The table below records a trial on a coastal barley farm. Wind had carried fungal spores from an infected field onto young plants. Two barley varieties were...
Question 1 Report
The table below records a trial on a coastal barley farm. Wind had carried fungal spores from an infected field onto young plants. Two barley varieties were grown in equal-sized plots. Variety M makes a thick waxy layer on each leaf, whereas variety N has a thinner leaf surface. After three weeks, the farmer counted plants showing brown fungal patches. Resistant plants are useful because fungal disease can reduce glucose production and leave less starch in the grain.
Table 1 shows the results.
| barley variety | number of plants examined | plants with fungal patches | mean grain mass per plant / g |
|---|---|---|---|
| M | 120 | 18 | 21.4 |
| N | 120 | 63 | 15.7 |
(a) Identify which variety is more resistant to the fungal disease. [1]
(b) Use Table 1 to calculate the difference in mean grain mass per plant between the two varieties. [2]
(c) Explain how a waxy leaf surface could reduce infection by fungal spores. [2]
(d) Explain how selective breeding could produce barley plants with improved resistance to this disease. [4]
(e) Suggest three controls needed to make this field comparison fair. [3]
Answer Details
(a) Variety M. [1]
(b) 21.4 - 15.7 [1] = 5.7 g. [1]
(c) Waxy surface prevents/reduces water remaining on the leaf. [1] Spores are less able to germinate, enter the leaf, or grow fungal threads. [1]
(d) Choose parent plants that show high resistance/few fungal patches. [1] Cross/breed these selected plants. [1] Their offspring inherit alleles for resistance. [1] Repeatedly select and breed the most resistant offspring over many generations. [1]
(e) Any three from: use the same species and starting age of plants; plant equal numbers in equal-sized plots; use the same soil/fertiliser; provide the same water; place plots where temperature/light exposure is similar or randomise plot positions; expose plants to the same amount of spores; measure after the same time period. [3]
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