Populations of European ash trees, Fraxinus excelsior, are susceptible to a chronic tree disease called ash dieback. Since 2012, this disease has spread through Europe causing large-scale loss of woodland. • Ash dieback is caused by a fungal pathogen. • Symptoms include stem lesions, death of growing shoots and wilting of leaves. • To limit the spread of the disease, 693 hectares of ash woodland were cleared in the UK between 2012 and 2015. Clearing the woodland involved uprooting the trees and burying them. [Table 2.1] shows the numbers of new cases of ash dieback in a variety of different environments in the UK between 2013 and 2015.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

1. [2] plant nurseries = (−) 69 (%) ;;
2. [2] descriptions of: woodland and roadside, increase in number of cases, (over 2013–2015)
3. [2] or nurseries (and gardens) and farmland, decrease in number of cases (over 2013–2015);
4. [2] explanations as ideas of: 1 (more) difficult to manage, 'wild' environments / woodland / roadside, ora
5. [2] or 2 as woodland and roadside, cover a large area / far from centres of habitation, so, many trees to get infected / hard to get access for management difficult to access, ora
6. [2] or 3 disease spreads (more) easily, in, dense woodland, ora
7. [2] or 4 ref to burying diseased trees could provide a reservoir of infection
8. [2] or 5 idea of number of reported findings have increased as awareness of ash dieback has spread / AW ;
9. [1] complementary base pairing;
10. [1] idea of intensity / brightness, of, fluorescence / fluorescent dye / colour
11. [1] or difference in intensity of, fluorescence / fluorescent dye / colour, (between healthy and diseased samples);
12. [1] (these trees) are (likely to be) tolerant / resistant
13. [1] or (these trees could be) a source of, tolerance / resistance, genes / alleles / mRNA / DNA
14. [1] or idea of comparing non-diseased and diseased trees ;
15. [2] any two of: multiple / several / many / 4, locations;
16. [2] varying ages ;
17. [2] from differently sized populations ;
18. [2] from, different countries / from across Europe ;
19. [2] varying degree of damage / healthy and non-healthy, sampled ;
20. [2] A description of a suitable, random / systematic, sampling technique for 1 mark if no other mp awarded.
21. [1] any one of: to allow (easier) comparison of data (from different sites) ;
22. [1] to allow (easier) analysis (of results) ;
23. [1] (easier) to plot, as graph / bar chart;
24. [1] idea of (bioinformatic) analysis will be carried out by a computer;
25. [1] guanine / G;
26. [1] idea of (mutation causes) a change in, protein / polypeptide / enzyme, which changes, function / tolerance / resistance
27. [1] or (mutation causes) a change in, protein / polypeptide / enzyme, that allows the plant to, respond to infection / repair damage
28. [1] or (mutation causes) a change in, protein / polypeptide / enzyme, that prevents the pathogen from, entering / spreading in, the ash plants ;