UPPSC 2025 Prelims GS Paper-I · Question 50 of 150

Correct — B, Both 1 and 2. Statement 1 is right: blood is a fluid connective tissue made of a straw-coloured liquid matrix called plasma, which is roughly 55 per cent of the volume and about nine-tenths water, in which three kinds of formed elements are suspended — red blood cells or erythrocytes, white blood cells or leucocytes, and platelets. So blood is indeed plasma plus different types of cells. Statement 2 is also right: the colour comes from haemoglobin, the iron-containing pigment packed inside red blood cells. Each haem group holds an iron atom that binds oxygen, and it is this haem-iron that absorbs light in a way that makes oxygenated blood bright scarlet and deoxygenated blood a darker, duller red.

• (a)Only 2 — This denies statement 1, but plasma plus formed elements is the standard description of blood in every textbook. A candidate might hesitate over the fact that platelets are strictly fragments of larger cells rather than complete cells; that technicality does not overturn the statement, which is about blood being a mixture of a liquid and cellular components.
• (c)Neither 1 nor 2 — Both statements are correct, so this rules out the answer altogether. It is the option for a candidate who over-thinks both clauses at once.
• (d)Only 1 — This denies statement 2, but haemoglobin is precisely what makes blood red. The proof runs the other way too: animals whose circulating fluid lacks haemoglobin are not red — a cockroach's haemolymph carries no respiratory pigment at all and looks colourless, while many molluscs and arthropods use the copper-based haemocyanin and have bluish blood.

Blood is classed as a fluid connective tissue: unlike other tissues its matrix is liquid. Plasma, about 55 per cent of blood by volume, is roughly 90 to 92 per cent water and carries proteins such as albumin, globulins and fibrinogen, along with glucose, salts, hormones and wastes. The remaining 45 per cent, the packed cell volume or haematocrit, consists of erythrocytes, leucocytes and platelets. Erythrocytes are the most numerous by far, and in adult humans they are biconcave discs that have lost their nucleus, which leaves the maximum room for haemoglobin — an iron-containing protein of four polypeptide chains, each carrying a haem group.

Two-statement questions like this are settled by testing each clause on its own rather than looking for a hidden catch. Statement 1 is the definition of blood; statement 2 is the reason for its colour. The only place a candidate can talk themselves out of the answer is by demanding textbook precision — that platelets are cell fragments, or that it is the haem group rather than the whole haemoglobin molecule that carries the colour. Neither refinement makes the statement wrong, and the way to check the second one is to remember what happens when haemoglobin is absent: the blood is no longer red.

• Plasma is about 55 per cent of blood volume and is roughly 90 to 92 per cent water; the formed elements make up the remaining 45 per cent, the packed cell volume
• The formed elements are erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets); mature human red blood cells have no nucleus
• Haemoglobin is the iron-containing pigment inside red blood cells; a healthy adult carries roughly 12 to 16 grams of it per 100 millilitres of blood, and a red blood cell lives about 120 days
• Oxygenated haemoglobin is bright red and deoxygenated haemoglobin is a darker red — the colour difference that distinguishes arterial from venous blood
• Not all animal blood is red: haemocyanin, a copper-based pigment, gives many molluscs and arthropods bluish blood, and a cockroach's haemolymph carries no respiratory pigment and looks colourless

• Treating plasma and serum as the same thing — serum is plasma with the clotting factors, chiefly fibrinogen, removed
• Assuming every animal's blood is red; the absence of haemoglobin, not the absence of blood, is what changes the colour
• Forgetting that mature human red blood cells are enucleate, or counting platelets as complete cells rather than fragments

UPPSC keeps this at the definitional level — two plain statements about composition or colour, to be marked correct or incorrect. UPSC turns the same material into applied questions: why carbon monoxide starves tissues of oxygen, whether blood holds more platelets than white cells, or what proportion of blood volume the cells occupy.

• practice — not a real PYQ

  Which of the following gives human blood its red colour?

  • (a)Haemocyanin
  • (b)Haemoglobin
  • (c)Melanin
  • (d)Fibrinogen

  Answer(b) Haemoglobin — the iron-containing pigment inside red blood cells; haemocyanin is the copper-based pigment that gives some invertebrates bluish blood.

• practice — not a real PYQ

  Approximately what proportion of the volume of human blood is plasma?

  • (a)About 25 per cent
  • (b)About 40 per cent
  • (c)About 55 per cent
  • (d)About 75 per cent

  Answer(c) About 55 per cent — the remaining 45 per cent or so is the packed cell volume made up of the formed elements.