30. Dreisch performed the “pressure plate experiment” to alter the distribution of nuclei in a 8-cell sea urchin embryo. He obtained normal larvae from these embryos. Following possible conclusions could be drawn:
    A. Prospective potency of the blastomeres is less than the actual prospective fate.
    B. Sea urchin embryo is a “harmonious equipotential system” implying that cell interaction is critical for normal development.
    C. Prospective potency of the blastomere is greater than the actual prospective fate.
    D. Prospective potency of the blastomere is equal to the prospective fate.
    Which one of the following combinations of statements represents the correct inference from the experiment?
    (1) A and B (2) Band C
    (3) B only (4) D only

The correct inference from Driesch’s “pressure plate” experiment on the 8-cell sea urchin embryo is:

(2) B and C

Where:

• B. Sea urchin embryo is a “harmonious equipotential system” implying that cell interaction is critical for normal development.

• C. Prospective potency of the blastomere is greater than the actual prospective fate.

Introduction

Hans Driesch’s seminal pressure plate experiments on sea urchin embryos challenged earlier deterministic views of embryonic development. By mechanically rearranging nuclei at the 8-cell stage, Driesch proved the embryo’s remarkable regulative capacity, showing that early cells could compensate for positional shifts and still produce normal larvae.

Key Findings from the Experiment

• Equipotentiality: Driesch demonstrated that the sea urchin embryo acts as a harmonious equipotential system. This means the early blastomeres are not rigidly fixed in their developmental fate but interact and regulate to form a complete organism.

• Potency vs. Fate: The experiment showed that the prospective potency (what a blastomere is capable of becoming) exceeds the prospective fate (what it actually becomes under normal conditions). This distinction underlined a regulative developmental mode, contrasting with mosaic development where potency equals fate.

• Cells are influenced more by their position and interactions rather than strictly by inherited determinants locally segregated in the cytoplasm or nucleus.

Biological Significance

• The experiment shifted scientific understanding, emphasizing the plasticity and communicative nature of embryonic cells.

• It indicated that embryonic development is robust, capable of self-regulation, and adaptable to perturbations.

• This insight paved the way for modern research into stem cells, cell fate determination, and developmental regulation.

Conclusion

Driesch’s pressure plate experiment remains a cornerstone of developmental biology. It firmly established that early sea urchin blastomeres possess greater developmental potential than their normal fate, and that embryonic development involves dynamic, harmonious cellular interactions, not merely predetermined, autonomous processes.

Final Answer:
(2) B and C