**Core Concept**
DNA is the primary target of ionizing radiation, leading to damage in the form of single-strand breaks, double-strand breaks, and base damage. This damage can activate DNA repair pathways or, if left unrepaired, result in mutations and cell death. Ionizing radiation can also cause damage to other cellular components such as proteins and lipids.

**Why the Correct Answer is Right**
Ionizing radiation, including X-rays, gamma rays, and alpha particles, has enough energy to remove tightly bound electrons from atoms, resulting in the formation of ions. This process can cause DNA damage, as mentioned earlier. Additionally, ionizing radiation can also generate free radicals, which can react with DNA and other cellular components, leading to further damage. The DNA damage caused by ionizing radiation can be repaired by various mechanisms, including base excision repair, nucleotide excision repair, and non-homologous end joining.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is a distractor as it does not directly relate to the effects of radiation on living organisms. While it is true that radiation can affect the nervous system, this is not the primary or most direct effect of radiation.
**Option B:** This option is incorrect as radiation does not primarily affect the immune system. While radiation can have immunosuppressive effects, this is a secondary consequence of radiation damage to other cellular components.
**Option C:** This option is a distractor as it refers to a different type of radiation-induced damage that is not the primary effect of ionizing radiation. While it is true that ionizing radiation can cause DNA damage, this is not the same as radiation-induced oxidative stress.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the effects of radiation on living organisms can be cumulative and long-lasting. Prolonged exposure to ionizing radiation can increase the risk of cancer, genetic mutations, and other health problems. This is why radiation safety is a critical concern in medical imaging, nuclear medicine, and other fields.

**Correct Answer: DNA. DNA is the primary target of ionizing radiation.**