**Core Concept**
Apoptosis is a highly regulated process of programmed cell death that plays a crucial role in maintaining tissue homeostasis and preventing cancer. It is characterized by a series of cellular changes, including cell shrinkage, DNA fragmentation, and membrane blebbing, which ultimately lead to the elimination of damaged or unwanted cells.

**Why the Correct Answer is Right**
Apoptosis is an internally controlled process, meaning that it is triggered by signals from within the cell itself. This is in contrast to necrosis, which is a form of cell death caused by external factors such as injury or infection. The process of apoptosis is tightly regulated by a complex interplay of pro-apoptotic and anti-apoptotic proteins, which ultimately lead to the activation of a family of cysteine proteases known as caspases. These caspases then cleave various cellular substrates, leading to the characteristic changes of apoptosis.

**Why Each Wrong Option is Incorrect**
**Option B:** This option is incorrect because apoptosis is not externally controlled, but rather is triggered by internal signals. While external factors such as radiation or chemotherapy can induce apoptosis, the process itself is not controlled by external factors.

**Option C:** This option is incorrect because apoptosis is a process of cell death, not enzyme degradation. While enzymes such as caspases are involved in the process of apoptosis, the overall process is one of cell death, not enzyme degradation.

**Option D:** This option is incorrect because apoptosis is a process of cell death, not karyolysis (the dissolution of the nucleus). While the nucleus is affected during apoptosis, the process is not one of karyolysis, but rather a series of cellular changes that ultimately lead to cell death.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that apoptosis plays a critical role in maintaining tissue homeostasis and preventing cancer. Dysregulation of the apoptotic pathway has been implicated in a wide range of diseases, including cancer, neurodegenerative disorders, and autoimmune diseases.

**✓ Correct Answer: A. Internally controlled, programmed cell death**