Identify the INCORRECT statement about the human lungs: MCQ with Answer and Explanation

Explanation:
Lignin is a complex organic polymer deposited in the secondary cell wall of xylem vessels and sclerenchyma fibers, providing rigidity, strength, and water resistance. It is the major non-carbohydrate component of wood. Cellulose is the main polysaccharide in the primary wall, chitin is in fungi and arthropods, pectin is in the middle lamella and primary wall.

Explanation:
The pleural cavity between the visceral and parietal pleura contains a thin layer of pleural fluid, lubricating the surfaces to reduce friction during lung expansion and contraction. Synovial fluid is in joints, cerebrospinal fluid surrounds the CNS, lymph is in the lymphatic system. Pleural effusion is excess accumulation.

Explanation:
A biological species is defined as a group of potentially interbreeding natural populations that are reproductively isolated from other such groups and produce fertile offspring. Physical similarity or shared habitat does not guarantee species status, as reproductive isolation is the key criterion.