AQA A2  (Module 6) Human Biology

 

ANSWERS TO IN-CHAPTER QUESTIONS

 

Unit 10: Transporting Respiratory gases

 

 

 

 

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Q1.    

Two a and two b polypeptide chains; associated with the haem group.

 

Q2.    

a)     The partial pressure of oxygen will be lowered, as it is used up during aerobic respiration in the mitochondria.

b)     This lower partial pressure of oxygen in the muscle will cause the % saturation of haemoglobin (Hb) to be lowered, i.e. the O2 carried by the Hb is given up to the muscle.  So the harder the muscle works the more O2 is supplied by the Hb.

 

Q3.    

In respiring muscle tissue.  The muscle is using up O2, i.e. low rO2.  It is producing CO2 due to respiration, i.e. there will be a high rCO2.  This results in the Hb giving up even more O2 to the muscle tissues.  CO2 combines with Hb to form carbamino-haemoglobin, which then cannot carry as much O2.  Thus, as CO2 levels rise, O2 supplied also rises.  Also CO2 is an acidic gas.  As CO2 rises the pH falls, the Bohr effect releases still more O2 to the tissue.

Q4.    

In heterozygotes some of their Hb is defective, i.e. the 6th amino acid in the b polypeptide sub unit has the amino acid valine instead of the glutamic acid.  This results in the Hb being less soluble in low rO2.  The abnormal Hb molecules stick together to form long fibres, which alters the red blood cell shape to sickle shape.  This is what occurs when the heterozygous individual is exercising vigorously as their muscle cells are respiring actively using up O2 causing CO2 levels to rise which makes the Hb give up the O2 to the respiring muscle tissue.  Sickle cells clump together blocking blood vessels and causing potential problems.

 

Q5.    

[4BIB

only]

A diving seal’s muscles are actively respiring, using up O2 and giving off CO2. 

Myoglobin (Mb) is a good O2 store, as it picks up O2 readily and becomes saturated, even at low rO2 and it readily gives up the O2 it is carrying as the tissues need it.  As the seal dives its blood will not be able to keep pace with the O2 demand, i.e. the O2 tension of the muscle falls to a very low level.  Now the Mb gives up its O2 to the muscles.  Once exercise ceases the Mb O2 stores are replenished from the Hb in the blood.  The seal surfaces and can breathe again and then dive again for up to 20 minutes.