IGCSE Biology Paper-2: Specimen Questions with Answers 190 - 190 of 203

Question 190

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Question

MCQ▾

Which substance is transported by haemoglobin?

Choices

Choice (4)
a.Nitrogen and oxygen
b.Oxygen and water
c.Urea and uric acid
d.Oxygen and carbon dioxide

Answer

d.

Explanation

  • Most of the oxygen in the blood is contained within the red blood cells, where it is chemically bonded to hemoglobin. Each hemoglobin molecule consists of four polypeptide chains called globins hemes. alpha chains, beta chains, and four iron-containing, disc-shaped organic pigment molecules called The protein part of hemoglobin is composed of two identical each 141 amino acids long, and two identical each 146 amino acids long. Each of the four-polypeptide chains is combined with one heme group.
  • In the center of each heme group is one atom of iron, which can combine with one molecule of oxygen. One hemoglobin molecule can thus combine with four molecules of oxygen and since there are about 280 million hemoglobin molecules per red blood cell, each red blood cell can carry over a billion molecules of oxygen. Normal heme contains iron in the reduced form (, or ferrous iron). In this form, the iron can share electrons and bond with oxygen to form oxyhemoglobin.
  • When oxyhemoglobin dissociates to release oxygen to the tissues, the heme iron is still in the reduced form and the hemoglobin is called Deoxy hemoglobin, reduced hemoglobin. or The term oxyhemoglobin oxidized is thus not equivalent to hemoglobin; hemoglobin does not lose an electron (and become oxidized) when it combines with oxygen. Oxidized hemoglobin, or Methemoglobin, has iron in the oxidized ( or ferric) state.
  • Methemoglobin thus lacks the electron it needs to form a bond with oxygen and cannot participate in oxygen transport. Blood normally contains only a small amount of Methemoglobin, but certain drugs can increase this amount. In carboxy hemoglobin, another abnormal form of hemoglobin, the reduced heme is combined with carbon monoxide instead of oxygen.
  • Because the bond with carbon monoxide is about 210 times stronger than the bond with oxygen, carbon monoxide tends to displace oxygen in hemoglobin and remains attached to hemoglobin as the blood passes through systemic capillaries.