A-LevelBiologyInherited change9700/42 · Feb/Mar 2023 · Q310 Marks

Salmon can be genetically modified (GM) to produce increased quantities of growth hormone, which is a protein. GM salmon modified in this way have a faster growth rate and reach their maximum body mass at a younger age than non-GM salmon.

(a)Within any population of salmon there is variation in body mass. This is an example of continuous variation. Explain what is meant by continuous variation and how it can be caused.[3]
(b)(i)The scientists used two groups of non-GM salmon: • a control group of salmon that were not injected with recombinant growth hormone • an experimental group of salmon that were injected with 1.0 µg of recombinant growth hormone at the start of the experiment and once a week for the next six weeks. The mean body mass of the salmon in the two groups at the start of the experiment was the same (5.3g). After six weeks, the body mass of every salmon was measured again. The results are summarised in Table 3.1. Table 3.1 no injection with injected with recombinant recombinant growth hormone growth hormone number of non-GM salmon (n) 28 27 range 6.5-8.6 7.2-12.7 body mass mean (x) 7.7 9.4 /g standard deviation (s) 0.4 1.1 A student decided that a t-test should be performed on the results shown in Table 3.1. Calculate the value of t for the results shown in Table 3.1 using the formula for the t-test: t= |x1-x2| 2 2 S S 1 2 + N1 N2 Give your answer to two decimal places. Show your working. t =[3]
(b)(ii)The critical value at p = 0.05 for these data is 2.01. The student used the results in Table 3.1 and the t-test to conclude that the injections of recombinant growth hormone cause an increase in the growth rate of the non-GM salmon. Comment on the extent to which the conclusion made by the student can be supported.[3]
(b)(iii)Suggest one advantage, other than cost, of farming GM salmon that produce increased quantities of growth hormone instead of farming non-GM salmon that are injected with recombinant growth hormone each week.[1]

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.

[3] (a) any three from:
[3] (a) max two from:
[3] (a) 1 (phenotype has) range of values / intermediates ;
[3] (a) 2 (phenotypes) not, in groups / in classes / categoric / discrete / qualitative or (phenotypes are) quantitative;
[3] (a) 3 normal distribution;
[3] (a) max two from:
[3] (a) 4 polygenic / controlled by many genes ;
[3] (a) 5 different genes / alleles, have additive effect;
[3] (a) 6 (named) environmental factors (contribute to the variation);
[3] (b)(i) difference between means = 9.4 – 7.7 or 1.7 ;
[3] (b)(i) denominator = (image representing sqrt(0.4^2/28 + 1.1^2/27));
[3] (b)(i) or (image representing sqrt(0.16/28 + 1.21/27));
[3] (b)(i) or 0.22 / 0.23 (no limit on number of decimal places);
[3] (b)(i) t = 7.56; must be to 2 decimal places allow ECF
[3] (b)(ii) 1 t-value / 7.56, is greater than, 2.01 / critical value;
[3] (b)(ii) 2 difference between two groups is, significant / not due to chance or null hypothesis rejected;
[3] (b)(ii) any two from:
[3] (b)(ii) 3 overlap in, data range / error bars ;
[3] (b)(ii) 4 ref. to correlation does not prove causation ;
[3] (b)(ii) 5 only a single investigation / needs repeating / small sample size;
[3] (b)(ii) 6 ref. to this is only at 5% probability so may not actually be different / AW ;
[3] (b)(ii) 7 t-test may not be valid due to unequal, standard deviations / variances;
[1] (b)(iii) any one from:
[1] (b)(iii) 1 idea of less labour intensive; e.g. no need for weekly injections / GM only needs to be done once
[1] (b)(iii) 2 idea of less stressful on GM salmon ;
[1] (b)(iii) 3 risk of infection with injections ;
[1] (b)(iii) 4 idea that growth hormone is continuously produced ;
[1] (b)(iii) 5 GM salmon may grow faster ;