**Core Concept**
Lysosomes are membrane-bound organelles responsible for cellular digestion and recycling of macromolecules, including proteins, lipids, and carbohydrates. They contain a variety of hydrolytic enzymes that break down these molecules, allowing for the recycling of cellular components.

**Why the Correct Answer is Right**
The primary function of lysosomes is to degrade and recycle cellular waste, including proteins, lipids, and carbohydrates. This process is essential for maintaining cellular homeostasis and preventing the accumulation of toxic substances within the cell. The enzymes within lysosomes, such as acid phosphatase and cathepsin B, play a crucial role in this process by breaking down complex molecules into smaller, more manageable components that can be reused by the cell.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lysosomes are not primarily involved in the synthesis of new molecules. While they do contain some enzymes that can synthesize molecules, their primary function is degradation and recycling.
* **Option B:** The mitochondria are responsible for generating energy for the cell through cellular respiration, not the degradation of cellular waste.
* **Option C:** The endoplasmic reticulum is involved in protein synthesis, folding, and transport, but it is not responsible for the degradation of cellular waste.

**Clinical Pearl / High-Yield Fact**
Lysosomal dysfunction can lead to a range of diseases, including lysosomal storage disorders, such as Tay-Sachs disease and Pompe disease, which result from the accumulation of toxic substances within the cell.

**Correct Answer:** C.