Blood vessels must be able to withstand and maintain varying blood pressures. There are several methods that could be used to determine the strength of a blood vessel. One method is called the circumferential tensile strength (CTS) test, as shown in Fig. 1.1. [Figure 1.1] The ring of blood vessel, shown in Fig. 1.1, was cut from a length of artery or vein that was prepared by removing surrounding tissues. A student wanted to use the apparatus in Fig. 1.1 to determine the mass needed to break an artery and the mass needed to break a vein.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

1. [1] independent variable type of blood vessel / artery and vein and dependent variable mass required to break (the blood vessel);
2. [6] any six from: 1 method to cut the blood vessel ; 2 method to measure blood vessel of, same / stated, length / AW ; 3 idea of discard samples that are damaged ; 4 idea of waiting (to see if the blood vessel breaks) before adding the next (10g) mass ; 5 use, artery and vein / blood vessels, from the same source ; 6 add (10 g) masses, to the mass hanger, until the blood vessel breaks ; 7 idea of measuring mass of mass hanger / including mass of mass hanger; 8 for each type of blood vessel, measure / note / record / AW, (total) mass when the blood vessel broke; 9 use at least three measurements for each type of blood vessel and calculate a mean ; 10 safety comment with hazard and precaution; hazard: knife / scalpel, risk: injury, precaution: cut away from hand hazard: blood vessels, risk: biohazard / pathogens / allergy, precaution: gloves / mask / PPE / use disinfectant / wash hands hazard: mass hanger falling, risk: injury, precaution: suitable precaution to prevent injury 11 idea of repeat procedure with smaller mass intervals near to breaking mass;
3. [2] three values correct ;; one or two correct max 1 (10g: 71, 40g: 95, 50g: 95)
4. [1] 1 to make a valid comparison (with other blood vessels / veins) ; 2 allows comparison as, initial / starting, length (of veins) is, not constant / AW;
5. [3] 1 correct orientation for axes and linear scale ; 2 axes labelled and units; 3 all points plotted correctly and line drawn accurately;
6. [2] 1 curve for artery starts at same point as the vein ; 2 curve for artery below curve for vein and does not intersect ;
7. [2] any two from: 1 starts at, same point/origin, as using percentage increase ; 2 (muscular) arteries have a thicker, wall / tunica media / muscle layer (than the vein) or 3 (muscular) arteries have more (smooth) muscle (than the vein) ; 4 idea of (muscular artery) withstands more (blood) pressure so stretches less (than the vein);
8. [2] any two from: 1 use smaller mass intervals ; 2 extend the range of the masses added ; 3 use a, force meter / Newton meter / data logger/AW, (to apply force); 4 attach a, pointer / fiducial mark, to the ring of blood vessel (to improve length measurement / removing parallax) ; 5 use, same / stated, width of blood vessel ;