Which of the following organisms has white blood?

Question

UnlockIAS · Accepted Answer

Correct — B, cockroach. The cockroach is the standard textbook example of an animal with 'white' blood: its body fluid is haemolymph, a colourless to milky-white fluid that carries no respiratory pigment at all. It looks white rather than red because it contains no haemoglobin and no red blood cells — oxygen never travels in it. Instead the cockroach breathes through a tracheal system: air enters through spiracles on the sides of the body and branching tracheae and tracheoles deliver it straight to the tissues, so the circulating fluid is freed of any oxygen-carrying job and only moves nutrients, hormones, wastes and immune cells (haemocytes) around the open, sinus-based circulatory system.

Why the other options are wrong — (a) A lizard is a vertebrate, and like all vertebrates it has red blood — haemoglobin packed inside red blood cells, circulating in a closed circulatory system with a heart and vessels. It is the clear odd one out among these four options.  (c) The household bug (khatmal/bed bug) is an insect, so its own haemolymph is also pigment-free. But it is an obligate blood-feeder: after a meal its abdomen is visibly swollen and red with ingested host blood, so it is never the organism cited as an example of white blood — and that visible red is exactly what the question is separating out.  (d) Same reason as the bug — the female mosquito engorges on vertebrate blood, and a fed mosquito is conspicuously red-bodied. The question wants the insect whose own fluid is what you see, not the one carrying somebody else's blood.

Concept: Insects do not have blood in the vertebrate sense. They have haemolymph, a colourless, pale-yellow or greenish fluid that fills the body cavity (haemocoel) and is pushed around by a dorsal tubular heart in an open circulatory system, bathing organs directly instead of running through capillaries. Because oxygen is delivered by the tracheal system straight to the tissues, haemolymph carries no respiratory pigment; its jobs are nutrient transport, hormone transport, waste removal, hydraulic pressure (used in moulting and wing expansion) and immunity through haemocytes.

State PCS 2019 Q10 — Science & Technology PYQ with Answer

State PCS 2019 Q10 — Science & Technology PYQ with Answer