Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
Correct answer
Explanation
The correct answer is B, haemoglobin of RBC can carry both oxygen and carbon dioxide. It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains.
Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs. In the tissues, oxygen is released and carbon dioxide joins the amino groups of the globin chains as carbaminohaemoglobin. About 20 to 25 per cent of the carbon dioxide in blood travels this way; most of the rest moves as bicarbonate ions in the plasma, and a small part dissolves directly.
Option A is wrong because haemoglobin does carry part of the carbon dioxide. Option C is wrong because its main job is carrying oxygen. Option D is wrong because blood clotting is the work of platelets and clotting factors such as fibrinogen and prothrombin, not haemoglobin.
Exam tip: O2 = oxyhaemoglobin; CO2 = carbaminohaemoglobin (about 20-25%) and mostly bicarbonate (about 70%); CO = carboxyhaemoglobin.
Practice Questions
View allWhich one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
Read the full explanation →The Hooke's law is valid for
- A.only proportional region of the stress-strain curve
- B.entire stress-strain curve
- C.entire elastic region of the stress-strain curve
- D.elastic as well as plastic region of the stress-strain curve
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Hooke's law says stress is directly proportional to strain, and that holds only up to the proportional limit, where the curve is a straight line.
Read the full explanation →What is a constellation?
- A.A particular pattern of equidistant stars from the earth in the sky
- B.A particular pattern of stars that may not be equidistant from the earth in the sky
- C.A particular pattern of planets of our solar system in the sky
- D.A particular pattern of stars, planets and satellites in the sky due to their position in the space
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A constellation is a group of stars that appears to form a shape when seen from the earth, but its stars usually lie at very different distances from us.
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