STPM Biology - chapter 2: Revision essay question 3

3. a) Discuss how erythrocyte and its pigments are related to their function.

   b) Explain why haemoglobin molecules are not found in blood plasma.

Answer:

a) -  Erythrocytes function to transport oxygen and some carbon dioxide.

    - Erythrocyte are small,biconcave discs with a diameter of 7-8 µm.This increases     the surface area per volume ratio and allow oxygen to diffuse quickly into or out of the cell.

  - The elastic membrane of the erythrocytes enable the erythrocytes to squeeze through the narrow blood capillaries.

 - The cells  move in a single line and are closer to the capillary to diffuse rapidly into the cell.

- Te erythrocyteshave no nucleus,no organelles such as mitochondria and ER.

- There is more space to contain haemoglobin,increasing the amount of oxygen which can be carried by he erythrocytes,There are about 250 million haemoglobin molecules in each erythrocyte.

- Since the erythrocyte are small cells,the haemoglobin molecules are not far from the plasma membrane and its source of oxygen.

- Haemoglobin has a quartenary structure.It is made up of four polypeptide chains,each chain has a haem group containing iron.Each molecule of haemoglobin can therefore combine with four oxygen molecules.

- Some carbon dioxide (10%) can combine with haemoglobin to form carbaminohaemoglobin which is carried by the erythrocytes.

b)  ~  If haemoglobin were suspended in the plasma rather than enclosed within erythrocytes,the blood would become too viscous for the heart to the heart to pump the blood through the blood vessels.

   ~  Haemoglobin would also affect the solute potential In the blood.

~  Membranes of Bowman’s capsule in the nephron allows only proteins of molecular weight below 68000 to pass.The haemoglobin molecules are smaller than 680000 threshold molecule weight.If present in the plasma,the haemoglobin can pass through the fitration membrane and be lost in the urine.

Assignment submitted by group chee tian 2011/2012 (IBM)