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GNDU Question Paper-2021

Ba/Bsc 3

Semester

ZOOLOGY : Paper – Zoo-III-B :

[(Biodiversity-III)(Chordates)]

Time Allowed: Three Hours Maximum 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 the following drawing relevant diagrams:

(A) Structure of Pharynx in Herdmania.

(B) External morphology of Herdmania (after removal of text).

2. Give an account of the circulatory system of Branchiostoma.

SECTION-B

3. Describe respiration in Labeo rohita.

4. Explain the following drawing relevant diagrams:

(A) External characters of Petromyzon.

(B) Female urinogenital system of Labeo rohita.

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SECTION-C

5. Explain the structure of heart in Uromastix.

6. Describe the following drawing relevant diagrams:

(A) Male urinogenital system in Rana tigrina.

(B) Structure of inner ear in Uromastix.

SECTION-D

1. Describe different kinds of feathers in Columba livia.

8. Explain the following drawing relevant diagrams:

(A) Structure of mammalian lung.

(B) Structure of kidney in rat.

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GNDU Answer Paper-2021

Ba/Bsc 3

Semester

ZOOLOGY : Paper – Zoo-III-B :

[(Biodiversity-III)(Chordates)]

Time Allowed: Three Hours Maximum 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 the following drawing relevant diagrams:

(A) Structure of Pharynx in Herdmania.

(B) External morphology of Herdmania (after removal of text).

Ans: Herdmania: An Overview

Herdmania is a genus of marine invertebrates belonging to the subphylum Tunicata, which

includes animals commonly known as "sea squirts." These creatures are important because

they are chordates, like vertebrates, but represent a simpler and more primitive form.

Herdmania is found in shallow waters attached to rocks, and its body is enclosed in a tough

outer covering called a "tunic."

In this detailed explanation, we will focus on two key aspects:

• Structure of the Pharynx in Herdmania

• External Morphology of Herdmania

Both of these structures are fundamental to understanding Herdmania’s biology and role in the

marine ecosystem.

(A) Structure of Pharynx in Herdmania

The pharynx in Herdmania is a critical organ involved in respiration and feeding. It is part of the

digestive system but also plays a significant role in the animal's filter-feeding mechanism. Here

is a detailed explanation of its structure and function:

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1. General Anatomy of the Pharynx

• The pharynx in Herdmania is a large sac-like structure that occupies most of the body

cavity.

• It opens to the mouth at the anterior end and connects to the esophagus at the

posterior end.

• The primary function of the pharynx is to filter food particles from water that enters

through the animal's siphons.

2. Pharyngeal Slits

• The walls of the pharynx are perforated by numerous small openings called pharyngeal

slits or stigmata. These slits are lined with cilia, tiny hair-like structures that help move

water through the slits.

• Water enters the pharynx through the mouth, passes through the pharyngeal slits, and

exits into a surrounding chamber called the atrium.

• This arrangement allows Herdmania to filter plankton and small food particles from the

water.

3. Endostyle

• The endostyle is a glandular structure that runs along the ventral side (bottom) of the

pharynx.

• It secretes mucus that helps trap food particles in the water as it passes through the

pharyngeal slits.

• The endostyle also produces iodine, a substance that is important for various metabolic

functions.

• The mucus-covered food particles are then moved by cilia to the dorsal side (top) of the

pharynx, where they are transported to the esophagus for digestion.

4. Branchial Basket

• The pharynx forms a structure called the branchial basket, which helps support the

pharyngeal slits and maintain the structure of the pharynx.

• The branchial basket is reinforced by a network of cartilaginous rods called gill bars or

stigmatal bars.

• These bars provide structural support to the pharyngeal slits and help keep them open

for water flow.

5. Function of the Pharynx

• The pharynx is responsible for both respiration and feeding. Water enters through the

incurrent siphon, passes through the pharyngeal slits where oxygen is absorbed, and

exits through the excurrent siphon.

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• At the same time, food particles trapped in the mucus are directed towards the

esophagus for digestion.

6. Respiratory Function

• The pharyngeal slits allow oxygen to diffuse from the water into the bloodstream. The

water that passes through the slits enters the atrial cavity, from which it is expelled

through the excurrent siphon.

• This dual role of respiration and feeding is typical of filter-feeding organisms like

Herdmania.

Diagrams of Pharynx in Herdmania:

1. A drawing showing the branchial basket with the endostyle at the bottom and

pharyngeal slits perforating the walls of the pharynx.

2. Cilia along the pharyngeal slits, demonstrating how food particles are trapped and

passed to the digestive system.

(B) External Morphology of Herdmania

1. General Appearance

• Herdmania has a sack-like body that is covered by a tough outer layer known as the

tunic. This structure gives it protection from predators and the environment.

• The body is relatively immobile and is attached to a substrate such as rocks or coral. It

resembles a cylindrical bag or barrel, which is where the name "sea squirt" comes from.

2. Siphons

• Herdmania has two siphons, an incurrent siphon (oral siphon) and an excurrent siphon

(atrial siphon).

o The incurrent siphon is larger and located at the anterior end. This is where

water enters the body.

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o The excurrent siphon is smaller and located near the posterior end. This is where

water, after being filtered, exits the body.

• Both siphons have a ring of small tentacles or papillae around them, which help detect

water flow and protect the openings.

3. Tunic

• The tunic is the outer covering of Herdmania’s body and is composed of a substance

called tunicin, which is similar to cellulose found in plants.

• The tunic is tough and leathery, serving as a protective layer that shields the animal

from external damage.

• The tunic also contains openings for the siphons, which protrude from it.

4. Attachment to Substrate

• Herdmania attaches itself to rocks or other hard surfaces using the basal part of its

body. This is done through root-like projections that help anchor the animal to the

substrate.

• This sedentary lifestyle makes it dependent on water currents to bring food and oxygen

to its body.

5. Musculature

• Beneath the tunic is a layer of muscles that allows Herdmania to contract its body. This

contraction helps expel water forcefully through the excurrent siphon, a behavior that

gave rise to the name "sea squirt."

• The muscular system is not well-developed because Herdmania is mostly immobile, but

the siphonal muscles play an important role in regulating water flow.

6. Internal Arrangement

• Inside the body, the pharynx occupies the largest portion of the space. It is surrounded

by the atrium, a cavity through which filtered water passes before being expelled.

• The digestive system includes a simple tube that runs from the mouth to the stomach,

where food is digested, and the waste is expelled through the anus, located near the

excurrent siphon.

7. Circulatory System

• The circulatory system in Herdmania is simple, with a heart located near the esophagus.

The heart pumps blood in two directions, forward and backward, alternating

periodically.

• Blood circulates through vessels and sinuses in the pharyngeal region, where gas

exchange occurs.

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8. Nervous System

• Herdmania has a rudimentary nervous system, consisting mainly of a nerve ganglion

located between the siphons.

• There are no complex sensory organs, but the siphonal tentacles have sensory

capabilities to detect water flow and external stimuli.

Diagrams of External Morphology of Herdmania:

1. A labeled diagram of Herdmania showing the incurrent siphon and excurrent siphon,

along with the tunic and attachment to substrate.

2. An internal view showing the arrangement of the pharynx, digestive system, and

circulatory system.

Conclusion

Herdmania, though simple in appearance, possesses a highly specialized structure suited to its

environment. Its pharynx plays a dual role in feeding and respiration, showcasing an efficient

filter-feeding system. The external morphology, with its tough tunic and siphons, reflects its

adaptation to a sedentary lifestyle in the marine ecosystem.

Understanding these aspects of Herdmania’s biology helps shed light on the evolutionary

development of chordates and their significance in marine habitats. While Herdmania might

seem primitive compared to vertebrates, it represents a key step in the evolutionary history of

animals with a notochord, linking invertebrates to vertebrates.

2. Give an account of the circulatory system of Branchiostoma.

Ans: Circulatory System of Branchiostoma (Amphioxus)

Branchiostoma, also known as amphioxus or lancelet, is a small, fish-like marine organism that

belongs to the subphylum Cephalochordata. It is one of the most primitive members of the

phylum Chordata, which includes vertebrates. The study of Branchiostoma provides insights

into the evolutionary origins of vertebrates, especially their anatomical structures. One such

structure is the circulatory system, which in Branchiostoma exhibits some primitive yet distinct

features.

The circulatory system of Branchiostoma is closed and is relatively simple compared to that of

higher vertebrates. It lacks a heart and the blood is propelled through the body by contractions

of the ventral aorta and other vessels. This system includes blood vessels, arteries, veins, and a

blood-like fluid but lacks true blood cells and respiratory pigments like hemoglobin.

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Let’s break down the circulatory system of Branchiostoma in a simple way, focusing on its

components, the flow of blood, and its unique features.

Main Components of the Circulatory System in Branchiostoma

1. Ventral Aorta: The ventral aorta in Branchiostoma functions as the primary vessel that

drives blood flow, somewhat analogous to the role of the heart in higher animals. It is

situated along the midline of the ventral (lower) side of the body.

2. Dorsal Aorta: The dorsal aorta is another major vessel, located on the dorsal (upper)

side of the body. It distributes blood throughout the body after it has been oxygenated

in the gill slits.

3. Gill Arteries (Branchial Arteries): These arteries carry blood from the ventral aorta to

the gills (pharyngeal slits) where gas exchange (oxygenation) takes place.

4. Cardinal Veins: These veins collect deoxygenated blood from various parts of the body

and return it to the ventral aorta, completing the circulatory loop. There are both

anterior and posterior cardinal veins.

5. Subintestinal Vein: The subintestinal vein collects nutrient-rich blood from the digestive

tract and plays a role in transporting this blood to other parts of the body.

6. Hepatic Portal System: A hepatic portal vein carries blood from the intestine to the

liver, where it is filtered and then passed into the general circulation.

Blood Flow in Branchiostoma

The blood flow in Branchiostoma follows a specific pattern, as described below:

1. Ventilation and Gas Exchange: Blood from the ventral aorta is pushed forward towards

the gill slits, which are located in the pharyngeal region. The gill slits are responsible for

gas exchange, meaning that oxygen is absorbed into the blood while carbon dioxide is

released into the water.

2. Blood Oxygenation: After the blood becomes oxygenated in the gill slits, it is collected

by a series of efferent branchial arteries. These arteries carry the oxygen-rich blood

towards the dorsal aorta.

3. Distribution of Oxygenated Blood: From the dorsal aorta, the oxygenated blood is

distributed to various tissues and organs of the body. The dorsal aorta branches off into

smaller vessels that supply the muscles, digestive organs, and other tissues with

oxygenated blood.

4. Return of Deoxygenated Blood: Once the oxygen is used up by the tissues, the now

deoxygenated blood is collected by the cardinal veins. These veins, divided into anterior

and posterior sections, return the blood to the ventral aorta. Additionally, blood from

the digestive tract is carried to the liver through the hepatic portal vein for filtration.

5. Nutrient Transport: The subintestinal vein also collects blood from the intestines, which

is rich in nutrients absorbed from food. This blood is transported to the liver through the

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hepatic portal system, where nutrients are processed before being sent into the general

circulation.

Unique Features of Branchiostoma’s Circulatory System

1. No Heart: Unlike higher vertebrates, Branchiostoma lacks a true heart. Blood is

propelled through the vessels by the rhythmic contraction of the ventral aorta and

surrounding muscles, a process called peristalsis.

2. Lack of Blood Cells: The blood of Branchiostoma is different from that of vertebrates. It

does not contain true blood cells like erythrocytes (red blood cells) or leukocytes (white

blood cells). Additionally, it lacks respiratory pigments like hemoglobin, which means

that the blood is colorless and carries oxygen in a much simpler form.

3. Simple Oxygen Exchange: Oxygen exchange in Branchiostoma takes place primarily in

the gill slits located in the pharyngeal region. The gill slits serve as a site where oxygen is

absorbed from the surrounding water, and carbon dioxide is expelled. Since

Branchiostoma lives in water, the efficiency of gas exchange is ensured through

continuous water flow.

4. Hepatic Portal System: The presence of a hepatic portal system is another interesting

feature. This system is responsible for transporting nutrient-rich blood from the

intestines to the liver. This function is important because the liver acts as a site for

processing nutrients before they are distributed to the rest of the body.

Functions of the Circulatory System in Branchiostoma

Despite its simplicity, the circulatory system in Branchiostoma performs essential functions,

which are similar to those in higher vertebrates:

1. Oxygen Transport: The primary function of the circulatory system is to transport oxygen

from the gills to the body’s tissues. Oxygen is absorbed in the gills and then distributed

throughout the body via the dorsal aorta and its branches.

2. Removal of Carbon Dioxide: Carbon dioxide, a waste product of cellular respiration, is

removed from the tissues and carried back to the gill slits, where it is released into the

water.

3. Nutrient Distribution: Blood carries nutrients absorbed from the digestive tract to the

liver, where they are processed. Afterward, the nutrient-rich blood is distributed to

various tissues of the body to supply energy for cellular activities.

4. Waste Removal: The circulatory system also helps in removing metabolic wastes

produced by the body’s cells. These wastes are transported to excretory organs where

they can be eliminated from the body.

5. Maintaining Homeostasis: By regulating the transport of oxygen, nutrients, and wastes,

the circulatory system plays a crucial role in maintaining homeostasis, the stable

internal environment required for the proper functioning of cells and tissues.

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Evolutionary Significance of Branchiostoma’s Circulatory System

The study of the circulatory system of Branchiostoma is important from an evolutionary

perspective. Though it is more primitive than that of vertebrates, it shares some basic features

with them. This suggests that the circulatory systems of modern vertebrates may have evolved

from a simpler system similar to that of Branchiostoma.

1. Absence of a Heart: In vertebrates, the development of a heart allowed for more

efficient pumping of blood. However, the rhythmic contractions of the ventral aorta in

Branchiostoma represent a primitive form of blood propulsion.

2. No Blood Cells or Hemoglobin: Higher vertebrates have evolved specialized cells (red

blood cells) and pigments (hemoglobin) to increase the efficiency of oxygen transport. In

contrast, Branchiostoma relies on simpler mechanisms for oxygen distribution.

3. Gill-Based Respiration: The use of gill slits for gas exchange in Branchiostoma reflects

the evolutionary roots of respiratory systems in vertebrates, many of which retain gills

during some stages of development (e.g., fish).

Conclusion

The circulatory system of Branchiostoma is simple yet efficient enough for the organism's

needs. It lacks a heart, blood cells, and respiratory pigments, which are found in higher

vertebrates, but it still performs vital functions such as oxygen transport, nutrient distribution,

and waste removal. Understanding the circulatory system of Branchiostoma provides insight

into the evolutionary progression from primitive chordates to more complex vertebrates,

highlighting the adaptations that have enabled organisms to thrive in different environments

over millions of years.

In essence, while Branchiostoma represents an early stage in the evolution of chordates, its

circulatory system is a key part of its biology and a valuable model for studying the origins of

more complex systems in higher animals.

SECTION-B

3. Describe respiration in Labeo rohita.

Ans: Introduction

Labeo rohita, commonly known as Rohu, is a freshwater fish found primarily in South Asia. It is

one of the most important species of fish in aquaculture due to its high nutritional value and

commercial importance. Like all animals, Rohu requires oxygen to survive, and it obtains this

oxygen through a process known as respiration. In this process, the fish takes in oxygen from

water and expels carbon dioxide, which is a waste product of metabolism. The respiratory

system in Rohu is specially adapted to extract oxygen from water.

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In this explanation, we will explore the respiratory system of Labeo rohita in detail, focusing on

how it breathes, the structures involved, and how the process of gas exchange occurs. We will

also touch on some additional factors such as adaptations that allow Rohu to survive in various

water conditions and environmental changes.

General Overview of Respiration

Respiration in all animals, including Rohu, can be divided into two main stages:

1. External Respiration (Breathing): This is the process by which oxygen is taken into the

body from the external environment and carbon dioxide is expelled.

2. Internal Respiration (Cellular Respiration): This involves the use of oxygen by cells for

the production of energy. Cells use oxygen to break down glucose into energy, releasing

carbon dioxide and water as by-products.

In Rohu, external respiration takes place in the gills, which are the primary respiratory

organs. Internal respiration occurs in the body’s cells.

The Structure of the Respiratory System in Labeo rohita

The respiratory system of Rohu consists of the following major components:

1. Gills: The gills are the primary organ of respiration in fish. They are located on either

side of the fish's head and are covered by a bony structure called the operculum. Gills

are made up of a series of thin, leaf-like structures called gill filaments, which are

responsible for gas exchange. The gill filaments are further divided into gill lamellae,

which increase the surface area for efficient oxygen absorption.

2. Gill Arches and Rakers: The gills are supported by gill arches, which are bony structures

that help maintain the shape and positioning of the gills. In addition, Rohu possesses gill

rakers, which are small, comb-like structures that prevent food particles from entering

the gills while the fish is feeding. This ensures that only water passes through the gills

during respiration.

3. Blood Vessels: The gills are rich in blood vessels. Oxygen is absorbed from the water

into the blood, and carbon dioxide from the blood is expelled into the water. Blood

vessels in the gills include a network of arteries and capillaries, which transport

oxygenated blood throughout the body.

4. Mouth and Operculum: The mouth and operculum play important roles in creating a

flow of water over the gills. When the fish opens its mouth, water enters, and when it

closes its mouth, the water is pushed over the gills and out through the operculum. This

flow of water ensures a continuous supply of oxygen.

Process of Respiration in Labeo rohita

The process of respiration in Rohu can be divided into the following steps:

1. Water Intake: The fish opens its mouth and allows water to flow in. This water contains

dissolved oxygen, which is essential for respiration.

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2. Flow of Water Over Gills: Once the water enters the mouth, the fish closes its mouth

and forces the water over the gills by contracting its mouth cavity. The operculum,

located on either side of the head, remains closed initially and then opens, allowing the

water to pass over the gills.

3. Gas Exchange in the Gills: As water flows over the gill filaments, oxygen from the water

diffuses into the blood vessels located in the gill lamellae. Simultaneously, carbon

dioxide in the fish's blood diffuses out of the blood and into the water. This process is

known as diffusion and occurs because of the concentration gradient—oxygen levels are

higher in the water and lower in the blood, while carbon dioxide levels are higher in the

blood and lower in the water.

4. Oxygen Transport: Once oxygen enters the blood, it is bound to a protein called

hemoglobin, which is present in red blood cells. The oxygenated blood is then

transported throughout the fish’s body to supply the organs and tissues with oxygen,

which is used for cellular respiration.

5. Carbon Dioxide Removal: After oxygen is absorbed and used by the fish's cells, carbon

dioxide is produced as a waste product. The carbon dioxide is carried back to the gills

through the bloodstream, where it diffuses out of the fish’s body and into the water.

6. Exhalation of Water: After the gas exchange takes place in the gills, the operculum

opens and the deoxygenated water, now containing carbon dioxide, is expelled from the

fish’s body.

Adaptations for Efficient Respiration

Fish like Rohu live in water, where the concentration of oxygen is much lower than in air. To

survive, Rohu has developed several adaptations for efficient respiration:

1. Large Surface Area of Gills: The gill filaments and lamellae provide a large surface area

for gas exchange, which allows the fish to absorb as much oxygen as possible from the

water.

2. Counter-Current Exchange System: Rohu uses a highly efficient system known as the

counter-current exchange system. In this system, the flow of blood in the gills runs

opposite to the flow of water. This ensures that oxygen continuously diffuses into the

blood even as the oxygen concentration in the water decreases. This system allows the

fish to extract up to 80-90% of the oxygen from the water.

3. Operculum Pumping Mechanism: The operculum helps maintain a continuous flow of

water over the gills, which is critical for uninterrupted gas exchange. By constantly

moving water over the gills, the fish ensures that fresh oxygen-rich water is always

available for respiration.

4. Hemoglobin with High Oxygen Affinity: The hemoglobin in Rohu's blood has a high

affinity for oxygen, meaning it can bind and transport oxygen efficiently, even in water

with lower oxygen levels.

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5. Behavioral Adaptations: Rohu can also exhibit certain behavioral adaptations, such as

swimming to areas with higher oxygen concentrations or gulping air from the surface in

extreme cases where the water has very low oxygen levels.

Environmental Factors Affecting Respiration

Several environmental factors can influence the respiration of Labeo rohita:

1. Water Temperature: The amount of dissolved oxygen in water decreases as the

temperature increases. Therefore, in warmer water, Rohu may need to breathe more

frequently or move to cooler areas to meet its oxygen demands.

2. Oxygen Levels in Water: In water with low oxygen levels (a condition known as

hypoxia), Rohu may struggle to get enough oxygen. In such cases, the fish may resort to

air-breathing behavior where it gulps air from the surface, although this is not a primary

mode of respiration in this species.

3. Pollution: Pollutants such as chemicals and sewage can reduce the oxygen content in

water, making it difficult for Rohu to breathe. In extreme cases, low oxygen levels can

cause stress, illness, or death in fish populations.

4. Water Flow and Current: Faster-moving water typically has higher levels of dissolved

oxygen, while stagnant water can become oxygen-depleted. Rohu may be more active

in areas with a good water flow to ensure a constant supply of oxygen.

Conclusion

Respiration in Labeo rohita, like in other fish, is a highly efficient process adapted to extracting

oxygen from water. The gills play a central role in this process, with their large surface area and

complex structure allowing for the maximum absorption of oxygen. The counter-current

exchange system, operculum pumping, and specialized hemoglobin are all critical adaptations

that help Rohu thrive in its aquatic environment.

However, the respiration of Rohu is also influenced by external factors such as temperature,

oxygen levels, and water pollution. By understanding the respiratory process of Labeo rohita,

we gain insights into the biological needs of this species and the importance of maintaining

healthy aquatic environments for their survival.

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4. Explain the following drawing relevant diagrams:

(A) External characters of Petromyzon.

(B) Female urinogenital system of Labeo rohita.

Ans: (A) External Characters of Petromyzon (Lamprey)

Petromyzon is a genus of jawless fish commonly referred to as lampreys. They are primitive

chordates belonging to the class Agnatha, which is part of the superclass Cyclostomata. This

class is known for its members' unique evolutionary features, especially their lack of jaws.

Let’s explore the external characters of Petromyzon, along with labeled diagrams, to

understand its distinctive morphology.

1. Body Shape and Size

• Petromyzon has an elongated, cylindrical body that tapers at both ends.

• They typically measure between 15 and 100 cm in length, depending on the species.

2. Head

• The head is smooth, lacking scales, and merges smoothly into the body.

• Eyes are located laterally (on the sides of the head), and they are relatively small, but

well-developed for detecting light.

• One distinct feature is a pineal eye (a small, light-sensitive organ) located on top of the

head, between the two eyes. This organ helps the lamprey sense changes in light.

3. Oral Disc

• The mouth of Petromyzon is in the form of a circular, sucker-like oral disc, equipped

with keratinized teeth. These teeth are used to latch onto prey (such as fish) to feed on

their blood.

• Lampreys lack true jaws. Instead, they use this sucker to create a strong hold on their

host or substrate.

4. Nostril

• A single median nostril is present at the top of the head, located between the eyes. This

is an important sensory structure used for detecting chemicals in the water.

5. Gills and Gill Slits

• One of the most notable external features of Petromyzon is its seven pairs of gill slits

located on each side of the body, behind the eyes. These gill slits are responsible for

respiration.

• Lampreys use a unique form of breathing known as tidal ventilation, where water enters

and exits through the gill slits rather than the mouth, especially when the lamprey is

feeding.

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6. Fins

• Lampreys lack paired fins (pectoral and pelvic fins) that are seen in most fish.

• However, they possess a dorsal fin that runs along the back, starting from the middle of

the body and extending to the tail.

• The caudal fin (tail fin) is symmetrical and helps in propulsion.

7. Tail

• The tail of Petromyzon is dorsoventrally flattened (flattened from top to bottom) and

ends with the caudal fin.

• This fin is helpful for swimming, enabling the lamprey to move efficiently through the

water.

8. Skin and Scales

• The skin of the lamprey is smooth and slimy, without scales, which aids in reducing

friction while swimming. The slime also provides protection against predators and

infections.

• Mucous glands secrete mucus, which makes the body surface slippery.

9. Lateral Line System

• Like many other fish, Petromyzon has a lateral line system, a series of sensory organs

that run along the sides of its body. This system helps the lamprey detect movements

and vibrations in the water, which is crucial for locating prey and avoiding predators.

10. Coloration

• The dorsal side (upper part) of the lamprey is generally dark, while the ventral side

(underneath) is lighter. This coloration helps with camouflage, making it harder for

predators to spot the lamprey from above or below.

Diagram of Petromyzon External Characters

[Create a diagram showing the elongated body, the oral disc with teeth, single nostril, eyes, gill

slits, dorsal fin, caudal fin, and lateral line system.]

(B) Female Urinogenital System of Labeo rohita (Rohu Fish)

Labeo rohita, commonly known as rohu, is an important freshwater fish species belonging to

the family Cyprinidae. It is widely found in rivers and freshwater ponds in South Asia. The

female urinogenital system of Labeo rohita is essential for both excretion and reproduction.

Let’s break down the structure of the female urinogenital system of Labeo rohita with clear

descriptions and labeled diagrams.

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1. Kidneys

• The kidneys of Labeo rohita are long, narrow, and reddish structures located along the

dorsal side (back) of the fish, near the vertebral column.

• They function in excretion by filtering waste products from the blood and maintaining

water balance (osmoregulation).

2. Ureter

• From each kidney, a pair of ureters extends downward. These tubes carry the urine

from the kidneys to the urinary bladder.

• The ureters are thin and connect directly to the bladder, ensuring the passage of

excretory fluids.

3. Urinary Bladder

• The urinary bladder is a small, sac-like structure that temporarily stores urine before it is

excreted through the urogenital aperture.

• In fish like Labeo rohita, the bladder is relatively simple in structure but essential for the

expulsion of waste products from the body.

4. Ovaries

• The female Labeo rohita has a pair of ovaries that are large, sac-like structures located

near the abdominal cavity.

• The ovaries produce eggs (ova) during the breeding season. They enlarge during the

reproductive phase and shrink after spawning.

• Each ovary is attached to the body wall and extends along most of the abdominal cavity.

5. Oviduct

• The oviduct is a thin, tubular structure that arises from each ovary. The eggs produced

in the ovaries travel down the oviduct.

• In Labeo rohita, the oviduct opens into the urogenital aperture, through which the eggs

are released into the external environment (usually into water for fertilization).

6. Urogenital Aperture

• The urogenital aperture is the common opening for both the urinary and genital systems

in female Labeo rohita.

• Located just behind the anus, it allows the release of urine from the bladder and eggs

from the oviduct.

• This structure is important for excretion and the laying of eggs during reproduction.

7. Fertilization

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• In Labeo rohita, fertilization is external. The female releases eggs through the urogenital

aperture into the water, where they are fertilized by the sperm released by the male.

8. Hormonal Control

• The female urinogenital system is regulated by hormones, particularly during the

breeding season. Hormones control the maturation of eggs, ovulation, and other

reproductive processes.

Diagram of the Female Urinogenital System in Labeo rohita

[Create a diagram showing the kidneys, ureters, urinary bladder, ovaries, oviduct, and

urogenital aperture.]

Conclusion

In summary, both Petromyzon and Labeo rohita have unique anatomical structures that reflect

their adaptation to their respective environments and lifestyles. Petromyzon, as a jawless,

parasitic lamprey, displays primitive features such as a sucker-like mouth, seven gill slits, and a

streamlined body suited for attaching to other fish and swimming efficiently. On the other

hand, the female Labeo rohita, being a freshwater fish, has a specialized urinogenital system

adapted for efficient excretion and reproduction, which includes structures like the kidneys,

ovaries, and the urogenital aperture.

SECTION-C

5. Explain the structure of heart in Uromastix.

Ans : The Structure of the Heart in Uromastix

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The Uromastix, also known as the spiny-tailed lizard, belongs to the family Agamidae and is

commonly found in arid and semi-arid regions. In zoology, studying the cardiovascular system

of reptiles like Uromastix helps us understand how these animals have evolved to survive in

their environments. The heart of Uromastix, like other reptiles, has unique adaptations that

allow it to function efficiently in various conditions.

This guide provides an in-depth, yet simplified, look into the structure of the heart in

Uromastix. We will explore the anatomy of the heart, its chambers, blood vessels, and how the

circulatory system works. Understanding the structure and function of the heart is key to

comprehending how Uromastix maintains oxygen transport and circulation throughout its

body.

Overview of the Heart Structure in Reptiles

Before diving into the specific structure of Uromastix’s heart, let’s take a quick look at the

general structure of the heart in reptiles. Most reptiles have a three-chambered heart, which

consists of:

1. Two atria: The upper chambers of the heart.

2. One ventricle: The lower chamber of the heart.

However, the ventricle in reptiles is partially divided, which helps prevent the mixing of

oxygenated and deoxygenated blood. This partial division provides efficiency in circulation,

which is critical for animals living in fluctuating environmental conditions.

Structure of the Heart in Uromastix

The heart of Uromastix shares similarities with other reptiles, but it has its own specific

adaptations. The main components of the Uromastix heart include:

1. Three-Chambered Heart: The heart of Uromastix consists of three main chambers:

o Right atrium: This chamber receives deoxygenated blood (low in oxygen) from

the body.

o Left atrium: This chamber receives oxygenated blood (high in oxygen) from the

lungs.

o Ventricle: The ventricle is partially divided into three sub-chambers by muscular

ridges, which help in maintaining some separation between oxygenated and

deoxygenated blood.

Atria

• Right Atrium: The right atrium collects deoxygenated blood from the body. This blood is

low in oxygen because it has circulated through the body, delivering oxygen to tissues

and organs. The blood enters the right atrium through a large vein known as the sinus

venosus.

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• Left Atrium: The left atrium collects oxygenated blood from the lungs. This blood is rich

in oxygen and is ready to be pumped to the rest of the body. The oxygenated blood

enters the left atrium through the pulmonary veins, which are connected to the lungs.

Ventricle

• The ventricle in Uromastix is unique because it is not completely divided, as it would be

in mammals. Instead, it is partially divided by muscular ridges. These ridges help in

directing blood flow, preventing significant mixing of oxygenated and deoxygenated

blood.

• The ventricle has three sub-chambers:

o Cavum venosum: This is the chamber where blood from the right atrium enters.

o Cavum pulmonale: This sub-chamber directs blood to the lungs.

o Cavum arteriosum: This chamber receives oxygenated blood from the left

atrium and pumps it to the body.

This unique design of the ventricle allows Uromastix to efficiently separate oxygenated and

deoxygenated blood despite having a three-chambered heart. The muscular ridges, along with

the timing of the heart’s contractions, prevent excessive mixing of blood, which would

otherwise reduce the efficiency of oxygen delivery to the body.

Blood Vessels Associated with the Heart

The heart of Uromastix is connected to several major blood vessels that play an essential role in

the circulation of blood between the heart, lungs, and body. These include:

1. Pulmonary Arteries and Veins:

o Pulmonary arteries carry deoxygenated blood from the heart to the lungs, where

it receives oxygen.

o Pulmonary veins carry oxygenated blood from the lungs to the heart.

2. Aorta: The aorta is the main artery that carries oxygenated blood from the heart to the

rest of the body. In Uromastix, the aorta arises from the cavum arteriosum and

distributes oxygen-rich blood to various organs and tissues.

3. Sinus Venosus: The sinus venosus is a large vein that collects deoxygenated blood from

the body and delivers it to the right atrium.

Circulatory Process in Uromastix

Now that we’ve covered the structure of the heart, let’s look at how the circulatory system

works in Uromastix.

1. Step 1: Deoxygenated Blood to the Right Atrium

o Blood low in oxygen (deoxygenated) returns from the body through veins and

enters the right atrium via the sinus venosus.

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2. Step 2: Blood Enters the Ventricle

o From the right atrium, deoxygenated blood flows into the cavum venosum,

which is part of the ventricle. From here, it is directed into the cavum pulmonale.

3. Step 3: Blood to the Lungs

o The cavum pulmonale pumps the deoxygenated blood into the pulmonary

arteries, which carry it to the lungs. In the lungs, blood picks up oxygen and

releases carbon dioxide.

4. Step 4: Oxygenated Blood to the Left Atrium

o Oxygenated blood returns from the lungs through the pulmonary veins and

enters the left atrium.

5. Step 5: Blood Enters the Ventricle (Cavum Arteriosum)

o From the left atrium, oxygenated blood flows into the cavum arteriosum, which

is part of the ventricle.

6. Step 6: Blood to the Body

o The cavum arteriosum pumps the oxygen-rich blood into the aorta, which

distributes it to the rest of the body.

Unique Adaptations in Uromastix Heart

The heart of Uromastix shows some specialized adaptations that make it efficient for its

environment:

1. Partial Separation of Blood: The partial division of the ventricle helps maintain some

separation between oxygenated and deoxygenated blood. This allows Uromastix to

have a more efficient circulatory system compared to amphibians, where there is more

mixing of blood.

2. Efficient Oxygen Delivery: The timing of the heart's contractions and the muscular

ridges in the ventricle help ensure that oxygen-rich blood is directed to the body while

deoxygenated blood is sent to the lungs for oxygenation.

3. Adaptation to Environmental Conditions: The efficient separation of blood and delivery

of oxygen allows Uromastix to survive in harsh environments like deserts, where it may

experience extreme temperatures and limited oxygen availability.

Comparison with Other Reptiles

The heart structure of Uromastix is similar to other reptiles, especially lizards, but there are

some differences compared to other animal groups:

• Amphibians: Amphibians also have a three-chambered heart, but their ventricle is less

divided, leading to more mixing of oxygenated and deoxygenated blood.

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• Crocodiles: Crocodiles have a four-chambered heart, which completely separates

oxygenated and deoxygenated blood, allowing for more efficient oxygen transport. This

is an adaptation for their semi-aquatic lifestyle.

• Mammals and Birds: Mammals and birds have a four-chambered heart, with complete

separation between the two types of blood. This is the most efficient system for oxygen

transport and is necessary for the high metabolic demands of these animals.

Conclusion

The heart of Uromastix is a three-chambered organ with specialized adaptations that allow it to

function efficiently in a variety of environmental conditions. Its partial division into three sub-

chambers helps maintain some separation between oxygenated and deoxygenated blood,

ensuring efficient circulation. Understanding the structure and function of the Uromastix heart

provides valuable insights into the evolutionary adaptations of reptiles and how they have

managed to thrive in diverse habitats.

By studying the heart of Uromastix, we also gain a better understanding of the general

principles of circulatory systems in vertebrates and how different animals have evolved to meet

their oxygen and energy needs in varying environments.

6. Describe the following drawing relevant diagrams:

(A) Male urinogenital system in Rana tigrina.

(B) Structure of inner ear in Uromastix.

Ans: Introduction

In the study of chordates, which belong to the phylum Chordata, amphibians and reptiles are

significant groups. In this paper, we will focus on two specific animals, Rana tigrina (Indian

bullfrog) and Uromastix (a type of lizard), to describe important systems and organs in these

animals. We will simplify the structure and function of the male urinogenital system in Rana

tigrina and the structure of the inner ear in Uromastix, ensuring the explanations are easy to

understand. To make this clear, relevant diagrams will also be referred to.

(A) Male Urinogenital System in Rana tigrina (Indian Bullfrog)

Overview of the Urinogenital System

In Rana tigrina, the urinogenital system is a combination of two systems: the urinary system,

which is responsible for the elimination of waste products, and the reproductive system, which

is involved in the production of sperm and its transportation out of the body. This merging of

the urinary and reproductive functions is common in amphibians.

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Components of the Male Urinogenital System

1. Kidneys:

o The kidneys are the primary organs responsible for filtering the blood to remove

nitrogenous wastes like urea, which is then excreted in the urine.

o Location: They are located on the dorsal (upper) side of the body cavity.

o Structure: Each kidney is long and dark red in color, divided into several lobes.

o Function: The kidneys remove wastes and regulate water balance in the body.

2. Ureters:

o The ureters are thin tubes that arise from the kidneys.

o Function: In male frogs, the ureters serve a dual function: they carry both urine

and sperm. This is why the system is called "urinogenital."

o Pathway: The ureters carry the urine and sperm to the cloaca.

3. Cloaca:

o The cloaca is a common chamber where the urinary, reproductive, and digestive

tracts open. It is located at the end of the body and is the exit for urine, feces,

and sperm.

o Function: It acts as a passage for all the materials to leave the body.

4. Testes:

o Male frogs have a pair of testes, which are yellowish, oval structures located

near the kidneys.

o Function: The testes produce sperm, which is transported through vasa

efferentia into the kidneys.

5. Vasa Efferentia:

o These are small ducts that connect the testes to the kidneys.

o Function: They transport sperm from the testes to the kidneys, where it enters

the ureters.

6. Seminal Vesicle:

o The seminal vesicles are found attached to the ureters. They store sperm before

it is released from the body.

o Function: They serve as temporary storage for sperm.

7. Fat Bodies:

o Yellow-colored fat bodies are found attached to the kidneys.

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o Function: These fat bodies store energy and provide nourishment, especially

during the breeding season.

Diagram of the Male Urinogenital System in Rana tigrine

The diagram below (hypothetical representation) highlights all major structures:

• Kidney (lobed, elongated)

• Ureters (tubular structures carrying urine and sperm)

• Testes (oval, attached to kidneys)

• Cloaca (common chamber)

• Vasa efferentia (small ducts connecting testes and kidneys)

• Seminal vesicle (attached to ureters)

Functionality of the System

• The male urinogenital system is designed for both waste excretion and reproduction.

Urine is produced by the kidneys, passes through the ureters, and exits via the cloaca.

Similarly, sperm is produced in the testes, transported through vasa efferentia to the

ureters, and released from the cloaca during mating.

(B) Structure of the Inner Ear in Uromastix (Spiny-Tailed Lizard)

Overview of the Inner Ear

The inner ear in reptiles like Uromastix is specialized for both hearing and balance. While their

sense of hearing is not as developed as mammals, the inner ear plays a crucial role in

maintaining equilibrium and detecting vibrations.

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Components of the Inner Ear

1. Semicircular Canals:

o The inner ear contains three semicircular canals, which are fluid-filled structures.

o Function: These canals are responsible for detecting rotational movements of

the head, helping the lizard maintain balance.

o Structure: Each canal lies in a different plane (horizontal, vertical, and oblique),

enabling the detection of movement in all directions.

2. Cochlea (Lagena):

o The cochlea is a coiled, tube-like structure that is primarily responsible for

hearing.

o Function: It converts sound vibrations into nerve impulses that are sent to the

brain.

o Structure: In reptiles, the cochlea is less coiled than in mammals, making their

hearing less sensitive to a wide range of frequencies.

3. Utricle and Saccule:

o The utricle and saccule are parts of the vestibular system involved in detecting

linear movements and changes in head position.

o Function: These structures help the animal sense its orientation in space,

whether it is moving straight or is stationary.

o Structure: The utricle is connected to the semicircular canals, while the saccule is

located below the utricle.

4. Auditory Nerve:

o The auditory nerve connects the inner ear to the brain.

o Function: It transmits signals from the cochlea and vestibular organs to the

brain, where they are interpreted as sound and balance information.

Diagram of the Inner Ear in Uromastix

A simplified diagram of the inner ear of Uromastix shows the following structures:

• Semicircular Canals (three loops oriented in different planes)

• Cochlea (Lagena) (a slightly coiled structure for hearing)

• Utricle and Saccule (small sac-like structures for detecting head movements)

• Auditory Nerve (connecting to the brain)

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Functionality of the Inner Ear

• The inner ear of Uromastix serves two primary functions: hearing and balance. The

semicircular canals detect changes in the animal’s orientation, while the cochlea

captures sound vibrations and transmits them to the brain. The combination of these

functions allows Uromastix to maintain equilibrium and detect environmental sounds.

Conclusion

The male urinogenital system in Rana tigrina and the inner ear of Uromastix demonstrate the

incredible specialization of organs in amphibians and reptiles. In Rana tigrina, the urinogenital

system efficiently handles both waste excretion and reproduction. On the other hand,

Uromastix's inner ear plays a key role in hearing and balance, crucial for survival. Through these

systems, we gain deeper insights into how these animals adapt and function in their respective

environments.

These explanations and diagrams offer a clear understanding of the biological systems in these

species, highlighting their roles and significance in the animal kingdom.

SECTION-D

1. Describe different kinds of feathers in Columba livia.

Ans: In Columba livia, commonly known as the rock pigeon or domestic pigeon, feathers play a vital role

in protecting the bird from environmental factors, helping with flight, regulating body temperature, and

even in courtship displays. Feathers are a characteristic feature of all birds and are specialized structures

made of keratin, a protein.

This response will explain the different types of feathers found in Columba livia and their

functions, simplified in an easy-to-understand language.

Overview of Feathers in Birds

Feathers in birds are divided into several categories based on their structure and function.

Generally, feathers are classified into the following categories:

1. Contour feathers

2. Down feathers

3. Flight feathers

4. Semiplumes

5. Filoplumes

6. Bristles

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Each of these feather types plays a specific role in the bird's body. Now, let’s explore these

types of feathers in detail.

1. Contour Feathers

Contour feathers are the outermost feathers that form the visible covering of the bird's body. In

Columba livia, these feathers give the bird its shape and smooth appearance. These feathers

cover the bird’s wings, tail, and body, and they are responsible for protecting the bird from

wind, water, and sunlight.

Key features:

• Contour feathers are firm and strong.

• They are made up of a central shaft and barbs that branch out from the shaft.

• These feathers are arranged in a way that creates a smooth, aerodynamic surface,

which is essential for flight.

Function:

• Contour feathers help in streamlining the bird's body for efficient flight.

• They also act as a protective barrier, keeping water from penetrating the bird’s skin.

• These feathers contribute to the bird’s coloring and play a role in camouflage or

attracting mates during the breeding season.

2. Down Feathers

Down feathers are found beneath the contour feathers and serve as an insulating layer for

pigeons. These feathers are soft and fluffy, helping to trap air close to the bird’s body, providing

warmth.

Key features:

• Down feathers lack the central shaft found in contour feathers.

• They consist of soft, loose barbs that are not tightly interlocked.

• Down feathers are usually white or light-colored, and they do not contribute much to

the bird's appearance.

Function:

• The primary role of down feathers is insulation, keeping the bird warm, especially during

cold weather.

• They are particularly important for young birds who rely on them for warmth before

their contour feathers develop.

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3. Flight Feathers

Flight feathers are the specialized feathers on the wings and tail of Columba livia, which are

essential for flight. These feathers are longer, stronger, and stiffer than contour feathers, and

they are divided into two main types:

1. Primary feathers: These are the long feathers found on the outer part of the wings,

attached to the hand bones of the bird. They are crucial for generating lift and

propulsion during flight.

2. Secondary feathers: These are attached to the inner part of the wing, closer to the

bird's body, and help in controlling direction and stability while flying.

Key features:

• Flight feathers have a strong central shaft, with tightly interlocking barbs to maintain

their strength.

• They are asymmetrical in shape, which aids in the aerodynamics of flight.

Function:

• Primary feathers provide the main thrust that allows pigeons to move forward during

flight.

• Secondary feathers help with steering, braking, and controlling the bird’s movements

while in the air.

• Together, primary and secondary feathers allow pigeons to fly efficiently, maneuver

through the air, and land safely.

4. Semiplumes

Semiplume feathers are a mix between contour and down feathers. They provide additional

insulation and help maintain the bird's shape, adding to the smoothness of the body contour

without contributing to flight.

Key features:

• Semiplume feathers have a central shaft like contour feathers, but their barbs are not as

tightly interlocked.

• They are softer than contour feathers but firmer than down feathers.

Function:

• Semiplumes help in insulation, keeping the bird warm by trapping air beneath the

contour feathers.

• These feathers also play a role in providing buoyancy in water birds, though this is less

relevant for pigeons.

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5. Filoplumes

Filoplumes are small, hair-like feathers that are found near the base of contour feathers. They

are not very visible because they are hidden beneath the larger feathers, but they serve an

important sensory function.

Key features:

• Filoplumes have a thin shaft with a few barbs at the tip.

• They resemble thin hairs, unlike other feathers that are broad and flat.

Function:

• Filoplumes act as sensory structures, providing feedback to the bird about the position

of the larger feathers, especially during flight.

• They help in detecting changes in feather alignment, allowing pigeons to adjust their

feathers for better flight control and aerodynamics.

6. Bristles

Bristles are stiff, hair-like feathers found around the bird’s face, particularly near the beak and

eyes. In pigeons, these feathers are not as prominent as in some other bird species, but they

still serve specific purposes.

Key features:

• Bristles have a stiff central shaft and lack barbs, giving them a hair-like appearance.

• They are usually short and sparse.

Function:

• Bristles around the bird’s beak help in sensing objects and food.

• They also provide protection for the eyes by deflecting dust, debris, or small insects that

might otherwise harm the bird.

Structure of a Feather

To understand feathers better, let’s break down their general structure:

1. Rachis: This is the central shaft of the feather, providing the framework and support.

2. Barbs: These are the small structures branching out from the rachis, which form the

main surface of the feather.

3. Barbules: Barbs are further divided into barbules, which interlock to provide strength

and smoothness to the feather.

4. Calamus: The base of the feather, where it attaches to the bird’s skin.

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Feathers and Molting

In pigeons, feathers wear out over time, and they go through a process called molting to

replace old feathers with new ones. Molting usually happens in a systematic way so that the

bird does not lose its ability to fly or regulate body temperature during this period.

• Molting pattern: Molting usually occurs in a specific sequence, starting with the

replacement of flight feathers, followed by contour and other body feathers.

• Duration: The molting process can take several weeks to months, depending on the

species and environmental conditions.

Functions of Feathers Beyond Flight

While flight is one of the most visible functions of feathers, they have many other important

roles in the life of Columba livia:

1. Thermoregulation: Feathers help regulate body temperature by trapping heat or

providing cooling in warm weather.

2. Protection: Feathers protect the bird’s skin from UV radiation, moisture, and

mechanical damage.

3. Camouflage: The coloration of feathers helps pigeons blend into their environment,

protecting them from predators.

4. Communication and courtship: Pigeons use their feathers for displays during mating

season to attract mates or to assert dominance in social groups.

Conclusion

Feathers in Columba livia are highly specialized structures that serve a variety of functions, from

enabling flight to providing insulation and protection. The different types of feathers—contour,

down, flight, semiplumes, filoplumes, and bristles—each have a unique structure and role,

contributing to the bird's overall survival and well-being.

The study of feathers is essential for understanding the biology of birds like pigeons. Not only

do they provide insights into how these birds fly, but they also reveal how they have adapted to

their environments, maintain their body temperature, and communicate with one another.

In summary, feathers are critical to the life of Columba livia, and each type of feather plays a

specific role that contributes to the bird's ability to thrive in its natural habitat.

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8. Explain the following drawing relevant diagrams:

(A) Structure of mammalian lung.

(B) Structure of kidney in rat.

Ans: (A) Structure of Mammalian Lung

Introduction

The mammalian lung is an essential organ for respiration, enabling the exchange of gases

(oxygen and carbon dioxide) between the body and the external environment. Its highly

specialized structure maximizes the surface area for efficient gas exchange, supporting the

energy demands of warm-blooded mammals.

External Structure of the Mammalian Lung

Mammalian lungs are located in the thoracic cavity, protected by the ribcage, and are divided

into two lobes. These lobes can vary between species:

• Right lung: Typically larger, divided into three or more lobes (depending on the species).

• Left lung: Usually smaller with two lobes, making room for the heart.

The lungs are spongy and elastic, allowing them to expand and contract during breathing. They

are covered by a thin double-layered membrane called the pleura:

1. Visceral pleura: Inner layer that covers the lungs.

2. Parietal pleura: Outer layer that lines the thoracic cavity.

Between these layers is a small amount of pleural fluid, which reduces friction during lung

movement and keeps the lungs attached to the thoracic wall, allowing for smooth expansion.

Internal Structure of the Mammalian Lung

The lungs are made up of smaller units that carry out gas exchange, with the following key

components:

1. Trachea (Windpipe): The air enters through the nose or mouth and passes into the

trachea. The trachea is a large tube made of rings of cartilage that prevent it from

collapsing. It divides into two branches known as bronchi.

2. Bronchi: The trachea splits into the left and right bronchi, which lead into the

corresponding lung. The bronchi continue branching into smaller tubes called

bronchioles.

3. Bronchioles: These are the smaller airways that distribute air throughout the lungs. The

bronchioles divide further, becoming finer until they lead to the alveoli.

4. Alveoli: These are tiny air sacs where gas exchange occurs. Alveoli have very thin walls

(one cell thick) and are surrounded by a dense network of capillaries. Oxygen from the

air passes into the blood through the alveolar walls, while carbon dioxide from the

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blood is expelled into the alveoli to be breathed out. The alveoli provide a massive

surface area for gas exchange, making the lungs highly efficient.

5. Diaphragm: The diaphragm is a sheet of muscle located below the lungs. It contracts

and flattens during inhalation, increasing the space in the thoracic cavity and allowing

the lungs to expand. During exhalation, it relaxes and pushes air out of the lungs.

Gas Exchange Process

• Inhalation: Air is drawn into the lungs through the trachea, bronchi, and bronchioles,

finally reaching the alveoli. Oxygen from the air diffuses into the blood in the capillaries

surrounding the alveoli.

• Exhalation: Carbon dioxide, a waste product from the cells, is transported in the blood

to the alveoli, where it diffuses out and is expelled during exhalation.

Control of Breathing

Breathing is controlled by the medulla oblongata in the brain. It sends signals to the diaphragm

and the intercostal muscles (between the ribs) to regulate breathing. This system responds to

the levels of carbon dioxide in the blood, ensuring that the body maintains the proper balance

of gases.

Diagram of Mammalian Lung

The diagram should depict:

1. Trachea

2. Bronchi and bronchioles

3. Alveoli

4. Pleura

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5. Diaphragm

(B) Structure of Kidney in Rat

Introduction

The kidney in mammals, including rats, is a crucial organ for excretion and osmoregulation. Its

primary function is to filter blood, remove waste products, and regulate water and salt balance

in the body. This process is essential for maintaining homeostasis.

External Structure of the Kidney

Each rat has two kidneys located on either side of the spine in the abdominal cavity. They are

bean-shaped and reddish-brown in color. The kidney is surrounded by a layer of protective fat

and a fibrous capsule known as the renal capsule.

Internal Structure of the Kidney

The kidney's internal structure can be divided into three major regions:

1. Cortex: The outermost layer, which contains the filtering units called nephrons. The

nephrons are responsible for the actual process of blood filtration.

2. Medulla: The middle layer, which consists of cone-shaped structures called renal

pyramids. The pyramids contain loops of nephrons and collecting ducts, which transport

the filtered substances (urine) to the central part of the kidney.

3. Renal Pelvis: The innermost part of the kidney. It collects the urine produced by the

nephrons and funnels it into the ureter, which leads to the bladder for storage.

The Nephron – Functional Unit of the Kidney

Each kidney contains millions of tiny filtering units called nephrons. Each nephron consists of:

1. Bowman’s capsule: A cup-shaped structure at the beginning of the nephron that

surrounds a ball of capillaries called the glomerulus. This is where filtration of blood

takes place.

2. Glomerulus: A network of capillaries inside the Bowman’s capsule. As blood flows

through the glomerulus, water, salts, and waste products are filtered out of the blood

and into the nephron.

3. Proximal convoluted tubule (PCT): The first twisted part of the nephron tubule. In the

PCT, most of the filtered water, glucose, and essential ions are reabsorbed back into the

blood.

4. Loop of Henle: A long, U-shaped section of the nephron that extends into the medulla.

This part of the nephron creates a concentration gradient in the kidney, allowing water

to be reabsorbed and concentrated urine to be produced.

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5. Distal convoluted tubule (DCT): The second twisted part of the nephron. Here, further

regulation of water and ion balance occurs, under the influence of hormones like

aldosterone.

6. Collecting duct: The final part of the nephron. It receives urine from many nephrons and

transports it through the medulla to the renal pelvis. Along the way, additional water

may be reabsorbed depending on the body's needs.

Blood Supply to the Kidney

The kidneys receive blood through the renal artery, which branches from the abdominal aorta.

Blood enters the kidney, gets filtered in the glomeruli, and the cleaned blood exits through the

renal vein.

Urine Formation Process

1. Filtration: Blood pressure forces water, salts, glucose, and wastes from the blood into

the Bowman’s capsule.

2. Reabsorption: As the filtrate moves through the PCT, Loop of Henle, and DCT, essential

substances like water, ions, and glucose are reabsorbed back into the blood.

3. Secretion: Additional waste products like hydrogen ions and certain drugs are actively

secreted into the tubule to be eliminated in urine.

4. Excretion: The urine collects in the renal pelvis and moves through the ureter to the

bladder for storage before being excreted through the urethra.

Regulation of Kidney Function

The kidneys regulate blood volume, blood pressure, and ion concentrations by adjusting the

amount of water and salt they reabsorb. Hormones like antidiuretic hormone (ADH) and

aldosterone play a significant role in this regulation.

Diagram of Kidney in Rat

The diagram should depict:

1. Cortex, medulla, and renal pelvis

2. Nephron, including Bowman’s capsule, glomerulus, PCT, Loop of Henle, DCT, and

collecting duct

3. Renal artery and renal vein

Conclusion

Both the lungs and kidneys are vital organs in mammals, including rats. The lungs are

responsible for gas exchange, while the kidneys filter blood, regulate water and salt balance,

and remove waste. Their specialized structures enable efficient functioning, contributing to the

overall homeostasis of the body. Understanding their anatomy and physiology provides insight

into how these organs sustain life in mammals.

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