Final answer:
Cystic fibrosis is caused by a mutation in the CFTR gene leading to defective transport of A) Cl− ions, resulting in thick mucus which causes various health issues.
Step-by-step explanation:
Cystic fibrosis is the result of a malfunction of a cellular ABC transporter that transports A) Cl− ions. The transporter in question is the cystic fibrosis transmembrane conductance regulator, or CFTR. This protein is responsible for moving Cl− ions out of cells, but when the CFTR gene is mutated, it leads to the production of a defective channel protein. The flawed CFTR results in abnormal mucus production, respiratory issues, and malabsorption of nutrients due to mucus obstructing various organs. CF is an autosomal recessive genetic disease, meaning that individuals with the condition have inherited two faulty copies of the gene, one from each parent.