Problem 5 - Biology: The Dynamic Science

Question

The slow block to polyspermy: a. is caused by a change in membrane potential from negative to positive. b. triggers the movement of \(\mathrm{Ca}^{2+}\) from the cytosol to the endoplasmic reticulum. c. triggers a decrease in egg oxidation and protein synthesis. describes the fusion of egg and sperm nuclei. e. includes the fusion of cortical granules with the egg's plasma membrane.

Step-by-Step Solution

Answer

From the given options, only option a is reliable in explaining an aspect of the slow block to polyspermy. The slow block to polyspermy involves a change in membrane potential from negative to positive. Other options do not correctly describe aspects of this biological mechanism. Still, due to incomplete sentences in options d and e, a final answer might require a review of their full context.

Step 1: Understanding the Concept of Polyspermy

Polyspermy refers to the fertilization of an egg by more than one sperm which can cause serious problems during subsequent embryonic development. Organisms have developed mechanisms that prevent polyspermy, known as blocks to polyspermy.

Step 2: Analyzing Option a

The slow block to polyspermy does involve a change in membrane potential, but it changes from negative to positive. This change, or depolarization, helps prevent other sperms from fertilizing the egg. So option a is correct.

Step 3: Analyzing Option b

The slow block to polyspermy actually causes an influx of \(\mathrm{Ca}^{2+}\) ions from the extracellular medium into the egg which then triggers the exocytosis of the cortical granules; not from the cytosol to the endoplasmic reticulum. Therefore, option b is incorrect.

Step 4: Analyzing Option c

This option is unclear, as the slow block to polyspermy does not typically involve a decrease in egg oxidation and protein synthesis. This part of fertilization focuses on preventing additional sperm from entering the egg, not on changing its metabolic processes. Therefore, option c is incorrect.

Step 5: Analyzing Option d and e

Option d and e do not give complete sentences so a review of the text is needed. If option d says 'describes the fusion of egg and sperm nuclei', this is not part of the slow block to polyspermy. If option e says 'includes the fusion of cortical granules with the egg's plasma membrane' this would be correct because the cortical reaction does involve fusion of cortical granules with the egg's plasma membrane, releasing their contents and thus preventing polyspermy. However, as they are incomplete, we cannot make definitive statements about these options.