Morphology of Frogs and Anatomy of Anurans Practice
Exam questions and correct answers– Updated 2026
(Graded A+) instant download pdf
Subject: Biology
Subtopic: External Morphology and Integumentary System of Rana tigrina
Question 1: A researcher treats the dorsal skin of a live specimen of Rana tigrina with a mild
adrenergic agonist. Which of the following physiological responses would be most
prominently observed, and what is its primary adaptive significance?
A) Increased mucus secretion to minimize friction during aquatic locomotion.
B) Dispersal of melanin granules within melanophores to facilitate cryptic countershading.
C) Release of toxic or noxious compounds from serous glands to deter potential predators.
D) Rapid lipid secretion from sebaceous glands to maintain skin compliance and prevent
desiccation.
Correct Answer: C - Release of toxic or noxious compounds from serous glands to deter
potential predators. Rationale: The skin of Rana tigrina contains two principal types of
multicellular exocrine glands located in the dermis: mucous glands and serous (poison)
glands. Serous glands are specialized for defense and are stimulated by sympathetic
(adrenergic) activation to release noxious or toxic secretions. Option A is incorrect because
mucous glands are primarily responsible for lubricating the skin to keep it moist for
cutaneous respiration, rather than being the primary adrenergic response for defense.
Option B is incorrect because adrenergic stimulation typically leads to the aggregation of
melanin granules (lightening the skin) rather than dispersal, and color change is regulated
primarily by melanophore-stimulating hormone (MSH). Option D is incorrect because frogs
lack mammalian-style sebaceous glands.
Question 2: Amphibian skin serves as a critical respiratory organ. During periods of complete
submergence, which morphological adaptation of the Rana tigrina integument maximizes
the efficiency of passive cutaneous respiration?
A) A highly keratinized, thick stratum corneum that prevents ion loss.
B) A dense, subepidermal capillary network coupled with a thin, moist stratum corneum.
C) The presence of deep dermal scales that create micro-turbulences in water.
D) Stratified columnar epithelium containing high densities of active transport ion pumps.
Correct Answer: B - A dense, subepidermal capillary network coupled with a thin, moist
stratum corneum. Rationale: For efficient gas exchange across the skin (cutaneous
,respiration), the respiratory surface must be thin, moist, and highly vascularized. Amphibian
skin achieves this through a thin, outermost stratum corneum and a highly developed
capillary network situated immediately beneath the epidermis in the stratum spongiosum of
the dermis. Option A is incorrect because high keratinization restricts gas diffusion. Option C
is incorrect because modern frogs (Anura) lack dermal scales entirely. Option D is incorrect
because the epidermis is stratified squamous epithelium, not columnar, and active ion
transport is related to osmoregulation rather than passive gas exchange.
Question 3: Examination of the hind limbs of Rana tigrina reveals five digits connected by
extensive webbing, whereas the forelimbs possess four digits lacking webs. What functional
and evolutionary trade-off does this sexual dimorphism or morphological asymmetry
highlight?
A) The hind limbs are specialized for saltatory and aquatic propulsion, while the forelimbs
absorb landing impact and assist in amplexus.
B) The forelimbs function as the primary generators of swimming velocity, while the hind
limbs steer.
C) The lack of webbing on the forelimbs is an adaptation designed to reduce drag during
high-speed swimming.
D) The reduction of digits in the forelimb represents an evolutionary transition toward a
completely limbless fossorial lifestyle.
Correct Answer: A - The hind limbs are specialized for saltatory and aquatic propulsion,
while the forelimbs absorb landing impact and assist in amplexus. Rationale: The muscular
hind limbs with webbed digits are highly adapted for powerful leaping (saltatory locomotion)
on land and swimming in water by pushing large volumes of fluid. The shorter forelimbs act
as shock absorbers during landings, and in males, the first digit develops a nuptial pad
during the breeding season to grip the female during amplexus. Option B is incorrect because
the hind limbs, not the forelimbs, generate swimming propulsion. Option C is incorrect
because webbing on forelimbs would increase surface area, but their lack of webbing
minimizes interference during terrestrial walking and handling. Option D is incorrect because
frogs are highly specialized for jumping and leaping, not evolving toward limblessness.
Subtopic: Digestive System and Feeding Mechanics
Question 4: During the feeding mechanism of Rana tigrina, the capture of prey relies on a
highly specialized tongue architecture. Which of the following correctly describes the
anatomical attachment and deployment of the frog's tongue?
A) It is attached at the posterior margin of the buccal cavity and extends via hydrostatic
pressure.
, B) It is attached at the anterior margin of the lower jaw and flips forward so the dorsal
surface hits the prey.
C) It is free at both ends and projected outward via the rapid contraction of the hyoglossus
muscle.
D) It is fixed along its entire ventral surface and depends on sticky salivary secretions to trap
insects passing close by.
Correct Answer: B - It is attached at the anterior margin of the lower jaw and flips forward
so the dorsal surface hits the prey. Rationale: The anuran tongue is bifid and attached
anteriorly at the front of the lower jaw (mandible), with its posterior tip lying free and
directed backward when at rest. During prey capture, the frog flips the tongue rapidly out of
the mouth, causing the inverted free end to strike the prey, adhering it via sticky mucous
secretions. Option A is incorrect because the posterior part is free. Option C is incorrect
because it is securely attached at the anterior end. Option D describes a non-protrusible
tongue, which is not characteristic of Rana.
Question 5: A histological cross-section of the frog's midgut reveals distinct structural layers.
Identify the correct sequence of these layers from the outermost surface facing the coelom
to the innermost surface facing the lumen.
A) Mucosa $\rightarrow$ Submucosa $\rightarrow$ Circular Muscle Layer $\rightarrow$
Longitudinal Muscle Layer $\rightarrow$ Serosa
B) Serosa $\rightarrow$ Longitudinal Muscle Layer $\rightarrow$ Circular Muscle Layer
$\rightarrow$ Submucosa $\rightarrow$ Mucosa
C) Mucosa $\rightarrow$ Circular Muscle Layer $\rightarrow$ Longitudinal Muscle Layer
$\rightarrow$ Submucosa $\rightarrow$ Serosa
D) Serosa $\rightarrow$ Circular Muscle Layer $\rightarrow$ Submucosa $\rightarrow$
Longitudinal Muscle Layer $\rightarrow$ Mucosa
Correct Answer: B - Serosa $\rightarrow$ Longitudinal Muscle Layer $\rightarrow$ Circular
Muscle Layer $\rightarrow$ Submucosa $\rightarrow$ Mucosa Rationale: The standard
vertebrate digestive tract plan, which is clearly defined in the frog, consists of the outermost
visceral peritoneum (serosa), followed by an external layer of longitudinal smooth muscle, an
internal layer of circular smooth muscle, a supportive connective tissue layer (submucosa),
and the innermost absorptive and secretory lining (mucosa). Options A, C, and D reflect
incorrect structural orientations or mixed muscle layers.
Question 6: In Rana tigrina, the hydrochloric acid ($\text{HCl}$) and pepsinogen required for
the initiation of protein digestion are secreted by which specific cells within the gastric
mucosa?
A) Oxyntopeptic cells secrete both $\text{HCl}$ and pepsinogen.
Exam questions and correct answers– Updated 2026
(Graded A+) instant download pdf
Subject: Biology
Subtopic: External Morphology and Integumentary System of Rana tigrina
Question 1: A researcher treats the dorsal skin of a live specimen of Rana tigrina with a mild
adrenergic agonist. Which of the following physiological responses would be most
prominently observed, and what is its primary adaptive significance?
A) Increased mucus secretion to minimize friction during aquatic locomotion.
B) Dispersal of melanin granules within melanophores to facilitate cryptic countershading.
C) Release of toxic or noxious compounds from serous glands to deter potential predators.
D) Rapid lipid secretion from sebaceous glands to maintain skin compliance and prevent
desiccation.
Correct Answer: C - Release of toxic or noxious compounds from serous glands to deter
potential predators. Rationale: The skin of Rana tigrina contains two principal types of
multicellular exocrine glands located in the dermis: mucous glands and serous (poison)
glands. Serous glands are specialized for defense and are stimulated by sympathetic
(adrenergic) activation to release noxious or toxic secretions. Option A is incorrect because
mucous glands are primarily responsible for lubricating the skin to keep it moist for
cutaneous respiration, rather than being the primary adrenergic response for defense.
Option B is incorrect because adrenergic stimulation typically leads to the aggregation of
melanin granules (lightening the skin) rather than dispersal, and color change is regulated
primarily by melanophore-stimulating hormone (MSH). Option D is incorrect because frogs
lack mammalian-style sebaceous glands.
Question 2: Amphibian skin serves as a critical respiratory organ. During periods of complete
submergence, which morphological adaptation of the Rana tigrina integument maximizes
the efficiency of passive cutaneous respiration?
A) A highly keratinized, thick stratum corneum that prevents ion loss.
B) A dense, subepidermal capillary network coupled with a thin, moist stratum corneum.
C) The presence of deep dermal scales that create micro-turbulences in water.
D) Stratified columnar epithelium containing high densities of active transport ion pumps.
Correct Answer: B - A dense, subepidermal capillary network coupled with a thin, moist
stratum corneum. Rationale: For efficient gas exchange across the skin (cutaneous
,respiration), the respiratory surface must be thin, moist, and highly vascularized. Amphibian
skin achieves this through a thin, outermost stratum corneum and a highly developed
capillary network situated immediately beneath the epidermis in the stratum spongiosum of
the dermis. Option A is incorrect because high keratinization restricts gas diffusion. Option C
is incorrect because modern frogs (Anura) lack dermal scales entirely. Option D is incorrect
because the epidermis is stratified squamous epithelium, not columnar, and active ion
transport is related to osmoregulation rather than passive gas exchange.
Question 3: Examination of the hind limbs of Rana tigrina reveals five digits connected by
extensive webbing, whereas the forelimbs possess four digits lacking webs. What functional
and evolutionary trade-off does this sexual dimorphism or morphological asymmetry
highlight?
A) The hind limbs are specialized for saltatory and aquatic propulsion, while the forelimbs
absorb landing impact and assist in amplexus.
B) The forelimbs function as the primary generators of swimming velocity, while the hind
limbs steer.
C) The lack of webbing on the forelimbs is an adaptation designed to reduce drag during
high-speed swimming.
D) The reduction of digits in the forelimb represents an evolutionary transition toward a
completely limbless fossorial lifestyle.
Correct Answer: A - The hind limbs are specialized for saltatory and aquatic propulsion,
while the forelimbs absorb landing impact and assist in amplexus. Rationale: The muscular
hind limbs with webbed digits are highly adapted for powerful leaping (saltatory locomotion)
on land and swimming in water by pushing large volumes of fluid. The shorter forelimbs act
as shock absorbers during landings, and in males, the first digit develops a nuptial pad
during the breeding season to grip the female during amplexus. Option B is incorrect because
the hind limbs, not the forelimbs, generate swimming propulsion. Option C is incorrect
because webbing on forelimbs would increase surface area, but their lack of webbing
minimizes interference during terrestrial walking and handling. Option D is incorrect because
frogs are highly specialized for jumping and leaping, not evolving toward limblessness.
Subtopic: Digestive System and Feeding Mechanics
Question 4: During the feeding mechanism of Rana tigrina, the capture of prey relies on a
highly specialized tongue architecture. Which of the following correctly describes the
anatomical attachment and deployment of the frog's tongue?
A) It is attached at the posterior margin of the buccal cavity and extends via hydrostatic
pressure.
, B) It is attached at the anterior margin of the lower jaw and flips forward so the dorsal
surface hits the prey.
C) It is free at both ends and projected outward via the rapid contraction of the hyoglossus
muscle.
D) It is fixed along its entire ventral surface and depends on sticky salivary secretions to trap
insects passing close by.
Correct Answer: B - It is attached at the anterior margin of the lower jaw and flips forward
so the dorsal surface hits the prey. Rationale: The anuran tongue is bifid and attached
anteriorly at the front of the lower jaw (mandible), with its posterior tip lying free and
directed backward when at rest. During prey capture, the frog flips the tongue rapidly out of
the mouth, causing the inverted free end to strike the prey, adhering it via sticky mucous
secretions. Option A is incorrect because the posterior part is free. Option C is incorrect
because it is securely attached at the anterior end. Option D describes a non-protrusible
tongue, which is not characteristic of Rana.
Question 5: A histological cross-section of the frog's midgut reveals distinct structural layers.
Identify the correct sequence of these layers from the outermost surface facing the coelom
to the innermost surface facing the lumen.
A) Mucosa $\rightarrow$ Submucosa $\rightarrow$ Circular Muscle Layer $\rightarrow$
Longitudinal Muscle Layer $\rightarrow$ Serosa
B) Serosa $\rightarrow$ Longitudinal Muscle Layer $\rightarrow$ Circular Muscle Layer
$\rightarrow$ Submucosa $\rightarrow$ Mucosa
C) Mucosa $\rightarrow$ Circular Muscle Layer $\rightarrow$ Longitudinal Muscle Layer
$\rightarrow$ Submucosa $\rightarrow$ Serosa
D) Serosa $\rightarrow$ Circular Muscle Layer $\rightarrow$ Submucosa $\rightarrow$
Longitudinal Muscle Layer $\rightarrow$ Mucosa
Correct Answer: B - Serosa $\rightarrow$ Longitudinal Muscle Layer $\rightarrow$ Circular
Muscle Layer $\rightarrow$ Submucosa $\rightarrow$ Mucosa Rationale: The standard
vertebrate digestive tract plan, which is clearly defined in the frog, consists of the outermost
visceral peritoneum (serosa), followed by an external layer of longitudinal smooth muscle, an
internal layer of circular smooth muscle, a supportive connective tissue layer (submucosa),
and the innermost absorptive and secretory lining (mucosa). Options A, C, and D reflect
incorrect structural orientations or mixed muscle layers.
Question 6: In Rana tigrina, the hydrochloric acid ($\text{HCl}$) and pepsinogen required for
the initiation of protein digestion are secreted by which specific cells within the gastric
mucosa?
A) Oxyntopeptic cells secrete both $\text{HCl}$ and pepsinogen.
