What type of reaction occurs when cortical granules are released from the egg?

The release of cortical granules from the egg is a critical event that occurs during fertilization, specifically known as the cortical reaction. This process serves to modify the zona pellucida, which is the extracellular matrix surrounding the egg.

When sperm successfully fertilizes an egg, calcium ions are released, initiating the cortical reaction. Cortical granules, which are specialized vesicles located beneath the egg's plasma membrane, fuse with the membrane and release their contents into the space between the plasma membrane and the zona pellucida. This release leads to the hardening of the zona pellucida and the prevention of additional sperm from entering the egg, providing a mechanism for block to polyspermy.

In this context, the cortical reaction is unique and specific to the events of fertilization, distinguishing it from other types of reactions such as acid-base reactions, oxidation-reduction reactions, or hydrophobic interactions. It is fundamentally a biological process integral to reproduction, making "cortical reaction" the correct and most relevant answer to the question.