans are binary fission and multiple fission.
 *    Binary fission occurs in favourable conditions. It occurs in either  longitudianal or tran sverse.
 *    Longitudinal binary fission occurs in the flagellates like Euglena, Trypanosoma and ciliates like Vorticella.
 *    Longitudinal binary fission in Euglena starts with karyokinesis which is followed by cytokinesis.
 *    Various organelles undergo following changes during binary fission in the following manner.
     a)    Some organelles divide and     distribute equally to both daughters….Nucleus,chroma- tophores & basal granules.
     b)    Some organelles of parent retained by one daughter..  other one gets new.. Flagella
     c)    Some organelles disintegrate during process. Both dau ghters get new---paraflagellar body, stigma and contractile vacuole.

 *    Longitudinal binary fission is considered as symmetrogenic division as the both daughters resemble each other like mirror images.
 *    Ciliates like Paramecium per- forms transverse binary fission.
 *    Micronucelus undergoes mitotic division while macro nucleus undergoes amitotic division.
 *    Anterior daughter is Proter and posterior one is Opisthe.
 *    Proter gets cytostome, anterior contractile vacuole from mother.
 *    Opisthe gets posterior contractile vacuole only from mother.
 *    Transverse binary fission is considered as homothetogenic fission as the plane of fission is at right angles to the longitudinal axis of the body.
 *    It is also known as perkinetal fission because it occurs at right angles to the kineties.
 *    Multiple fission occurs in the form of schizogony, male game- togony, sporogony in Plas- modium and sporulation in Amoeba.
 *    Sexual reproduction in proto- zoans occurs by the fusion of pronuclei of gametes.
 *    Syngamy is fusion of two gametes. It is either isogamy with the fusion of similar type of gametes  or anisogamy with the fusion of dissimilar type of gametes.
 *    Hologamy is the fusion of mature organisms without formation of gametes.