The fluid that lubricates joints and reduces friction is: MCQ with Answer and Explanation

Explanation:
In plant tissue culture, when an explant (a piece of plant tissue) is placed on a nutrient medium containing specific plant hormones (like auxins and cytokinins), the cells dedifferentiate and undergo rapid, unorganized division to form a mass of cells called a callus. This callus is undifferentiated. Under appropriate hormonal conditions, this callus can then be induced to redifferentiate and form organized structures like shoots and roots (organogenesis) or somatic embryos.

Explanation:
Kidneys filter blood (1) and produce erythropoietin (3). Glucose reabsorption occurs in the proximal tubule, not collecting duct. So 2 is incorrect.

Explanation:
Adenosine triphosphate (ATP) stores and transfers energy in cells via high-energy phosphate bonds. Hydrolysis of ATP to ADP releases energy for endergonic reactions. Glucose and NADH/FADH₂ are energy sources but not direct energy carriers usable by most enzymes; ATP is the immediate energy donor.