The amount of air that remains in the lungs after a normal tidal expiration is the: MCQ with Answer and Explanation

Explanation:
The water vascular system is a unique network of fluid-filled canals found exclusively in Echinodermata (e.g., starfish, sea urchins). It is primarily used for locomotion (via tube feet), capturing and handling food, and respiration. Adult echinoderms exhibit radial symmetry, while their larvae are bilaterally symmetrical.

Explanation:
The Blood-Brain Barrier (BBB) is a highly selective semipermeable border that protects the brain from many substances in the blood. It is primarily formed by the tight junctions between the endothelial cells of the brain's capillaries. These endothelial cells are closely associated with the foot processes of astrocytes (a type of glial cell), which induce and maintain the tight junctions, restricting the passage of large molecules, toxins, and pathogens into the brain tissue.

Explanation:
Filippo Pacini first observed Vibrio cholerae in 1854, but Robert Koch later independently identified it and demonstrated its role. Koch is often credited, but Pacini's discovery was earlier. John Snow linked cholera to water.