Anatomy of frog Questions in English

(B) In the frog's circulatory system,the $Precaval$ $veins$ (also known as $Superior$ $venae$ $cavae$) collect deoxygenated blood from the anterior parts of the body and head region.
Since these veins drain blood directly from the tissues where oxygen has been consumed,they carry the most deoxygenated blood before it enters the sinus venosus.
In contrast,the $Pulmocutaneous$ $artery$ carries deoxygenated blood from the heart to the lungs and skin for oxygenation.
The $Pulmonary$ $vein$ carries oxygenated blood from the lungs to the left atrium.
Therefore,the $Precaval$ $vein$ is the correct answer.

(D) Frogs exhibit cutaneous respiration,which is respiration through the skin.
This process occurs when the frog is in water,on land,and during hibernation (or aestivation).
Since the skin is moist and rich in blood vessels,it allows for the exchange of gases in all these environments.
Therefore,the correct answer is $D$ (All of the above).

(C) The heart rate of a frog is typically around $64$ beats per minute.
This rate can vary depending on factors such as temperature and the physiological state of the organism,but $64$ beats/minute is the standard value cited in biological studies for a resting frog.

(A) During hibernation (winter sleep) and aestivation (summer sleep),the metabolic rate of the frog decreases significantly.
In this state,the frog remains buried in the soil and does not use its lungs for breathing.
Instead,it performs respiration through its moist skin,which is known as cutaneous respiration.
Therefore,the correct answer is $A$.

(D) The renal portal system is a circulatory arrangement where blood from the posterior part of the body is transported to the kidneys before returning to the heart. This system is well-developed in amphibians (like frogs),reptiles,and birds,but it is absent in mammals (such as rabbits,rats,and horses). Therefore,among the given options,the frog possesses a renal portal system.

(A) Frogs exhibit multiple modes of respiration,including cutaneous (through skin),pulmonary (through lungs),and buccopharyngeal (through the mouth lining).
Cutaneous respiration is the most critical mode for a frog's survival,especially during hibernation and aestivation,as it is the only method that allows for continuous gas exchange when the frog is submerged in water or buried in mud.
Therefore,cutaneous respiration is essential for the survival of a frog.

(D) In the heart of a frog, the $Sinus$ $\text{venosus}$ is a thin-walled, triangular chamber that receives deoxygenated blood from the venae cavae.
It acts as the pacemaker of the frog's heart because it initiates the heartbeat.
Therefore, the correct option is $D$.

(A) The heart of a frog is $3$-chambered, consisting of two atria and one ventricle. It also possesses a triangular structure called the $Sinus venosus$ which joins the right atrium and receives deoxygenated blood from the body. In contrast, the heart of a rabbit (a mammal) is $4$-chambered and lacks a $Sinus venosus$. Therefore, the presence of the $Sinus venosus$ is a characteristic feature that distinguishes the amphibian heart from the mammalian heart.

(A) The skin of a frog is moist and slimy due to the presence of mucus. This moisture is maintained by the cutaneous glands located in the skin. These glands are classified as $Simple$ $tubular$ glands. They are unicellular or multicellular structures that secrete mucus to keep the skin moist for cutaneous respiration.

(A) When a bone is placed in dilute $HCl$ (hydrochloric acid),the acid reacts with the calcium salts (calcium phosphate and calcium carbonate) present in the bone matrix.
This process is known as decalcification.
As the calcium salts are dissolved by the acid,the bone loses its hardness and rigidity.
Consequently,the remaining organic matrix,primarily composed of collagen fibers,makes the bone soft and flexible,allowing it to be bent easily.

(B) The venous system of a frog includes a $Renal$ $portal$ $system$,which is a network of veins that carries blood from the hind limbs to the kidneys before it enters the systemic circulation.
In contrast,mammals like rabbits lack a $Renal$ $portal$ $system$.
Both frogs and rabbits possess a $Hepatic$ $portal$ $system$,which transports blood from the digestive tract to the liver.
Therefore,the presence of the $Renal$ $portal$ $system$ is a distinguishing feature of the frog's venous system compared to that of a rabbit.

(D) The teeth in a frog are $Acrodont$,meaning they are attached to the surface of the jaw bone without being embedded in sockets. They are also $Homodont$,as all teeth are similar in shape and structure. However,in the context of attachment type,$Acrodont$ is the specific term used to describe the teeth of a frog.

(C) In male frogs,the ureters emerge from the kidneys and open into the cloaca.
In males,the ureters act as a urinogenital duct,which carries both urine and sperms.
Therefore,the ureter serves the dual function of transporting excretory waste (urine) and reproductive cells (sperms) in male frogs.

(D) In frogs,the upper jaw contains teeth,but the lower jaw is toothless. This is a characteristic feature of the frog's oral anatomy,where teeth are primarily used for holding prey rather than chewing.

(A) In frogs,the kidneys are compact,dark red,and bean-like structures situated a little towards the posterior side in the body cavity on both sides of the vertebral column.
They are located at the same level in the body cavity.

(A) In frogs,the vocal sac is a specialized structure present only in the male.
It acts as a resonator to amplify the croaking sound produced by the male frog during the mating season to attract females.
Female frogs do not possess vocal sacs.

(B) The skull of a frog is $Dicondylic$.
This means that the skull articulates with the vertebral column by means of two occipital condyles.
These condyles are present on the exoccipital bones of the skull,which fit into the atlas vertebra of the frog.

(D) Frogs exhibit cutaneous respiration during hibernation and aestivation.
In this process,the skin acts as an aquatic respiratory organ because it is moist and rich in blood capillaries,allowing for the diffusion of gases directly between the blood and the environment.
Since the frog remains inactive and buried in mud during hibernation,it does not use its lungs for breathing.

(B) In amphibians like frogs,the kidneys are of the $Mesonephric$ type.
During embryonic development,the pronephros is the first kidney to form,but it is non-functional in adult frogs.
The mesonephros develops later and serves as the functional kidney in both the larval stage and the adult stage of the frog.
Metanephros is the type of kidney found in higher vertebrates like reptiles,birds,and mammals.

(A) Frogs are amphibians that require water for their reproductive cycle.
They exhibit external fertilization,where the male and female release their gametes into the water.
The eggs are laid in water,where they develop into tadpoles.
Therefore,water is essential for their breeding process.

(D) The kidney of a frog is mesonephric and compact. Unlike the mammalian kidney,which contains renal pyramids (medullary pyramids) within the medulla,the frog's kidney does not possess such structures. Therefore,renal pyramids are absent in the frog's kidney.

(B) Frogs exhibit seasonal variations in their activity patterns to survive extreme temperatures.
$1$. Hibernation is the period of winter sleep,where the frog remains inactive during cold months to conserve energy.
$2$. Aestivation is the period of summer sleep,where the frog remains inactive during hot and dry months to prevent desiccation and conserve energy.
Therefore,the summer sleep of a frog is known as Aestivation.

(A) In the kidney of a frog,the internal structure is not as complex as that of mammals. The kidney is composed of numerous uriniferous tubules or nephrons. Unlike the mammalian kidney,the frog's kidney does not show a clear demarcation between the outer cortex and the inner medulla. Therefore,these regions are less differentiated.

(A) In male frogs,the $Bidder's$ canal is located within the $kidney$.
It is a longitudinal canal that receives the $vasa$ $efferentia$ from the $testis$.
These $vasa$ $efferentia$ carry spermatozoa from the $testis$ to the $Bidder's$ canal,which then connects to the $urinogenital$ $duct$ to transport sperm out of the body.

(D) In frogs,the kidneys are the primary excretory organs.
They perform two major functions:
$1$. Excretion: They filter nitrogenous wastes (primarily urea) from the blood to form urine.
$2$. Osmoregulation: They maintain the water and electrolyte balance in the body fluids.
While blood cell formation (haemopoiesis) primarily occurs in the bone marrow in higher vertebrates,in frogs,the kidney and other organs like the liver and spleen play roles in blood-related processes during different developmental stages.
Therefore,all the listed functions are associated with the renal system in frogs.

(A) The skin of a frog is smooth and slippery due to the presence of mucus. The skin contains numerous mucous glands that secrete mucus to keep the skin moist,which is essential for cutaneous respiration. Frogs do not possess sweat glands or mammary glands.

(A) In a frog,the spinal cord gives rise to spinal nerves that emerge through the intervertebral foramina.
There are $10$ pairs of spinal nerves in a frog.
These nerves are responsible for transmitting sensory and motor signals between the spinal cord and various parts of the body.

(D) Frogs exhibit cutaneous respiration,meaning they can breathe through their moist,slimy skin. This process is essential for their survival,especially when they are submerged in water or during hibernation. Because their skin must remain moist to facilitate the diffusion of gases ($O_2$ and $CO_2$),they are restricted to living in or near aquatic environments.

(C) In vertebrates,including frogs and rabbits,the liver and pancreas are glandular organs associated with the digestive system.
These organs develop from the endoderm,which is the innermost germ layer formed during gastrulation.
The endoderm is responsible for forming the epithelial lining of the digestive tract and its associated glands,such as the liver and pancreas.

(D) In frogs,there are $10$ pairs of cranial nerves.
The $9^{th}$ pair of cranial nerves is the Glossopharyngeal nerve.
It primarily supplies the tongue and the pharynx.
Therefore,the correct option is $D$.

(C) The optic ventricle,also known as the optic lobe cavity or optocoel,is a characteristic feature of the brain of lower vertebrates,particularly amphibians like the frog.
In the frog's brain,the optic lobes (mesencephalon) contain a cavity called the optocoel,which connects to the cerebral aqueduct (iter).
In higher vertebrates like mammals (rabbits and humans),the optic lobes are represented by the corpora quadrigemina,which are solid structures and do not contain a ventricle.

(C) The $Swammerdam$ gland,also known as the $calcareous$ gland,is found in amphibians,particularly in the $paravertebral$ region of frogs.
These glands are specialized structures that store calcium carbonate.
They are primarily involved in calcium metabolism and are associated with the skeletal system (bones) as they provide a reservoir of calcium for bone formation and physiological processes.
Therefore,the correct option is $C$.

(B) In frogs,the sclera of the eye is not composed of fibrous connective tissue like in mammals,but rather it is supported by a cartilaginous structure known as the sclerotic cartilage. This provides structural integrity and protection to the eyeball within the orbit. Therefore,the correct option is $B$.

(C) The lens of a frog's eye is spherical in shape. Unlike the human eye,which has a biconvex lens that changes shape for accommodation,the frog's lens is a fixed,spherical structure. Accommodation in frogs is achieved by moving the lens forward or backward rather than changing its curvature.

(A) In frogs,the eyes are protected by a transparent,movable membrane called the nictitating membrane. The upper eyelid is fixed,while the lower eyelid is movable (active). Therefore,the eyelid in a frog is considered active.

(A) In frogs $(Rana \, tigrina)$, the spinal cord gives rise to spinal nerves that emerge through the intervertebral foramina.
There are $10$ pairs of spinal nerves in a frog.
These nerves are responsible for transmitting sensory and motor signals between the spinal cord and various parts of the body.

(B) In frogs $(Rana \, tigrina)$, the nervous system includes a brain enclosed in a cranium. There are $10$ pairs of cranial nerves that arise from the brain. These nerves are responsible for sensory and motor functions in the head and neck region.

(C) In frogs,the cranial nerves are responsible for sensory and motor functions in the head region.
Specifically,the $5^{th}$ cranial nerve,known as the Trigeminal nerve,branches into several parts.
The Maxillary branch innervates the upper jaw,while the Palatine branch is associated with the roof of the mouth (palate).
Therefore,both the Maxillary and Palatine nerves are involved in the innervation of the upper jaw region of the frog.

(A) The brain of a rabbit (a mammal) is more advanced than that of a frog (an amphibian).
$1$. The $Corpus \ Callosum$ is a thick band of nerve fibers that connects the two cerebral hemispheres,which is present in mammals like rabbits but absent in frogs.
$2$. The optic lobes in frogs are two in number (bilobed),whereas in rabbits,they are four in number (corpora quadrigemina).
$3$. Therefore,the presence of the $Corpus \ Callosum$ and the number of optic lobes are key anatomical differences.
$4$. Since $Corpus \ albicans$ is not a standard comparative feature of the brain,the most significant structural difference listed is the $Corpus \ Callosum$.

(B) Frogs have eyes located on the sides of their head,which allows them to have a wide field of view. This type of vision,where each eye sees a different field,is known as monocular vision. Therefore,the correct answer is monocular.

(C) Frogs and humans both possess paired cerebral hemispheres,a hepatic portal system,and thyroid/parathyroid glands. However,the most significant difference in their blood characteristics is that frogs have nucleated red blood cells (erythrocytes),whereas mature human red blood cells are enucleated (lack a nucleus) to provide more space for hemoglobin.

(D) In frogs,the cloaca is a common chamber that serves as the exit point for multiple systems.
$1$. The digestive system ends at the cloaca,where undigested waste (feces) is expelled.
$2$. The excretory system (urinary system) opens into the cloaca to release urine.
$3$. The reproductive system (gametes) also discharges into the cloaca during reproduction.
Therefore,all three systems open into the cloaca.

(B) In frogs, the alimentary canal is short because frogs are carnivores and hence the length of the intestine is reduced. The alimentary canal terminates into a common chamber called the $Cloaca$. The $Cloaca$ receives the products of the digestive, reproductive, and excretory systems and opens to the exterior through the $Cloacal$ \text{ } $aperture$.

(A) Frogs exhibit cutaneous respiration,meaning they can exchange gases through their skin. This is possible because their skin is kept moist and slimy by mucus secretions,which facilitates the diffusion of oxygen and carbon dioxide. Furthermore,the skin is highly vascularized and lacks an exoskeleton,allowing for efficient gas exchange. Therefore,both the assertion and the reason are correct,and the reason explains why the skin functions as a respiratory organ.

(D) The cloaca is a common chamber or opening for the digestive,urinary,and reproductive tracts in many vertebrates,including amphibians,reptiles,and birds. It serves as the exit point for feces,urine,and reproductive products (eggs or sperm). Therefore,it acts as the terminal part of the digestive system (after the rectum),the urinary tract,and the reproductive tract. Thus,all the given options are correct.

(A) The statement 'Frogs do not have teeth' is incorrect because frogs possess vomerine teeth and maxillary teeth in their upper jaw to hold their prey. Birds lack teeth and have a beak instead. Mammals typically exhibit diphyodont dentition,meaning they have two sets of teeth during their lifetime: milk teeth (deciduous) and permanent teeth. Reptiles generally possess teeth,although the number and type vary significantly among species.

(D) The correct evaluation of the statements is as follows:
$A.$ False: Frogs perform cutaneous respiration (through skin) in addition to pulmonary respiration. Even if the mouth is kept closed,they can survive by breathing through their moist skin.
$B.$ False: The heart of a frog is three-chambered,consisting of two atria and one ventricle.
$C.$ False: Frogs are ureotelic (excrete urea) and do not change their mode of nitrogenous waste excretion to uricotelic (excreting uric acid) on land.
$D.$ True: The life cycle of a frog involves external fertilization in water,followed by the development of aquatic larvae (tadpoles) which eventually undergo metamorphosis to become adults.
Thus,the correct sequence is $(A)-F, (B)-F, (C)-F, (D)-T$. Since this sequence is not provided in the options,the correct choice is 'None of these'.

(C) The correct route for the transport of sperms in a male frog is:
Testes $\rightarrow$ Vasa efferentia $\rightarrow$ Kidney $\rightarrow$ Bidder’s canal $\rightarrow$ Urinogenital duct $\rightarrow$ Cloaca.
In male frogs,sperms are produced in the testes. They travel through $10-12$ vasa efferentia into the kidneys. Within the kidneys,they enter the Bidder’s canal,which communicates with the urinogenital duct. Finally,the sperms are released into the cloaca and then to the exterior.

(B) : Human erythrocytes are enucleated (lack a nucleus) and discoidal in shape. In contrast,frog erythrocytes are large,oval,biconvex,and nucleated cells. Both human and frog erythrocytes contain the respiratory pigment haemoglobin,which is responsible for oxygen transport.

(C) : Human erythrocytes are enucleated and discoidal,whereas in frogs,erythrocytes are large,oval,and biconvex nucleated cells. Erythrocytes are the carriers of haemoglobin.