Final answer:
The loss of function of the CFTR protein causes the production of thick mucous in the lungs and pancreas of cystic fibrosis patients.
Step-by-step explanation:
The loss of function of the CFTR protein causes the body to produce thick mucous in the lungs and pancreas of cystic fibrosis patients. The CFTR protein is responsible for transporting chloride ions out of the cell, but when it is mutated or absent, the ions are not transported properly. As a result, there is no osmotic pressure to pull water into the mucus, leading to the thick and sticky mucus that clogs the respiratory and digestive organs.