REPRODUCTION IN PARAMECIUM

In case of paramecium, the process of reproduction is of the following types:-

1. Asexual method
2. Sexual method

 

ASEXUAL METHOD:-

In case of asexual method, reproduction in paramecia reproduces by transverse binary fission. This occurs in favorable conditions, i.e., under good condition of food and water etc. The division of the body is transverse i.e., at right angle of the longitudinal axis of the body.

 

• Firstly, the paramecium stops the feeding and its oral groove disappears.
• The micronucleus divides by the complicated process of mitosis, during nuclear division. The nuclear membrane remain intact, the two daughter nuclei towards the opposite ends of the cell.

• 36     o 50 chromosomes appears during mitosis (depending upon the race).
• Macronucleus divides a mitotically by simple elongation of the nucleus and constricted off in the middle.
• In the same time when macro nucleus divides, a transverse constriction forms around the middle of the body.
• The furrow continues to deeper and deeper ultimately dividing the cytoplasm into two halves or daughter paramecia.
• The anterior part called porter and posterior opisthe, before the separation of each half, new parts develops i.e., necessary for complete paramecium.
• Each daughter receives one contractile vacuole form the parent and second one is formed. Oral groove develops in each and buccal structures again constituted. These two daughter paramecia are equal in size with complete organelles. These grow to full size before dividing again.
• The process is completed 20 to 120 minutes depending upon condition of food and temperature. It may occur 2 to 3 times a day in Paramecium candatum and 5 times in paramecium aurelia.

Sexual reproduction takes place by the following methods

CONJUGATION:-

This process is given by the HERTAIG and MAUPAS (1889).

Conjugation is the simple temporary union of two individuals of one and the same species for the purpose of exchanging the part of nuclear material.

Two individual comes in contact ventrally by their oral grooves and attached till the end of process. Pellicle and endoplasm degenerates and form protoplasmic bridge between the two individuals.

Each individual called conjugate or gametocytes. The conjugating pair swim actively. Then a sequence of complicated nuclear change takes place in each conjugate in the following manner-

• Macronucleus breaks up into fragments and lastly absorbed by the cytoplasm.
• The micronucleus of each divides twice, forming four (4) Haploid micronuclei. One division is reduction division.
• Out of four, three degenerates in each conjugation and disappears. Remaining one micronucleus divide unequally forming two pronuclei or gametic nuclei (Genetically identical).
• Out of two, one is smaller is called active male pronucleus and the larger is called stationary female pronucleus in each conjugate.
• The male pronucleus passes from one conjugate to the other through protoplasmic bridge into the female pronucleus.
• Now the fusion of male and female pronucleus takes place forming a diploid zygote nucleus or Synkaryon or amphinucleus. The fusion of two nuclei from two different individuals is called Amphimixis.
• The two paramecia now separate after 12-48 hours and are now called as ex-conjugates. In each ex-conjugate, zygote nucleus divides 3 times forming 8 nuclei.
• Of these four become macronuclei and four become micronuclei.
• Three micronuclei disintegrate and disappears, one remaining micronucleus divides with the binary fission of each ex-conjugates.
• Thus, two daughter paramecia are obtained having two macronuclei and one micronucleus.
• The daughter paramecia again divide, with division forms two individuals. Each containing one macronucleus and one micronucleus.
• Thus, each conjugate produces four daughter individuals.

AUTOGAMY OR AUTOMIXIS :-

Autogamy resembling conjugation, Diller 1936 reported this type of reproduction in Paramecium aurelia. Autogamy takes place in a single paramecium.

 Diller called the autogamy as self-fertilization.

•  Two micronuclei of the same organism fuse together forming a Synkaryon.
• During the process in P. aurelia, the macronucleus grows into an irregular mass and breaks into pieces and lastly disappears.
• The two micro -nuclei divide twice, once meiotically to form 8 haploid nuclei.
• Out of 8, 7 nuclei degenerate and one divide to form 2 sister gamete nuclei. These two are homologous to the stationery and migratory pronuclei.
• These enter a protoplasmic cone, temporarily formed near cytostome and then fuse together to form a zygote nucleus or Synkaryon.
• Synkaryon divide twice two form four nuclei, two of which macronuclei and two become micronuclei.
• The Cell body divides and 2 micronuclei also divides to form 4 nuclei, 2 macronuclei as such.
• Paramecium divides into two daughter individuals   having one macronucleus and two micronuclei.
• The process is completed In about two days involving a readjustment   of the nucleo-cytoplasmic relationship. 

 

CYTOGAMY :-

Cytogamy recently reported by WICHTERMAN in 1940 in P. caudatum. Cytogmy is a process without nuclear exchange. The process resembles conjugation in that two small paramecia (200 µ long) fuse together by their oral surfaces.

• The early nuclear division are similar to the conjugation but there are no nuclear exchange between the two individuals.
• The two gametic nuclei in each parent are said to be fused to form a synkaryon as in autogamy. This process is completed in about 13 hours.
•  The genetical consequence of cytogamy is always homozygocity.

 

ENDOMIXIS :-

 Endomixis is an interesting phenomenon involving total internal nuclear reorganization within a single individual.

WOODRUFT and ERDMANN 1914 reported in bimicronucleate species P. aurelia. It is occurring periodically at regular interval of about 30 days in P. caudatum and 16 days in P. aurelia. It occurs as follows-

 

• Micronucleus disintegrates and disappears.
• Two micronuclei divide twice forming 8 daughter nuclei.
• Out of 8, 6 degenerates.
• The paramecium divides, each individual getting one micronucleus, which divide twice forming 4 nuclei.
• Two nuclei become macronucleus and two micronuclei.
•  Paramecium with 2 macro and 2 micro nuclei divides and at the same time 2 micronuclei divides.
• Two daughter cells obtained, each with one macro nucleus and two micro nuclei. In the end, four daughter cells are formed from single individual.

 

HEMIXIS :-

This process is pointed out by DILLER 1936. It is a simple method of nuclear exchange different from conjugation, binary fission and autogamy in single individual.

During these changes termed Hemixis by DILLER.

• The micronuclei do not participate.
• But the macronucleus throws out 2 to many equal or unequal fragments of chromatin balls (DNA) to be absorbed in the cytoplasm.
• Some of the macronuclei, they behave normally at the cell division.
• The significance of hemixis is not well understood.

 

ENCYSTMENT

 Encystment occurs in green species (P. bursaria). It has not been seen except Michelson’s on P. caudatum. The cysts are said to be looks like sand grains. 

                                      

REPRODUCTION IN PROTOZOA

Reproduction is the process by which living organism produce young ones of their own species.  Reproduction is defined as behavioral instinct of living organism to maintain the race.

In protozoa reproduction takes place by:-

1. Asexual method
2. Sexual method

1.       Asexual method of reproduction in protozoa:-

• Many Protozoa reproduces by Asexual method, in which single parent is involved.
• The development of new individuals without the fusion of male and female gametes.
• Asexual reproduction may be of following types-

1. Binary fission and multiple fission
2. Budding
3. Plasmotomy

 

BINARY FISSION IN PROTOZOA:- 

It is most common in protozoa. During binary fission animal body divides in such a place that two identical halves are produced.

 

Simple binary fission or orthodox type:-

This simple binary fission is found in irregular shaped organism like – amoeba. Plane of division is unknown or division is in any plane. Nucleus divides first than cytoplasm divides like mitosis.

 Transverse binary fission:-

Transverse binary fission is found in Paramecium (ciliates).

Plane of division is always transverse to the longitudinal axis of the body of organism. It takes place during favorable conditions; when food, temperature and water is suitable.

• Micro nucleus divides into two nuclei by process of mitosis.
• Mega or Macro nucleus divides by Amitosis.
• Micro and Macro nuclei moves towards opposite pole.
• Constriction appears in the middle.
• One contractile vacuole goes to one daughter paramecium, other is reformed.
• Parental oral groove, vestibule, cytopharynx goes to one daughter paramecium but in other daughter paramecia, new set of these structures are formed.
• Binary fission takes 30-120 minutes to complete the process.

 

Longitudinal binary fission:-

Longitudinal binary fission is found in certain ciliates and flagellates. e.g., Vorticella, Euglena.

In longitudinal binary fission, nucleus and cytoplasm divides in longitudinal plane.

Oblique binary fission:-

In this type of binary fission, organism divides by oblique plane. Oblique binary fission takes place in dianoflagellates.

 

MULTIPLE FISSION IN PROTOZOA :-

In multiple fission, the nucleus of the cell divides very rapidly into many nuclei. Each daughter nucleus gradually surrounded by little mass of cytoplasm and forming pseudopodia spores, as in Amoeba. In case of malarial parasite it forms schizont.

Multiple fission is found in most protozoans like – Amoeba, Plasmodium and monocysts etc. By the rupture of cell membrane, daughter nuclei with cytoplasm released in the environment (water or Blood) etc.

Each daughter schizont or pseudopodia spores forming gradually into young.

BUDDING IN PROTOZOA:-

• Asexual reproduction by budding takes place in many protozoa.

E.g., – Class :- Suctoria: vorticella, Ephalota

           Class :- Flagellata: Acinata

• By budding, one or more smaller individuals are formed from single parent body. Budding may be Exogenous or Endogenous.

 

IN EXOGENOUS BUDDING:- 

Buds develops as an out growth on the parent body, Which after sometime detached and leads free life.

 

IN ENDOGENOUS BUDDING:-

The buds are produced inside the parent’s body in special space called brood pouch or brood chamber. After sometime, bud detached from the parent body and leads free life.

 

PLASMOTOMY IN PROTOZOA:-

In certain multinucleate protozoa like OPALINA and PELOMYXA, the cytoplasm divides but nuclei don’t divide. Each daughter cell regains the normal number of nuclei by nuclear division. 

   

 

 

 

CHARACTERS AND CLASSIFICATION OF PORIFERA

Robert E. Grant, used the term of porifera in 1839. Meaning of porifera is pore bearer. Therefore, those organism in which body bears pore are called porifera.

 

CHARACTERS:-

• Porifera are diploblastic i.e., the two layers are found in the body (Ectoderm and Endoderm).
• The animals of porifera are multicellular.
• All animals of porifera are marine found in sea water (except spongilla, fresh water).
• These are plant like fixed and generally cylindrical in shape.
• Over body surface, pore or ostia are found. From the ostia water enters into the body.
• Definite organs and systems are not found. It has cellular level of body organization. 
• Digestion intracellular.
• Water current enters in the body helps in feeding and respiration, reproduction and excretion.
• Nervous system absent.
• Reproduction takes place by asexual and sexual method.
• Asexually reproduction by budding. Sexual reproduction by gametes or sperms and ovum.

The whole body is formed of 3 types of spicules. Spicules helps as Skeleton. On the basis of spicules, Phylum porifera has been classified into 3 classes-

1. Calcarea or calcispongae
2. Hexactenillida or Hyalospongae
3. Desmospongae

Class- Calcarea

• In this class calcareous spicules are found.
• In this class small sponges are found. These sponges are found all over the world in sea water.
• Canal system is found either Ascon type or Sycon type.
• This class has been divided  into 2 orders-

1. Homocoela
2. Heterocoela

 

Order -  Homocoela

• The body is simple cylindrical.
• The inner most layer of body is lined with flagellated collar cells.
• Body wall thin.
• Canal system Ascon type.

Example – Lecucosolenia

• Spongocoel is lined by flagellated cells.

 Order- Heterocoela

• Spongocoel lined by flat cells.
• Flagellated cells found in flagellated chamber.
• Body wall thick and folded.
• Complicated type of canal system syconoid or lecuconoid type.

Example :- Sycon or Grantia

Class :- Hexactenillida

• In this class large size sponges are placed.
• These sponges are found depth of sea, nearly 300 ft below.
• Sponges are cylindrical, Cup shaped, funnel like, pitcher like, flower vase like etc.
•  Spicules are triaxon type.

• Body glass like beautiful. e.g., glass sponges (Hyalonemma)
• Canal system Rhagon type.
• This class has been divided into 2 orders-

1. Hexasterophora
2. Amphidiscophora

 

Order :- Hexasterophora:

• In the mesenchyme Hexasters spicules present.

• Body skeleton frame like, irregular.

e.g :- Euplectella  (Venous flower basket)

 

Order :- Amphidiscophora

• Hexasters absent, but amphidiscs monoxon spicules present.
• Both sides of spicules bear crown of rays.

• Sponges are spiral rope like. e.g :- Glass sponges.

 

Class :- Desmospongia

• Skeleton are absent in this class of sponges.
• In some sponges, Spongian fibres or siliceous spicules present.
• All are generally marine.
• Body rounded, cup shaped or club shaped.
• Canal system Leucon type.
• This class has been divided into 4 orders :-

1. Tetractenillida
2. Monoaxonida
3. Keratosa
4. Myxospongia

 

ORDER :- TETRACTENILLIDA

• Tetraxon spicules present, sometimes spicules absent.
• Sponges are round or flat. e.g :- Chondrilla

ORDER:- MONAXONDIA

• Monaxon Spicules present.
• Shape flask like, branched, found attached with  Mollusca shell. e.g :- Cliona, fresh water Spongilla.

ORDER :-  KERATOSA

• Spongilla spicules present.
• Body rounded leathery. e.g.:- Horse sponge.

ORDER :- MYXOSPONGIA

• Skeleton absent in this type of sponges.
• Body blistering. e.g :- Oscarella ( Blacksponges), Heliosarca   
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