Correct option is A
Explanation-
Statement A - In primary neurulation, the cells surrounding the neural plate direct the neural plate cells to proliferate, invaginate and separate from the surface ectoderm to form an underlying hollow tube. - CORRECT
In primary neurulation, the neural plate forms, folds inwards (invagination), and separates from the surface ectoderm to form the neural tube. This process involves morphogenetic movements, especially guided by the notochord and surrounding tissues.
Statement B - In secondary neurulation, the neural tube arises from the aggregation of mesenchyme cells into a solid cord that subsequently forms cavities to create a hollow tube. - CORRECT
In secondary neurulation, a solid rod of mesenchymal cells forms in the tail region, which later cavitates to become a hollow tube. This is typical in the caudal (posterior) regions of many vertebrates.
Statement C - In birds, primary neurulation generates the neural tube from anterior up to the hind limb developing region. - CORRECT
In birds (and mammals), primary neurulation forms the anterior neural tube down to the level of the hindlimb buds. Beyond that, secondary neurulation takes over.
Statement D - In mammals, secondary neurulation begins at the level of sacral vertebrae. - CORRECT
In mammals, secondary neurulation generally begins caudal to the hindlimbs, around the sacral region, and extends to form the tail portion of the neural tube.
Statement E - Anencephaly results when a failure to close the neural tube occurs, resulting in the forebrain remaining in contact with amniotic fluid. - CORRECT
Anencephaly is a neural tube defect (NTD) where the anterior neural tube fails to close, leaving the developing brain exposed to amniotic fluid, causing degeneration of nervous tissue. It leads to a fatal condition characterized by the absence of a major portion of the brain and skull.
Final Answer:
All statements A, B, C, D, and E are correct.
Therefore, the correct option is a : A, B, C, D and E.
