The fluid that reduces friction during breathing in the pleural cavity is: MCQ with Answer and Explanation

Explanation:
Centrioles are cylindrical microtubular structures found near the nucleus in animal cells, forming the centrosome. They organize spindle fibers during cell division (mitosis and meiosis) and are also the basal bodies of cilia and flagella. They are absent in higher plant cells. Centrioles duplicate during S phase and migrate to poles during prophase.

Explanation:
The vocal cords (folds) in the larynx vibrate as air passes, producing sound. Pitch is controlled by tension. Epiglottis prevents food entry, trachea is airway.

Explanation:
Intrinsic factor, a glycoprotein secreted by gastric parietal cells, binds to vitamin B₁₂ and facilitates its absorption in the ileum. Absence or deficiency (pernicious anemia) leads to B₁₂ deficiency, causing megaloblastic anemia and neurological symptoms. HCl activates pepsin, pepsinogen is precursor, mucus protects.