Final answer:
A mutation in haploid Neurospora that results in a defective enzyme A can disrupt the metabolic pathway it is involved in, potentially leading to a buildup of intermediates, a lack of essential products, or cell death.
Step-by-step explanation:
If a mutation in haploid Neurospora leads to an allele of enzyme A that codes for a defective or inactive form of the enzyme, the metabolic consequence would be significant. Enzyme A is important for a specific metabolic pathway, and without its activity, the cell cannot produce a vital product or might accumulate toxic substances. This scenario is often seen in enzyme-deficiency disorders, where an enzyme's absence or defect, due to a genetic mutation, can lead to a buildup of certain chemicals or a deficiency in essential compounds. An example includes mutations affecting enzymes in glycolysis, which can be lethal if the enzyme activity is completely knocked out.
In this case, the defective enzyme A likely leads to a similar outcome. Metabolic pathways depend on the sequential action of enzymes, and when one enzyme is dysfunctional, the entire pathway can be disrupted. Depending on the specific function of enzyme A, this can result in a failure to synthesize necessary molecules, the accumulation of intermediate compounds, or the inability to break down substrates, potentially leading to cell dysfunction or death.