Zoology Sem 1 # Unit 1# PARAMECIUM
PARAMECIUM
Systematic position:
Phylum:. Protozoa
Subphylum. Cilliophora
Class. Ciliata
Subclass. Holotrichia
Order. Hymenostomatida
Genus. Paramecium
Species. caudatum
aurelia
multimicronucleatum
bursaria
calkinsi
woodruffi
trichium
polycaryum
The first three species belong to aurelia group as these are elongated ,circular in TS and cytoproct is lateral.Remaining species come under bursaria group as these are short ,broad , flat in TS ,posterior end is broad and cytoproct is subterminal.
Structure: P.caudatum is described in detail:
Size: 170 to 290 microns(0.17 to 0.29mm)
Shape: Slipper-like or sole of shoe-like , so known as slipper animalcule.
(i) It's slender anteriorly with blunt/round end and pointed / cone-shaped posteriorly.
(ii) Body is asymmetric : flat oral/ventral surface and convex dorsal/aboral surface.
Cellular body has the following structure:
1.Pellicle:
The above diagram clears that:
(i) A thin , double layered ,firm, flexible and gelatinous body-covering membrane is the pellicle.
(ii) The outer layer is continuous with cilia ,where the inner one is with the ectoplasm.
(iii)Hexagonal depressions appear on the surface with central holes through which cilia projects and openings of trichocysts at anterior and posterior margins .
2. Cilia:
(i) No: 10,000 to 14,000
(ii) Length: 10 to 12 micro meter.
(iii) Diameter: 0.27 micro meter.
(iv) Cilia cover the entire body and are hair-like cytoplasmic projections. Length is uniform except the longer posterior caudal tuft.
3.Cytoplasm:
Cytoplasm lies beneath the pellicle.
Cytoplasm
-------------------.---. I------------------------
I. l
Ectoplasm. Endoplasm
Ectoplasm
(I) Ectoplasm is the narrow, external , cortical zone forming the firm ,clear,thin and dense outer layer.
(ii)It contains trichocyst,oral apparture and fibrillar structure.
(ii)External to it is the pellicle and internal to it is endoplasm.
(a) Trichocyst:
(i) Length: 4 micron.
(ii) Shape: Flask like/ fusiform sac-like.
(iii) Location: Embedded in ectoplasm, alternate with basal granules, opens through small pores on the ridges of hexagonal area and arise from kinetosome of cilia.
(iv) It has conical head/ conical herb / spike ; a shaft filled with refractive, dense fluid having swelling substance / trichinin protein.
(b) Oral apparture:
(i) Oral grove/ peristome is placed on the ventral surface.
(ii) It runs obliquely backward and opens into a funnel-shaped depression /gullet /vestibule.
(iii) Gullet ends in oval apparture /mouth/cytostome.
(iv) Mouth leads to short oesophagus/ cytopharynx that opens into a food vacuole .
(v) 8 rows of cillia (2 groups ;4 rows in each / quadrulus) fuse to form penniculus are found at the lining of gullet to control the passage of food.
(c) Cytopyge/cytoproct/anal spot:
Ventral in position just behind the cytostome is the anus to eliminate undigested food particles.
(d) Infraciliary system:
It consists of basal body/ kinetosome and fibrillar kinetodesmata.
(I) Basal body:
* Tubular in structure to which base of each cilium is connected.
** It contains 9 peripheral fibres with 3 microtubules in each:
Tubule A: complete
Tubule B : incomplete
Tubule C: incomplete
Central tubule/centrole:absent.
(ii) Kinetodesmata:
Basal bodies are inter connected by cytoplasmic fibrillar kinetodesmata. Kinetosome and fibrils of a row are termed kinety. All kinetia make Infraciliary system.
Endoplasm
The medullary cytoplasmic volumnous fluid having cytoplasmic inclusions like mitochondria, Golgi bodies, vacuome, crystals,granules ,chromidia alongwith micro- and macro nuclei, contractile vacuole and food vacuole is endoplasm.
(a) Nuclei:
There are two nuclei in a Paramecium:
Macronucleus: (i) Large,conspicuous, ellipsoidal/kidney-shaped vegetative body
(ii) Rich in chromatin granules embedded in achromatic matrix.
(iii) Chromosomes are polyploid.
(iv)Divided amitotically, synthesise DNA and RNA , control metabolism .
Micronucleus: (i) A small , spherical body at the concavity of macronucleus.
(ii) Rich in fine chromatin granules and threads.
(iii) Divedes mitotically, controls the reproduction.
(b)Contractile vacuole:
There are an anterior and one posterior contractile vacuoles lie between ecto- and endoplasm.
(i) Each one is connected to 5-12 tubular radiating canals.
(ii)Each canal have terminal long ampulla and short injector canal opens into the vacuole.
Contractile vacules are hydrostatic and removes excess water from protoplasm.
(c) Food vacuoles/ Gastrioles:
The term Gastrioles was coined by Volkonsky(1934).There are about 50 such vacuoles in a Paramecium . Ingested foods specially bacteria and a small amount of fluid are found in each vacuole bounded by thin membrane.
LOCOMOTION
Paramecium performs two methods of locomotion:
(1) Metaboly :
(a)A Paramecium can change it's body shape temporarily; then squeeze itself through a very narrow passage which is smaller than it's diameter .
(b) After that it regains it's original shape due to elasticity of pellicle.
(c) According to Grunstone 1961, Steigh 1962 , Stair 1974 etc. contractions of myonemes causes Metaboly i.e. shape changing motion in a Paramecium .
(2) Ciliary locomotion:
B-- Rapid effective stroke
D-- Less rapid effective stroke
(i) Ciliary method is the main locomotion process in a Paramecium .
(ii) When cilia beat forwards Paramecium swim anteriorly; backwards beat help in posterior swimming.
(iii) The ciliary strokes are of two types:
(a) Effective stroke: Normally cilia beat backward obliquely to result forward swim . During this at first cilia turn stiff then bend backward rapidly to almost touch the body surface (Fig B and D).
It may be rapid(cilia position 6->7->8->9->10) and less rapid( cilia position 4->5->6) illustrated in fig B and D respectively.
(b) Recovery stroke: After a effective stroke cilia become limp and return slowly by to the original vertical position by a forward movement, this phenomenon is called as recovery stroke( Fig. A & C)
It also rapid (fig A -cilia position 1->2->3->4->5 ) and less rapid(fig.C -cilia position 1->2->3).
(iv) All the cilia of a transverse row beat together.But cilia of the same longitudinal row beat one after the other from anterior to posterior end.Such a coordinated ciliary movement is called metachronal rhythm, which is illustrated by the following fig:
Thus, an intraciliary system resulted in a forward swimming of a Paramecium.
(v) Rotation: Oblique backward beating of body cilia and vigorous beating of long oral groovelong at a time resulted in left hand swerve of anterior end of the animal.
The activity of body cilia and oral groove make a Paramecium left hand spiral rotation (P.calkinsi shows right hand spiral rotation).
(vi) The combination of forward motion, swerving and rotation resulted to counter- clockwise spiral path locomotion. This path has a straight axis and the body surface of Paramecium remain fixed in this .
Each kinetodesmata lies right to the cilia shaft , this results in right hand spital rotational locomotion in Paramecium.
(vii) During backward swimming all species rotate to the right and cilia move obliquely forward.
(ix) Shifts in the membrane potential and accompanying changes in ion concentration in the cell are the controlling factors of such kind of ciliary motion
Following fig. illustrates a spiral path :
According to Jennings spiraling is due to the fact that while the cilia strike backward they do so obliquely to the right ,so it roll over to the left.
REPRODUCTION
Paramecium can perform both of the (1) Asexual and (2) Sexual mode of reproduction.
Asexual reproduction:-by means of binary fission.
Sexual reproduction:- by means of (a) endomixis ,(b) hemixis,(c) autogamy , (d) cytogamy and (e) conjugation .
Conjugation: The process is illustrated by means of diagrams and word description:
(A) Two conjugants / gametocytes adhere ventrally by their oral grooves.
(C) Changes in macronucleus:
It breaks into fragments and absorbed in the cytoplasm .
(D) Changes in micronucleus:
(i) Diploid micronucleus (2n) divides first meiotically into four haploid nuclei (n) ; three of them degenerate and one nucleus survives.
2n
I
-------------------------------
I I
n. n
I. I
----------------------. ------------------
I. I. I. I
n. n n. n
√ x. x. x
n
________I_________
I. I
Smaller migratory. Larger stationary
Male.(n) Female (n)
(iii) Male pronuclei of each conjugants then exchanged through cytoplasmic bridge and fuse to the female pronuclei to form Diploid zygotic nuclei/ synkaryon.
n(male)+n(female)=2n synkaryon
This event is called amphimixis.
Significance: To restore Diploidy .
(iv) After 12-48 hours conjugants with 2n nuclei separate and each one known as exconjugants.
Karyogamy
Formation of exconjugants
(v) In each conjugants 2n nuclei performs mitosis three times , hence eight daughter nuclei are formed in each individual cell.
I. II. III
2n(1)------->2n(2)------>2n(4)------>2n(8)
Out of these eight , four grow in size to turn into macronuclei and remaining four remain same as micronuclei; out of them three degenerate and one survives .
2n
__________l_____________
I. I
4 nuclei turn. 4 nuclei remain
Macronucleus. as micronuclei
I
3 nuclei degenerate
1 nuclei(2n) survives
Hence, each individual gets five nuclei .
(vi) In each individual micronuclei divides mitotically , then performs binary fission.
Exconjugate, 4 macronucleus
1 micronucleus
I
IMitosis(micronucleus)
I. Binary fission
-------------------------------
I. I
Cell (1) Cell(2)
Thus, each daughter cell consists of 3 nuclei (2 macro- and 1 micronucleus).
(vii) The micro nuclei again divides mitotically, thus each cell contains 2 macro- and 2 micronucleus.
(viii) In the last step, cytolasmic division takes place, thus a conjugant ultimately divides into four Paramecium with 1 macro and 1micronuclei.
Hence, by conjugation 2 conjugants turn into 4x2=8 daughter Paramecium.
Significance of conjugation:
(1) Continued binary fission results in the weakness of Paramecium, conjugation help to restore the vitality of the organism.
(2) Macronucleus of daughter Paramecium is obtained from the zygote nucleus of the exconjugants which discharges the physiological activities more vigorously .
(3) Continued binary fission results in the abnormalities in chromosome number in macronucleus, conjugation corrects it and restores the lost vigour .
Model questions
(1)Why is Paramecium called slipper animalcule?
2/2015
(2) What is metachronal rhythm of locomotion?
2/2015
(3)Write the ultrastructure of cilium with labelled diagram .
5/2017
(4) Discuss the ciliary movement in Paramecium with labelled diagram.
5/2017
(5)What is conjugation? Describe the process in Paramecium with labelled diagram with importance . 1+5+1=7/2016,2018
So helpful sir. Thanks💕
ReplyDelete