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GNDU Question Paper-2023
Bachelor of Computer Application (BCA) (Hons.)
1
st
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-I-B
[Biodiversity-1 (Protozoa to Annelida)|
Time Allowed: Three Hours Max. Marks:75
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
I. Explain detailed structure of Amoeba proteus.
II. Write in detail about asexual cycle of Plasmodium vivax
SECTION-B
III. Write in detail about microscopic organization of body wall of Sycon.
IV. Discuss asexual reproduction in Obelia.
SECTION-C
V. Write in detail about life cycle of Fasciola hepatica inside the host.
VI. Differentiate different types of proglottids in Taenia solium.
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SECTION-D
VII. Explain Nervous system of Ascaris in detail.
VIII. Write in detail about excretory system of Pheretima posthuma
GNDU Answer Paper-2023
Bachelor of Computer Application (BCA) (Hons.)
1
st
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-I-B
[Biodiversity-1 (Protozoa to Annelida)|
Time Allowed: Three Hours Max. Marks:75
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
I. Explain detailed structure of Amoeba proteus.
Ans: Amoeba proteus is a single-celled, microscopic organism that belongs to the kingdom
Protista. Although it consists of only one cell, this tiny organism performs all the life
processessuch as movement, feeding, respiration, digestion, excretion, and
reproductionjust like a complete animal. It lives mainly in freshwater ponds, lakes, and
slow-moving streams. The word "proteus" comes from a Greek word meaning "changing
shape," because the amoeba constantly changes its body shape while moving or capturing
food.
To understand the structure of Amoeba proteus, imagine a small jelly-like water balloon
that can stretch, shrink, and change its shape whenever needed. Unlike higher animals, it
has no fixed body shape and no cell wall. Its entire body is surrounded by a thin, flexible
membrane that allows it to change shape freely.
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Diagram of Amoeba proteus
Pseudopodium
↑
____/ \____
__/ \__
_/ \_
/ \
| Food Vacuole |
| (Food) |
| |
| ○ Nucleus |
| |
| Contractile |
| Vacuole |
| |
\ /
\__ __/
\_____________/
Outer Boundary = Cell Membrane
Inside = Cytoplasm (Ectoplasm + Endoplasm)
Detailed Structure of Amoeba proteus
1. Cell Membrane (Plasma Membrane)
The cell membrane is the outer covering of the amoeba. It is very thin, flexible, and living,
made mainly of proteins and lipids. Unlike plant cells, amoeba does not have a cell wall, so
the membrane alone forms the body's boundary.
Functions
Gives shape to the cell.
Protects the internal parts.
Controls the entry of food, water, and oxygen.
Allows waste materials to leave the cell.
Helps the amoeba change its shape.
Without this membrane, the amoeba would not be able to survive or control what enters
and leaves its body.
2. Cytoplasm
The cytoplasm is a jelly-like material present inside the cell membrane. It contains all the
important cell organelles and is divided into two regions.
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(a) Ectoplasm
Outer transparent layer.
Thick and clear.
Helps in forming pseudopodia.
Gives temporary support to the cell.
(b) Endoplasm
Inner granular layer.
Contains nucleus, food vacuoles, contractile vacuole, and other organelles.
Site where most metabolic activities occur.
Together, these two layers help the amoeba move, digest food, and perform other life
activities.
3. Nucleus
The nucleus is usually round or oval and lies within the endoplasm. It is enclosed by a
nuclear membrane and contains genetic material (DNA).
Functions
Controls all activities of the cell.
Regulates growth and metabolism.
Stores hereditary information.
Helps in reproduction by cell division.
The nucleus acts like the "brain" of the amoeba, directing every activity.
4. Pseudopodia ("False Feet")
The most interesting part of Amoeba proteus is its pseudopodia, meaning "false feet."
These are temporary finger-like projections formed by the movement of cytoplasm.
Functions
Help the amoeba move.
Capture food by surrounding it.
Assist in swallowing food through phagocytosis.
When food comes near, the pseudopodia surround it from all sides and form a food vacuole
where digestion begins.
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5. Food Vacuoles
Food vacuoles are temporary sacs formed after food is captured.
Functions
Store food.
Digest food using digestive enzymes.
Absorb nutrients into the cytoplasm.
Expel undigested food outside the cell.
They work much like the stomach of the amoeba.
6. Contractile Vacuole
The contractile vacuole is a clear, bubble-like structure found in freshwater amoeba.
Functions
Collects excess water entering the cell.
Removes extra water periodically.
Maintains water balance (osmoregulation).
Helps remove some waste products.
Without this vacuole, the amoeba could burst because freshwater constantly enters the cell
by osmosis.
7. Cytoplasmic Organelles
The cytoplasm also contains tiny organelles such as:
Mitochondria produce energy.
Ribosomes make proteins.
Endoplasmic reticulum transports materials.
Golgi bodies package and secrete substances.
These organelles help the amoeba perform all essential life processes.
How All Parts Work Together
Each part of the amoeba has a specific role, but they all work together.
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The cell membrane protects the cell and controls material exchange.
The pseudopodia help in movement and food capture.
The food vacuole digests the food.
The contractile vacuole removes excess water.
The cytoplasm serves as the medium where activities occur.
The nucleus controls and coordinates every function.
Even though Amoeba proteus has only one cell, it performs every life process efficiently,
showing that a single cell can function as a complete living organism.
Conclusion
Amoeba proteus is one of the simplest yet most fascinating unicellular organisms. Its body
consists of a cell membrane, cytoplasm (ectoplasm and endoplasm), nucleus,
pseudopodia, food vacuoles, contractile vacuole, and other cell organelles. Each structure
performs an important function, allowing the amoeba to move, obtain food, digest
nutrients, remove waste, maintain water balance, grow, and reproduce. Thus, Amoeba
proteus is an excellent example of how a single cell can perform all the functions necessary
for life, making it an important organism for studying basic cell biology.
II. Write in detail about asexual cycle of Plasmodium vivax
Ans: The asexual cycle of Plasmodium vivax is the part of the malaria parasite's life cycle
that takes place inside the human body. This stage is responsible for causing the symptoms
of malaria such as high fever, chills, headache, weakness, sweating, and anemia.
Think of the parasite as a tiny invader. It first enters the human body through the bite of an
infected female Anopheles mosquito. Once inside, it travels quietly to the liver, multiplies
rapidly, and then attacks the red blood cells. This repeated attack causes the typical malaria
fever that comes every 48 hours (tertian malaria).
Simple Diagram of the Asexual Cycle
Infected Female Anopheles Mosquito
│
▼
Sporozoites enter blood
│
▼
Liver
(Hepatic Schizogony - Multiplication)
│
Thousands of Merozoites
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│
▼
Red Blood Cells (RBCs)
│
Ring Stage (Young Trophozoite)
│
▼
Mature Trophozoite (Feeds on Hemoglobin)
│
▼
Schizont Formation
│
▼
RBC Bursts → Merozoites Released
│
▼
Infect New RBCs (Cycle Repeats Every 48 Hours)
Stages of the Asexual Cycle
1. Entry of Sporozoites into the Human Body
The asexual cycle begins when an infected female Anopheles mosquito bites a healthy
person.
During the bite, the mosquito injects sporozoites, which are the infectious stage of
the parasite.
These sporozoites quickly enter the bloodstream.
Within about 30 minutes, they reach the liver.
Key Point:
Sporozoite is the infective stage for humans.
2. Liver Stage (Pre-Erythrocytic or Hepatic Schizogony)
Inside the liver, each sporozoite enters a liver cell.
Here it grows larger and repeatedly divides many times.
This process is called schizogony, which means multiple division.
One sporozoite produces thousands of merozoites.
The liver cells finally burst.
These merozoites are released into the bloodstream.
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An important feature of Plasmodium vivax is that some parasites remain in the liver as
hypnozoites (dormant forms). These can become active months or even years later and
cause a relapse of malaria.
Key Point:
The liver stage increases the parasite's number without causing noticeable symptoms.
3. Red Blood Cell Stage (Erythrocytic Schizogony)
The released merozoites now enter the red blood cells (RBCs).
This stage causes the actual symptoms of malaria.
(a) Ring Stage
Inside the RBC, the merozoite changes into a young trophozoite, which looks like a tiny ring
under the microscope.
This is called the ring stage.
(b) Trophozoite Stage
The trophozoite grows by feeding on hemoglobin, the oxygen-carrying protein inside RBCs.
As it digests hemoglobin, it forms a dark pigment called hemozoin.
(c) Schizont Stage
The mature trophozoite divides repeatedly to form a schizont.
The schizont contains many new merozoites.
(d) Rupture of Red Blood Cells
Finally, the infected RBC bursts.
This releases:
Many new merozoites
Hemozoin pigment
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Toxic substances
The released merozoites infect fresh RBCs, repeating the cycle again and again.
Why Does Fever Occur?
Every time infected RBCs burst, they release parasites and toxic substances into the
bloodstream.
The body's immune system reacts to these substances, producing:
High fever
Chills
Shivering
Sweating
Headache
Body pain
Since Plasmodium vivax completes this RBC cycle every 48 hours, the fever also appears
every 48 hours. This is known as benign tertian malaria.
Importance of the Asexual Cycle
The asexual cycle is important because:
It multiplies the parasite rapidly inside the human body.
It destroys red blood cells, causing anemia.
It is responsible for all major symptoms of malaria.
It helps the parasite spread throughout the bloodstream.
Some parasites later develop into gametocytes, which are taken up by another
mosquito to continue the life cycle.
Important Terms
Term
Meaning
Sporozoite
Infective stage injected by the mosquito into humans
Schizogony
Asexual multiplication by repeated cell division
Merozoite
Form released from liver or RBCs that infects new red blood cells
Trophozoite
Feeding and growing stage inside RBCs
Schizont
Stage containing many newly formed merozoites
Hypnozoite
Dormant liver stage in P. vivax that causes relapse
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Hemozoin
Pigment formed after digestion of hemoglobin
Conclusion
The asexual cycle of Plasmodium vivax occurs entirely in the human host and consists of
two major phases: liver schizogony and red blood cell schizogony. After an infected female
Anopheles mosquito injects sporozoites, they multiply first in the liver and then repeatedly
inside red blood cells. The bursting of infected RBCs every 48 hours causes the characteristic
attacks of malaria, including fever, chills, sweating, and weakness. A unique feature of P.
vivax is the presence of hypnozoites in the liver, which can remain dormant and later
reactivate, leading to repeated episodes (relapses) of malaria. Understanding this cycle is
essential because it explains how the parasite survives, multiplies, produces disease, and
spreads from one host to another.
SECTION-B
III. Write in detail about microscopic organization of body wall of Sycon.
Ans: The body wall of Sycon is made up of different layers of cells that work together to
protect the animal, help it obtain food, and allow water to flow through its body. Since
Sycon belongs to the phylum Porifera (sponges), its body wall is porous and specially
adapted for filter feeding.
Think of the body wall of Sycon like a three-layered sponge filter. The outer layer protects
the sponge, the middle layer provides support and carries different cells, and the inner layer
helps in feeding. Together, these layers allow water carrying oxygen and tiny food particles
to enter the sponge, while waste water leaves through the top opening called the osculum.
Microscopic Structure of the Body Wall
Outside Water
│
┌────────────────────┐
│ Pinacoderm │ ← Outer Layer
├────────────────────┤
│ Mesohyl │ ← Middle Layer
│ (Amoebocytes & │
│ Spicules) │
├────────────────────┤
│ Choanoderm │ ← Inner Layer
│ (Choanocytes) │
└────────────────────┘
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│
Spongocoel
│
Osculum
1. Outer Layer Pinacoderm
The outermost layer of the body wall is called the Pinacoderm. It is made up of flat, thin
cells called pinacocytes.
Functions:
Protects the sponge from external damage.
Gives shape to the body.
Some cells form tiny openings called ostia, through which water enters the sponge.
Easy to remember:
Pinacoderm = Protective outer skin.
2. Middle Layer Mesohyl
Between the outer and inner layers lies a jelly-like layer called the Mesohyl.
This layer contains many important cells:
(a) Amoebocytes (Archaeocytes)
Move freely within the mesohyl.
Digest and distribute food.
Carry nutrients to other cells.
Help in repair and regeneration.
Can form reproductive cells.
(b) Scleroblasts
Produce spicules, the tiny needle-like skeletal structures.
Spicules provide support and protection.
(c) Collagen Fibres
Give strength and flexibility to the body wall.
Easy to remember:
Mesohyl = Support and transport centre.
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3. Inner Layer Choanoderm
The innermost layer is called the Choanoderm. It is made up of choanocytes, also known as
collar cells.
Each choanocyte has:
A flagellum (whip-like structure)
A collar made of tiny projections.
Functions:
The flagellum beats continuously, creating water currents.
The collar traps tiny food particles.
Food is digested inside the cell.
Helps in respiration and removal of waste because water is always flowing.
Easy to remember:
Choanoderm = Feeding layer.
Water Flow Through the Body Wall
The body wall is specially designed for water circulation.
The path of water is:
Ostia → Incurrent Canal → Prosopyle → Radial Canal (Choanocytes) → Apopyle →
Spongocoel → Osculum
As water flows:
Oxygen enters.
Food particles are captured by choanocytes.
Carbon dioxide and wastes leave the body.
This continuous water flow is the key to the survival of Sycon.
Importance of the Microscopic Organization
The microscopic organization of the body wall helps Sycon in many ways:
Protects the body from injury.
Provides skeletal support through spicules.
Creates continuous water currents.
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Captures and digests food efficiently.
Helps in respiration and excretion.
Repairs damaged tissues and assists in reproduction.
Quick Revision Table
Layer
Main Cells
Main Function
Pinacoderm
Pinacocytes
Protection and body covering
Mesohyl
Amoebocytes,
Scleroblasts
Support, food transport, repair, skeleton
formation
Choanoderm
Choanocytes
Water current, food capture, digestion
Conclusion
The microscopic organization of the body wall of Sycon is simple but highly efficient. It
consists of three layersthe Pinacoderm, Mesohyl, and Choanoderm. Each layer has
specialized cells that perform different functions such as protection, support, feeding,
respiration, excretion, and reproduction. The coordinated action of these layers allows
Sycon to survive by continuously filtering water for food and oxygen. Thus, the body wall is
not just a protective covering but a well-organized system that performs almost all the
essential life processes of the sponge.
IV. Discuss asexual reproduction in Obelia.
Ans: Introduction
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Obelia is a small marine animal that belongs to the phylum Cnidaria. It lives in seawater and
forms branched colonies that look like tiny underwater plants. Even though the colony
appears to be one organism, it is actually made up of many small, connected individuals
called zooids.
One of the most interesting features of Obelia is that it reproduces asexually. In asexual
reproduction, only one parent is needed, and no fusion of male and female gametes takes
place. The offspring produced are genetically identical (clones) to the parent colony. This
method helps Obelia multiply rapidly and spread over a large area in a short time.
What is Asexual Reproduction?
Asexual reproduction is a process in which a new organism develops from a single parent
without fertilization. Since no gametes are involved, the offspring are exact copies of the
parent.
In Obelia, asexual reproduction mainly occurs through budding.
Colony Structure of Obelia
The Obelia colony contains two important types of zooids:
1. Hydranths (Feeding Polyps)
o Capture food using tentacles.
o Digest food and provide nutrition to the whole colony.
2. Gonangia (Reproductive Polyps)
o Do not capture food.
o Their main function is reproduction.
o Produce tiny buds called medusa buds.
These zooids remain connected by a common living tube called the coenosarc, through
which nutrients are shared throughout the colony.
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Asexual Reproduction by Budding
The steps of asexual reproduction in Obelia are:
Step 1: Formation of Gonangium
Special reproductive zooids called gonangia develop on the colony. These are covered by a
protective layer known as the gonotheca.
Step 2: Development of Medusa Buds
Inside the gonangium, many small buds begin to grow. These are called medusa buds
because they develop into tiny free-swimming medusae.
Step 3: Growth of Buds
Each bud gradually develops important body parts such as:
Umbrella-shaped body
Mouth
Tentacles
Sense organs
The buds receive nourishment from the parent colony through the coenosarc.
Step 4: Release of Medusae
When fully developed, the young medusae detach from the gonangium and swim freely in
the sea.
Step 5: Further Reproduction
The released medusae later reproduce sexually, producing eggs and sperms. After
fertilization, a larva called the planula is formed, which settles on a surface and develops
into a new Obelia colony.
Thus, budding is the asexual phase, while the medusa stage carries out sexual
reproduction.
Simple Flow Diagram
Parent Obelia Colony
│
▼
Gonangium Forms
│
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▼
Medusa Buds Develop
│
▼
Young Medusae Released
│
▼
Free-Swimming Medusae
│
Sexual Reproduction
│
▼
Planula Larva
│
▼
New Obelia Colony
Labeled Diagram
Obelia Colony
Hydranth
(Feeding Polyp)
/\
Tentacles
|
|
------------------------|---------------- Stem
|
Gonangium
(Reproductive Polyp)
______________
| Medusa Buds |
| ○ ○ ○ ○ |
|______________|
|
Young Medusae
Released Out
Importance of Asexual Reproduction in Obelia
It allows rapid multiplication of colonies.
Only one parent is required.
It saves energy because fertilization is not needed.
All offspring are genetically identical, preserving successful characteristics.
It helps Obelia quickly colonize new areas in the sea.
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Key Points for Exams
Obelia belongs to the phylum Cnidaria.
Asexual reproduction occurs by budding.
Gonangia are reproductive zooids.
Medusa buds develop inside the gonangium.
Young medusae are released into the water.
Medusae later reproduce sexually, forming a planula larva.
The planula develops into a new Obelia colony.
Conclusion
Asexual reproduction in Obelia is a simple and efficient process carried out through
budding. Specialized reproductive polyps called gonangia produce medusa buds, which
grow into free-swimming medusae. This method enables Obelia colonies to increase their
numbers quickly without the need for fertilization. Later, the medusae perform sexual
reproduction, completing the life cycle. The combination of asexual and sexual reproduction
makes Obelia highly successful in surviving and spreading in marine environments.
SECTION-C
V. Write in detail about life cycle of Fasciola hepatica inside the host.
Ans: Introduction
Fasciola hepatica, commonly known as the sheep liver fluke, is a parasitic flatworm
(trematode) that mainly infects sheep, cattle, goats, and sometimes humans. It causes a
disease called fascioliasis, which mainly affects the liver and bile ducts. The parasite has a
complex life cycle involving two hosts:
Primary (Definitive) Host: Sheep, cattle, goats, and humans
Intermediate Host: Freshwater snail
The question asks specifically about the life cycle inside the host (definitive host), beginning
when the infective stage enters the body and ending when eggs are released.
Simple Diagram of the Life Cycle Inside the Host
Metacercariae (infective stage)
│
▼
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Eaten with contaminated water or aquatic plants
│
▼
Excystation in Small Intestine
│
▼
Larvae penetrate Intestinal Wall
│
▼
Move through Abdominal Cavity
│
▼
Enter Liver
│
▼
Migrate through Liver Tissue
│
▼
Reach Bile Ducts
│
▼
Adult Flukes Develop
│
▼
Eggs Produced
│
▼
Eggs pass through bile → intestine → feces
Detailed Explanation
1. Entry of the Infective Stage
The infective stage of Fasciola hepatica is called the metacercaria. These are tiny cysts
attached to aquatic plants like watercress or floating in contaminated water.
When a human or grazing animal eats these infected plants or drinks contaminated water,
the metacercariae enter the digestive system.
Key Point:
Infective Stage: Metacercaria
Mode of Infection: Eating contaminated aquatic plants or drinking contaminated
water
2. Excystation in the Small Intestine
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After reaching the duodenum (small intestine), the protective cyst wall dissolves because of
digestive enzymes.
This process is called excystation.
A young larva, known as the juvenile fluke, comes out from the cyst.
Meaning of Excystation:
Removal of the protective cyst so that the young parasite becomes active.
3. Penetration of the Intestinal Wall
The juvenile fluke uses its strong body and enzymes to pierce the intestinal wall.
Instead of staying inside the intestine, it leaves the digestive tract and enters the abdominal
cavity.
This migration may damage tissues and cause inflammation.
4. Migration to the Liver
From the abdominal cavity, the juvenile parasite travels to the surface of the liver.
It then penetrates the liver capsule and enters the liver tissue.
Inside the liver, it moves through the liver cells while feeding on tissue and blood.
This migration usually lasts 68 weeks.
During this stage:
Liver cells are damaged.
Bleeding may occur.
The liver becomes swollen.
The host may experience fever, abdominal pain, and weakness.
5. Development in the Bile Ducts
After moving through the liver tissue, the parasite reaches the bile ducts, which carry bile
from the liver.
Here, the juvenile develops into a fully mature adult fluke.
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Adult flukes measure about 23 cm in length and have leaf-shaped flattened bodies.
They attach to the bile ducts using oral and ventral suckers, feeding on bile and blood.
6. Reproduction
Adult Fasciola hepatica are hermaphrodites, meaning each worm has both male and
female reproductive organs.
They usually reproduce by cross-fertilization, although self-fertilization may also occur.
Each adult fluke lays thousands of eggs every day.
7. Eggs Leave the Host
The eggs pass from the bile ducts into the intestine through the bile.
Finally, they leave the body through the feces.
Once the eggs reach fresh water, the next part of the life cycle (outside the host and inside
the snail) begins.
Important Concepts Asked in the Question
Definitive Host
The animal or human in which the adult parasite lives and reproduces sexually.
Examples:
Sheep
Cattle
Goat
Human
Intermediate Host
The host in which larval development occurs.
Example:
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Freshwater snail
Infective Stage
The stage capable of infecting the definitive host.
Answer: Metacercaria
Habitat in the Host
Adult Fasciola hepatica lives in the:
Bile ducts of the liver
Disease Caused
Fascioliasis (Liver Fluke Disease)
Symptoms include:
Fever
Abdominal pain
Enlarged liver
Jaundice
Weakness
Digestive problems
Quick Revision Table
Stage
What Happens?
Metacercaria
Infective cyst enters the body through contaminated plants or water
Excystation
Larva comes out of the cyst in the small intestine
Penetration
Larva pierces the intestinal wall
Migration
Travels through the abdominal cavity to the liver
Liver Stage
Moves through liver tissue, causing damage
Adult Stage
Becomes an adult in the bile ducts
Reproduction
Produces thousands of eggs
Egg Release
Eggs pass into the intestine and leave the body through feces
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Conclusion
The life cycle of Fasciola hepatica inside the host begins when the metacercaria is
swallowed with contaminated water or aquatic plants. In the small intestine, it undergoes
excystation, releasing a juvenile fluke that penetrates the intestinal wall and migrates to the
liver. The parasite travels through the liver tissue, causing damage, before settling in the
bile ducts, where it matures into an adult. Adult flukes reproduce and lay thousands of eggs,
which pass through the bile into the intestine and are finally excreted in the feces. This
completes the host phase of the life cycle. Understanding each stage is important because it
explains how the parasite spreads, causes disease, and why preventing contamination of
food and water is essential for controlling fascioliasis.
VI. Differentiate different types of proglottids in Taenia solium.
Ans: Introduction
Taenia solium, commonly called the pork tapeworm, is a long, flat parasitic worm that lives
inside the small intestine of humans. Imagine it as a long train. The head (scolex) is like the
engine, while the body is made up of many small compartments or coaches. These
compartments are called proglottids.
Each proglottid has a different job depending on its stage of development. As new segments
are formed near the head, the older ones move backward and become more mature.
Therefore, the body of Taenia solium contains three different types of proglottids:
1. Immature proglottids
2. Mature proglottids
3. Gravid proglottids
Understanding these three types is easy if you think of them as young, adult, and pregnant
stages of the same segment.
1. Immature Proglottids
These are the youngest segments and are located just behind the scolex (head).
Characteristics
Small and short.
Wider than they are long.
Reproductive organs are not yet developed.
Mainly responsible for growth.
New segments are continuously formed here.
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Function
Their main job is to grow and develop into mature segments.
Easy Memory Tip:
Immature = Infant Stage
They are still growing and cannot reproduce.
2. Mature Proglottids
These are found in the middle region of the tapeworm.
Characteristics
Larger than immature segments.
Fully developed male and female reproductive organs are present.
Hermaphrodite (contains both sexes in one segment).
Fertilization takes place here.
Function
Their main role is reproduction by producing eggs.
Easy Memory Tip:
Mature = Adult Stage
They are capable of reproduction.
3. Gravid Proglottids
These are the oldest segments, present at the posterior end of the worm.
Characteristics
Longer than broad.
Reproductive organs disappear because the uterus becomes filled with eggs.
Uterus contains thousands of fertilized eggs.
Detach from the worm and pass out with human feces.
Function
Their purpose is to spread the parasite by releasing eggs into the environment.
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Easy Memory Tip:
Gravid = Pregnant Stage
These segments are completely filled with eggs.
Simple Diagram
Scolex
(Head)
│
▼
┌─────────────────────────────────────────────────────────────
┐
│ Immature │ Immature │ Mature │ Mature │ Gravid │ Gravid │
│ (Young) │ (Young) │ (Adult)│ (Adult)│ (Eggs) │ (Eggs) │
└─────────────────────────────────────────────────────────────
┘
Development Direction →
Young → Adult → Egg-filled
Difference Between the Three Types of Proglottids
Immature Proglottid
Mature Proglottid
Gravid Proglottid
Near scolex
Middle part
Posterior end
Small
Medium
Largest and longest
Absent or
undeveloped
Fully developed
Degenerated
None
Few developing
eggs
Thousands of fertilized
eggs
Growth
Reproduction
Egg dispersal
Young
Adult
Pregnant
Easy Story to Remember
Imagine a school:
Immature proglottids are like students who are still learning and growing.
Mature proglottids are like working adults who can start a family.
Gravid proglottids are like parents carrying babies, whose main job is to produce
and spread the next generation.
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This is exactly how the segments of Taenia solium developfrom young → reproductive →
egg-filled.
Key Points for Exams
Taenia solium has a body made of many proglottids.
Proglottids are of three types: immature, mature, and gravid.
Immature proglottids are found near the scolex and help in growth.
Mature proglottids contain both male and female reproductive organs and perform
reproduction.
Gravid proglottids are filled with fertilized eggs and are released with human feces
to continue the parasite's life cycle.
Conclusion
The three types of proglottids in Taenia solium represent the life stages of each body
segment. Immature proglottids grow and develop, mature proglottids reproduce by
forming eggs, and gravid proglottids store thousands of fertilized eggs and detach from the
worm to spread infection. Remember the simple sequence Young → Adult → Pregnant, and
you can easily understand and differentiate all three types of proglottids in Taenia solium.
SECTION-D
VII. Explain Nervous system of Ascaris in detail.
Ans: The nervous system of Ascaris is the control center of its body. Just as the human brain
and nerves help us think, move, and respond to our surroundings, Ascaris also has a simple
but efficient nervous system that performs similar basic functions. Although Ascaris is only a
parasitic roundworm, its nervous system is well-organized enough to help it survive inside
the intestine of its host.
Unlike humans, Ascaris does not have a true brain or spinal cord. Instead, it has a nerve
ring and several long nerve cords that work together to control all body activities.
What is the Nervous System?
The nervous system is a network of nerve cells (neurons) that receives information from the
environment, processes it, and sends commands to different parts of the body. It helps an
organism:
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Detect changes in its surroundings.
Control movement.
Coordinate body organs.
Respond to stimuli like touch and chemicals.
In Ascaris, the nervous system is simple but highly effective for its parasitic lifestyle.
Main Parts of the Nervous System of Ascaris
1. Circumpharyngeal Nerve Ring (Brain-like Structure)
The most important part of the nervous system is the circumpharyngeal nerve ring, also
called the nerve ring.
It surrounds the pharynx (muscular food pipe) near the mouth.
It acts like the brain of Ascaris.
It receives information from sensory organs.
It sends nerve impulses to the entire body.
Although it is much simpler than the human brain, it is the main coordinating center of the
worm.
2. Longitudinal Nerve Cords
From the nerve ring arise six long nerve cords that extend along the length of the body.
The most important are:
One dorsal nerve cord (on the back)
One ventral nerve cord (on the belly side)
Two lateral nerve cords
Two smaller subdorsal cords
These nerve cords carry messages between the nerve ring and different body muscles.
Functions:
Control movement.
Coordinate muscle contractions.
Help in locomotion.
Control reproductive organs and digestive movements.
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3. Ganglia
The nerve ring contains groups of nerve cells called ganglia.
Ganglia work like small processing centers.
Different ganglia include:
Dorsal ganglion
Ventral ganglion
Lateral ganglia
These ganglia help coordinate nerve impulses before sending them throughout the body.
4. Peripheral Nerves
Many small nerves branch out from the longitudinal nerve cords.
These nerves reach:
Body muscles
Sense organs
Reproductive organs
Digestive organs
They allow different parts of the body to communicate with the nervous system.
Sense Organs Associated with the Nervous System
Although Ascaris has no eyes or ears, it possesses simple sensory organs.
Amphids
Located near the mouth.
Detect chemicals present in the surroundings.
Help the worm locate suitable environments inside the host.
Phasmids
Found near the tail region.
Function as sensory receptors.
Help detect changes in the environment.
Tactile Papillae
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Tiny projections around the mouth.
Sensitive to touch.
Help the worm recognize obstacles.
How Does the Nervous System Work?
The nervous system works in a very organized way.
1. Sense organs detect changes.
2. Information travels to the nerve ring.
3. The nerve ring processes the information.
4. Signals travel through nerve cords.
5. Muscles receive commands.
6. The worm moves or reacts accordingly.
For example:
If Ascaris touches the wall of the intestine, its tactile receptors send a signal to the nerve
ring. The nerve ring immediately sends messages through the ventral and dorsal nerve
cords, causing the body muscles to contract and change direction.
Functions of the Nervous System of Ascaris
The nervous system performs several important functions:
Controls body movement.
Coordinates muscle contractions.
Receives sensory information.
Controls feeding movements.
Regulates reproductive activities.
Helps respond to touch and chemicals.
Maintains coordination between different organs.
Helps the worm survive inside the host.
Simple Diagram of the Nervous System of Ascaris
Mouth
│
┌───────────┐
│ Nerve Ring│
└───────────┘
/ | \
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/ | \
Dorsal Cord | Ventral Cord
│ | │
│ | │
Lateral Cords (Both Sides)
│ │
│ │
Small Peripheral Nerves
│
Body Muscles
Key Features (Exam Points)
Ascaris has a simple nervous system.
It does not have a true brain.
The circumpharyngeal nerve ring acts as the main control center.
Six longitudinal nerve cords arise from the nerve ring.
The dorsal and ventral nerve cords are the largest and most important.
Ganglia help process nerve signals.
Amphids and phasmids are the main sensory organs.
The nervous system controls movement, feeding, sensation, and coordination.
Conclusion
The nervous system of Ascaris is simple when compared with higher animals, yet it is
perfectly suited to the worm's parasitic lifestyle. Instead of a complex brain, Ascaris uses a
circumpharyngeal nerve ring connected to longitudinal nerve cords to control all body
functions. Sensory organs such as amphids, phasmids, and tactile papillae help it detect
touch and chemicals in its environment. Together, these structures enable the worm to
move, feed, reproduce, and survive efficiently inside its host. Even with its basic
organization, the nervous system performs all the essential tasks required for the successful
life of this parasitic roundworm.
VIII. Write in detail about excretory system of Pheretima posthuma.
Ans: The excretory system of Pheretima posthuma (the common Indian earthworm) is a
system that removes waste materials from the body and also helps maintain the right
balance of water and salts. Just like humans use kidneys to filter blood and produce urine,
earthworms use tiny tube-like organs called nephridia to clean their body.
Imagine the earthworm's body as a small city. Every day, waste is produced by the cells. If
this waste is not removed, the body becomes unhealthy. Therefore, the earthworm has
thousands of tiny cleaning units called nephridia, which continuously collect and remove
harmful waste.
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What is Excretion?
Excretion is the process of removing harmful metabolic waste such as ammonia, urea,
excess water, and salts from the body.
Importance of Excretion
Removes poisonous wastes.
Maintains water balance (osmoregulation).
Maintains salt and ion balance.
Keeps body cells healthy.
Excretory Organs Nephridia
The excretory organs of Pheretima posthuma are called nephridia.
Nephridia are long, coiled, microscopic tubes that filter waste from the body fluid and
remove it from the body.
An adult earthworm contains thousands of nephridia distributed throughout its body.
Types of Nephridia
There are three types of nephridia in Pheretima posthuma.
1. Pharyngeal Nephridia
Present in the 4th, 5th and 6th body segments.
Arranged in clusters.
Open into the pharynx and alimentary canal.
Remove wastes into the digestive tract.
2. Septal Nephridia
Present from the 15th segment to the last segment.
Attached to the intersegmental septa.
Very large and numerous.
Open into the intestine.
These are called enteronephric nephridia because they discharge waste into the intestine.
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3. Integumentary Nephridia
Present in almost all body segments except the first two.
Found in the body wall.
Very small but extremely numerous.
Open directly outside through tiny pores.
These are called exonephric nephridia because they remove waste directly outside the
body.
Diagram of Nephridia Distribution
Head
|
| Segments 46
| [Pharyngeal Nephridia]
|
|-----------------------------
| Body Wall
| [Integumentary Nephridia]
|
| Segment 15 onwards
| [Septal Nephridia]
|
Tail
Structure of a Nephridium
Each nephridium consists of:
Nephrostome
│
Coiled Tubule
│
Loop
│
Terminal Duct
│
Nephridiopore / Intestine
Parts Explained
1. Nephrostome
Funnel-shaped opening.
Collects body fluid containing waste.
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2. Coiled Tubule
Long twisted tube.
Filters useful substances.
Reabsorbs water and salts.
3. Terminal Duct
Carries the remaining waste.
4. Nephridiopore
Tiny opening through which waste leaves the body (in exonephric nephridia).
Working (Mechanism) of Nephridia
The working of nephridia is similar to the human kidney.
Step 1
Body fluid carrying waste enters the nephrostome.
Step 2
The fluid passes through the coiled tubule.
Step 3
Useful substances like:
Water
Salts
Nutrients
are reabsorbed back into the body.
Step 4
The remaining waste becomes concentrated.
Step 5
The waste is discharged:
Outside the body (integumentary nephridia), or
Into the intestine (septal and pharyngeal nephridia).
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Enteronephric and Exonephric Nephridia
Enteronephric
Waste enters the intestine before leaving the body.
Examples:
Septal nephridia
Pharyngeal nephridia
Exonephric
Waste leaves the body directly through pores.
Example:
Integumentary nephridia
Nitrogenous Waste
The earthworm removes different nitrogenous wastes depending on environmental
conditions:
Ammonia mainly when enough moisture is available.
Urea when conditions are drier to conserve water.
Thus, Pheretima posthuma can be ammonotelic (excreting ammonia) or ureotelic (excreting
urea), depending on its surroundings.
Osmoregulation
Besides excretion, nephridia also perform osmoregulation, which means maintaining the
proper balance of:
Water
Salts
Body fluids
This prevents dehydration or excess water accumulation.
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Functions of the Excretory System
1. Removes metabolic waste products.
2. Eliminates nitrogenous wastes.
3. Maintains water balance.
4. Regulates salt concentration.
5. Prevents accumulation of toxic substances.
6. Maintains a stable internal environment (homeostasis).
Summary
The excretory system of Pheretima posthuma is made up of thousands of nephridia, which
act like tiny kidneys. They filter body fluids, remove harmful wastes, conserve useful water
and salts, and help maintain the body's internal balance. There are three types of
nephridiapharyngeal, septal, and integumentaryeach located in different parts of the
body and serving specific roles. Together, these organs keep the earthworm healthy by
continuously cleaning its internal environment and regulating water and salt levels.
Exam Points to Remember
Excretory organ: Nephridia
Types: Pharyngeal, Septal, Integumentary
Pharyngeal nephridia: Segments 46
Septal nephridia: From 15th segment onwards
Integumentary nephridia: Body wall (except first two segments)
Enteronephric: Septal and Pharyngeal
Exonephric: Integumentary
Main functions: Excretion and osmoregulation
Nitrogenous wastes: Ammonia and urea (depending on environmental conditions)
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