Assertion (A): DNA replication is semiconservative. Reason (R): Each new DNA molecule consists of one old and one new strand. MCQ with Answer and Explanation

Explanation:
The limbic system is a group of brain structures located on both sides of the thalamus, supporting emotion, behavior, motivation, long-term memory, and olfaction. The amygdala is an almond-shaped collection of nuclei located deep within the medial temporal lobes. It is a crucial component of the limbic system primarily associated with processing emotions, particularly fear, anxiety, and aggression. It plays a key role in the 'fight or flight' response and in attaching emotional significance to memories. The hippocampus is primarily for forming new declarative memories.

Explanation:
The spleen is the largest lymphoid organ in the body. It is located in the abdominal cavity, specifically in the upper left quadrant, tucked between the stomach and the diaphragm, protected by the rib cage (ribs 9-11). It functions primarily in filtering blood, removing old or damaged red blood cells, storing platelets, and mounting immune responses against blood-borne pathogens. It is not located in the thoracic, pelvic, or cranial cavities.

Explanation:
Melatonin, synthesized from serotonin, is released in darkness, regulating circadian rhythms and promoting sleep. Serotonin is a neurotransmitter, dopamine reward, acetylcholine muscle contraction.