O-LevelBiologyEcology & Environment5090/21 · May/June 2020 · Q312 Marks

The photograph shows an insect called a leafhopper. When it feeds, its mouthparts penetrate the xylem of the plant on which it lives. [Figure 3.1] Leafhoppers carry disease-causing bacteria from plant to plant.

(a)(i)State the term used for a disease-causing organism.[1]
(a)(ii)State the term used for an animal, such as an insect, that carries disease-causing organisms.[1]
(b)(i)Suggest and explain why this can cause the leaves of the plant to wilt.[4]
(b)(ii)The leaves of plants affected by these bacteria may also develop white patches. Suggest reasons for this.[2]
(b)(iii)Suggest an explanation for the fact that the fruits of plants affected by these bacteria are small and poorly developed.[4]

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Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[1] pathogen;
[1] vector;
[4] water lost from leaves ; by evaporation / transpiration; cannot be replaced / cannot pass up stem ; water lost from cells ; lose their turgor / turgidity;
[2] can't make chlorophyll ; reference to magnesium / zinc not getting to leaves ;
[4] reduced photosynthesis ; less sugar / starch / protein made ; less water available to fruit ; fewer nutrients or named nutrient sent to fruit ; less growth or development (linked to protein) ;

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