Final answer:
The cessation of mitochondrial function would result in a stop to cellular respiration and ATP production, severely affecting the cell's energy supply and leading to possible cell malfunction or death.
Step-by-step explanation:
If the mitochondria stopped working, the most direct consequence would be that cellular respiration would cease, leading to a halt in ATP production. This is because the mitochondria are the powerhouse of the cell, responsible for producing ATP through the process of oxidative phosphorylation. In this process, a protein gradient is created by pumping protons into the intermembrane space, creating a high proton concentration. ATP synthesis is driven by the flow of these protons back into the mitochondrial matrix through ATP synthase. If this process stops, no ATP would be generated.
Without ATP, the cell would have no energy to fuel its various required activities which could lead to cell malfunction or death. This also means that any process depending on ATP, such as active transport, cell motility, and biosynthesis, would be negatively affected.
In terms of the answer choices provided, 'b. Cellular respiration would cease' is the correct answer, as cellular respiration in the mitochondria is what generates most of the cell's ATP. The reference to proton concentration highlights the importance of the mitochondrial function for ATP synthesis. When ions like protons cannot be effectively managed across the mitochondrial membrane, ATP cannot be produced efficiently.