The substance that makes the plant cell wall rigid and is a major component of wood is:
A. Chitin
B. Pectin
C. Lignin
D. Cellulose
Answer: Option C
Solution (By JKExamLibrary)
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:
Melatonin, synthesized from serotonin, is released in darkness, regulating circadian rhythms and promoting sleep. Serotonin is a neurotransmitter, dopamine reward, acetylcholine muscle contraction.
Explanation:
Guttation is the exudation of water droplets from hydathodes, driven by root pressure under high humidity and low transpiration conditions.
Explanation:
Seminal vesicles produce a fructose-rich fluid (energy for sperm), and the prostate gland adds a milky, alkaline fluid to form semen. The testis produces sperm, epididymis stores them, vas deferens transports.
No comments yet. Be the first to start the discussion!