The pumping of blood is a vital process. Explain the roles of the atria and ventricles in the pumping of blood.

Explain how the structure of an artery allows it to carry out its function efficiently.

Describe the inheritance of ABO blood groups.

atria collect blood from veins (vena cava/pulmonary);
collect blood while ventricles are contracting;
atria pump blood into ventricles/ensure ventricles are full;
ventricles pump blood into arteries/out of the heart;
ventricles pump blood at high pressure because of their thicker, muscular walls;
mention of heart valves working with atria and ventricles to keep blood moving;
left ventricle pumps blood to systems and right ventricle pumps blood to lungs;

Both left and right ventricles with correct function required for mark to be awarded.

thick wall to withstand high blood pressures/avoid bursting/leaks;
many muscle fibres to help pump blood;
many elastic fibres to stretch and pump blood after each heart beat;
narrow lumen to maintain high pressure/because blood flows along rapidly;
thick outer layer of collagen to give strength/prevent aneurism;
no valves as pressure is high enough to prevent backflow;
endothelium/smooth inner lining to reduce friction;

one gene determines (ABO) blood groups / one gene for ABO blood groups;
genes have different/alternative forms called alleles;
there are three alleles (I^A, I^B and i) of the gene for (ABO) blood groups;
(ABO) blood groups are an example (of the effect of) multiple alleles (in this instance three alleles can result in four phenotypes);
each individual has two alleles of the gene but only one is passed to offspring;
alleles that are codominant both affect the phenotype in a heterozygote;
(alleles) I^A and I^B are codominant;
(alleles) I^A and I^B are dominant over i / i is recessive to I^A and I^B;
(genotypes) I^AI^A and I^Ai both give blood group A;
(genotypes) I^BI^B and I^Bi both give blood group B;
(genotype) I^AI^B gives blood group AB;
(genotype) ii/homozygous i gives blood group O;
example of a cross involving ABO blood groups;

Most candidates answered the question by trying to trace the blood flow through the heart rather than collectively explaining the roles of atria and ventricles. It was generally known that the right atrium collects blood from the body and pumps it into the right ventricle but the timing was misunderstood. Blood flow to and from the lungs was usually mentioned, including the pulmonary artery and pulmonary vein.   

Valves were mentioned but not their prevention of backflow. The idea of ventricles generating high pressure due to thick walls was mostly lacking.

The only structural feature of an artery consistently mentioned in relation to its function was that the thick wall of an artery enables it to withstand high blood pressure.  Many other important features such as muscle fibres to help blood movement or elastic fibres to allow an artery to stretch were ignored.  Statements such as “arteries are the biggest blood vessels in the body” or “are bigger than other blood pathways” suggest that candidates lack an understanding that the relative sizes of blood vessels can vary. Very few candidates included mention of the role of a narrow lumen or smooth inner lining

Candidates often confused the term blood group with blood allele. The terms were used synonymously without distinction. Though the question called for a description of the inheritance of ABO blood groups, that whole realm of thought was often neglected.  

Most marks were gained only because candidates gave the correct genotypes for the various blood groups. However, potential marks were lost here because candidates failed to use the standard notion I with superscripts and I to represent the alleles. Sometimes a Punnett square was used successfully to support an answer when inheritance was addressed. Much irrelevant information was given about universal blood donors or recipients and the related antigens and antibodies.