**Core Concept**
Ionophores are a class of compounds that facilitate the movement of ions across cell membranes, often disrupting normal ion gradients and causing cellular dysfunction. This can lead to various physiological effects, depending on the ionophore and the specific ion it affects.

**Why the Correct Answer is Right**
Ionophores typically act by forming complexes with specific ions, allowing them to pass through the cell membrane and disrupting normal ion homeostasis. For example, valinomycin is an ionophore that selectively transports potassium ions, while monensin transports sodium ions. By disrupting these ion gradients, ionophores can cause cellular dysfunction and have various effects on cellular processes.

**Why Each Wrong Option is Incorrect**
**Option A:** Not all ionophores affect calcium ions; some may target other ions like potassium or sodium.
**Option B:** Ionophores can indeed increase the permeability of the cell membrane to certain ions, but this is their primary mechanism of action, not a secondary effect.
**Option C:** Ionophores can cause cellular dysfunction by disrupting normal ion homeostasis, but this is not a direct effect on mitochondrial function.

**Clinical Pearl / High-Yield Fact**
Ionophores can be used as antibiotics, disrupting the normal ion balance in bacterial cells and leading to their death. For example, ionophores like monensin are used to treat bacterial infections in animals.

**Correct Answer: D.**