Okok i think it is 2 but like i might be wrong so dont get mad at me if its wrong
Answer:
A <u><em>receptor</em></u> is a protein that recognizes and responds to a signal.
Explanation:
A receptor is a protein molecule present on the cells on which the signalling molecules can bind and generate a physiological response. Some receptor molecules can also respond to Sun and light. Each type of cell has specific receptors molecules and hence can respond to specific signals. The receptor molecules hence tend to receive signals for a cell. Molecules such as hormones bind to the receptors.
The endoderm layer may have developed abnormally" is the possible reason among the choices given in the question. The correct option among all the options that are given in the question is the third option or the last option. I hope that this is the answer that has actually come to your great help.