Biology 9700 · AS & A Level · Testing for biological molecules

Testing for biological molecules — practice question

Carrots are the storage roots of the carrot plant. The carrot plant is a major food crop cultivated across the world. Their flavour is sweet because sugars make up part of the total carbohydrate content. Plant breeding has created many carrot varieties with different degrees of sweetness.
(a)[1]

State how the molecular structure of galactose, shown in Fig. 3.1, differs from the molecular structure of $\alpha$-glucose.

(b)[3]

Explain the evidence in Table 3.1 that backs these three further conclusions: Conclusion 1: The carrots contain both non-reducing sugars and reducing sugars. Conclusion 2: The carrots contain both monosaccharide and disaccharide sugars. Conclusion 3: The carrots show the same pattern of results.

(c)[1]

Name one carbohydrate found in carrots that is not a sugar.

(d)[3]

Each carrot plant forms a carrot during the first year of growth. If the carrot is not taken off the plant after it has matured, the plant goes through a dormant stage and shoots grow from the carrot in the second year of growth. This enables flowers to be produced and seed formation to take place before the plant dies. Explain, with reference to the carrot plant life cycle, when the carrot functions as a source and when it functions as a sink.

(e)[2]

Carrot virus Y is a pathogen that infects carrot plants. The virus, which is classified in the Potyvirus group, replicates its viral nucleic acid and proteins inside host carrot cells. The overall structure of potyviruses is shown in Fig. 3.2. Viral protein synthesis in host carrot cells involves only translation. Transcription does not take place. Suggest why translation takes place in host carrot cells during viral protein synthesis, but transcription does not take place.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: The positions of $\ce{H}$ and $\ce{OH}$ on C1 and C4 are swapped

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