The cortical reaction of sea urchin eggs functions directly in
a. The formation of a fertilization envelope.
b. The production of a fast block to polyspermy.
c. The generation of an electrical impulse by the egg.
d. The fusion of egg and sperm nuclei.

Verified step by step guidance

1. Understand the context: The cortical reaction is a process that occurs in sea urchin eggs after a sperm fertilizes the egg. It is crucial for preventing polyspermy, which is the fertilization of an egg by multiple sperm.
2. Identify the role of the cortical reaction: The cortical reaction involves the release of cortical granules from the egg, which leads to changes in the egg's outer layer.
3. Connect the cortical reaction to the formation of a fertilization envelope: The release of cortical granules causes the vitelline layer of the egg to lift and harden, forming a fertilization envelope.
4. Recognize the purpose of the fertilization envelope: The fertilization envelope acts as a barrier to additional sperm, thus preventing polyspermy.
5. Conclude the function: Based on the steps above, the cortical reaction directly results in the formation of a fertilization envelope, which is option a.

Key Concepts

Cortical Reaction

The cortical reaction is a process that occurs in the egg cells of many animals, including sea urchins, following fertilization. It involves the release of enzymes from cortical granules in the egg's cortex, leading to changes in the egg's outer layer. This reaction is crucial for preventing polyspermy, which is the fertilization of an egg by multiple sperm, by forming a fertilization envelope.

Fertilization Envelope

The fertilization envelope is a protective layer that forms around the egg after the cortical reaction. It is created by the hardening of the vitelline layer, which is lifted away from the egg's plasma membrane. This envelope acts as a barrier to additional sperm, ensuring that only one sperm fertilizes the egg, thus preventing polyspermy.

Polyspermy Prevention

Polyspermy prevention is a critical mechanism in fertilization that ensures only one sperm fertilizes an egg. In sea urchins, this is achieved through the fast block and slow block mechanisms. The fast block involves a rapid electrical change in the egg's membrane, while the slow block, facilitated by the cortical reaction, involves the formation of the fertilization envelope to block additional sperm entry.