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 concept of the cortical reaction: The cortical reaction in sea urchin eggs occurs just after a sperm binds to the egg. It involves the release of enzymes from cortical granules within the egg, which modify the egg's outer layer.
2. Identify the purpose of the cortical reaction: The main purpose of this reaction is to prevent other sperms from fertilizing the same egg, a phenomenon known as polyspermy.
3. Relate the cortical reaction to the options given: The cortical reaction leads to changes in the egg's membrane and the space around it, which helps in preventing additional sperm from entering the egg.
4. Analyze the options in relation to the cortical reaction: Option (a) mentions the formation of a fertilization envelope, which is a direct result of the cortical reaction. This envelope forms as a physical barrier around the egg.
5. Conclude the correct answer: Since the cortical reaction results in the formation of a fertilization envelope that helps prevent polyspermy, the correct answer is 'a. the formation of a fertilization envelope.'

Key Concepts

Cortical Reaction

The cortical reaction is a crucial process that occurs in the egg of sea urchins following fertilization. It involves the release of enzymes from cortical granules, which leads to the modification of the egg's outer layer, forming a fertilization envelope. This envelope serves as a barrier to prevent additional sperm from entering the egg, thus ensuring that only one sperm fertilizes the egg.

Fertilization Envelope

The fertilization envelope is a protective layer that forms around the egg after fertilization, primarily as a result of the cortical reaction. This structure is essential for preventing polyspermy, which is the fertilization of an egg by multiple sperm. The formation of this envelope is a key mechanism that ensures the genetic integrity of the resulting zygote.

Polyspermy Prevention

Polyspermy prevention is a critical biological mechanism that ensures that only one sperm fertilizes an egg. In sea urchins, this is achieved through both a fast block, which involves a rapid change in the egg's membrane potential, and a slow block, which is the formation of the fertilization envelope. These processes work together to maintain the proper diploid state of the zygote and prevent developmental issues.