Correct option is C
The question asks which combination of statements accurately describes the fertilization process in sea urchins.
Breakdown of Statements:
Statement A: "Chemoattraction of the sperm to the egg is mediated by sperm activating peptides like bindin."
Incorrect: Bindin is indeed important for the sperm-egg binding process, but chemotaxis (the attraction of sperm to the egg) is actually mediated by resact, not bindin. Resact is the sperm-activating peptide that triggers sperm chemotaxis toward the egg. Bindin, on the other hand, is involved in the later stages of sperm-egg recognition and fusion. Therefore, Statement A is incorrect.
Statement B: "Exocytosis of the sperm acrosomal vesicles and release of enzymes occur."
Correct: This is a key process in fertilization. When the sperm approaches the egg, it undergoes the acrosome reaction, where the acrosomal vesicles fuse with the sperm membrane, releasing enzymes that help break down the egg's outer layers, allowing sperm penetration. This statement is true and correctly describes a crucial step in fertilization.
Statement C: "The capacitated sperm undergoes acrosome reaction."
Incorrect: This is misleading. Capacitation refers to the final maturation of sperm in the female reproductive tract that allows them to undergo the acrosome reaction. However, capacitated sperm itself does not undergo the acrosome reaction directly. The acrosome reaction happens when the capacitated sperm comes in contact with the egg's outer layer. So, this statement is not fully accurate.
Statement D: "The acrosome protein mediating the critical species-specific binding event is resact."
Incorrect: Resact is a peptide that helps with sperm chemotaxis (guiding sperm to the egg) but is not the acrosome protein that mediates the critical species-specific binding event. Bindin, a protein found in the acrosome, mediates the species-specific binding between the sperm and the egg. Hence, this statement is incorrect.
Statement E: "The slow block to polyspermy is accomplished by the cortical granule reaction."
Correct: This statement is accurate. The cortical granule reaction is the key mechanism that creates a slow block to polyspermy. After fertilization, cortical granules in the egg fuse with the egg membrane and release enzymes that modify the egg's extracellular matrix, preventing additional sperm from entering and ensuring only one sperm fertilizes the egg.
Correct Combination:
Option 3 (B and E only) is the correct answer because:
Statement B is correct regarding the exocytosis of the acrosomal vesicles and enzyme release, which is a crucial event during fertilization.
Statement E correctly explains how the cortical granule reaction prevents polyspermy, ensuring that only one sperm fertilizes the egg.
Information Booster:
Acrosome Reaction: The acrosomal vesicles in the sperm head contain enzymes that are released upon sperm-egg interaction. These enzymes digest the egg's protective layers, allowing sperm to penetrate and fertilize the egg.
Cortical Granule Reaction: The cortical granules in the egg contain enzymes that modify the egg’s surface after fertilization, creating a slow block to polyspermy. This ensures that no additional sperm can fertilize the egg, which is crucial for the successful development of the embryo.
Additional Information:
Option (1) A and B only: Statement A is incorrect as it confuses bindin (which is involved in binding the sperm to the egg) with resact, which is responsible for chemotaxis. Hence, Option 1 is not correct.
Option (2) A, B, and D: Statement A is still incorrect, and Statement D mistakenly assigns the role of the acrosomal protein to resact. Therefore, Option 2 is incorrect.
Option (4) A, B, and E: Statement A is incorrect, so this combination cannot be correct.
