Final answer:
The semi-fluid matrix within the cell is known as the cytoplasm, which is the region between the plasma membrane and the nucleus containing organelles, cytosol, the cytoskeleton, and various other components where many metabolic reactions occur.
Step-by-step explanation:
The semi-fluid matrix found within the cell is called the cytoplasm. The cytoplasm refers to the region of the cell between the plasma membrane and the nuclear envelope, comprising organelles suspended in the gel-like substance known as cytosol, as well as the cytoskeleton and various chemicals.
Although the cytoplasm consists mainly of water (70 to 80 percent), it has a semi-solid consistency due to the proteins it contains. Many metabolic reactions, such as protein synthesis, take place in the cytoplasm. Therefore, the correct answer to the student's question is a) Cytoplasm.