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What is true about RBCs in humans?
A
They do not carry $CO_2$ at all
B
They carry about 20–25 percent of $CO_2$
C
They transport 99.5 percent of $O_2$
D
They transport about 80 percent oxygen only and the rest 20 percent of it is transported in dissolved state in blood plasma
Detailed Solution
About 97 per cent of $O_2$ is transported by RBCs in the blood, bound to haemoglobin as oxyhaemoglobin; the remaining 3 per cent is carried in a dissolved state in the plasma.
So the figures 99.5 per cent and 80 per cent are both wrong.
Nearly 20–25 per cent of $CO_2$ is transported by RBCs as carbamino-haemoglobin.
About 70 per cent of $CO_2$ is carried as bicarbonate and about 7 per cent in a dissolved state in the plasma.
Hence the true statement is that RBCs carry about 20–25 percent of $CO_2$.
So the figures 99.5 per cent and 80 per cent are both wrong.
Nearly 20–25 per cent of $CO_2$ is transported by RBCs as carbamino-haemoglobin.
About 70 per cent of $CO_2$ is carried as bicarbonate and about 7 per cent in a dissolved state in the plasma.
Hence the true statement is that RBCs carry about 20–25 percent of $CO_2$.