Which of the following is the fluid part of the blood ?

Question

UnlockIAS · Accepted Answer

Correct — A, Plasma. Blood is classed as a fluid connective tissue, and like every connective tissue it has a matrix in which cells sit. In blood the matrix is liquid, and that liquid is plasma. Spin a sample in a centrifuge and it separates cleanly: about 55 per cent of the volume is a straw-coloured supernatant, the plasma, and about 45 per cent is a packed red column of cells at the bottom, with a thin greyish buffy coat of white cells and platelets at the boundary. Plasma is roughly 90 to 92 per cent water; the remaining 6 to 8 per cent is plasma proteins — fibrinogen, which makes clotting possible, globulins, which carry antibodies, and albumin, which maintains the osmotic balance that keeps water inside the vessels — together with dissolved glucose, amino acids, lipids, mineral ions such as sodium, potassium, calcium and bicarbonate, hormones, dissolved gases and nitrogenous wastes like urea. Everything else offered in the question is a formed element, that is, a cell or a cell fragment suspended in that liquid rather than part of it. One term worth separating now: serum is plasma from which fibrinogen and the clotting factors have been removed, which is what remains as the pale fluid above a clot.

Why the other options are wrong — (b) White blood cells, or leucocytes, are true nucleated cells — the least numerous of the formed elements at roughly 6,000 to 8,000 per cubic millimetre — and are the body's immune patrol. They are suspended in the plasma and carried by it, but they are cells, not fluid.  (c) Red blood cells are the most numerous formed element, about 5 to 5.5 million per cubic millimetre, biconcave and, in mammals, without a nucleus so that they can pack in more haemoglobin. They give blood its colour and are what settles to the bottom on centrifugation — the packed cell volume, precisely the fraction that is not plasma.  (d) Platelets, or thrombocytes, are cell fragments budded off from megakaryocytes in the bone marrow, numbering roughly 1.5 to 3.5 lakh per cubic millimetre, and they initiate clotting. Being fragments rather than whole cells makes them the most plausible wrong choice for 'fluid part', but they are still particulate matter suspended in plasma.

Concept: Blood is a connective tissue whose extracellular matrix happens to be liquid, and the division into plasma and formed elements is the organising idea of the whole topic. An adult carries about five litres of it. The formed elements are erythrocytes, leucocytes and thrombocytes, all produced in the red bone marrow; red cells live about 120 days and are broken down in the spleen, sometimes called the graveyard of red blood cells, while most white cells survive only days. Plasma does the transport work that cells cannot: it carries digested nutrients from the intestine to the tissues, hormones from the endocrine glands to their targets, carbon dioxide and urea to the lungs and kidneys, and heat around the body. Its protein content also makes it the medium of clotting and of humoral immunity.

State PCS 2024 Q70 — Science & Technology PYQ with Answer

State PCS 2024 Q70 — Science & Technology PYQ with Answer