BSc 1st Year Lower Non-chordates Taenia Solium Sample Model Practice Question Answer Papers
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Q.1. Give an illustrated account of the structure and life-history of Taenia.
Give an illustrated account of the reproductive organs of Taenia Solium. What is meant by gravid proglottid?
Show the life cycle of Taenia by neat labelled diagram only.
Habit and Habitat
Taenia Solium is an intestinal parasite of man found attached to its mucosa by the scolex, while the rest of the body lies free. It is most common in the pork-eating population of tropical and subtropical regions, where pork is utilized as food without being thoroughly cooked.
Shape, size and colour: The body is elongated, dorsoventrally flattened and ribbon-like. It is metamercially segmented consisting of linear series of almost similar segments.
The size of adult worm varies from 3-5 metres i.e. 9-16 feet, but few are recorded to attain a length of about 8 metres.
The body is opaque white but may be grey, yellow or cream,
Division of body: The body of Taenia is distinguished into three parts (1) Head and scolex (ii) Neck (iii) Body or strobila
1. Scolex or Head: The scolex is the knob-like anterior part of the size of pin head. It is a four-sided, pear-shaped structure distinguished into two part:
(i) Proximal rostellar part: It is a eonical part. It is slightly retractile. At its base are present two rows of curved and pointed chitionous hooks. These are about 28 in number.
The hooks of anterior circle are large, about 0.14-0.18 mm. The hooks of posterior circle are small, about 0.11-0.14 mm. Each hook consists of abuse, a blunt handle and conical outwardly directed blade.
(ii) Distal four sided part: It lies posterior to rostellum and bear four cup-shaped suckers one dorsal, one ventral and two lateral.
Scolex is the organ of attachment. It lies buried in the intestinal mucosa of host and is firmly attached to it by its hooks and suckers. It does not help in food capture. It simply acts as a holdfast.
2. Neck: Lying behind the scolex is a short, dorsoventrally flattened and unsegmented neck. It is also called budding zone, region of proliferation or area of segmentation because new segments are budded off from this region and are pushed back
3. Strobila: The rest of the body is known as strobila. It is composed of a linear series of 800 to 1,000 sets of reproductive organs or genitalia, each set being contained in a segment. This linear repetition of genital organs is termed as proglottisation and each segment is known as proglottid. Since the segments are budded off form the neck region in an orderly succession, the youngest segments are towards the neck and the oldest segments are posteriormost. Depending upon the development of genital organs, the segments are distinguished into three types:
(i) Immature proglottids: These are newly formed undifferentiated segments next to the neck region. These are first 200 proglottids. The reproductive organs are either absent or in stage of development. Their width is more then the length.
(ii) Mature or reproductive proglottids: These are next 400-600 proglottids. These are sexually mature, consisting of a complete set of male and a female of reproductive organs. They are usually as long as broad and are found in the middle of the body.
(iii) Gravid or ripe proglottids : These are found in the posterior part of the body and are about 200 in number. These possess a large, highly branched uterus filled with developing embryos. The rest of the genital organs have disappeared in them after performing their function. They are longer than broad.
The posteriormost 5 or 6 gravid proglottids detach from the strobila and are expelled out of host body along with host faeces. This process of separation of gravid proglottids is known as apolysis.
Bodywall in tapeworm similar to that of Fasciola’s bodywall is without cuticle and without cellular or ciliated epidermis. It is differentiated into following layers :
(i) Tegument, (ii) basement membrane, (iii) integumentary muscles and (iv) parenchyma.
1. Tegument: It is the outer thick and resistant layer of the bodywall. It is composed of protein impregnated with calcium carbonate and is perforated by numerous channels. Under light microscope, three distinct layers are seen in the integument. These are :
(i) Outermost comidial layer
(ii) middle homogenous layer and
(iii) innermost basement membrane.
- Under electron microscope, the outer comidial layer is non-cellular syncytial layer. The outer plasma membrane is produced into microvilli like folds, the microtriches. Each microtrich has an electron dense apical tip. Microtriches help in the absorption of host food and also act as holdfast organs.
- The middle homogeneous layer contains cytoplasmic organelles, like mitochondria, Golgi complex, endoplasmic reticulum, ribosomes and glycogen granules etc. It also contains tegumental discs, dense bodies and multilaminar bodies.
The tegument does not contain nucleus but it remains connected with sub tegumentary cells or tegument secreting cells. Their secretion continuously renews the tegument. The tegument is perforated by numerous pore canals.
Functions of tegument: Tegument or surface coat helps in the absorption of digested food from host intestine. It helps in excretion and osmoregulation. It protects the body against the effect of digestive enzymes of host intestine and against host’s immune system.
(iii) Basement membrane : It is the innermost thin non-cellular layer of tegument.
2. Integumentary muscle layer: Immediately underneath the basement membrane is a layer of circular muscles, followed by a layer of longitudinal muscles. These muscles are strongly developed in and around the suckers.
3. Parenchyma or mesenchyma : The whole body cavity is packed with loose parenchyma. It consists of loosely packed parenchyma cells with fluid filled interspaces. These form packing around various internal organs. The muscles, nerves and body organs lie embedded in parenchyma. It also contains tegument secreting cells and lime gland cells.
4. Parenchyma muscles : In each proglottid a circular band of circular muscles divides the parenchyma into (i) outer cortical region and (ii) inner medullary region. The band is incomplete on the margins. A number of dorsoventral muscle bundles run in the medullary region between the two hands of circular muscles.
Organs of Digestion
The organs of digestion are absent in Taenia because the parasite absorbs predigested food from the host intestine through the tegument of body by surface diffusion. The absorptive surface is greatly increased by the presence of microtriches on the surface of tegument.
Taenia absorbs glucose, amino acids and glycerol. Glycogen is the stored food. Because of obtaining predigested food, Taenia does not need alimentary canal and hence it is absent.
Organs of Respiration
The respiration is of anaerobic or anoxybiotic type since very little or no oxygen is available to the parasite in host intestine. During respiration glycogen is broken into CO2 and fatty acids with the release of energy. Other organic acids such as lactic acid are also produced.
The excretory system is very well developed and mostly helps in maintaining the hydrostatic pressure (water balance). It consists of flame cells, their collecting canals and the excretory vessels.
1. Lateral excretory vessels : There are four lateral longitudinal excretory vessels in the anterior part situated laterally just inside the marginal parenchyma. Two of them are dorsal and are present in the anterior segments only, while the outer two are ventral and extend throughout the length. These are connected by a transverse excretory canal in the posterior part of each segment and unite in the last segment to form a pulsatile caudal vesicle, opening to the exterior by a single excretory pore. The excretory canals are joined together by nephridial plexus inside the scolex. These are lined internally by cuticle and are devoid of cilia.
2. Tubules: Each longitudinal excretory vessel receives numerous secondary canals all along its length. Each secondary canal is formed by the union of several fine capillaries. Each capillary is connected with a flame cell.
3. Flame cells : These are irregular bodies with granular nucleated cytoplasm and a central funnel-shaped space. A bundle of flagella flickers constantly like the flame inside this space, which is continuous with the space of excretory vessels through connecting vessels.
The nervous system comprises of nerve ring connecting the two ganglia. Nerves are issued from these ganglia to the suckers and rostellum. Posteriorly, three pairs of longitudinal nerves are also given out from them. One pair of them runs along the excretory canals throughout the length of body.
The reproductive organs are segmentally repeated and each segment carries a complete set of male and female reproductive organs (i.e. hermaphrodite). But Taenia is protandrous.
Male Reproductive Organs
The male reproductive organs are: (i) Testes, (ii) Vasa efferentia, (iii) Vas deferens, (iv) Cirrus and cirrus sac.
1. Testes : The testes are numerous minute round bodies scattered throughout in the dorsal part of the proglottid. The number of testes varies from 15 to 200.
2. Vasa efferentia : These are numerous minute ducts which arise from testes and collectively open into the vas deferens.
3. Vas deferens: It is a long coiled tube which arises from the middle of the segment and runs transversely either to the left or right to open into the genital atrium.
4. Cirrus, cirrus-sac and genital atrium : The distal end of vas deference forms a thick, muscular and eversible penis or cirrus. It is surrounded by a muscular pouch, the cirrus sac or cirrus sheath. Cirrus is covered with spines, bristles or hooks. It opens into a cup-shaped genital atrium by male genital pore. Genital atrium opens outside by common gonopore. The gonopore is situated on a tiny genital papilla in the middle of the lateral margin of proglottid. Common gonopores of successive proglottids lie alternately.
Female Reproductive Organs
The female reproductive organs are :
(i) Ovaries, (ii) oviducts, (iii) ootype, (iv) vagina, (v) uterus, (vi) vitelline gland and (vii) Mehlis glands.
1. Ovaries: These are two ovaries situated in the medulla towards the posterior end. These are dorsoventrally flattened, highly branched and connected together by a transverse bridge called ovarian isthmus. Some scientists regard two ovaries as two lobes of a single ovary or germarium. It consists of a number of radially arranged germinal cords or follicles.
2. Oviduct: The oviduct arises from the middle of the bridge. It is short but wide duct and joins the ootype distally.
3. Ootype: It is a small rounded chamber developed at the junction of oviduct with the vitelline duct. It is surrounded by numerous unicellular shell glands or Mehlis glands.
4. Uterus : A blind sac-like or tube-like uterus arises from the ootype and runs forward in the segment. In gravid proglottids the uterus enlarges and gets branched to occupy the whole of the proglottid. It remains filled with the fertilised ova or developing embryos.
5. Vagina : The narrow tubular vagina arises from rises from the receptaculum seminis and runs obliquely outward to open into the genital chamber by female genital opening.
The seminal receptacle or receptaculum seminis is a small wide tube connected on one hand with the ootype by a narrow spermatic duct and on the other with vagina.
6. Vitelline gland: The vitelline gland is a compact, elliptical mass of numerous follicles situated posterior to the ovaries. The secretion of the vitelline duct is rich in yolk and forms a covering of yolk around the fertilised egg.
7. Shell glands or Mehlis glands: These are numerous minute unicellular glands situated around the ootype and emptying into it.
BSc 1st Year Lower Non-chordates Taenia Solium Sample Model Practice Question Answer Papers