During respiration, about 97% of oxygen is transported by RBC’s by forming oxyhaemoglobin and the remaining 3% gets dissolved in the plasma.
Since haemoglobin pigment has less affinity for CO2, it is mainly transported in the dissolved form. Around 20 -25% of CO2 is carried by haemoglobin as carbamino-haemoglobin, 7% is in a dissolved state in the plasma and the remaining is carried as bicarbonate. This deoxygenated blood gives CO2 to lung alveoli.
