Frog anatomy is a recurring NEET topic that tests whether you can correctly match organs, structures, and systems to their specific locations and functions in Rana tigrina (Indian bull frog). The common confusion: mixing up features across organ systems — placing the sinus venosus in the arterial side, confusing the hepatic portal system with the renal portal system, or swapping sensory cranial nerves.
External morphology. The frog body divides into head and trunk (no neck, no tail in adult). Skin is smooth, moist, and permeable — functions in cutaneous respiration. The dorsal side is olive green (camouflage); ventral side is pale yellow. The tympanum (external ear) sits behind each eye. Forelimbs have four digits; hindlimbs have five webbed digits (NCERT Class 11 Biology Chapter 7, page 80).
Digestive system. Mouth → buccal cavity (with bilobed tongue attached anteriorly, free posteriorly — flips out to catch prey) → oesophagus → stomach → duodenum → ileum → rectum → cloaca. Liver secretes bile stored in the gall bladder; pancreas lies between stomach and duodenum.
Circulatory system. Three-chambered heart: two atria + one ventricle. The sinus venosus receives deoxygenated blood and opens into the right atrium. Conus arteriosus arises from the ventricle. The hepatic portal system carries blood from intestine to liver; the renal portal system carries blood from lower body to kidneys. RBCs are nucleated and biconvex.
Nervous system. Brain has forebrain (olfactory lobes, cerebral hemispheres), midbrain (optic lobes), and hindbrain (cerebellum, medulla oblongata). Ten pairs of cranial nerves. Spinal cord with spinal nerves.
Watch out: NEET frequently tests portal systems (hepatic vs renal), tongue attachment (anterior, not posterior), heart chamber count, and the number of cranial nerves (10, not 12 — that is mammals).
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
How many pairs of cranial nerves are present in a frog?
Answer: C. Frogs have 10 pairs of cranial nerves, as stated in NCERT Class 11 Biology Chapter 7. Mammals have 12 pairs — a frequent confusion point.
Why A is wrong: A is wrong because 12 pairs of cranial nerves is the count for mammals, not amphibians. This is a common term-swap between frog and human nervous system facts.
Why B is wrong: B is wrong because 31 is the number of pairs of spinal nerves in humans, not cranial nerves in frogs.
Why D is wrong: D is wrong because no standard vertebrate group studied in NCERT has exactly 8 pairs of cranial nerves.
The tympanum in a frog is located:
Answer: D. The tympanum (external ear) is a circular membrane located behind each eye, as described in NCERT Class 11 Biology Chapter 7, page 80. It receives sound vibrations and transfers them to the middle ear.
Why A is wrong: A is wrong because the ventral side of the head contains the mouth opening, not the tympanum.
Why B is wrong: B is wrong because the buccal cavity contains the tongue, vomerine teeth, and internal nares — the tympanum is an external structure.
Why C is wrong: C is wrong because the dorsal surface near the nostrils houses the external nares, not the tympanum.
The tongue of a frog is attached at the:
Answer: A. The frog's tongue is bilobed, attached anteriorly and free posteriorly. This arrangement allows it to flip out rapidly to catch insects — NCERT Class 11 Biology Chapter 7.
Why B is wrong: B is wrong because it reverses the attachment. In humans the tongue is attached posteriorly, but in frogs it is the opposite — attached anteriorly. This is a high-frequency swap in NEET questions.
Why C is wrong: C is wrong because the tongue is not centrally attached; it is fixed at the front margin of the lower jaw.
Why D is wrong: D is wrong because while the hyoid supports the tongue, the tongue does have a free posterior end that flips outward.
A student observes nucleated, biconvex red blood cells in a blood smear. The sample most likely belongs to:
Answer: A. Frog RBCs are nucleated and biconvex. Mammalian RBCs (human, rat) are enucleated and biconcave. Camel RBCs are oval but enucleated. NCERT Class 11 Biology Chapter 7.
Why B is wrong: B is wrong because human RBCs are enucleated (no nucleus in mature cells) and biconcave, not biconvex.
Why C is wrong: C is wrong because camel RBCs, while oval-shaped, are enucleated like all mammalian RBCs.
Why D is wrong: D is wrong because rat RBCs are enucleated and biconcave — typical mammalian pattern.
Blood from the intestine of a frog travels to the liver before reaching the heart. This pathway is called the:
Answer: B. The hepatic portal system carries nutrient-rich blood from the intestine to the liver for processing before it enters the general circulation. The renal portal system, by contrast, carries blood from the lower body to the kidneys. NCERT Class 11 Biology Chapter 7.
Why A is wrong: A is wrong because the renal portal system connects the lower limbs/body to the kidneys, not the intestine to the liver. Swapping hepatic and renal portal systems is a frequent confusion.
Why C is wrong: C is wrong because pulmonary circulation refers to blood flow between the heart and lungs for gas exchange, not nutrient processing.
Why D is wrong: D is wrong because systemic circulation is the general circuit supplying oxygenated blood to body tissues — it does not specifically describe the intestine-to-liver portal route.
The sinus venosus in a frog's heart receives blood and opens into the:
Answer: B. The sinus venosus collects deoxygenated blood from the body and empties it into the right atrium. The left atrium receives oxygenated blood from the lungs. NCERT Class 11 Biology Chapter 7.
Why A is wrong: A is wrong because the left atrium receives oxygenated blood from the lungs via pulmonary veins, not deoxygenated blood from the sinus venosus.
Why C is wrong: C is wrong because the conus arteriosus is the outflow vessel from the ventricle — it distributes blood away from the heart, not into it.
Why D is wrong: D is wrong because the ventricle receives blood from both atria, not directly from the sinus venosus.
A frog can respire through its skin even when submerged underwater. Which property of frog skin makes this possible?
Answer: C. Frog skin is thin, moist, and richly supplied with blood capillaries, enabling cutaneous respiration by direct diffusion of gases across the skin surface. NCERT Class 11 Biology Chapter 7.
Why A is wrong: A is wrong because frog skin is NOT keratinised or thick. Heavy keratinisation would block gas diffusion. This describes reptilian skin.
Why B is wrong: B is wrong because spiracles are respiratory openings found in insects and some cartilaginous fishes, not in frogs.
Why D is wrong: D is wrong because frogs lack skin scales entirely. Scales are characteristic of reptiles and fishes.
A frog's heart has two atria and one ventricle. The conus arteriosus distributes blood from the ventricle to different arteries. If the conus arteriosus were absent, which of the following would be the most direct consequence?
Answer: D. The conus arteriosus contains a spiral valve that helps direct relatively deoxygenated blood toward the lungs and skin, and relatively oxygenated blood toward the body. Without it, the differential distribution of mixed ventricular blood to pulmonary vs systemic circuits would be lost. NCERT Class 11 Biology Chapter 7.
Why A is wrong: A is wrong because mixing of blood in the ventricle already occurs to some degree — this is a structural feature of the single ventricle, not a consequence of losing the conus arteriosus.
Why B is wrong: B is wrong because cutaneous respiration depends on moist, vascularised skin — it is independent of cardiac outflow structures. The frog would still use buccal and pulmonary respiration; only the efficiency of blood distribution would be impaired.
Why C is wrong: C is wrong because the sinus venosus receives blood from systemic veins (vena cavae). Its inflow is independent of the conus arteriosus, which is on the outflow side.
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Given
A question states: "In a frog, the portal system that carries blood from the hind limbs to the kidneys before it returns to the heart is called ___."
Four options are offered:• A. Hepatic portal system• B. Renal portal system• C. Pulmonary portal system• D. Systemic portal system
Required
Identify which portal system connects the hind limbs/lower body to the kidneys.
Concept
Frogs possess two portal systems. A portal system is a venous pathway where blood passes through two capillary beds before returning to the heart. The hepatic portal system routes intestinal blood through the liver. The renal portal system routes blood from the posterior body through the kidneys.
Formula
No formula applies — this is a recall-and-apply concept question. The key mapping:• Intestine → Liver = Hepatic portal• Hind limbs → Kidneys = Renal portal
Substitution
The question specifies "hind limbs to kidneys." Match to: Renal portal system.
Calculation
No calculation. Direct conceptual matching.
Final answer
B. Renal portal system.
Common trap
The most common error is selecting "Hepatic portal system" because students remember "portal system" and default to the more frequently discussed hepatic version. The word "hepatic" (liver) vs "renal" (kidney) is the distinguishing cue — read the destination organ in the stem.
Similar NEET-style question
"The blood from the digestive tract of a frog reaches the liver through the ___." (Answer: Hepatic portal system — the mirror question testing the same two-portal mapping.)
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Frog (*Rana tigrina*): poikilothermic; smooth, moist skin (cutaneous respiration); two-chambered atrium + one ventricle; mesonephric kidney; urinogenital duct in male; cleidoic egg in some species.
-- NCERT Class 11 Biology, Ch. 7, p. 82More in Structural Organisation in Animals and Plants: 17 exam traps and mistakes · 1 question pattern from its other lessons.
10 questions from NEET 2021, 2023, 2024, 2025, 2026. Answers verified against NTA official keys.
In water, frogs respire using ______.
In frogs, the number of pairs of cranial nerves arising from the brain are ______.
In frog, the Renal portal system is a special venous connection that acts to link :
Which of the following statement is correct about location of the male frog copulatory pad?
Which of the following is characteristic feature of cockroach regarding sexual dimorphism?
Which of the following characteristics is incorrect with respect to cockroach?
All 49 past-paper questions from Structural Organisation in Animals and Plants →
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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