Final answer:
The second part of the process takes place in the (a) mitochondria, which are known as the energy 'powerhouses' of the cells.
Step-by-step explanation:
Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. It takes place in the cytoplasm of both prokaryotic and eukaryotic cells. In stage one, glucose is broken down in the cytoplasm in a process called glycolysis.
In stage two, the pyruvate molecules are transported into the mitochondria, where they enter the Krebs cycle. The mitochondria, known as the energy 'powerhouses' of the cells, produce ATP during this stage.
Therefore, the second part of the process takes place in the mitochondria.