The condition caused by insufficient secretion of thyroxine in adults is: MCQ with Answer and Explanation

Explanation:
Active immunity occurs when the body's own immune system is stimulated by an antigen (either through infection or vaccination) to produce its own antibodies and memory cells, providing long-lasting protection. Passive immunity occurs when an individual is directly given pre-formed antibodies (like through mother's milk or antiserum), providing immediate but temporary protection. Vaccination stimulates the body to produce its own immune response, thus providing artificial active immunity, not passive. Thus, statements 1 and 2 are correct.

Explanation:
Lymphatic filariasis, caused by Wuchereria bancrofti and transmitted by Culex mosquito, leads to chronic swelling of limbs (elephantiasis) due to blockage of lymphatic vessels. Amoebiasis is Entamoeba, sleeping sickness Trypanosoma, kala-azar Leishmania.

Explanation:
The cohesion-tension theory, primarily proposed by Dixon and Joly (and later supported by Denison), is the most widely accepted mechanism for the ascent of sap in tall trees. It relies on the physical properties of water. Transpiration from the leaves creates a negative pressure (tension) in the xylem. This tension pulls the water column upwards. The water column remains unbroken due to the high cohesive force between water molecules (hydrogen bonding) and the adhesive force of water to the hydrophilic walls of the xylem vessels and tracheids. This creates a continuous, passive pull from the top.