Species Diversity

The question is related to the events following the fertilization of a sea urchin egg. Specifically, it asks what a rise in cytosolic calcium ion concentration leads to immediately after fertilization.

Let's break down the process step by step:

1. When a sperm enters the egg, it triggers a release of calcium ions (Ca²⁺) in the cytosol of the egg. This increase in calcium ion concentration is crucial for subsequent cellular changes.
2. This influx of Ca²⁺ acts as a signaling mechanism that initiates several downstream processes. The primary event triggered by this calcium wave is the formation of a fertilization envelope.
3. The fertilization envelope is formed through the exocytosis of cortical granules. These granules release their contents outside the plasma membrane of the egg, leading to a modification of the vitelline layer, which hardens into a protective envelope.

The formation of the fertilization envelope serves a critical role in protecting the fertilized egg from being penetrated by additional sperm, thus preventing polyspermy.

Examining the options provided:

• Formation of fertilization envelope: This is the correct answer, as discussed above. The rise in cytosolic calcium triggers the cortical reaction leading to its formation.
• Acrosomal reaction: This occurs in the sperm, not the egg, and involves the release of hydrolytic enzymes needed for penetrating the egg membrane.
• Formation of vegetal pole: This refers to a part of the egg containing the yolk, which is determined before fertilization and is not a result of calcium concentration changes.
• Formation of animal pole: Similarly, the animal pole is pre-determined and does not form as a result of post-fertilization calcium changes.

Thus, the correct answer is clearly the Formation of fertilization envelope.

To solve the given question, we must correctly match each term with its corresponding description. Let's analyze each pair:

1. Thermophile:
   • Thermophiles are organisms that thrive at relatively high temperatures, typically between 41°C and 122°C. Therefore, the optimal temperature mentioned in option (d), which is 67°C, aligns with the characteristics of thermophiles.
   • Correct Pair: (i)-(d)
2. Mesophile:
   • Mesophiles are organisms that grow best at moderate temperatures, usually around 20°C to 45°C. The most common optimal temperature for mesophilic growth is around 37°C.
   • Hence, none of the given options directly matches this typical description, as no pair mentions 37°C for mesophiles.
   • Correct Pair: Not listed explicitly in the options.
3. Psychrophile:
   • Psychrophiles thrive at low temperatures, generally around 0°C to 20°C.
   • Option (b) states growing optimally at low temperatures, which is characteristic of psychrophiles, but psychrophile (iii) is not correctly matched in the options given.
   • Correct Pair: Not listed explicitly in the options.
4. Halophile:
   • Halophiles are organisms that grow optimally in high saline conditions. This matches option (c).
   • Correct Pair: (iv)-(c)

Thus, the correct pairs from the given options are:

• (i)-(d)
• (iv)-(c)