Class-Amphibia Questions in English

(B) The heart structure varies across vertebrate classes:
$1$. Two-chambered heart with one auricle and one ventricle is present in $Pisces$ (fishes).
$2$. Three-chambered heart,having two auricles and one ventricle,is present in $Amphibia$ and most $Reptilia$ (except crocodiles).
$3$. Four-chambered heart with two auricles and two ventricles is present in crocodiles,$Aves$ (birds),and $Mammalia$ (mammals).
Therefore,amphibians possess a three-chambered heart.

(A) The correct answer is $A$.
Amphibians are characterized by having moist,glandular skin that is typically devoid of scales.
While some amphibians like caecilians may have dermal scales embedded in the skin,the general diagnostic feature of the class $Amphibia$ is the absence of external scales,unlike the class $Reptilia$.
Options $B$,$C$,and $D$ are characteristic features of amphibians: they possess two pairs of limbs for movement,have eyelids,and are ectothermic (cold-blooded).

(B) Tails are not present in all amphibians; for example,the order $Anura$ (e.g.,$Bufo$ (Toad),$Rana$ (Frog)) is tailless in the adult stage.
Excretion in amphibians occurs via mesonephric kidneys.
In amphibians,the alimentary canal,urinary tract,and reproductive tract open into a common chamber called the $cloaca$.
The heart in amphibians is three-chambered,consisting of two auricles (atria) and one ventricle.

(A) The skin of a toad is characterized by being rough,dry,and warty,often with a brown-spotted dorsal surface and a pale ventral surface.
In contrast,frogs possess skin that is moist,smooth,and slimy to facilitate cutaneous respiration.
The body of $Ichthyophis$ (a caecilian) is also covered by smooth,slimy skin.
Therefore,the correct answer is $A$.

(D) The heart of a frog is three-chambered,consisting of two atria and a single ventricle.
In this structure,oxygenated blood from the left atrium and deoxygenated blood from the right atrium enter the same single ventricle.
Consequently,the blood gets mixed within the ventricle before being pumped out to the rest of the body.
This phenomenon is referred to as incomplete double circulation.

(C) The first amphibians originated during the $Devonian$ period.
This period is often referred to as the 'Age of Fishes'.
The $Carboniferous$ period is known as the 'Age of Amphibians' because they became dominant and diversified significantly during that time.

(C) Ectothermic animals are organisms that cannot regulate their internal body temperature through metabolic processes. Instead,they rely on external environmental sources to control their body temperature. These animals are also known as poikilothermic or cold-blooded animals. Examples include reptiles,fish,and amphibians,whose body temperatures fluctuate according to the changes in the ambient environmental temperature.

(C) $Bufo$ (Toad) possesses a pair of large parotoid glands located behind the eyes. These glands secrete a milky,toxic fluid that acts as a defense mechanism against predators.

(B) $Ambystoma$ belongs to the order $Urodela$ of the class $Amphibia$.
The larva of $Ambystoma$ is known as the $Axolotl$ larva.
$Axolotl$ larvae exhibit $paedogenesis$,a phenomenon where the larval stage attains sexual maturity and reproduces.

(B) In toads belonging to the genus $Bufo$,teeth are completely absent in both the upper and lower jaws. In contrast,frogs like $Rana$ possess teeth in the upper jaw.

(C) Paedogenesis is the phenomenon where sexual reproduction occurs in the larval stage,$i.e.$,the larva becomes sexually mature.
Neoteny is the retention of larval characters in a sexually mature individual.
$Ambystoma$ (specifically the Axolotl larva) exhibits both paedogenesis and neoteny.

(C) The Assertion is correct because both amphibians and mammals possess a dicondylic skull,which means the skull articulates with the vertebral column via two occipital condyles.
The Reason is incorrect because the number of cranial nerves differs between these two classes. Amphibians typically have $10$ pairs of cranial nerves,whereas mammals possess $12$ pairs of cranial nerves.

(N/A) $\rightarrow$ As the name indicates (Gr.,$Amphi$: dual,$bios$: life),amphibians can live in both aquatic and terrestrial habitats.
$\rightarrow$ Most of them have two pairs of limbs.
$\rightarrow$ The body is divisible into head and trunk. $A$ tail may be present in some.
$\rightarrow$ The skin is moist and lacks scales.
$\rightarrow$ The eyes have eyelids.
$\rightarrow$ $A$ tympanum represents the ear.
$\rightarrow$ The alimentary canal,urinary,and reproductive tracts open into a common chamber called the cloaca,which opens to the exterior.
$\rightarrow$ Respiration occurs through gills,lungs,and the skin.
$\rightarrow$ The heart is three-chambered (two auricles and one ventricle).
$\rightarrow$ These are cold-blooded (poikilothermous) animals.
$\rightarrow$ Sexes are separate,and fertilization is usually external. They are oviparous and undergo indirect development.

(N/A) $\rightarrow$ As the name indicates (Gr.,Amphi : dual,bios : life),amphibians can live in both aquatic and terrestrial habitats.
$\rightarrow$ Most of them possess two pairs of limbs.
$\rightarrow$ The body is divisible into head and trunk; a tail may be present in some.
$\rightarrow$ The skin is moist and lacks scales.
$\rightarrow$ The eyes have eyelids.
$\rightarrow$ $A$ tympanum represents the ear.
$\rightarrow$ The alimentary canal,urinary,and reproductive tracts open into a common chamber called the cloaca,which opens to the exterior.
$\rightarrow$ Respiration occurs through gills,lungs,and the skin.
$\rightarrow$ The heart is three-chambered (two auricles and one ventricle).
$\rightarrow$ These are cold-blooded (poikilothermic) animals.
$\rightarrow$ Sexes are separate,and fertilization is usually external.

(N/A) $\rightarrow$ Amphibians are adapted to live in both aquatic and terrestrial habitats.
$\rightarrow$ Their skin is moist and devoid of scales,which acts as a major respiratory organ during cutaneous respiration in water.
$\rightarrow$ The hind limbs are often webbed,which facilitates efficient swimming in aquatic environments.
$\rightarrow$ Fertilization is external and occurs in water,and the larval stage (e.g.,tadpole) undergoes metamorphosis exclusively in water.
$\rightarrow$ These dual adaptations allow them to successfully exploit both water and land environments.

(N/A) $\rightarrow$ Amphibians are cold-blooded $(poikilothermic)$ animals.
$\rightarrow$ During extreme winter and summer seasons,they bury themselves deep in the mud of dried lakes or ponds to remain inactive,which helps them survive extreme fluctuations in temperature.
$\rightarrow$ Hibernation refers to the period of inactivity during winter to escape cold,while aestivation refers to the period of inactivity during summer to escape heat and desiccation.
$\rightarrow$ Thus,amphibians exhibit both hibernation and aestivation.

(D) In amphibians,the cloaca is a common chamber that serves as the exit point for three distinct systems:
$1$. The alimentary canal (digestive tract) opens into the cloaca to discharge fecal matter.
$2$. The urinary tract (excretory system) opens into the cloaca to discharge urine.
$3$. The reproductive tract (genital system) opens into the cloaca to discharge gametes (sperm or eggs).
Therefore,all these tracts open into the cloaca.

(C) External fertilization is a process where the fusion of male and female gametes occurs outside the body of the female organism.
In the class $Amphibia$,most species,including toads and frogs,release their eggs and sperm into the water,where fertilization takes place.
Tree lizards,crocodiles,and leopards are amniotes that exhibit internal fertilization,where the fusion of gametes occurs inside the female's body.

(A) Amphibians are unique among vertebrates as they can live in both aquatic and terrestrial habitats. They possess a dual mode of respiration: they use their moist skin for cutaneous respiration (often in water) and lungs for pulmonary respiration (on land). This allows them to survive in both environments.

(D) Indirect development refers to a life cycle that includes a larval stage that is morphologically distinct from the adult.
In the class $Amphibia$,most species undergo metamorphosis.
$Toad$ $(Bufo)$,$Salamander$ $(Salamandra)$,and $Ichthyophis$ are all amphibians.
These organisms typically lay eggs in water,which hatch into aquatic larvae (such as tadpoles in toads) that undergo metamorphosis to become adults.
Therefore,all the given organisms exhibit indirect development.

(B) The correct answer is $Ichthyophis$.
$1$. $Hippocampus$ (Sea horse) belongs to the class $Osteichthyes$ (bony fishes).
$2$. $Ichthyophis$ is a limbless amphibian belonging to the class $Amphibia$.
$3$. $Pterophyllum$ (Angel fish) belongs to the class $Osteichthyes$.
$4$. $Calotes$ (Garden lizard) belongs to the class $Reptilia$.

(D) In many amphibians and reptiles,the external ear is absent,and the tympanum (eardrum) is exposed on the surface of the head to receive sound vibrations.
$Bufo$ (toad) and $Hyla$ (tree frog) are amphibians that possess a visible tympanum.
$Chameleon$ is a reptile that also possesses a visible tympanum representing the ear.
Therefore,all the given organisms represent the ear by a tympanum.

(A) The class $Amphibia$ is characterized by the following features:
$1$. They can live in both aquatic and terrestrial habitats.
$2$. The heart is $3$-chambered ($2$ atria and $1$ ventricle).
$3$. The skin is moist and lacks scales; it usually contains mucous glands.
$4$. They are cold-blooded (poikilothermic) animals.
Evaluating the options:
- Option $A$: $Amphibians$ have a $3$-chambered heart. This statement is correct.
- Option $B$: They are not restricted to terrestrial habitats; they are found in both aquatic and terrestrial environments.
- Option $C$: These are characteristics of the class $Aves$ (birds),not $Amphibia$.
- Option $D$: $Amphibian$ skin is moist and contains glands,not dry and glandless.
Since the question asks for the statement that is 'not incorrect' (i.e.,the correct statement),Option $A$ is the correct answer.