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GNDU Question Paper-2022
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. Explain in detail about different locomotion theories in Amoeba proteus.
2. Discuss in detail about Exoerythrocytic stage: In liver of man.
SECTION-B
3. Explain canal system in Sycon in detail.
4. Discuss in detail about development and structure of medusa in Obelia.
SECTION-C
5. Discuss reproductive system of Fasciola hepatica in detail.
6. Discuss in detail about larvae of Fasciola hepatica and Taenia solium.
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SECTION-D
7. Write in detail about parasitic adaptations in Helminthes.
8. Discuss in detail about circulatory system of Pheretima posthuma.
GNDU Answer Paper-2022
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. Explain in detail about different locomotion theories in Amoeba proteus.
Ans: Amoeba proteus is one of the simplest single-celled organisms, yet it can move from
one place to another without having legs, wings, or fins. Its movement is called amoeboid
locomotion, and it takes place with the help of temporary finger-like projections called
pseudopodia (pseudo = false, podia = feet). Scientists have studied this movement for many
years and proposed different theories to explain how an amoeba moves. Although no single
theory explains every detail perfectly, each theory helps us understand one part of the
movement process.
What is Locomotion in Amoeba proteus?
Locomotion means the movement of an organism from one place to another. In Amoeba
proteus, locomotion helps it:
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Search for food.
Escape from harmful conditions.
Find a suitable environment for survival.
Capture prey like bacteria and small protozoans.
The amoeba moves by extending a pseudopodium in the direction it wants to travel. The
rest of the body gradually flows into this projection.
Structure Involved in Locomotion
Before understanding the theories, it is important to know two important parts of the
amoeba's cytoplasm:
1. Ectoplasm
o Outer layer of cytoplasm.
o Clear, transparent, and more rigid.
o Gives temporary support to pseudopodia.
2. Endoplasm
o Inner layer of cytoplasm.
o Granular, fluid, and contains cell organelles.
o Flows into the pseudopodium during movement.
Diagram of Amoeboid Locomotion
Direction of Movement →
Pseudopodium
▲
/ \
/ \
__________________/ \__________________
/ \
| Ectoplasm |
| |
| Endoplasm (flows forward) →→→ |
| |
\___________________________________________/
Different Theories of Locomotion in Amoeba proteus
1. Surface Tension Theory (Bütschli)
This was one of the earliest explanations of amoeboid movement.
Main Idea
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According to this theory, the surface tension of the amoeba is not the same all over the
body. The front end has lower surface tension than the rear end. Because of this difference,
the cytoplasm naturally flows toward the front, forming a pseudopodium.
How it Works
The front surface becomes softer.
Cytoplasm flows toward this region.
A pseudopodium develops.
The remaining body follows.
Limitation
Scientists later found that differences in surface tension alone cannot explain the complex
movement of amoeba.
2. Sol-Gel Theory (Hyman)
This is one of the most widely accepted theories.
Main Idea
The cytoplasm continuously changes between two physical states:
Sol state: Fluid and flowing.
Gel state: Thick, semi-solid, and firm.
How it Works
1. At the front of the amoeba, the gel changes into sol.
2. The fluid endoplasm flows into this region.
3. At the tip of the pseudopodium, the sol again changes into gel.
4. This newly formed gel provides support.
5. The entire cell gradually moves forward.
This continuous conversion between sol and gel causes movement.
Importance
This theory explains why amoeba can continuously extend and withdraw pseudopodia.
3. Contractile Protein Theory
This theory explains movement using special proteins inside the cell.
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Main Idea
The cytoplasm contains proteins similar to those found in human muscles.
The two important proteins are:
Actin
Myosin
These proteins contract and relax to produce movement.
How it Works
Actin and myosin interact.
Their contraction pushes cytoplasm forward.
A pseudopodium forms.
Relaxation allows the rest of the cytoplasm to flow.
The amoeba moves in the desired direction.
Importance
Modern cell biology strongly supports this theory because these proteins have been
observed in amoeba cells.
4. Fountain Flow Theory
This theory describes how cytoplasm circulates inside the amoeba.
Main Idea
The endoplasm flows forward through the center of the pseudopodium and returns
backward along the outer edges, creating a fountain-like circulation.
How it Works
Cytoplasm moves to the tip through the middle.
It spreads outward.
Some cytoplasm flows backward along the sides.
Continuous circulation helps maintain movement.
Importance
This theory explains the internal streaming of cytoplasm seen under a microscope.
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5. Hydraulic Pressure Theory
This theory focuses on pressure inside the cell.
Main Idea
The movement of amoeba is produced by changes in internal hydrostatic (water) pressure.
How it Works
Pressure increases inside the cell.
Cytoplasm is pushed toward the weaker front region.
A pseudopodium forms.
The rest of the body follows due to pressure differences.
Limitation
Pressure alone cannot fully explain all aspects of locomotion, but it contributes to
movement.
Comparison of Different Theories
Theory
Main Concept
Key Feature
Surface Tension
Theory
Difference in surface
tension
Cytoplasm flows toward low
surface tension
Sol-Gel Theory
Sol ↔ Gel transformation
Most accepted classical theory
Contractile Protein
Theory
Actin and myosin proteins
Explains movement at the
molecular level
Fountain Flow Theory
Circular cytoplasmic
streaming
Explains internal flow pattern
Hydraulic Pressure
Theory
Internal pressure changes
Pressure pushes cytoplasm forward
Modern Understanding
Today, scientists believe that amoeboid locomotion is not explained by a single theory.
Instead, movement results from the combined action of:
Solgel transformation of the cytoplasm.
Actin and myosin protein interactions.
Cytoplasmic streaming.
Changes in internal hydrostatic pressure.
Together, these processes allow the amoeba to extend pseudopodia and move efficiently.
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Conclusion
Amoeba proteus demonstrates that even a single-celled organism can perform complex
movement. It uses temporary pseudopodia, formed by the coordinated flow of cytoplasm.
Over time, scientists proposed several theoriesSurface Tension Theory, Sol-Gel Theory,
Contractile Protein Theory, Fountain Flow Theory, and Hydraulic Pressure Theoryto
explain this fascinating process. Among these, the Sol-Gel Theory and Contractile Protein
Theory are the most widely accepted today because they best match modern microscopic
and molecular observations. Understanding these theories helps us appreciate how living
cells can move without muscles or specialized organs, making amoeboid locomotion an
important topic in cell biology and zoology.
2. Discuss in detail about Exoerythrocytic stage: In liver of man.
Ans: 2. Discuss in Detail About the Exoerythrocytic Stage (Liver Stage) of Plasmodium in
Man
The exoerythrocytic stage is the first stage of malaria parasite development 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. It
is one of the most important stages because it allows the parasite to multiply silently
without causing any symptoms at first.
To understand this stage, imagine the human liver as a hidden training camp. When the
malaria parasite enters the body, it first goes to this camp, where it grows, multiplies, and
prepares a huge army. Only after building this army does it attack the red blood cells,
leading to malaria symptoms like fever, chills, and sweating.
How Does the Exoerythrocytic Stage Begin?
When an infected female Anopheles mosquito bites a healthy person, it injects thousands
of sporozoites (the infective stage of the parasite) into the bloodstream.
Instead of attacking red blood cells immediately, these sporozoites quickly travel to the
liver within about 3060 minutes.
Inside the liver, each sporozoite enters a liver cell and begins its development.
Stages of Exoerythrocytic Development
1. Entry of Sporozoites into the Liver
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During the mosquito bite, sporozoites enter the bloodstream.
They travel rapidly to the liver.
They invade healthy liver cells (hepatocytes).
Key Point: No symptoms appear during this stage because red blood cells are not yet
affected.
2. Growth Inside Liver Cells
Once inside the liver cell:
The sporozoite becomes larger.
It starts feeding on nutrients from the liver cell.
It develops into a structure called a trophozoite.
The trophozoite continues growing until it becomes a schizont.
3. Formation of Liver Schizont
A schizont is a large cell containing many nuclei.
Instead of producing only one parasite, the schizont divides repeatedly.
Through a process called multiple fission (schizogony), one sporozoite produces thousands
of daughter parasites known as merozoites.
This multiplication greatly increases the number of parasites before they enter the
bloodstream.
4. Rupture of Liver Cell
When the liver schizont becomes fully mature:
The liver cell bursts.
Thousands of merozoites are released into the bloodstream.
These merozoites now invade the red blood cells (RBCs) and start the erythrocytic stage,
which causes malaria symptoms.
5. Dormant Stage (Hypnozoite) in Some Species
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In Plasmodium vivax and Plasmodium ovale:
Some sporozoites do not develop immediately.
They remain inactive in the liver as hypnozoites.
These dormant forms may become active after months or even years.
Because of hypnozoites, malaria may relapse even after successful treatment.
Note: Plasmodium falciparum does not form hypnozoites.
Simple Flow Diagram
Female Anopheles Mosquito Bite
│
▼
Sporozoites Enter Blood
│
▼
Reach Liver Cells
│
▼
Enter Hepatocytes
│
▼
Grow into Trophozoites
│
▼
Develop into Schizonts
│
▼
Multiple Fission (Schizogony)
│
▼
Thousands of Merozoites Form
│
▼
Liver Cell Bursts
│
▼
Merozoites Enter Bloodstream
│
▼
Invade Red Blood Cells
Importance of the Exoerythrocytic Stage
This stage is very important because:
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It is the first developmental stage in humans.
The parasite multiplies enormously before entering the blood.
No malaria symptoms appear during this stage.
It prepares the parasite for infection of red blood cells.
It helps the parasite spread rapidly throughout the body.
In some species, dormant hypnozoites cause malaria relapse.
Characteristics of the Exoerythrocytic Stage
Occurs in liver cells.
Happens before the blood stage.
Starts with sporozoites.
Ends with the formation of merozoites.
Multiplication occurs by schizogony (multiple fission).
Usually symptomless because RBCs are not yet infected.
Hypnozoites are present only in P. vivax and P. ovale.
Difference Between Exoerythrocytic and Erythrocytic Stages
Exoerythrocytic Stage
Erythrocytic Stage
Occurs in liver cells
Occurs in red blood cells
Begins with sporozoites
Begins with merozoites
No fever or chills
Causes fever, chills, and sweating
Produces thousands of merozoites
Produces more merozoites by infecting RBCs
Silent stage
Symptomatic stage
Conclusion
The exoerythrocytic stage is the liver stage of the malaria parasite (Plasmodium) in
humans. It begins when an infected female Anopheles mosquito injects sporozoites into the
bloodstream. These sporozoites quickly reach the liver, invade liver cells, and multiply by
schizogony, producing thousands of merozoites. When the liver cells burst, these
merozoites enter the bloodstream and infect red blood cells, marking the beginning of the
disease-causing stage of malaria. In species such as Plasmodium vivax and Plasmodium
ovale, dormant hypnozoites may remain in the liver and later cause relapse. Thus, the
exoerythrocytic stage is essential for parasite multiplication, survival, and the successful
establishment of malaria infection in humans.
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SECTION-B
3. Explain canal system in Sycon in detail.
Ans: The canal system is one of the most important features of Sycon, a simple marine
sponge belonging to the phylum Porifera. Although Sycon looks like a small tube attached to
rocks in the sea, inside it has a highly organized network of canals. This canal system helps
the sponge perform all its life activities such as feeding, respiration, excretion, and
reproduction because sponges do not have organs like the heart, lungs, or digestive system.
Think of the canal system as a water-filtering machine. Just as a water purifier allows dirty
water to enter, filters it, and releases clean water, Sycon allows seawater to enter its body,
filters out food and oxygen, removes wastes, and lets the water leave through the top
opening.
What is the Canal System?
The canal system is a network of pores, canals, and chambers through which water
continuously flows inside the sponge's body.
The movement of water is created by the beating of tiny hair-like structures called flagella
present on special cells known as choanocytes (collar cells).
This continuous water current is essential because it provides:
Food particles for nutrition
Oxygen for respiration
Removal of carbon dioxide and other wastes
Transport of sperm during reproduction
Thus, the canal system acts as the life-support system of Sycon.
Type of Canal System in Sycon
Sycon has the Syconoid Canal System.
The syconoid canal system is more advanced than the asconoid type because the body wall
is folded into many canals. These folds increase the surface area and contain more
choanocytes, allowing the sponge to filter much more water and obtain more food.
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Path of Water Flow in Sycon
The flow of water inside Sycon follows this sequence:
Sea Water
↓
Dermal Pores (Ostia)
↓
Incurrent Canals
↓
Prosopyles
↓
Radial Canals (Choanocyte-lined)
↓
Apopyles
↓
Spongocoel
↓
Osculum
↓
Outside
Explanation of Each Part
1. Dermal Pores (Ostia)
These are tiny openings present on the outer surface of Sycon.
Water enters through these pores.
They act like the entrance gate.
Food particles and oxygen enter along with water.
2. Incurrent Canals
After entering through the ostia, water reaches the incurrent canals.
These canals:
Carry water deeper into the body.
Are not lined with choanocytes.
Simply transport water toward the feeding chambers.
3. Prosopyles
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Prosopyles are very small openings connecting the incurrent canals with the radial canals.
Their function is to:
Regulate water movement.
Direct water into the feeding chambers.
4. Radial Canals
These are the most important part of the canal system.
The radial canals are lined by choanocytes (collar cells).
Each choanocyte has:
A collar
A flagellum
The beating of the flagella creates water currents.
Functions of radial canals:
Capture microscopic food particles.
Absorb oxygen.
Begin intracellular digestion.
Keep water moving.
Most feeding occurs here.
5. Apopyles
Apopyles are openings connecting radial canals to the central cavity.
Their function is simply to allow filtered water to move into the spongocoel.
6. Spongocoel
The spongocoel is the central cavity of Sycon.
Unlike in simple sponges, very little feeding occurs here.
Its main job is to collect filtered water before it leaves the body.
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7. Osculum
The osculum is the large opening at the top of the sponge.
Functions:
Releases filtered water.
Removes carbon dioxide and nitrogenous wastes.
Helps maintain continuous water circulation.
Diagram of Canal System in Sycon
Osculum
▲
│
Spongocoel
▲
(Apopyles)
▲
Radial Canals
(Choanocyte-lined)
▲
(Prosopyles)
▲
Incurrent Canals
▲
Dermal Pores (Ostia)
▲
Sea Water
Role of Choanocytes
Choanocytes are called collar cells because each cell has a collar surrounding a flagellum.
Their functions are:
Produce water current.
Capture food particles.
Digest food inside the cell.
Help in respiration.
Assist in reproduction by trapping sperm.
Without choanocytes, the canal system would not function.
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Importance of the Canal System
The canal system is extremely important because Sycon lacks complex organs. It performs
several essential functions:
Nutrition: Filters tiny food particles like bacteria and plankton.
Respiration: Supplies oxygen to body cells.
Excretion: Removes waste products with outgoing water.
Reproduction: Helps transport sperm during sexual reproduction.
Water circulation: Maintains a constant flow of fresh seawater through the body.
Why is the Syconoid Canal System Better than the Asconoid Type?
Compared with the simpler asconoid canal system, the syconoid canal system has several
advantages:
The body wall is folded, creating many radial canals.
It has a larger surface area for filtering water.
More choanocytes are present, increasing food capture.
It is more efficient in respiration and excretion.
It supports a larger body size.
Conclusion
The canal system of Sycon is a specialized network of ostia, incurrent canals, prosopyles,
radial canals, apopyles, spongocoel, and osculum through which water continuously flows.
The beating of choanocyte flagella drives this water current, allowing the sponge to obtain
food and oxygen while removing wastes. Because Sycon has no digestive, circulatory, or
respiratory organs, the canal system performs all these vital functions. The syconoid canal
system is more advanced and efficient than the asconoid type due to its folded body wall
and numerous choanocyte-lined radial canals, making Sycon a highly effective filter-feeding
organism.
4. Discuss in detail about development and structure of medusa in Obelia.
Ans: The life cycle of Obelia is one of the best examples of alternation of generations
(metagenesis). It has two different body forms:
Polyp (colony) fixed to a surface and reproduces asexually.
Medusa free-swimming, umbrella-shaped and reproduces sexually.
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The medusa stage is produced from the polyp colony and plays an important role in sexual
reproduction. Let us understand its development and structure in a simple and interesting
way.
Development of Medusa in Obelia
Imagine the Obelia colony as a small underwater tree attached to a rock. This colony has
different types of zooids (individuals), each with a special function.
1. Formation of Gonangium
The reproductive zooid of the colony is called the gonangium. It does not catch food; its
main function is to produce medusae.
Inside the gonangium is a central stalk called the blastostyle.
2. Formation of Medusa Buds
Small outgrowths called medusa buds develop on the blastostyle.
These buds grow gradually by repeated cell division. Each bud starts developing important
body parts like:
Umbrella
Tentacles
Manubrium (feeding tube)
Mouth
Radial canals
Thus, every bud slowly transforms into a tiny medusa.
3. Liberation of Medusa
When fully developed, the young medusae detach from the gonangium and swim freely in
water.
They are now independent organisms and begin their own life.
4. Growth of Medusa
The free-swimming medusa feeds on tiny plankton and grows into a mature medusa.
Male and female medusae are separate individuals.
5. Sexual Reproduction
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The mature medusa develops gonads on the radial canals.
Male medusa produces sperms.
Female medusa produces eggs.
Fertilization usually takes place in seawater (external fertilization).
6. Formation of Planula Larva
The fertilized egg forms a zygote, which develops into a planula larva.
The planula swims freely for some time and then settles on a hard surface.
7. Formation of New Colony
The planula develops into a young polyp.
The polyp reproduces by budding and forms a new Obelia colony.
Thus, the life cycle continues.
Flow Diagram of Medusa Development
Obelia Colony
│
▼
Gonangium
│
▼
Blastostyle
│
▼
Medusa Buds
│
▼
Young Medusa
│
▼
Mature Medusa
│
▼
Eggs + Sperms
│
▼
Fertilization
│
▼
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Zygote
│
▼
Planula Larva
│
▼
Young Polyp
│
▼
New Obelia Colony
Structure of Medusa in Obelia
The medusa resembles a tiny transparent jellyfish. It is delicate, umbrella-shaped, and
specially adapted for swimming and sexual reproduction.
1. Umbrella (Bell)
The body is shaped like an umbrella or bell.
It helps the medusa swim by rhythmic contraction and relaxation.
2. Exumbrella
The outer convex surface is called the exumbrella.
It is smooth and protects the body.
3. Subumbrella
The inner concave surface is called the subumbrella.
This cavity helps in movement.
4. Velum
Near the margin is a thin circular membrane called the velum.
Function
Makes swimming more efficient.
Pushes water backward during movement.
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The presence of the velum is an important feature of Hydrozoan medusae.
5. Manubrium
A tube-like structure hangs from the center of the umbrella.
This is called the manubrium.
At its tip lies the mouth.
Functions
Intake of food.
Removal of undigested material.
6. Mouth
The mouth opens directly into the stomach.
Food such as tiny plankton enters through it.
7. Gastrovascular Cavity (Stomach)
Located at the center of the medusa.
Functions:
Digestion
Distribution of nutrients
8. Radial Canals
Four radial canals extend outward from the stomach toward the edge.
Functions:
Carry digested food.
Transport nutrients to all body parts.
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9. Ring Canal
A circular canal runs around the margin of the umbrella.
It connects all radial canals.
Function:
Distributes nutrients evenly.
10. Tentacles
Many hollow tentacles arise from the margin.
Each tentacle bears numerous nematocysts (stinging cells).
Functions:
Catch prey.
Protection.
Help in movement.
11. Gonads
Located on the radial canals.
Function:
Produce eggs or sperms.
Responsible for sexual reproduction.
12. Sense Organs
At the edge of the umbrella are small sensory organs.
They help the medusa detect:
Light
Water movement
Balance
These organs assist in swimming and responding to the environment.
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Labeled Diagram of Obelia Medusa
Tentacles
\ | | | | /
\ /
-----------------------
/ \
/ Exumbrella \
| |
| Ring Canal |
| ------------------ |
| \ | | / |
| \ | / |
| Radial Canals |
| | |
| Gonads |
| | |
| Manubrium |
| | |
| Mouth |
\ /
\_________________________/
Velum
Importance of the Medusa Stage
The medusa stage is important because:
It performs sexual reproduction.
It increases genetic variation.
Being free-swimming, it helps in the wide distribution of the species.
It produces gametes that form the planula larva, giving rise to a new Obelia colony.
Key Points for Exams
The gonangium is the reproductive zooid of the Obelia colony.
Medusa buds develop on the blastostyle.
Mature medusae are free-swimming and dioecious (male and female are separate).
Gonads are present on the radial canals.
Fertilization forms a zygote, which develops into a planula larva.
The planula settles and forms a new polyp colony.
Main parts of the medusa include the umbrella, velum, manubrium, mouth,
stomach, radial canals, ring canal, tentacles, gonads, and sense organs.
The medusa represents the sexual generation, while the polyp represents the
asexual generation, together completing the alternation of generations in Obelia.
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SECTION-C
5. Discuss reproductive system of Fasciola hepatica in detail.
Ans: The reproductive system of Fasciola hepatica (commonly called the sheep liver fluke)
is one of the most advanced and interesting systems among parasitic flatworms. Since this
parasite spends most of its adult life inside the bile ducts of sheep, goats, cattle, and
sometimes humans, it may not always find another fluke nearby for mating. To solve this
problem, nature has made it hermaphroditic (bisexual), meaning one individual possesses
both male and female reproductive organs. This special adaptation allows it to reproduce
successfully even when living alone, ensuring the continuation of its species.
Why is Fasciola hepatica Hermaphroditic?
Imagine a traveler living alone in a remote place where meeting others is rare. If
reproduction depended only on finding a partner, survival would become difficult.
Similarly, Fasciola hepatica lives inside the liver of its host, where another fluke may not
always be present. Therefore, each fluke has both male and female reproductive organs,
enabling:
Cross-fertilization when another fluke is available.
Self-fertilization if it is alone.
This increases its chances of producing thousands of eggs throughout its life.
Male Reproductive System
The male reproductive system is highly developed and produces a large number of sperm.
1. Testes
There are two large, highly branched testes.
They lie one behind the other in the middle region of the body.
Their function is to produce sperm cells (male gametes).
2. Vasa Efferentia
Fine ducts arise from each testis.
These ducts collect sperm and carry them forward.
3. Vas Deferens
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The small ducts join to form a single vas deferens.
It transports sperm toward the copulatory organ.
4. Seminal Vesicle
This enlarged portion stores sperm temporarily before mating.
5. Cirrus Sac
It contains the cirrus, a muscular copulatory organ.
During mating, the cirrus transfers sperm to another fluke.
Female Reproductive System
The female reproductive organs produce eggs and help in their fertilization and
development.
1. Ovary
There is one branched ovary located near the front of the testes.
It produces ova (egg cells).
2. Oviduct
The ovary is connected to a short oviduct.
It carries mature eggs toward the fertilization chamber.
3. Ootype
This is the chamber where fertilization takes place.
Eggs receive nutrients and shell material here.
4. Mehlis' Gland
Surrounds the ootype.
Secretes substances that help in egg-shell formation and proper development of the
egg.
5. Vitelline Glands (Yolk Glands)
These glands are spread along both sides of the body.
They provide:
o Yolk for nourishment.
o Materials for egg-shell formation.
6. Uterus
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After fertilization, eggs pass into the uterus.
The uterus stores numerous eggs before they are released.
7. Female Genital Pore
Eggs leave the body through the common genital opening.
Fertilization
Fertilization usually occurs in the ootype.
Two types of fertilization are possible:
Cross-fertilization
o Takes place between two different flukes.
o This is the most common method.
Self-fertilization
o Happens when another fluke is absent.
o The sperm fertilizes eggs of the same individual.
After fertilization:
Egg shell is formed.
Eggs become fully developed.
They move into the uterus.
Egg Formation
Each fertilized egg contains:
A developing embryo.
Nutritive yolk cells.
A thick protective shell.
The shell protects the embryo from drying and damage when the egg leaves the host.
Egg Release
The mature eggs are released into the bile ducts.
From there:
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Bile duct → Intestine → Passed out with feces
Once the eggs reach water, they continue the life cycle by developing into larvae.
Simple Diagram of the Reproductive System
Fasciola hepatica
Male Organs
__________________________
Branched Testis
│
Branched Testis
│
Vasa Efferentia
│
Vas Deferens
│
Seminal Vesicle
│
Cirrus Sac
│
Genital Opening
__________________________
Female Organs
Branched Ovary
│
Oviduct
│
Mehlis' Gland
(Ootype)
│
Vitelline Glands
(on both body sides)
│
Uterus
│
Genital Opening
Important Features of the Reproductive System
Feature
Description
Type
Hermaphrodite (both sexes in one organism)
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Testes
Two, highly branched
Ovary
Single, branched
Vitelline glands
Produce yolk and shell material
Fertilization
Mainly cross-fertilization; self-fertilization also possible
Egg shell
Formed with the help of Mehlis' gland and vitelline glands
Eggs
Released through bile duct into feces
Conclusion
The reproductive system of Fasciola hepatica is highly specialized and perfectly adapted for
a parasitic lifestyle. Because the fluke lives inside the liver of its host, where finding a mate
may be difficult, it possesses both male and female reproductive organs. The branched
testes produce sperm, while the single branched ovary produces eggs. Fertilization occurs
in the ootype, where Mehlis' gland and vitelline glands help form a protective eggshell. The
fertilized eggs are stored in the uterus and eventually pass through the bile duct into the
intestine and are expelled with the host's feces. This efficient reproductive system enables
Fasciola hepatica to produce thousands of eggs, ensuring the survival and spread of the
species even in challenging conditions.
6. Discuss in detail about larvae of Fasciola hepatica and Taenia solium.
Ans: Parasitic worms do not become adults in a single step. Just like a butterfly first passes
through the stages of egg, caterpillar, and pupa before becoming an adult, parasites also
pass through different larval stages before reaching adulthood. These larval forms are
specially adapted to survive, grow, and infect their next host.
Two important parasites studied in zoology are Fasciola hepatica (Liver Fluke) and Taenia
solium (Pork Tapeworm). Both have different larval stages, but each stage plays an
important role in completing the parasite's life cycle.
A. Larvae of Fasciola hepatica (Liver Fluke)
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Fasciola hepatica is a digenetic parasite, meaning it requires two hosts to complete its life
cycle.
Definitive host: Sheep, cattle, and humans
Intermediate host: Freshwater snail
The parasite passes through five larval stages.
1. Miracidium
This is the first larval stage that hatches from the egg in freshwater.
Characteristics
Pear-shaped body
Covered with tiny cilia for swimming
Has two eye spots to detect light
Contains germ cells for future development
Function
Swims actively in water.
Searches for a suitable freshwater snail.
Penetrates the snail's body using enzymes.
Importance: Without entering the snail, the life cycle cannot continue.
2. Sporocyst
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Once inside the snail, the miracidium loses its cilia and transforms into a sporocyst.
Characteristics
Sac-like structure
No digestive organs
Absorbs nutrients directly from the snail
Function
Produces many rediae through asexual reproduction.
Importance: It increases the number of parasites inside the snail.
3. Redia
The sporocyst develops into redia.
Characteristics
Elongated body
Possesses a mouth and simple intestine
Can move inside the snail
Function
Feeds on snail tissues.
Produces daughter rediae or cercariae.
Importance: This stage further multiplies the parasite population.
4. Cercaria
The next stage is the cercaria.
Characteristics
Tadpole-like body
Long muscular tail
Free-swimming larva
Function
Leaves the snail.
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Swims through water.
Attaches to aquatic plants.
Importance: It carries the parasite from the snail to vegetation.
5. Metacercaria
This is the infective larval stage for humans and grazing animals.
Characteristics
Round, thick-walled cyst
Tail is lost
Resistant to environmental conditions
Function
Remains attached to water plants.
Humans or animals become infected by eating contaminated plants such as
watercress.
After entering the intestine, it migrates to the liver and develops into an adult fluke.
Simple Flow Diagram
Egg
│
▼
Miracidium
│
▼
Sporocyst
│
▼
Redia
│
▼
Cercaria
│
▼
Metacercaria
│
▼
Adult Liver Fluke
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B. Larvae of Taenia solium (Pork Tapeworm)
Taenia solium is also a digenetic parasite.
Definitive host: Humans
Intermediate host: Pig
Unlike Fasciola hepatica, it has two important larval stages.
1. Oncosphere (Hexacanth Embryo)
The oncosphere develops inside the egg.
Characteristics
Spherical embryo
Possesses six hooks, so it is called a hexacanth embryo
Surrounded b-.
y a protective shell
Function
Pig swallows the eggs while feeding.
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In the pig's intestine, the embryo emerges.
Hooks help it penetrate the intestinal wall.
It enters the bloodstream and travels to muscles.
Importance: It enables the parasite to invade the pig's tissues.
2. Cysticercus (Bladder Worm)
The oncosphere develops into the cysticercus, which is the infective larva.
Characteristics
Fluid-filled bladder-like cyst
Contains an inverted scolex with suckers and hooks
White and oval in appearance
Function
Lives in pig muscles.
Humans become infected by eating undercooked pork containing cysticerci.
Inside the human intestine, the scolex comes out, attaches to the intestinal wall, and
develops into the adult tapeworm.
Importance: This is the infective stage for humans.
Special Note: Human Cysticercosis
If humans accidentally swallow Taenia solium eggs instead of cysticerci (for example,
through contaminated food or water), the larvae may migrate into human muscles, eyes, or
even the brain.
This disease is called cysticercosis. When the brain is affected (neurocysticercosis), it can
cause headaches, seizures, and other neurological problems.
Simple Flow Diagram
Egg
│
▼
Oncosphere (Hexacanth Embryo)
│
▼
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Pig Muscles
│
▼
Cysticercus (Bladder Worm)
│
▼
Human eats infected pork
│
▼
Adult Tapeworm
Difference Between the Larvae of Fasciola hepatica and Taenia solium
Fasciola hepatica
Taenia solium
Five
Two
Freshwater snail
Pig
Miracidium
Oncosphere
Metacercaria
Cysticercus
Metacercaria
Cysticercus
Eating contaminated aquatic
plants
Eating undercooked
pork
Conclusion
The larval stages of Fasciola hepatica and Taenia solium are highly specialized and essential
for completing their life cycles. Fasciola hepatica passes through five larval stages
Miracidium, Sporocyst, Redia, Cercaria, and Metacercaria, using a freshwater snail as its
intermediate host. In contrast, Taenia solium has two major larval stagesOncosphere and
Cysticercus, with the pig acting as the intermediate host. Understanding these larval forms
helps explain how these parasites spread, infect new hosts, and cause disease, making this
topic important in zoology, parasitology, and public health.
SECTION-D
7. Write in detail about parasitic adaptations in Helminthes.
Ans: Introduction
Helminthes are parasitic worms that live inside the body of other animals or humans, called
the host. They depend on the host for food, shelter, and protection. Since they spend most
or all of their lives inside the host, they have developed many special adaptations that help
them survive, grow, and reproduce successfully. These changes are called parasitic
adaptations.
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Think of a parasite like a person living in someone else's house without paying rent. To stay
there for a long time, it must avoid being noticed, find food easily, and make sure its family
continues. Similarly, helminthes have evolved many features that help them remain inside
the host without being removed.
Diagram: Parasitic Adaptations of Helminthes
PARASITIC ADAPTATIONS
│
┌───────────────────────┼────────────────────────┐
│ │ │
Morphological Physiological Reproductive
Adaptations Adaptations Adaptations
│ │ │
├─ Hooks & suckers ├─ Anaerobic respiration ├─ Large number of eggs
├─ Thick body covering ├─ Absorb food directly ├─ Hermaphroditism
├─ Flat body shape ├─ Reduced digestion ├─ Complex life cycle
└─ Reduced sense organs └─ High resistance └─ Multiple larval stages
Parasitic Adaptations of Helminthes
1. Strong Attachment Organs
The biggest challenge for a parasite is staying attached inside the host. Food moves
continuously through organs like the intestine, so the parasite could easily be washed away.
To solve this problem, helminthes possess:
Hooks
Suckers
Adhesive discs
For example, tapeworm (Taenia) has a head called the scolex, which bears four suckers and
hooks. These structures firmly attach the worm to the intestinal wall.
Importance:
Prevents the parasite from being removed.
Helps it remain in one place for a long time.
2. Thick Protective Body Covering
Inside the host, parasites are surrounded by digestive enzymes and immune cells that can
destroy them.
To protect themselves, helminthes possess:
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Thick cuticle
Tegument (special outer covering)
This covering protects them from:
Digestive juices
Chemicals
Immune attacks
Some parasites can even repair or renew this outer layer.
Importance:
Prevents damage.
Helps the parasite survive for many years.
3. Reduced or Absent Digestive System
Many helminthes do not need a complete digestive system because their host has already
digested the food.
For example:
Tapeworms have no mouth or intestine.
They absorb nutrients directly through their body surface.
This saves energy because they do not need to digest food themselves.
Importance:
Efficient nutrition.
Energy conservation.
4. Flat or Cylindrical Body Shape
Most helminthes have:
Long
Flat
Cylindrical
Flexible bodies
This body shape helps them:
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Fit inside narrow organs.
Move easily through the intestine or tissues.
Increase surface area for absorbing nutrients.
5. Reduction of Sense Organs
Since parasites live in a stable environment inside the host, they do not need well-
developed eyes or ears.
Therefore:
Eyes are absent.
Sense organs are poorly developed.
Nervous system is simple.
Importance:
Saves energy.
Resources are used for reproduction instead.
6. Anaerobic Respiration
There is very little oxygen inside the intestine.
Therefore, many helminthes perform:
Anaerobic respiration (respiration without oxygen).
This adaptation allows them to survive in oxygen-poor environments.
7. High Reproductive Capacity
Many eggs and larvae die before reaching a new host.
To overcome this loss, helminthes produce thousands or even millions of eggs.
Example:
Female Ascaris lays nearly 200,000 eggs every day.
Importance:
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Increases chances that at least a few offspring survive.
Ensures continuation of the species.
8. Hermaphroditism
Many helminthes possess both:
Male reproductive organs
Female reproductive organs
This condition is called hermaphroditism.
Advantages:
Self-fertilization is possible.
Reproduction can occur even if only one worm is present.
This greatly increases survival.
9. Complex Life Cycle
Many parasitic worms pass through several developmental stages before becoming adults.
Example:
Egg → Larva → Intermediate Host → Final Host → Adult Worm
Some parasites require:
Snails
Fish
Cattle
Mosquitoes
as intermediate hosts.
Importance:
Helps spread infection widely.
Increases chances of reaching suitable hosts.
10. Formation of Resistant Eggs and Cysts
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The eggs of helminthes possess:
Thick protective shells
Strong outer covering
These eggs can survive:
Heat
Cold
Dry conditions
Chemicals
Some larvae form cysts, which remain alive for months or even years until they enter a
suitable host.
11. High Resistance to Host Immunity
The host's immune system tries to kill parasites.
Helminthes avoid this by:
Changing their surface proteins.
Covering themselves with substances from the host.
Producing chemicals that suppress immune responses.
This allows them to remain inside the body for long periods.
12. Well-Developed Reproductive Organs
Although many body systems are reduced, the reproductive system is highly developed.
Large portions of the body are occupied by:
Ovaries
Testes
Uterus
Egg-producing organs
This ensures continuous production of offspring.
Summary Table
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Function
Attach firmly to host tissues
Protects against digestive enzymes and immunity
Absorbs already-digested food
Fits easily inside host organs
Saves energy
Survival without oxygen
Ensures survival of species
Allows reproduction even with a single worm
Helps spread to new hosts
Survive harsh external conditions
Avoids destruction by host
Produces many offspring
Conclusion
Parasitic helminthes have evolved a wide range of morphological, physiological, and
reproductive adaptations that allow them to live successfully inside their hosts. Features
such as hooks, suckers, a protective body covering, reduced digestive organs, anaerobic
respiration, enormous egg production, hermaphroditism, and complex life cycles help
them obtain food, avoid the host's defenses, reproduce efficiently, and spread from one
host to another. These remarkable adaptations make helminthes highly successful parasites
and explain why they can survive inside humans and animals for many years. Understanding
these adaptations is important for diagnosing, preventing, and controlling parasitic worm
infections.
8. Discuss in detail about circulatory system of Pheretima posthuma.
Ans: The circulatory system is one of the most important systems in the body of an
earthworm. It is responsible for transporting oxygen, nutrients, digested food, hormones,
and waste materials from one part of the body to another. Unlike humans, where the heart
pumps blood through arteries and veins, the earthworm has a closed circulatory system,
meaning the blood always flows inside blood vessels and never directly comes in contact
with body tissues.
This closed system helps the earthworm efficiently carry nutrients and oxygen throughout
its long body, allowing it to survive underground where oxygen levels are often low.
What is a Closed Circulatory System?
A closed circulatory system means that blood remains enclosed within a network of blood
vessels. It does not flow freely into body cavities.
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Advantages
Faster transportation of nutrients and oxygen.
Better control of blood flow.
Higher efficiency compared to an open circulatory system.
Maintains proper blood pressure.
This is why earthworms have a more advanced circulatory system than insects, which
possess an open circulatory system.
Main Parts of the Circulatory System
The circulatory system of Pheretima posthuma consists of:
1. Blood
2. Blood vessels
3. Hearts (Aortic arches)
Each part performs a specific function.
1. Blood
The blood of an earthworm is red in colour because it contains haemoglobin dissolved
directly in the blood plasma. Unlike humans, the haemoglobin is not enclosed inside red
blood cells (RBCs).
Blood contains:
Plasma
Haemoglobin
White blood cells (phagocytes)
Amoeboid cells
Functions of Blood
Carries oxygen.
Transports food to all body cells.
Removes carbon dioxide.
Carries nitrogenous wastes.
Helps fight infections.
Maintains internal balance.
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2. Blood Vessels
The earthworm possesses many blood vessels, but the important ones are:
A. Dorsal Blood Vessel
Present on the upper (dorsal) side of the intestine.
Thick and muscular.
Collects blood from the body.
Carries blood from the posterior end towards the anterior end (back → front).
Function: Acts mainly as a collecting vessel.
B. Ventral Blood Vessel
Present on the lower (ventral) side.
Lies beneath the digestive tract.
Carries blood from the anterior end towards the posterior end (front → back).
Function: Supplies oxygen and nutrients to different organs.
C. Sub-Neural Blood Vessel
Located below the nerve cord.
Carries blood towards the anterior side.
Connected with other vessels.
D. Lateral Oesophageal Hearts
These connect the dorsal vessel with the ventral vessel.
E. Supra-intestinal Blood Vessel
Located above the intestine.
Collects blood from intestinal walls.
Supplies nutrients to the dorsal vessel.
3. Hearts (Aortic Arches)
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Earthworms do not possess one large heart like humans.
Instead, they have five pairs of muscular hearts, also called aortic arches.
Location
They are situated around the oesophagus between the 7th and 11th body segments.
There are:
Four pairs of lateral hearts
One pair of lateral oesophageal hearts
Function
These hearts continuously pump blood between the dorsal and ventral blood vessels and
maintain blood circulation throughout the body.
Flow of Blood
The movement of blood in the earthworm follows a definite pattern.
Posterior Body
│
▼
Dorsal Blood Vessel
│
▼
Five Pairs of Hearts
│
▼
Ventral Blood Vessel
│
▼
Body Organs
│
▼
Capillaries
│
▼
Back to Dorsal Vessel
This continuous circulation ensures that every cell receives oxygen and nutrients.
How Does Oxygen Reach the Blood?
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Earthworms do not have lungs or gills.
Instead:
Their skin remains moist.
Oxygen dissolves in the moisture present on the skin.
Oxygen diffuses through the skin into blood capillaries.
Haemoglobin carries oxygen to all body tissues.
Similarly, carbon dioxide leaves the body through the moist skin.
This process is called cutaneous respiration.
Functions of the Circulatory System
The circulatory system performs several essential functions:
1. Transport of Oxygen
Carries oxygen absorbed through the skin to every body cell.
2. Transport of Food
Distributes digested nutrients from the intestine to all body parts.
3. Removal of Waste
Carries carbon dioxide and nitrogenous wastes to excretory organs (nephridia).
4. Hormone Transport
Moves hormones and other chemical messengers throughout the body.
5. Protection
White blood cells protect the earthworm against harmful microorganisms.
6. Maintaining Internal Balance
Helps regulate the internal environment and body functions.
Special Features of the Circulatory System
Closed circulatory system.
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Blood is always confined within vessels.
Blood is red due to dissolved haemoglobin.
No red blood cells are present.
Five pairs of hearts pump blood.
Blood flows continuously throughout the body.
Oxygen is absorbed through moist skin.
Simple Diagram
Dorsal Blood Vessel
↑
│
(Blood from Back)
│
-------------------------------
| Five Pairs of Hearts |
-------------------------------
│
▼
Ventral Blood Vessel
│
Blood supplied to all organs
│
Body Capillaries
│
▼
Returns to Dorsal Vessel
Easy Way to Remember
Imagine the earthworm as a small underground water pipeline system.
The dorsal blood vessel works like a main collecting pipeline, bringing blood toward
the front.
The five pairs of hearts act like powerful water pumps, pushing the blood forward.
The ventral blood vessel is the main supply pipeline, delivering oxygen and food to
every body part.
After supplying nutrients, the blood returns through smaller vessels to the dorsal
vessel, and the cycle repeats continuously.
This efficient closed system allows the earthworm to survive and remain active even while
living underground.
Conclusion
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The circulatory system of Pheretima posthuma is a closed, highly organized transport
system consisting of blood, blood vessels, and five pairs of muscular hearts. Blood flows
through the dorsal and ventral vessels, carrying oxygen, nutrients, hormones, and waste
materials to every part of the body. Since the earthworm breathes through its moist skin,
oxygen absorbed from the environment is transported by haemoglobin dissolved in the
plasma. This efficient circulation ensures proper nutrition, respiration, excretion, and overall
survival of the earthworm, making it an excellent example of a simple yet highly effective
circulatory system.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
have suggestions, feel free to share your feedback.