Model Paper – II

Department of Zoology,

Guru Ghasidas Vishwavidyalaya, Bilaspur

LZC – 401 (Parasitology and Microbiology)

Q 1: Multiple Choice questions (Tick the appropriate answer) (1 x 10)

(1) Hyperparasites are:

(a) parasititizing other species

(2) Mutualism is the way two organisms of different species exist in a relationship in which

(a) each individual benefits

(3) The infective stage of Trypanosome is:

(c) metacyclic form

(4) Leptomonad form of Leishmania is found in:

(b) sand fly

(5) “Demarquay” first discovered the larval form of Wuchereria bancrofti in:

(a) hydrocele fluid of man

(6) Intermediate host of Schistosoma haematobium:

(b) fresh water snail

(7) When milk and other products are heated for about half an hour at about 62ºC and then

cooled, the process is called:

(a) Pasturization

(8) Genetic material of TMV is

(a) RNA

(9) Antibiotics are commonly classified on the basis of

(d) All of them

(10) DDT belongs to the which family of insecticides

(b) Organochloride

Q 2: Descriptive type (attempt any four question within 150 words) (5 x 10)

Question 2: What is symbiosis? Explain with suitable examples.

Symbiosis is derived from Ancient Greek word that means "together living" is close and often

long-term interaction between two or more different biological species. Bennett (1877) used the

word symbiosis to describe the mutualistic relationship in lichens. In a symbiotic mutualistic

relationship, the clownfish feeds on small invertebrates that otherwise have potential to harm the

sea anemone, and the fecal matter from the clownfish provides nutrients to the sea anemone. The

clownfish is additionally protected from predators by the anemone's stinging cells, to which the

clownfish is immune.

Some symbiotic relationships are obligate, meaning that both symbionts entirely depend on each

other for survival. For example, many lichens consist of fungal and photosynthetic symbionts

that cannot live on their own. Others are facultative, meaning that they can, but do not have to

live with the other organism. Symbiosis or the interactions between two different animals is

divided into three type of relationship: mutualistic, commensalism and parasitism.

Symbiotic relationships include those associations in which one organism lives on another

(ectosymbiosis) or where one partner lives inside the other (endosymbiosis). Symbiosis is also

classified by physical attachment of the organisms; symbiosis in which the organisms have

bodily union is called conjunctive symbiosis, and symbiosis in which they are not in union is

called disjunctive symbiosis.

Endosymbiosis is any symbiotic relationship in which one symbiont lives within the tissues of

the other, either within the cells or extracellularly. Ectosymbiosis, also referred to as

exosymbiosis, is any symbiotic relationship in which the symbiont lives on the body surface of

the host, including the inner surface of the digestive tract or the ducts of exocrine glands.

Examples of this include ectoparasites such as lice, commensal ectosymbionts such as the

barnacles that attach themselves to the jaw of baleen whales, and mutualist ectosymbionts such

as cleaner fish.

Mutualism:

Mutualism is any relationship between individuals of different species where both individuals

benefit.. Mutualistic relationships may be either obligate for both species, obligate for one but

facultative for the other, or facultative for both. A large percentage of herbivores have

mutualistic gut fauna that help them digest plant matter, which is more difficult to digest than

animal prey. Coral reefs are the result of mutualisms between coral organisms and various types

of algae that live inside them. Best example of mutual symbiosis is the relationship between the

ocellaris clownfish that dwell among the tentacles of Ritteri sea anemones. The territorial fish

protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the

anemone protect the clownfish from its predators. A special mucus on the clownfish protects it

from the stinging tentacles.

Commensalism:

Commensalism describes a relationship between two living organisms where one benefits and

the other is not significantly harmed or helped. It is derived from the English word commensal

used of human social interaction. The word derives from the medieval Latin word, formed from

com- and mensa, meaning "sharing a table". Examples of metabiosis are hermit crabs using

gastropod shells to protect their bodies and spiders building their webs on plants.

Parasitism:

A parasitic relationship is one in which one member of the association benefits while the other is

harmed. This is also known as antagonistic or antipathetic symbiosis. Parasitic symbioses take

many forms, from endoparasites that live within the host's body to ectoparasites that live on its

surface. An example of a biotrophic relationship would be a tick feeding on the blood of its host.

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Question 3: Define symptoms, diagnosis, treatment and prevention of kala azar.

Answer:

Kala-azar is also known as, visceral leishmaniasis, black fever and Dumdum fever. It is the

most severe form of leishmaniasis. Leishmaniasis is a disease caused by protozoan parasites of

the Leishmania genus. This disease is the second-largest parasitic killer in the world, responsible

for an estimated 500,000 infections each year worldwide. The parasite migrates to the internal

organs such as liver, spleen and bone marrow.

Symptoms:

Signs and symptoms include fever, weight loss, mucosal ulcers, fatigue, anemia, and substantial

swelling of the liver and spleen. Kala-azar is spread through an insect vector, the sandfly. Adult

female sand fly is a bloodsucker, usually feeding at night on sleeping prey.

When a human patient does develop kala azar, the most typical symptoms are fever and the

enlargement of the spleen, or splenomegaly, with enlargement of the liver—hepatomegaly—

sometimes being seen as well. The blackening of the skin that gave the disease its common name

in India does not appear in most strains of the disease, and the other symptoms are very easy to

mistake for those of malaria. Even with recovery, kala-azar does not always leave its hosts

unmarked. Sometime after successful treatment—generally a few months a secondary form of

the disease may set in, called post kala-azar dermal leishmaniasis, or PKDL. This condition

manifests first as small, measle-like skin lesions on the face, which gradually increase in size and

spread over the body. Eventually the lesions may coalesce to form disfiguring, swollen structures

resembling leprosy, and occasionally causing blindness if they spread to the eyes.

Diagnosis:

Kala azar can be diagnosed by microscopical examination of blood film of biopsy material taken

from spleen or bone marrow of patient. Serological testing is much more frequently used in areas

where leishmaniasis is endemic. Examination of WBC count shows decrease of neutrophils but

increase of lymphocytes and monocytes. Number of erythrocytes is also decreased.

Treatments:

For the treatment of Kala azar two groups of drugs are used. Pentavalent antimony compounds

extensively used are sodium-antimony tartrate and gluconate, urea stibamine, aminostiburea,

neostobosan etc. Pentaamidine isethionate is also used.

Prevention: Preventive measures include:

Eradication of the insect vector, i.e. sand-fly: In endemic areas, low trees and bushes, etc.

should be carried out. Periodic fumigation and spray of insecticides of sleeping quarters should

be done.

Attack on the parasite: In area where dogs act as reservoir hosts, all street dogs should be killed.

Personal defense: For avoiding bite of sandflies, use mosquito-nets on screens and avoid

sleeping on ground floors.

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Question 3: Describe the life cycle and pathogenicity of a protozoan parasite causing amoebic

dysentery?

Answer:

Life cycle Entamoeba histolytica is an anaerobic parasitic protozoan. Predominantly infecting humans and

other primates, E. histolytica is estimated to infect about 50 million people worldwide. E.

histolytica is monogenetic, i.e., only one host is required for its complete life cycle. Pigs, dogs,

rat and rabbit are supposed to be the reservoir host. It undergoes reproduction and completes its

life cycle only in man. Its life cycle has different stages:

Binary fission: Trophozoites multiply asexually by binary fission with in the wall of large

intestine. Two daughter organisms are formed, which grows rapidly in size.

Encystation: The precyctic or minuta form encysts only in the lumen of the intestine. They

round up and secrete a thin, refractile, tough and flexible cyst wall around them. The cysts at this

stage are uninucleated. The single nucleus of the cyst divide and form binucleated and then

tetranucleated cyst. Tetanucleated cysts constitute the transmissive or infective stage. They do

not develop further but pass out of the host in the faeces.

Transmission and infection: Infection depends upon intake of food or water contaminated with

faecal matter containing tetra nucleate cysts of E. histolytica.

Encystation: The ingested cyst pass down the alimentary canal and reach the small intestine.

The cyst wall protect them from the action of host’s gastric juice during their passage through the

stomach. After 5 to 6 hours, encystation takes place as the cyst wall is digested by trypsin in

small intestine releasing the tetranucleate amoeba, called the excystic amoeba and metacyst.

Metacyctic development: Each metacyst immediately proceeds to divide by binary fission. Its

nuclei divide in a specific pattern, accompanied by simultaneous cytoplasmic division to produse

8 small uninucleated amoebulae or metacystic trophozoites. These metacystic trophozoites pass

into the large intestine, invade the mucous lining and grow into mature trophozoites.

Life-cycle of Entamoeba histolytica

Pathogenicity

Infections of E. histolytica vary in intensity from asymptomatic to severe or fatal invasions.

Asymptomatic infections are responsible for the spread of the parasite with numerous cysts being

passed in normal stools. Diarrheic stools primarily contain trophozoites which cannot persist in

the environment.

Invasive forms of the disease lead to amoebic dysentery in which the trophozoites invade the

intestinal wall, leading to the formation of amoebic ulcers. This results in severe diarrhea with

blood and mucus present. In such cases it is important to identify E. histolytica in the stools to

differentiate among other causes of dysentery.

If trophozoites penetrate the intestinal wall, serious problems can occur, including liver abcesses,

or spread to the lungs and brain, usually resulting in death.

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Question 4: Draw well labeled diagram of dog tape worm and Microfilariae.

Answer:

Question 5: Describe the various modes of nutrition in bacteria?

Answer:

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Question 6: Give an account on insecticide?

Answer:

An insecticide is a pesticide used against insects. They include ovicides and larvicides used

against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine,

industry, and general home use. The use of insecticides is believed to be one of the major factors

behind the increase in agricultural productivity in the 20th century.[1]

Nearly all insecticides have

the potential to significantly alter ecosystems; many are toxic to humans; and others are

concentrated in the food chain.

The classification of insecticides is done in several different ways:

• Systemic insecticides are incorporated by treated plants. Insects ingest the insecticide

while feeding on the plants.

• Contact insecticides are toxic to insects brought into direct contact. Efficacy is often

related to the quality of pesticide application, with small droplets (such as aerosols) often

improving performance.[2]

• Natural insecticides, such as nicotine, pyrethrum and neem extracts are made by plants as

defenses against insects. Nicotine-based insecticides are still being widely used in the US

and Canada though they are barred in the EU.[3]

• Plant-incorporated protectants (PIPs) are insecticidal substances produced by plants after

genetic modification.[4]

For instance, a gene that codes for a specific Baccilus

thuringiensis biocidal protein is introduced into a crop plant's genetic material. Then, the

plant manufactures the protein. Since the biocide is incorporated into the plant, additional

applications, at least of the same compound, are not required.

• Inorganic insecticides are manufactured with metals and include arsenates, copper

compounds and fluorine compounds, which are now seldom used, and sulfur, which is

commonly used.

• Organic insecticides are synthetic chemicals which comprise the largest numbers of

pesticides available for use today.

• Mode of action—how the pesticide kills or inactivates a pest—is another way of

classifying insecticides. Mode of action is important in predicting whether an insecticide

will be toxic to unrelated species, such as fish, birds and mammals.

Classes of insecticides

Organochlorides

The insecticidal properties of the best known representative of this class of insecticides, DDT,

was made by the Swiss Scientist Paul Müller. For this discovery, he was awarded the Nobel

Prize for Physiology or Medicine in 1948.[5]

DDT was introduced on the market in 1944. The

contemporary rise of the chemical industry facilitated the large-scale production of DDT and

related chlorinated hydrocarbons. DDT functions by opening the sodium channels in the nerve

cells of the insect.

Organophosphates and carbamates

Another large class of synthetic insecticides are the organophosphates. Again these target the

insect's nervous system. Organophosphates interfere with the enzymes acetylcholinesterase and

other cholinesterases, disrupting nerve impulses, killing or disabling the insect. Organophosphate

insecticides and chemical warfare nerve agents (such as sarin, tabun, soman and VX) work in the

same way. Organophosphates have an accumulative toxic effect to wildlife, so multiple

exposures to the chemicals amplifies the toxicity.

Carbamate insecticides have similar toxic mechanisms to organophosphates, but have a much

shorter duration of action and are thus somewhat less toxic.

Pyrethroids

To mimic the insecticidal activity of the natural compound pyrethrum another class of pesticides,

pyrethroid pesticides, has been developed. These compounds are nonpersistent sodium channel

modulators, and are much less acutely toxic than organophosphates and carbamates. Compounds

in this group are often applied against household pests.

Neonicotinoids

Neonicotinoids are synthetic analogues of the natural insecticide nicotine (with a much lower

acute mammalian toxicity and greater field persistence). These chemicals are nicotinic

acetylcholine receptor agonists. Broad-spectrum—systemic insecticides, they have a rapid action

(minutes-hours). They are applied as sprays, drenches, seed and soil treatments—often as

substitutes for organophosphates and carbamates. Treated insects exhibit leg tremors, rapid wing

motion, stylet withdrawal (aphids), disoriented movement, paralysis and death. Imidacloprid may

be the most commonly used neonicotinoid. It has recently come under scrutiny for its deleterious

effects on honeybees, and its potential to increase the susceptibility of rice to planthopper

attacks.

Ryanoids

Ryanoids are synthetic analogues with the same mode of action as ryanodine, a naturally

occurring insecticide extracted from Ryania speciosa (Flacourtiaceae). They bind to calcium

channels in cardiac and skeletal muscle, blocking nervous transmission. Only one such

insecticide is currently registered, Rynaxypyr, generic name chlorantraniliprole.

Insect growth regulators

Insect growth regulator (IGR) is a term coined to include insect hormone mimics and an earlier

class of chemicals, the benzoylphenyl ureas, which inhibit chitin (exoskeleton) biosynthesis in

insects. Diflubenzuron is a member of the latter class,used primarily to control caterpillars which

are pests.

Biological insecticides

Many plants exude substances to prevent insects from eating. Premier examples are substances

activated by the enzyme myrosinase. This enzyme converts glucosinolates to a variety of

compounds that are toxic to herbivorous insects. One product of this enzyme is allyl

isothiocyanate, the pungent ingredient in horseradish sauces.

Bacterial insecticides

Bacillus thuringiensis is a bacterial disease that affects Lepidopterans and some other insects.

Toxins produced by different strains of this bacterium are used as a larvicide against caterpillars,

beetles, and mosquitoes. Toxins from Saccharopolyspora spinosa are isolated from

fermentations and sold as Spinosad. Because these toxins have little effect on other organisms,

they are considered more environmentally friendly than synthetic pesticides.

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Question 7: Give an account on tissue culture techniques used for microbiology?

Answer:

A microbiological culture, or microbial culture, is a method of multiplying microbial

organisms by letting them reproduce in predetermined culture media under controlled laboratory

conditions. Microbial cultures are used to determine the type of organism, its abundance in the

sample being tested, or both. It is one of the primary diagnostic methods of microbiology and

used as a tool to determine the cause of infectious disease by letting the agent multiply in a

predetermined medium. For example, a throat culture is taken by scraping the lining of tissue in

the back of the throat and blotting the sample into a medium to be able to screen for harmful

microorganisms, such as Streptococcus pyogenes, the causative agent of strep throat.

Furthermore, the term culture is more generally used informally to refer to "selectively growing"

a specific kind of microorganism in the lab

Microbial cultures are foundational and basic diagnostic methods used extensively as a research

tool in molecular biology. It is often essential to isolate a pure culture of microorganisms. A pure

(or axenic) culture is a population of cells or multicellular organisms growing in the absence of

other species or types. A pure culture may originate from a single cell or single organism, in

which case the cells are genetic clones of one another.

For the purpose of gelling the microbial culture, the medium of agarose gel (agar) is used. Agar

is a gelatinous substance derived from seaweed. A cheap substitute for agar is guar gum, which

can be used for the isolation and maintenance of thermophiles.

A culture of Bacillus anthracis

Microbiological cultures can be grown in petri dishes of differing sizes that have a thin layer of

agar-based growth medium. Once the growth medium in the petri dish is inoculated with the

desired bacteria, the plates are incubated at the best temperature for the growing of the selected

bacteria (for example, usually at 37 degrees Celsius for cultures from humans or animals, or

lower for environmental cultures).

Another method of bacterial culture is liquid culture, in which the desired bacteria are suspended

in liquid broth, a nutrient medium. These are ideal for preparation of an antimicrobial assay. The

experimenter would inoculate liquid broth with bacteria and let it grow overnight (they may use

a shaker for uniform growth). Then they would take aliquots of the sample to test for the

antimicrobial activity of a specific drug or protein (antimicrobial peptides).

Liquid cultures of cyanobacterium Synechococcus PCC 7002

As an alternative, the microbiologist may decide to use static liquid cultures. These cultures are

not shaken and they provide the microbes with an oxygen gradient.

Culture collections

Microbial culture collections focus on the acquisition, authentication, production, preservation,

catalogueing and distribution of viable cultures of standard reference microorganisms, cell lines

and other materials for research in microbial systematics. Culture collection are also repositories

of type strains.

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