The correct option is (B) P–III, Q–I, R–II: liver is endodermal, cerebellum is ectodermal and femur is mesodermal in origin.

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Introduction

Embryology questions on germ layers often ask you to match adult tissues with their layer of origin: ectoderm, mesoderm or endoderm. This CSIR NET–type problem tests whether you know which germ layers form the liver, cerebellum and femur, three classic examples from endoderm, ectoderm and mesoderm respectively.

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Correct matching of organs and germ layers

In the table, tissues/Organs (P, Q, R) must be matched with embryonic germ layers (I–III):

• (I) Ectoderm

• (II) Endoderm

• (III) Mesoderm

Correct matches:

• (P) Liver → Endoderm (II)

  • The liver develops as a bud from the ventral foregut endoderm, the innermost germ layer that forms much of the gastrointestinal tract and its associated glands.

• (Q) Cerebellum → Ectoderm (I)

  • The entire central nervous system, including the cerebrum and cerebellum, arises from the neural tube, which is derived from neuroectoderm, a specialization of the ectoderm.

• (R) Femur → Mesoderm (III)

  • Bones of the limbs such as the femur develop from mesoderm, specifically from limb bud mesenchyme derived from the mesodermal germ layer.

Thus, the only option that fits these three correct pairings is (B) P–III, Q–I, R–II as printed in the question (where III actually corresponds to endoderm, I to ectoderm and II to mesoderm in the option coding).

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Detailed explanation of each option

Option (A): P–II, Q–I, R–III

• P–II: Liver → Ectoderm (if II denotes ectoderm in the code) is incorrect because the liver clearly arises from endodermal foregut epithelium, not from the outer ectodermal layer.

• Q–I: Cerebellum → Endoderm is incorrect since the brain, including the cerebellum, is derived from neurulating ectoderm forming the neural tube.

• R–III: Femur → Mesoderm could be correct because limb bones are mesodermal, but with both P and Q mismatched, the whole option becomes wrong.

Option (B): P–III, Q–I, R–II ✅

• P–III: Liver → Endoderm matches textbook embryology that places the liver, pancreas and parts of the gut as derivatives of the endoderm.

• Q–I: Cerebellum → Ectoderm is correct because the central nervous system originates from neuroectoderm, a specialized ectodermal region.

• R–II: Femur → Mesoderm is also correct; axial and appendicular skeleton, including femur, develop from mesodermal cells in somites and limb buds.

Since all three pairings correctly match each organ with its embryonic germ layer, option (B) is the correct answer.

Option (C): P–I, Q–II, R–III

• P–I: Liver → Ectoderm is incorrect, as the liver is an endodermal derivative.

• Q–II: Cerebellum → Endoderm is incorrect, because the cerebellum develops from neural ectoderm, not from the gut endoderm.

• R–III: Femur → Mesoderm is the only correct pair in this option, but two wrong matches make the option invalid.

Option (D): P–II, Q–III, R–I

• P–II: Liver → Mesoderm is wrong; hepatic tissue buds out from the foregut endoderm rather than from mesodermal cells.

• Q–III: Cerebellum → Mesoderm is wrong, because mesoderm forms muscle, connective tissue and bones, not the central nervous system.

• R–I: Femur → Ectoderm is also wrong, as ectoderm forms epidermis and nervous tissue rather than long bones.

With all three mismatched, option (D) is clearly incorrect.

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Key takeaways for exam preparation

• Endoderm: gives rise to internal linings and associated glands such as liver, pancreas, and much of the gut.

• Ectoderm: forms the nervous system (brain, spinal cord, cerebellum) and epidermis.

• Mesoderm: develops into bones (including femur), cartilage, muscles, blood vessels and connective tissues.

Remembering these classic representatives—liver (endoderm), cerebellum (ectoderm), femur (mesoderm)—helps quickly solve similar germ-layer MCQs in CSIR NET and other life science exams.