Q.27 In chick embryo, the ectoderm generates
(A) alveolar cells
(B) germ cells
(C) neurons
(D) red blood cells
The correct answer is (C) neurons.
In chick embryo development, the ectoderm primarily differentiates into neural tissues, including neurons, as part of the nervous system formation during gastrulation and neurulation. This occurs when the neural plate, derived from ectoderm, folds to form the neural tube, generating neuronal precursors.
Option Analysis
Alveolar cells (A): These are specialized epithelial cells in lung alveoli for gas exchange, originating from endoderm during respiratory system development, not ectoderm.
Germ cells (B): Primordial germ cells in chick embryos arise from the epiblast via the hypoblast or germinal crescent region (extra-embryonic endoderm), not directly from ectoderm.
Neurons (C): Ectoderm cells remaining after gastrulation form the neural plate, which develops into the central nervous system, producing neurons and neural crest derivatives.
Red blood cells (D): These develop from mesoderm in the yolk sac blood islands during primitive hematopoiesis, later from intra-embryonic mesoderm.
In chick embryo development, the ectoderm generates neurons as its primary contribution to the nervous system, a key fact for CSIR NET Life Sciences aspirants preparing for developmental biology questions. This process highlights ectoderm’s role in forming neural tissues during early embryogenesis.
Germ Layers in Chick Embryo
The chick blastoderm’s epiblast forms three germ layers during gastrulation via the primitive streak: ectoderm (outer), mesoderm (middle), and endoderm (inner). Ectoderm specifies into neural and epidermal fates early, influenced by signals like BMP inhibitors.
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Ectoderm derivatives: Neurons, neural crest (ganglia, melanocytes), epidermis, feathers, eyes.
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Mesoderm derivatives: Blood cells, muscles, bones, heart.
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Endoderm derivatives: Gut lining, lungs (alveolar cells), glands.
Why Ectoderm Generates Neurons
Post-gastrulation, central ectoderm thickens into the neural plate under Noggin and Chordin signals from underlying notochord, folding into the neural tube by stage 10 (HH stages). Neural tube cells proliferate into neurons for brain and spinal cord.
Incorrect Options Breakdown
| Option | Origin Layer | Explanation |
|---|---|---|
| Alveolar cells | Endoderm | Lung epithelium from respiratory diverticulum . |
| Germ cells | Epiblast/hypoblast | Migrate via blood to gonads, not ectoderm . |
| Red blood cells | Mesoderm | Yolk sac blood islands, primitive erythropoiesis . |
This table clarifies why only neurons align with ectoderm fate in chick embryos.
