Anatomy of Earthworm Questions in English

(D) In the earthworm ($Pheretima$ $posthuma$),the body is divided into segments called metameres. Each segment,except for the first,the last,and the clitellum,bears $S$-shaped structures called setae. Setae are primarily involved in locomotion. Therefore,the correct answer is $D$.

(B) In the reproductive system of an earthworm,the $clitellum$ secretes mucus and albumin. The $albuminous$ $glands$ (or cells) present in the clitellar region are responsible for providing nutrition to the unfertilized eggs within the cocoon. Thus,the correct answer is $B$.

(B) In the earthworm (Pheretima),the body is divided into segments called metameres.
The clitellum is a prominent dark band of glandular and non-glandular tissue.
It is located in the $14^{th}$,$15^{th}$,and $16^{th}$ segments of the body.
This region is responsible for secreting mucus and cocoons for reproduction.

(A) The body of an earthworm is primarily composed of soft tissues,muscles,and organs that are soluble in strong alkaline solutions like $40\%$ $KOH$.
However,the setae $(Setae)$ are chitinous structures.
Chitin is a complex polysaccharide that is resistant to the action of strong alkalis.
Therefore,the setae remain insoluble even after prolonged exposure to $40\%$ $KOH$.

(C) In $Pheretima$ (earthworm),fertilization and development occur within a structure called the cocoon.
After copulation,the clitellar glands secrete mucus and albumin to form the cocoon.
The ova and the sperms (received from the partner during copulation) are deposited into the cocoon.
Fertilization occurs externally within this cocoon,which is then deposited in the soil.

(B) In the earthworm $(Pheretima \text{ } posthuma)$, two pairs of accessory glands are present.
These glands are located in the $17^{th}$ and $19^{th}$ segments, one pair in each.
They are associated with the genital papillae and play a role during the process of copulation.

(D) In the earthworm ($Pheretima$ $posthuma$),the body cavity is divided into compartments by transverse partitions called septa.
These septa are absent in the first four segments of the body.
Additionally,the septa are also absent in the $9^{th}$ and $10^{th}$ segments to accommodate the gizzard and stomach,respectively.
Therefore,both the first four segments and the $9^{th}$ and $10^{th}$ segments lack septa.

(D) The movement in an earthworm is facilitated by the contraction and relaxation of its body wall muscles.
Specifically,the earthworm possesses both circular and longitudinal muscles.
Additionally,the earthworm has $S$-shaped structures called setae,which are embedded in the epidermal pits of each segment (except the first,last,and clitellum).
These setae help in gripping the soil and provide anchorage during locomotion.
Therefore,the coordinated action of muscles and the grip provided by the setae allow the earthworm to move effectively.

(B) In the earthworm ($Pheretima$ $posthuma$),the circulatory system is of the closed type. It consists of blood vessels,capillaries,and hearts. There are four pairs of tubular hearts in segments $7, 9, 12,$ and $13$. The hearts in segments $7$ and $9$ are known as lateral hearts,while those in segments $12$ and $13$ are known as lateral-oesophageal hearts. Therefore,lateral hearts are a characteristic feature of the earthworm's circulatory system.

(B) The body surface of an earthworm is kept moist and protected from pathogens by the secretion of mucus and coelomic fluid. The coelomic fluid,which is present in the body cavity,contains various cells including amoebocytes that possess antimicrobial properties. These secretions help in destroying bacteria and other microorganisms on the body surface,thereby protecting the earthworm from infections.

(D) In earthworms,nephridia are classified based on their location into three types: septal,integumentary,and pharyngeal.
Septal nephridia are present on both sides of the intersegmental septa from the $15^{th}$ segment to the last segment.
These nephridia open into the intestine.
Therefore,they discharge their excretory waste products directly into the intestinal lumen,which is then eliminated through the anus along with the faecal matter.

(D) In $Pheretima$ (earthworm), the blood is red in color due to the presence of a respiratory pigment dissolved in the plasma.
This pigment is $Hemoglobin$ (also known as $Erythrocruorin$ in annelids).
Therefore, both $Hemoglobin$ and $Erythrocruorin$ refer to the same respiratory pigment found in the earthworm's blood.
Thus, the correct option is $D$.

(C) In an earthworm $(Pheretima \ posthuma)$,the body is divided into segments called metameres. The first body segment is known as the $Peristomium$ (or buccal segment). The mouth is located in this $Peristomium$ segment. The $Prostomium$ is a fleshy lobe that overhangs the mouth,which is used as a wedge to force open cracks in the soil.

(C) In the earthworm ($Pheretima$ $posthuma$),the suprapharyngeal ganglia (also known as the cerebral ganglia or brain) act as an endocrine center. These ganglia secrete hormones that regulate various physiological processes,including growth,reproduction,and regeneration. While chloragogen cells are involved in excretion and storage of glycogen/lipids,and nerve cords are part of the nervous system,the neurosecretory cells located within the suprapharyngeal ganglia are specifically responsible for hormonal secretion.

(D) In $Pheretima$ (earthworm),there are four pairs of spermathecae located in the $6^{th}$ to $9^{th}$ segments.
These structures are responsible for receiving and storing spermatozoa during the process of copulation.
Therefore,they function as storage organs for sperms received from another earthworm.

(C) Earthworms are commonly known as 'friends of farmers' because they make burrows in the soil and make the soil porous,which helps in respiration and penetration of the developing plant roots.
According to biological studies and $NCERT$ data,it is estimated that there are approximately $50,000$ earthworms in $1$ acre of land.
Therefore,the correct option is $C$.

(B) The clitellum is a prominent glandular and non-segmented section of the body wall near the head in earthworms. Its primary function is to secrete mucus and albumin,which are essential for the formation of a cocoon. The cocoon serves as a protective casing for the developing embryos.

(C) The scientific name of the common South Indian earthworm is $Megascolex$.
$Pheretima$ is a common genus of earthworms found in North India.
$Lumbricus$ is a genus commonly found in Europe and North America.
Therefore,the correct option is $C$.

(A) In earthworms,the blood is red in color due to the presence of the respiratory pigment $Hemoglobin$.
Unlike humans,where $Hemoglobin$ is contained within red blood cells,in earthworms,$Hemoglobin$ is dissolved directly in the blood plasma.
This pigment helps in the transport of oxygen throughout the body.

(B) Chloragogen cells are specialized cells found in the coelomic fluid and surrounding the intestine of earthworms (Annelida).
These cells function similarly to the vertebrate liver,playing a crucial role in the metabolism of proteins,carbohydrates,and lipids.
They are primarily involved in the synthesis of glycogen and the storage of fat.
Furthermore,they play a significant role in the excretion of nitrogenous waste products,making them essential for the excretory system of the earthworm.

(A) In earthworms,nephridia are the excretory organs.
These structures are ectodermal in origin.
They are segmentally arranged tubules that help in osmoregulation and excretion.

(B) The blood of an earthworm $(Pheretima)$ is red in color due to the presence of hemoglobin. However,unlike vertebrates,the hemoglobin in earthworms is dissolved directly in the blood plasma,not contained within red blood cells. Therefore,earthworms have red blood but lack red blood cells (erythrocytes).

(C) Earthworms do not have specialized respiratory organs like lungs or gills.
They respire through their moist skin,which is rich in blood capillaries.
Oxygen from the surrounding environment dissolves in the moisture on the skin surface and diffuses into the blood,while carbon dioxide diffuses out.
Therefore,the correct answer is moist skin.

(C) In $Pheretima$ (earthworm),the alimentary canal is differentiated into various regions.
$1$. The intestine starts from the $15^{th}$ segment and continues to the last segment.
$2$. Intestinal caeca are present in the $26^{th}$ segment.
$3$. Prostate glands are present in the $17^{th}$ to $19^{th}$ segments.
$4$. Therefore,at the $20^{th}$ segment,only the intestine is present.
Thus,the correct option is $(c)$.

(B) The excretory organs of an earthworm ($Pheretima$ $posthuma$) are segmentally arranged coiled tubules called nephridia.
Flame cells are the excretory organs in Platyhelminthes.
Malpighian tubules are the excretory organs in insects.
Skin acts as a respiratory organ in earthworms,not an excretory organ.

(D) In the earthworm $(Pheretima)$, the nervous system consists of a central nervous system, a peripheral nervous system, and a sympathetic nervous system. The peripheral nervous system includes nerves that arise from the nerve ring and the ventral nerve cord. These nerves are classified into three types based on their function:
$1$. Sensory nerves: These carry impulses from sensory receptors to the central nervous system.
$2$. Motor nerves: These carry impulses from the central nervous system to the effector organs (muscles).
$3$. Adjustor nerves: These act as interneurons, connecting sensory and motor neurons to coordinate responses.
Therefore, all these types of nerves are present in the earthworm.

(C) Earthworms are known as the 'friends of farmers' because they make burrows in the soil,which makes the soil porous and helps in the respiration and penetration of the developing plant roots.
They also feed on decaying organic matter and dead leaves,and their excreta (worm castings) are rich in nutrients,which significantly increase the fertility of the soil.

(A) In earthworms ($Pheretima$ $posthuma$),there are four pairs of tubular hearts that help in the circulation of blood.
These hearts are located in segments $7, 9, 12,$ and $13$.
- The lateral hearts are present in segments $7$ and $9$.
- The latero-oesophageal hearts are present in segments $12$ and $13$.

(C) Locomotion in earthworms is primarily achieved through the contraction and relaxation of the body wall muscles.
$1$. The body wall contains both circular and longitudinal muscles.
$2$. The contraction and relaxation of these muscles result in the periodic shortening and lengthening of the body segments,which facilitates movement.
$3$. Setae (present in all segments except the first,last,and clitellum) help in gripping the ground during this process.
$4$. Therefore,the periodic contraction and relaxation of body segments is the fundamental mechanism for locomotion.

(D) The $typhlosole$ is a longitudinal fold of the inner wall of the intestine in an earthworm $(Pheretima)$.
Its primary function is to increase the internal surface area of the intestine.
By increasing the surface area,it enhances the absorption of digested food nutrients into the bloodstream.

(B) The earthworm (e.g.,$Pheretima$ $posthuma$) belongs to the phylum $Annelida$.
Within the phylum $Annelida$,the earthworm is classified under the class $Oligochaeta$ because it possesses few setae per segment and lacks parapodia.

(C) The typhlosole is a longitudinal fold of the intestinal wall that projects into the lumen of the intestine in earthworms.
Its primary function is to increase the surface area of the intestinal lining,which significantly enhances the absorption of digested nutrients.
Therefore,the correct option is $C$.

(B) In the alimentary canal of an earthworm ($Pheretima$ $posthuma$), the $Gizzard$ is a specialized muscular organ.
Its primary function is to grind the soil and decaying organic matter.
To withstand the abrasive nature of the food particles, the inner lining of the $Gizzard$ is covered by a thick, protective layer known as the $cuticle$.

(D) In the circulatory system of an earthworm,the lateral oesophageal vessels are responsible for collecting blood from the seminal vesicles and other reproductive organs. These vessels run along the sides of the oesophagus and drain into the supra-oesophageal vessel or directly into the heart.

(C) In earthworms $(Pheretima)$,nephridia are classified based on their location and the site of waste discharge.
$1$. Integumentary nephridia are attached to the lining of the body wall of segments $3$ to the last and open directly to the exterior of the body surface.
$2$. Because they discharge their waste directly to the outside,they are termed 'exonephric'.
$3$. Septal and pharyngeal nephridia discharge their waste into the alimentary canal,hence they are 'enteronephric'.

(C) $Chloragogen$ cells (also known as yellow cells) are specialized cells found in the earthworm $(Pheretima)$.
These cells are primarily located in the coelomic fluid and are associated with the intestine,where they perform functions analogous to the vertebrate liver,such as glycogen storage,fat metabolism,and excretion.

(C) In earthworms ($Pheretima$ $posthuma$),the male genital pores are a pair of apertures located on the ventro-lateral sides of the $18^{th}$ segment. These pores serve as the exit point for the male reproductive products. In contrast,the female genital pore is single and located mid-ventrally on the $14^{th}$ segment,while the genital papillae are present on the $17^{th}$ and $19^{th}$ segments.

(D) In earthworms,nephridia are classified into three types based on their location: pharyngeal,integumentary,and septal nephridia.
Pharyngeal nephridia occur as three pairs of tufts located in the $4^{th}, 5^{th},$ and $6^{th}$ segments.
They are arranged around the pharynx and are responsible for the excretion of nitrogenous waste.

(C) In the earthworm ($Pheretima$ $posthuma$),the intestine starts from the $15^{th}$ segment.
The typhlosole is a longitudinal fold of the inner wall of the intestine,which increases the effective surface area for absorption.
It begins from the $26^{th}$ segment and extends up to the $25^{th}$ segment before the anus (i.e.,up to the $22^{nd}-25^{th}$ segment from the posterior end).

(B) In earthworms ($Pheretima$ $posthuma$),spermatogenesis takes place in the testes.
Earthworms have two pairs of testes located in the $10^{th}$ and $11^{th}$ segments.
The germ cells in the testes undergo spermatogenesis to produce spermatozoa.
These spermatozoa are then released into the seminal vesicles for maturation and storage.

(C) The correct statement is that the earthworm possesses a brain but no head.
$1$. Earthworms do not have a distinct head region (acephalic).
$2$. They possess a cerebral ganglion,which functions as a brain,located in the anterior segments.
$3$. Option $A$ is incorrect because they require setae for movement.
$4$. Option $B$ is incorrect because the cocoon is secreted by the clitellar glands,but it is not specifically limited to 'fertilized' eggs in the context of the definition of the clitellum's function.
$5$. Option $D$ is incorrect because they possess setae,which are locomotory organs.

(B) Chloragogen cells are specialized cells found in the coelomic fluid and surrounding the intestine of earthworms. They are analogous to the vertebrate liver. Their primary functions include the synthesis of glycogen and fat,deamination of amino acids,and the formation of urea. Because they play a crucial role in metabolic waste processing and nitrogenous waste management,they are primarily associated with the excretory system.

(C) The clitellum is a prominent glandular and non-segmented section of the body wall in earthworms,typically found in segments $14-16$.
Its primary function is the secretion of mucus and albumin,which are essential for the formation of a cocoon.
During the reproductive process,the clitellum secretes a mucous tube that hardens to form a cocoon,within which fertilization and development of the embryos occur.

(B) The cocoon of an earthworm,also known as an ootheca,is a small,lemon-shaped structure.
Its size typically ranges from $2.0$ mm to $2.4$ mm in length.
These cocoons are produced by the clitellar glands and contain the developing embryos.

(B) In earthworms,the pharyngeal region (segments $4, 5,$ and $6$) contains three pairs of pharyngeal glands. These glands consist of chromophil cells. These cells secrete saliva containing mucin and proteolytic enzymes,which help in the digestion of food.

(C) In $Pheretima$ (earthworm),the spermathecae are sensory and reproductive organs.
They are located in the $6^{th}$ to $9^{th}$ segments.
Specifically,four pairs of spermathecae are situated in the $6^{th}, 7^{th}, 8^{th},$ and $9^{th}$ segments,one pair in each segment.
Therefore,the structures found in the $7^{th}$ and $9^{th}$ segments are the spermathecae.

(B) In the earthworm ($Pheretima$ $posthuma$),the circulatory system is of the closed type. The dorsal blood vessel acts as the main distributing vessel. The blood in the dorsal blood vessel flows from the posterior end to the anterior end of the body. This is facilitated by the rhythmic contractions of the vessel walls,which pump the blood towards the anterior region,specifically towards the heart and the anterior segments.

(D) The porphyrin pigment in earthworms is primarily located in the dorsal body wall. Its main function is to protect the earthworm from the harmful effects of ultraviolet $(UV)$ radiation from sunlight. Since earthworms are nocturnal and live in moist soil,they are sensitive to intense light,and this pigment acts as a protective shield.

(C) The famous Indian scientist who conducted extensive research and provided a detailed description of the anatomy and biology of the earthworm $Pheretima$ $posthuma$ is $K. N. Bahl$. His work is considered a classic study in the field of invertebrate zoology in India.

(C) Chloragogen cells are specialized cells found in the coelomic fluid and surrounding the intestine of earthworms $(Pheretima)$.
These cells are analogous to the vertebrate liver in terms of their physiological functions.
They are involved in the synthesis of glycogen and fat,the deamination of amino acids,and the formation of urea,which are primary metabolic functions performed by the liver in vertebrates.