Body Fluids and Circulation — NEET Biology Questions 2026

The heart is myogenic because its activity is initiated by nodal tissue present in the heart itself (SA node), not in the medulla oblongata. The medulla only modulates it.

Atrial contraction increases ventricular filling by ~30%.

Hypertension is high blood pressure, confirmed if multiple readings exceed 140/90 mm Hg.

NCERT confirms valves ensure efficient pumping (Assertion true). NCERT states “The valves in the heart allows the flow of blood only in one direction, i.e., from the atria to the ventricles and from the ventricles to the pulmonary artery or aorta” (Reason true). The Reason explains HOW efficient pumping is achieved - through unidirectional flow mechanism.

The question asks to identify the incorrect statements regarding leucocytes. Let's evaluate each statement based on NCERT text: S1: Neutrophils are the most abundant cells (60-65 per cent) of the total WBCs and are phagocytic cells. This statement is correct. S2: Basophils are the least (0.5-1 per cent) among WBCs and secrete histamine, serotonin, heparin, etc. This statement is correct. S3: Eosinophils (2-3 per cent) resist infections and are also associated with allergic reactions. This statement is correct. S4: Monocytes are agranulocytes. However, lymphocytes (specifically B-lymphocytes) are responsible for producing antibodies, not monocytes. Monocytes are phagocytic cells. Therefore, this statement is NOT correct. S5: Neutrophils and monocytes are phagocytic cells which destroy foreign organisms entering the body. Lymphocytes are responsible for immune responses, not primarily phagocytosis for destroying foreign organisms directly. Therefore, this statement is NOT correct. Thus, S4 and S5 are the incorrect statements.