The type of WBC that is the first to respond to bacterial infection and performs phagocytosis is: MCQ with Answer and Explanation

Explanation:
The cortical reaction is a mechanism to prevent polyspermy, ensuring that only one sperm fertilizes the egg. It is triggered immediately after the plasma membrane of the sperm fuses with the plasma membrane of the oocyte. This fusion causes a sudden release of calcium ions inside the oocyte, which triggers the cortical granules (located just beneath the oocyte membrane) to release their contents into the perivitelline space. These enzymes modify the zona pellucida (zona reaction), making it impermeable to other sperm.

Explanation:
Azotobacter is a free-living, aerobic, nitrogen-fixing soil bacterium used as a biofertilizer for non-legume crops like wheat, maize, and cotton. Rhizobium is symbiotic, Nostoc is a cyanobacterium (algal biofertilizer), and mycorrhiza is a fungal symbiont that enhances phosphorus uptake. Biofertilizers reduce the need for chemical nitrogen fertilizers and are eco-friendly.

Explanation:
Bacterial cell walls contain peptidoglycan (murein), a unique polymer that maintains cell shape and protects against osmotic pressure. The reason correctly explains why peptidoglycan is essential.