Questions

Passage

Consider a single-step reaction R → P that can proceed by an uncatalysed pathway or, in the presence of a suitable catalyst, by a catalysed pathway. The energy of each pathway is plotted against reaction progress below.

Figure 1. Energy of the system (kJ/mol) versus reaction progress. Solid curve: uncatalysed pathway. Dashed curve: catalysed pathway. Both share the same reactants and products. Brackets mark the activation energies for the two pathways and the overall enthalpy change ΔH.

1 MCQ · Question 1 of 4

From the diagram, what is the activation energy of the uncatalysed reaction?

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2 MCQ · Question 2 of 4

The enthalpy change ΔH for the reaction shown is:

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3 MCQ · Question 3 of 4

What is the principal effect of adding the catalyst, as illustrated by the dashed curve?

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4 MCQ · Question 4 of 4

A different single-step reaction has an activation energy of 25 kJ/mol and ΔH = +15 kJ/mol. Compared with the uncatalysed reaction shown in the diagram, the new reaction will be:

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Passage

A family has been referred for genetic counselling. Two members — II-1 (a male) and III-2 (a female) — have a clinically confirmed monogenic disorder. All other family members studied in the pedigree are unaffected. The pedigree below summarises three generations.

Figure 1. Three-generation pedigree. Squares denote males, circles denote females. Filled symbols indicate individuals affected by the disorder.

5 MCQ · Question 1 of 4

Which mode of inheritance is most consistent with the pedigree shown?

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6 MCQ · Question 2 of 4

Using the allele symbols A (wild-type, dominant) and a (disease allele, recessive), what is the genotype of individual II-2?

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7 MCQ · Question 3 of 4

II-2 and II-3 are planning a further child. Given the pedigree, the affected daughter III-2 confirms that both II-2 and II-3 are carriers (Aa). What is the probability that their next child is affected?

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8 MCQ · Question 4 of 4

The disorder in this family is cystic fibrosis (CF), caused by recessive loss-of-function mutations in the CFTR gene. Which statement best describes the molecular basis of disease in homozygous (aa) individuals?

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A. Loss of cilia from respiratory epithelium without any change in ion transport.

B. An excess of functional CFTR chloride channels at the apical membrane of epithelial cells, causing hypersecretion of chloride.

C. Production of a constitutively active CFTR channel that hyperpolarises epithelial cells.

D. A deficiency of functional CFTR chloride channels at the apical membrane of epithelial cells, leading to impaired chloride and bicarbonate secretion and thick, dehydrated mucus.