A-LevelBiologyBiodiversity and conservation9700/41 · Oct/Nov 2025 · Q213 Marks

Exserohilum turcicum is a fungal pathogen. The growth of the mycelium of the fungus damages the leaves of maize plants, Zea mays. Leaf damage reduces crop yield.

(a)(i)Complete Table 2.1 to show one structural difference and one functional difference between E. turcicum and Z. mays. Table 2.1 structural difference functional difference E. turcicum Z. mays[2]
(a)(ii)Describe the principles by which organisms such as E. turcicum and Z. mays are classified in the taxonomic hierarchy.[4]
(b)(i)Explain how Fig. 2.1 can be used to determine which parent maize variety shows the greatest resistance to infection by E. turcicum.[2]
(b)(ii)State the name of the type of variation shown by the maize F2 generation in Fig. 2.1.[1]
(b)(iii)Explain the genetic basis of the type of variation shown by the maize F2 generation.[4]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[1] (a)(i) 1 structural difference: E. turcicum: chitin cell wall OR no chloroplasts OR hyphae / cells long and branching OR syncytial / multinucleate / several nuclei per cell ; Z. mays: cellulose cell wall OR chloroplasts OR no hyphae / cells not long and branching OR one nucleus per cell ;
[1] 2 functional difference: E. turcicum: heterotroph(ic) / parasitic / obtain food from host / do not photosynthesise ; Z. mays: autotroph(ic) / phototrophic / photosynthesis(e) ;
[4] (a)(ii) any four from: 1 large groups divide into smaller groups ; 2 common / similar / shared, features within a group ; 3 ref. three of: kingdom – phylum – class – order – family; 4 genus and species = binomial / Linnaean / Latin / scientific, name; 5 (both in domain) Eukarya ; 6 different kingdoms / Fungi and Plantae ;
[2] (b)(i) any two from: 1 low percentage leaf damage means high resistance (to infection); 2 SKV50 = 22% and CML153 = 58% ; 3 SKV50 shows greater resistance (to infection) ;
[1] (b)(ii) continuous;
[4] (b)(iii) any four from: 1 many / different / several / multiple, genes ; 2 affect, same trait / (percentage) area of leaf damage / resistance ; 3 alleles of, one / each, gene have a small effect ; 4 (different) genes have, additive / combined / interactive, effects ; 5 mathematical treatment to illustrate additive effect ;

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