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GNDU Question Paper-2021
BA/Bsc
1
st
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-I-B
[Biodiversity-I (Protozoa to Annelida)]
Time Allowed: Three Hours Max. Marks:35
Note: Attempt Five questions in all, selecting at least One question from each section. The
Fifth question may be attempted from any section. All questions carry equal marks.
SECTION-A
1. Discuss in detail about locomotion in Amoeba proteus.
2. Explain in detail about exoerythrocytic stage of Plasmodium vivax in liver of man.
SECTION-B
3. Discuss in detail about canal system in Sycon.
4. Explain phenomenon of polymorphism in Obelia in detail.
SECTION-C
5. While giving brief written account, draw labelled diagram of male and female
reproductive organs of Fasciola hepatica.
6. Discuss life history of Taenia solium in detail.
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SECTION-D
7. Discuss in detail about Body Walls of Ascaris.
8. Discuss reproductive system of Pheretima posthuma in detail.
GNDU Answer Paper-2021
Bachelor of Computer Application (BCA) (Hons.)
1
st
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-I-B
[Biodiversity-I (Protozoa to Annelida)]
Time Allowed: Three Hours Max. Marks:35
Note: Attempt Five questions in all, selecting at least One question from each section. The
Fifth question may be attempted from any section. All questions carry equal marks.
SECTION-A
1. Discuss in detail about locomotion in Amoeba proteus.
Ans: Discuss in Detail About Locomotion in Amoeba proteus
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Introduction
Amoeba proteus is a single-celled (unicellular) microscopic organism that belongs to the
kingdom Protista. Even though it is made up of only one cell, it is capable of carrying out all
the basic life activities such as movement, feeding, respiration, excretion, growth, and
reproduction.
One of the most interesting features of Amoeba proteus is its locomotion, which means its
ability to move from one place to another. Unlike humans and animals that move with the
help of legs, wings, or fins, an amoeba has no fixed body shape and no specialized organs
for movement. Instead, it moves by forming temporary projections of its body called
pseudopodia.
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The word pseudopodia comes from Greek:
Pseudo = False
Podia = Feet
Therefore, pseudopodia literally mean "false feet."
What is Locomotion?
Locomotion is the movement of an organism from one place to another. It helps organisms
to:
Search for food.
Escape from enemies.
Find suitable environmental conditions.
Reproduce and survive.
In Amoeba proteus, locomotion takes place by the formation of pseudopodia, and this type
of movement is called amoeboid movement.
Structure Involved in Locomotion
Before understanding movement, it is important to know the parts involved.
1. Cell Membrane
The cell membrane is the thin outer covering of the amoeba. It is flexible and allows the
body to change shape easily.
2. Cytoplasm
The cytoplasm is the jelly-like material inside the cell. It is divided into two parts:
Ectoplasm
o The outer, clear, transparent layer.
o More rigid and helps maintain the temporary shape of pseudopodia.
Endoplasm
o The inner, granular, semi-fluid layer.
o Contains the nucleus, food vacuoles, and other cell organelles.
o Flows into the pseudopodia during movement.
3. Pseudopodia
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Pseudopodia are temporary finger-like extensions formed by the cell membrane and
cytoplasm. They are used for:
Movement
Capturing food
Engulfing microorganisms
How Does Amoeba Move? (Step-by-Step)
The movement of an amoeba may look simple, but it is a carefully coordinated process.
Step 1: Detecting Direction
The amoeba senses food or a suitable environment. It decides the direction in which it
wants to move.
Step 2: Formation of Pseudopodium
The cell membrane pushes outward, forming a finger-like projection called a pseudopodium.
Step 3: Cytoplasmic Streaming
The fluid endoplasm flows into the newly formed pseudopodium. This flow of cytoplasm is
called cytoplasmic streaming.
As more cytoplasm enters the pseudopodium, it becomes larger and stronger.
Step 4: Forward Movement
The pseudopodium attaches to the surface, and the rest of the cell gradually flows into it. As
a result, the entire amoeba moves forward.
Step 5: Repetition
The old pseudopodium disappears, and a new one forms in another direction whenever
needed. By repeating this process, the amoeba keeps moving.
Mechanism of Amoeboid Movement
Scientists explain amoeboid movement mainly by cytoplasmic streaming.
During movement:
The ectoplasm changes into endoplasm at the front.
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The endoplasm flows forward.
The rear portion contracts.
The cell membrane continuously changes shape.
This continuous flow of cytoplasm pushes the organism in the desired direction.
Characteristics of Amoeboid Movement
It is slow compared to many other organisms.
The body has no permanent shape.
Pseudopodia are temporary structures.
The movement depends on the flow of cytoplasm.
The same pseudopodia are also used for feeding.
Advantages of Pseudopodia
Pseudopodia provide several benefits:
Help the amoeba move toward food.
Allow it to escape harmful conditions.
Enable it to capture bacteria and tiny organisms.
Help change direction at any moment.
Perform both locomotion and feeding without specialized organs.
Simple Analogy
Imagine placing a drop of thick jelly on a table and gently pushing one side. The jelly slowly
flows in that direction while the rest follows behind.
An amoeba moves in almost the same way. Instead of legs, it extends a pseudopodium,
flows its cytoplasm into it, and gradually pulls the rest of the body forward.
Conclusion
Locomotion in Amoeba proteus is a fascinating example of how even a single-celled
organism can move efficiently without legs or muscles. It moves by forming temporary
pseudopodia (false feet) through the flow of cytoplasm, a process known as amoeboid
movement. This movement helps the amoeba find food, escape danger, and survive in
changing environments. Thus, pseudopodia are multifunctional structures that play an
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essential role in both movement and feeding, making Amoeba proteus one of the best
examples of simple yet effective locomotion.
2. Explain in detail about exoerythrocytic stage of Plasmodium vivax in liver of man.
Ans: Explain in detail about the Exoerythrocytic Stage of Plasmodium vivax in the Liver of
Man
The exoerythrocytic stage is the first stage of malaria infection inside the human body. The
word "exoerythrocytic" means "outside the red blood cells (RBCs)." This stage takes place
inside the liver cells (hepatocytes) before the parasite enters the blood.
To understand it easily, imagine that Plasmodium vivax is a thief trying to rob a city. Before
attacking the city (blood), the thief first hides in a safe house (the liver), prepares an army,
and then launches a large attack. This hidden preparation stage is called the exoerythrocytic
stage.
Step-by-Step Explanation
1. Entry of the Parasite into the Human Body
The life cycle begins when an infected female Anopheles mosquito bites a healthy person.
During the bite, the mosquito injects sporozoites into the bloodstream.
Sporozoites are long, slender, infective forms of the parasite.
They remain in the blood for only a short time before moving to the liver.
Important Point:
The mosquito injects sporozoites, not parasites inside red blood cells.
2. Sporozoites Reach the Liver
Within about 30 minutes to 1 hour, the sporozoites travel through the bloodstream and
enter the liver cells (hepatocytes).
Inside the liver:
They become inactive for a short time.
They start growing rapidly.
They are protected from the body's immune system.
The liver acts like a training camp where the parasite prepares itself.
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3. Formation of Liver Schizonts (Schizogony)
Inside each liver cell, the sporozoite grows larger and becomes a schizont.
This process is called schizogony, which means multiple cell division.
During schizogony:
The nucleus divides many times.
Thousands of daughter parasites are produced.
These daughter cells are called merozoites.
One liver cell can produce thousands of merozoites.
4. Rupture of Liver Cells
After the schizont becomes fully mature:
The liver cell bursts.
Thousands of merozoites are released into the bloodstream.
These merozoites are now ready to infect red blood cells (RBCs).
This marks the end of the exoerythrocytic stage and the beginning of the erythrocytic stage
(blood stage).
5. Formation of Hypnozoites (Special Feature of Plasmodium vivax)
One unique characteristic of Plasmodium vivax is that not all sporozoites become schizonts
immediately.
Some sporozoites become hypnozoites.
Hypnozoites are:
Dormant (sleeping) forms.
They remain inside liver cells for months or even years.
Later they become active again and produce new merozoites.
This causes relapse of malaria, even after the patient seems completely cured.
This is the most important feature of Plasmodium vivax.
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Why is the Exoerythrocytic Stage Important?
This stage is very important because:
It is the first stage of infection in humans.
The parasite multiplies greatly before entering the blood.
It prepares thousands of merozoites for infection.
Dormant hypnozoites cause repeated malaria attacks (relapse).
No malaria symptoms appear during most of this liver stage because red blood cells
have not yet been infected.
Simple Flow Diagram
Infected Female Anopheles Mosquito
│
▼
Injects Sporozoites
│
▼
Bloodstream (Few Minutes)
│
▼
Liver Cells (Hepatocytes)
│
▼
Sporozoite becomes Schizont
│
(Schizogony / Multiple Division)
│
▼
Thousands of Merozoites Form
│
▼
Liver Cell Bursts
│
▼
Merozoites Enter Blood
│
▼
Infect Red Blood Cells (RBCs)
Some Sporozoites
│
▼
Hypnozoites (Dormant)
│
▼
Reactivate Later → Relapse
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Key Terms Explained
Term
Simple Meaning
Sporozoite
Infective stage injected by the mosquito.
Hepatocyte
Liver cell where the parasite first grows.
Exoerythrocytic Stage
Stage occurring outside red blood cells, in the liver.
Schizogony
Multiple cell division producing many daughter cells.
Schizont
Mature liver stage containing many merozoites.
Merozoite
Daughter parasite that infects red blood cells.
Hypnozoite
Dormant liver stage responsible for malaria relapse in P. vivax.
Relapse
Return of malaria due to activation of dormant hypnozoites.
Exam Points to Remember
The exoerythrocytic stage occurs inside the liver cells.
It begins when sporozoites are injected by the female Anopheles mosquito.
Sporozoites multiply by schizogony to form thousands of merozoites.
Liver cells rupture and release merozoites into the bloodstream.
Plasmodium vivax forms hypnozoites, which remain dormant in the liver and can
cause relapse after months or years.
This stage occurs before infection of red blood cells, so malaria symptoms generally
appear only after the parasite enters the blood.
Conclusion
The exoerythrocytic stage of Plasmodium vivax is the initial liver stage of malaria infection
in humans. After an infected female Anopheles mosquito injects sporozoites, they travel to
the liver, multiply by schizogony, and produce thousands of merozoites. These merozoites
then enter the bloodstream to infect red blood cells. A special feature of P. vivax is the
formation of hypnozoites, dormant liver forms that can reactivate later and cause relapse,
making this stage highly significant in the disease cycle and treatment of malaria.
SECTION-B
3. Discuss in detail about canal system in Sycon.
Ans: The canal system is the most important feature of the sponge Sycon (also called
Scypha). It is a network of tiny canals and chambers through which water continuously flows
inside the body. Since Sycon has no mouth, digestive system, blood vessels, or respiratory
organs, it completely depends on this flowing water for food, oxygen, and removal of
waste.
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Think of Sycon as a living water filter. Just as a water purifier allows water to pass through
different filters to remove impurities, Sycon allows water to pass through many tiny canals.
During this journey, it traps food particles, absorbs oxygen, and finally throws out waste
along with the water.
What is the Canal System?
The canal system is a series of openings, canals, and chambers that carry water from
outside the sponge to the inside and then back outside.
Its main functions are:
To bring food particles into the body.
To supply oxygen for respiration.
To remove carbon dioxide and other wastes.
To carry reproductive cells (sperm) during reproduction.
Without the canal system, Sycon cannot survive.
Parts of the Canal System
1. Ostia (Incurrent Pores)
These are numerous tiny pores present on the outer surface of the sponge.
Water enters the body through these pores.
They act like small entrance gates.
Function: Allow water carrying food and oxygen to enter.
2. Incurrent Canals
After entering through the ostia, water reaches the incurrent canals.
These canals distribute water to different parts of the sponge.
Function: Carry water towards the radial canals.
3. Prosopyles
These are very small openings between the incurrent canals and radial canals.
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Function: Allow water to move into the radial canals.
4. Radial Canals
Radial canals are the most important part of the canal system.
Their walls contain choanocytes (collar cells).
The beating of choanocyte flagella keeps water moving continuously.
Function:
Capture food particles.
Absorb oxygen.
Start digestion.
5. Choanocytes (Collar Cells)
Choanocytes have a collar-like structure and a flagellum.
Their jobs are:
Produce water current.
Trap microscopic food.
Digest food particles.
Help in reproduction by capturing sperm.
These cells are called the feeding cells of the sponge.
6. Apopyles
Small openings connecting radial canals to the spongocoel.
Function: Carry filtered water into the central cavity.
7. Spongocoel
A large central cavity inside the sponge.
Water collected from all radial canals enters here.
Function: Collect water before it leaves the body.
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8. Osculum
A single large opening present at the top of the sponge.
Function: Water carrying wastes and carbon dioxide leaves the body through the osculum.
Flow of Water in Sycon
The movement of water follows a fixed pathway:
Outside Water → Ostia → Incurrent Canals → Prosopyles → Radial Canals (Choanocytes
filter food) → Apopyles → Spongocoel → Osculum → Outside
This continuous water current supplies everything the sponge needs for survival.
Type of Canal System in Sycon
The canal system of Sycon is called the Syconoid Canal System.
It is more advanced than the Asconoid canal system found in simple sponges but less
advanced than the Leuconoid canal system found in highly developed sponges.
Characteristics of the Syconoid Canal System
Thick body wall.
Numerous radial canals.
Choanocytes are present only in radial canals.
Better filtration than the asconoid type.
Larger body size due to increased filtering surface.
Advantages of the Canal System
1. Increases the surface area for food collection.
2. Improves the efficiency of filter feeding.
3. Provides oxygen for respiration.
4. Removes metabolic wastes.
5. Helps transport reproductive cells.
6. Allows the sponge to grow larger than simple sponges.
Simple Diagram
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Osculum
↑
┌──────────┐
│Spongocoel│
└────┬─────┘
↑
Apopyles
↑
┌─────────────────┐
│ Radial Canals │
│ (Choanocytes) │
└──────┬──────────┘
↑
Prosopyles
↑
Incurrent Canals
↑
Ostia
↑
Water from Outside
Conclusion
The canal system of Sycon is a highly organized network of pores and canals that enables
the sponge to obtain food, breathe, remove wastes, and reproduce. Water enters through
the ostia, passes into the incurrent canals, moves through the prosopyles into the radial
canals, where choanocytes filter food and absorb oxygen. The filtered water then flows
through the apopyles into the spongocoel and finally exits through the osculum. This
syconoid canal system is more efficient than the simple asconoid type because it provides a
larger filtering surface, making Sycon a more effective filter feeder.
4. Explain phenomenon of polymorphism in Obelia in detail.
Ans:
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Introduction
Polymorphism means the occurrence of different types of individuals (or zooids) in the
same colony, where each individual performs a different function. The word comes from:
Poly = many
Morph = forms
So, polymorphism means "many forms."
In Obelia, all the individuals are genetically the same because they develop from a single
fertilized egg. However, they look different and perform different jobs. This is an excellent
example of division of labour in animals, just as different workers in a company perform
different tasks.
Imagine a school:
Teachers teach.
Principal manages.
Peons maintain the school.
Students study.
Everyone has a different role, but together they make the school function properly.
Similarly, in an Obelia colony, different zooids work together to help the colony survive and
reproduce.
What is Obelia?
Obelia is a small, colonial, marine hydrozoan belonging to the phylum Cnidaria.
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It is attached to rocks, shells, or seaweed in the ocean and forms a branching colony.
Each branch contains specialized zooids that are connected by a common tube called the
coenosarc, through which nutrients are shared.
Types of Zooids in Obelia (Polymorphism)
1. Hydranth (Gastrozooid) Feeding Zooid
Structure
Located at the tip of the branches.
Has a mouth surrounded by tentacles.
Tentacles contain nematocysts (stinging cells).
Functions
Captures tiny aquatic organisms.
Paralyzes prey with stinging cells.
Digests food.
Supplies nutrients to the entire colony through the coenosarc.
Simple understanding:
The hydranth is like the kitchen or cook of the colony because it prepares food for
everyone.
2. Gonangium (Gonozooid) Reproductive Zooid
Structure
Cylindrical and enclosed within a protective covering called the gonotheca.
Does not have a mouth or tentacles.
Contains reproductive buds called medusa buds.
Functions
Produces young medusae by budding.
Helps in reproduction.
Ensures continuation of the species.
Simple understanding:
The gonangium is like the maternity ward or nursery because it produces the next
generation.
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3. Medusa
The gonangium releases tiny medusae.
Characteristics
Free-swimming.
Bell-shaped body.
Separate male and female individuals.
Produce eggs and sperms.
After fertilization:
Egg + sperm → zygote
Zygote develops into a planula larva.
Planula settles on a suitable surface.
It develops into a new Obelia colony.
The medusa stage increases genetic variation through sexual reproduction.
Why is Polymorphism Important?
Polymorphism provides several advantages:
Division of Labour
Each zooid performs only one specialized function, making the colony more efficient.
Better Feeding
Hydranths continuously capture food for the whole colony.
Efficient Reproduction
Gonangia produce medusae, ensuring survival of the species.
Higher Survival
Since different zooids perform specialized jobs, the colony functions smoothly and has a
better chance of survival.
Energy Saving
Each zooid specializes in its own work instead of doing everything.
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Life Cycle Showing Polymorphism
Adult Medusa
(Male / Female)
│
Sexual Reproduction
│
Fertilization
│
Zygote
│
Planula Larva
│
Settles on Surface
│
Young Obelia Colony
│
┌───────────┴───────────┐
│ │
Hydranth Gonangium
(Feeding Zooid) (Reproductive Zooid)
│ │
└────── Shares food ────┘
│
Produces Medusae
│
Free-swimming Medusae
Diagram of Polymorphism in Obelia
Tentacles
\ | | /
\ | | /
(Mouth)
│
Hydranth
(Feeding Zooid)
│
=============================== Stem
===============================
│
Coenosarc
│
-----------------
| |
Gonotheca Gonotheca
│ │
Gonangium Gonangium
(Reproductive) (Reproductive)
│ │
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Medusa buds Medusa buds
Key Features of Polymorphism in Obelia
Zooid
Main Function
Special Feature
Hydranth
(Gastrozooid)
Feeding
Mouth, tentacles and nematocysts
Gonangium
(Gonozooid)
Reproduction
Produces medusa buds, enclosed in
gonotheca
Medusa
Sexual
reproduction
Free-swimming; produces eggs or sperm
Conclusion
Polymorphism in Obelia is the presence of different specialized zooids within the same
colony, each carrying out a particular function. Hydranths are responsible for feeding,
gonangia are responsible for reproduction by producing medusae, and the medusae carry
out sexual reproduction to form new colonies. This division of labour makes the colony
highly organized, efficient, and well adapted for survival. It is one of the best examples of
specialization among colonial animals and demonstrates how different body forms can work
together as a single, successful living unit.
SECTION-C
5. While giving brief written account, draw labelled diagram of male and female
reproductive organs of Fasciola hepatica.
Ans: Fasciola hepatica Male and Female Reproductive Organs (Simple Explanation)
Fasciola hepatica, commonly called the sheep liver fluke, is a flat, leaf-shaped parasitic
worm that lives in the liver and bile ducts of sheep, goats, cattle, and sometimes humans.
One interesting fact about this parasite is that each individual worm has both male and
female reproductive organs. This condition is called hermaphroditism (monoecious).
Because it has both reproductive systems in one body, it can reproduce very efficiently,
which helps the parasite survive and spread.
Male Reproductive Organs
The male reproductive system is responsible for producing and releasing sperm.
It includes:
Two highly branched testes These are located in the middle part of the body. They
produce sperm cells.
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Vasa efferentia Small tubes that collect sperm from the testes.
Vas deferens A larger tube that carries sperm towards the front of the body.
Seminal vesicle A storage sac where sperm is temporarily stored before mating.
Cirrus pouch (cirrus sac) Contains the cirrus, a muscular copulatory organ that
transfers sperm during fertilization.
Male genital pore The external opening through which sperm is released.
Female Reproductive Organs
The female reproductive system produces eggs and helps in fertilization and egg formation.
It includes:
Single branched ovary Produces ova (eggs).
Oviduct Carries eggs from the ovary.
Seminal receptacle Stores sperm received during copulation.
Mehlis' gland Secretes substances that help in the formation of eggshells.
Ootype A chamber where fertilization occurs and the egg shell begins to form.
Vitelline glands (Yolk glands) Present along both sides of the body. They provide
yolk (food) and shell material for developing eggs.
Vitelline ducts Carry yolk cells to the ootype.
Uterus A long coiled tube that stores fertilized eggs before they are released.
Female genital pore Opening through which eggs leave the body.
How Reproduction Takes Place
Although Fasciola hepatica has both male and female organs, it usually prefers cross-
fertilization, where two worms exchange sperm. However, self-fertilization can also occur if
another worm is not available.
After fertilization:
1. Eggs are formed in the ootype.
2. The vitelline glands provide yolk and shell material.
3. Eggs move into the uterus.
4. Finally, they leave the body through the genital pore and are passed out with the
host's feces.
This high reproductive capacity allows a single parasite to produce thousands of eggs,
increasing its chances of completing its life cycle.
Simple Labelled Diagram
Fasciola hepatica (Internal Reproductive Organs)
Anterior End
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│
Male Genital Pore
│
Cirrus Sac
│
Seminal Vesicle
│
Vas Deferens
│
┌──────────┴──────────┐
│ │
Branched Testis Branched Testis
(Left) (Right)
Branched Ovary
│
Oviduct
│
Seminal Receptacle
│
Mehlis' Gland
│
Ootype
│
Long Coiled Uterus
│
Female Genital Pore
Vitelline Glands ───────────── Vitelline Glands
(Left Side) (Right Side)
Key Points to Remember
Fasciola hepatica is a hermaphrodite (monoecious) parasite.
It possesses both male and female reproductive organs in the same body.
Male organs: Two branched testes, vas deferens, seminal vesicle, cirrus sac, and
male genital pore.
Female organs: Branched ovary, oviduct, seminal receptacle, Mehlis' gland, ootype,
uterus, vitelline glands, and female genital pore.
Cross-fertilization is common, but self-fertilization is also possible.
The parasite produces a very large number of eggs, helping it spread efficiently to
new hosts.
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6. Discuss life history of Taenia solium in detail.
Ans: Life History of Taenia solium (Pork Tapeworm)
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The life history of Taenia solium is one of the most important topics in zoology and
parasitology. Although it looks complicated at first, it becomes very easy if you remember
that the parasite needs two hosts to complete its life cycle.
Definitive host (where the adult worm lives): Human
Intermediate host (where the larval stage develops): Pig
Think of it as a journey of the tapeworm from human → pig → human.
What is Taenia solium?
Taenia solium, commonly called the pork tapeworm, is a long, flat, ribbon-like parasitic
worm that lives in the small intestine of humans. It absorbs nutrients directly from the food
eaten by its host and can grow 27 meters long.
The head (called the scolex) has:
Four suckers
A crown of hooks
These structures help the worm attach firmly to the wall of the intestine.
Step 1: Adult Worm Lives in Human Intestine
The adult tapeworm lives in the small intestine of humans.
Here it:
Attaches to the intestinal wall using hooks and suckers.
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Feeds on digested food.
Grows continuously by producing many body segments called proglottids.
The last segments become gravid proglottids, which are filled with thousands of eggs.
Step 2: Eggs Leave the Human Body
The mature gravid segments detach from the worm.
They are passed outside the body with human feces.
Now the soil, water, grass, and surroundings become contaminated with tapeworm eggs.
This stage spreads the parasite from one host to another.
Step 3: Pig Becomes Infected
While grazing, pigs may eat:
Contaminated grass
Food
Water containing tapeworm eggs
Inside the pig's intestine:
The eggs hatch.
A tiny larva called the oncosphere (hexacanth larva) emerges.
It has six hooks, which help it penetrate the intestinal wall.
Step 4: Larva Travels Through Blood
After entering the intestinal wall, the larva enters the bloodstream.
The blood carries it to different organs, mainly:
Muscles
Tongue
Heart
Neck muscles
Here the larva develops into a fluid-filled cyst called the Cysticercus (bladder worm).
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This is the infective stage for humans.
The cyst contains the future tapeworm head (scolex).
Step 5: Human Eats Undercooked Pork
If a person eats:
Raw pork
Half-cooked pork
Improperly cooked pork
containing Cysticercus, the parasite enters the human body.
The stomach juices digest the cyst wall.
The scolex comes out and attaches to the wall of the small intestine.
Step 6: Adult Worm Develops
Once attached:
Neck region starts producing new body segments.
The worm grows longer every day.
Within about 23 months, it becomes a fully mature adult tapeworm.
Now it again produces eggs, completing the life cycle.
The cycle continues from human → pig → human.
What Happens if Humans Swallow Eggs Instead of Cysts?
This is a very important exam point.
Normally humans become infected by eating Cysticercus in pork.
However, if a person accidentally swallows Taenia solium eggs (through contaminated food,
water, or poor hygiene), the eggs hatch inside the human body.
The larvae then travel through the bloodstream and form cysts in different organs such as:
Brain
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Eyes
Muscles
Liver
This disease is called Cysticercosis.
If the cysts develop in the brain, it causes Neurocysticercosis, which can lead to:
Headache
Seizures (fits)
Dizziness
Serious neurological problems
Important Stages of the Life Cycle
Stage
Host
Adult worm
Human
Eggs
Outside body
Oncosphere
Pig
Cysticercus
Pig muscles
Adult tapeworm
Human
Flow Diagram (Easy to Remember)
Adult Taenia in Human Intestine
│
▼
Eggs and Gravid Proglottids Passed in Feces
│
▼
Pig Eats Contaminated Food or Grass
│
▼
Eggs Hatch → Oncosphere (6-hooked larva)
│
▼
Larva Enters Bloodstream
│
▼
Forms Cysticercus in Pig Muscles
│
▼
Human Eats Undercooked Pork
│
▼
Scolex Attaches to Human Intestine
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│
▼
Adult Tapeworm Develops
│
└──────────────► Life Cycle Repeats
Prevention
The infection can be prevented by:
Eating well-cooked pork.
Maintaining good personal hygiene.
Washing hands before eating.
Using clean drinking water.
Proper disposal of human feces.
Regular inspection of pork before sale.
Exam Points to Remember
Scientific name: Taenia solium
Common name: Pork tapeworm
Definitive host: Human
Intermediate host: Pig
Adult stage: Human intestine
Larval stage: Cysticercus in pig muscles
Infective stage for humans: Cysticercus
Mode of infection: Eating undercooked infected pork
Disease caused by swallowing eggs: Cysticercosis (especially neurocysticercosis if
the brain is affected)
Conclusion
The life cycle of Taenia solium is completed between humans and pigs. The adult worm lives
in the human intestine and releases eggs through feces. Pigs consume these eggs, and the
larvae develop into Cysticercus cysts in their muscles. Humans become infected by eating
undercooked pork containing these cysts, allowing the parasite to grow into an adult worm
in the intestine. Understanding each stage of this cycle is important because it explains how
the infection spreads and highlights simple preventive measures such as proper sanitation,
good hygiene, and thoroughly cooking pork.
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SECTION-D
7. Discuss in detail about Body Walls of Ascaris.
Ans: 7. Discuss in detail about the Body Wall of Ascaris
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The body wall of Ascaris forms the outer covering of the roundworm. It acts like a strong
protective suit, giving the worm its shape, protecting it from the digestive juices of the
human intestine, and helping it move. Since Ascaris lives inside the small intestine of
humans, its body wall is specially designed to survive in such a harsh environment.
The body wall is made up of three main layers:
1. Cuticle (Outer Layer)
The cuticle is the outermost layer of the body wall. It is thick, transparent, elastic, and non-
living. It is secreted by the layer below it, called the hypodermis.
Functions:
Protects the worm from the host's digestive enzymes.
Prevents injury from food particles inside the intestine.
Maintains the body's shape.
Reduces water loss.
Helps in movement by working together with muscles.
The cuticle is made mainly of protein (collagen) and is arranged in several layers, making it
very strong. As the worm grows, it sheds the old cuticle and forms a new one. This process is
called molting (ecdysis).
2. Hypodermis (Epidermis)
Just below the cuticle is the hypodermis, also known as the epidermis. Unlike the epidermis
in humans, it does not have separate cells. Instead, it is a continuous layer of living material
called a syncytium.
The hypodermis forms four thick longitudinal cords that run from the head to the tail.
These are:
One dorsal cord (upper side)
One ventral cord (lower side)
Two lateral cords (one on each side)
Functions:
Produces the cuticle.
Provides support to the body.
Contains nerves and excretory canals within the cords.
Helps connect the muscles with the nervous system.
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3. Muscle Layer
Below the hypodermis lies the muscle layer.
Unlike earthworms, Ascaris has only longitudinal muscles. It does not have circular
muscles.
The muscles are arranged in four groups, separated by the hypodermal cords.
Functions:
Helps the worm move.
Produces side-to-side (thrashing) movements.
Works against the pressure of the body fluid present in the pseudocoel.
Since circular muscles are absent, Ascaris cannot crawl like an earthworm. Instead, it bends
from side to side while moving.
Pseudocoel (Body Cavity)
Just inside the muscle layer is the pseudocoel, a fluid-filled body cavity.
Although it is not a part of the body wall, it plays an important role.
Functions:
Acts as a hydrostatic skeleton, providing support.
Helps muscles produce movement.
Transports nutrients and waste materials.
Maintains internal pressure and body shape.
Simple Diagram of the Body Wall
Outside
│
┌───────────────────┐
│ Cuticle │
├───────────────────┤
│ Hypodermis │
├───────────────────┤
│ Longitudinal │
│ Muscles │
├───────────────────┤
│ Fluid-filled │
│ Pseudocoel │
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└───────────────────┘
│
Internal organs
How the Body Wall Helps Ascaris
Imagine a person wearing a strong waterproof raincoat while carrying a backpack filled with
air. The raincoat protects them from rain and sharp objects, while the air-filled backpack
helps them stay upright. In the same way:
The cuticle acts like the raincoat by protecting the worm.
The hypodermis produces and supports this protective covering.
The longitudinal muscles provide movement.
The fluid-filled pseudocoel acts like an air cushion (hydrostatic skeleton), allowing
the muscles to bend the body efficiently.
Together, these parts help Ascaris survive inside the human intestine, resist digestion, and
move easily through the intestinal contents.
Key Points for Exams
The body wall of Ascaris consists of Cuticle, Hypodermis, and Longitudinal Muscles.
The cuticle is thick, non-living, elastic, and protects the worm from digestive juices.
The hypodermis secretes the cuticle and forms one dorsal, one ventral, and two
lateral cords.
Ascaris possesses only longitudinal muscles; circular muscles are absent.
Movement is side-to-side (thrashing) due to the action of longitudinal muscles.
The pseudocoel functions as a hydrostatic skeleton, helping in movement, support,
and transport of nutrients.
Conclusion
The body wall of Ascaris is a highly specialized structure that enables the worm to live
successfully as a parasite inside the human intestine. Its tough cuticle provides protection,
the hypodermis produces and supports the outer covering, the longitudinal muscles
generate movement, and the fluid-filled pseudocoel acts as a hydrostatic skeleton.
Together, these adaptations allow Ascaris to maintain its shape, move efficiently, and
survive in the challenging environment of its host.
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8. Discuss reproductive system of Pheretima posthuma in detail.
Ans: Reproductive System of Pheretima posthuma (Earthworm)
The reproductive system of Pheretima posthuma (the common Indian earthworm) is one of
the most interesting examples of reproduction in animals. Earthworms are hermaphrodites
(bisexual), which means a single earthworm possesses both male and female reproductive
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organs. However, even though both sex organs are present in one individual, self-
fertilization does not occur. Instead, two earthworms exchange sperms with each other
during mating, ensuring cross-fertilization, which increases genetic variation.
The reproductive organs are located in specific body segments. Understanding these organs
and their functions makes the entire process easy to remember.
1. Male Reproductive Organs
The male reproductive system produces and transfers sperms.
(a) Testes
There are two pairs of testes.
They are located in the 10th and 11th body segments.
Their function is to produce sperm cells.
Simple Example:
Think of the testes as a factory where sperm cells are manufactured.
(b) Testis Sacs
Each pair of testes is enclosed inside testis sacs.
These sacs protect the testes and help in sperm development.
(c) Seminal Vesicles
There are two pairs, located in the 11th and 12th segments.
They store and nourish developing sperm cells until they become mature.
Simple Example:
Just as food is stored in a refrigerator until needed, mature sperms are stored in the seminal
vesicles.
(d) Spermiducal Funnels
Present in the 10th and 11th segments.
They collect mature sperms from the testes.
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(e) Vasa Deferentia (Sperm Ducts)
These are long tubes carrying sperms toward the outside.
Both ducts finally open through the male genital pores.
(f) Prostate Glands
One pair is present.
They secrete a fluid that helps transport and protect sperms.
(g) Male Genital Pores
Located on the 18th segment.
Sperms leave the body through these openings.
2. Female Reproductive Organs
The female reproductive organs produce eggs and help in fertilization.
(a) Ovaries
There is one pair of ovaries.
They are located in the 13th segment.
Their function is to produce eggs (ova).
Simple Example:
The ovaries are like a seed-producing plant, where eggs are formed.
(b) Oviducal Funnels
Located in the 13th segment.
They collect eggs released by the ovaries.
(c) Oviducts
These tubes carry eggs to the female genital opening.
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(d) Female Genital Pore
A single female genital opening is present on the 14th segment.
Eggs leave the body through this pore.
3. Spermathecae (Sperm Storage Sacs)
There are four pairs of spermathecae.
They are present in the 6th, 7th, 8th, and 9th segments.
Their function is to receive and store sperms from another earthworm during
mating.
Important Point:
These sacs do not produce sperm. They only store sperm received from the partner until
fertilization occurs.
4. Copulation (Mating)
During the rainy season, two mature earthworms come together.
They lie head to tail in opposite directions.
A sticky mucus secreted by the clitellum keeps them attached.
Each earthworm transfers sperms through its male genital pores into the
spermathecae of the other.
The exchange usually lasts for about one hour, after which both worms separate.
5. Fertilization
After mating:
1. The clitellum secretes a thick mucous ring.
2. The ring moves forward over the body.
3. Eggs from the female pore and stored sperms from the spermathecae enter this ring.
4. Fertilization occurs inside the ring (outside the body).
5. The ring slips off the head and closes at both ends, forming a cocoon.
Thus, fertilization in earthworms is called external fertilization because it occurs outside the
body but inside the cocoon.
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6. Development
The fertilized egg develops inside the cocoon.
There is no larval stage.
A young earthworm emerges directly from the cocoon.
This type of development is called direct development.
Role of the Clitellum
The clitellum is a thick glandular band found in sexually mature earthworms.
Its functions are:
Produces mucus during mating.
Forms the cocoon.
Provides nourishment to the developing embryo inside the cocoon.
Without the clitellum, successful reproduction cannot occur.
Important Segment-wise Location
Organ
Segment
Spermathecae
6th9th
Testes
10th & 11th
Seminal Vesicles
11th & 12th
Ovaries
13th
Female Genital Pore
14th
Male Genital Pores
18th
Easy Flow Chart
Testes
↓
Sperms Produced
↓
Seminal Vesicles (Storage)
↓
Vasa Deferentia
↓
Male Genital Pores
↓
Transferred to Partner's Spermathecae
↓
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Eggs Released from Ovaries
↓
Fertilization in Cocoon
↓
Young Earthworm
Conclusion
The reproductive system of Pheretima posthuma is highly organized and well adapted for
successful reproduction. Although each earthworm possesses both male and female
reproductive organs, it reproduces by cross-fertilization, where two worms exchange
sperms. The testes produce sperms, the ovaries produce eggs, and the spermathecae store
sperms received from another worm. The clitellum plays a crucial role by forming a cocoon
in which external fertilization takes place. The embryo develops directly into a young
earthworm without any larval stage. This efficient reproductive mechanism helps
earthworms maintain healthy populations and ensures greater genetic diversity.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
have suggestions, feel free to share your feedback.