Final answer:
Cells need substances to go in and out for cellular homeostasis, energy production, communication, and nutrient storage.
Step-by-step explanation:
Cells need some substances to go in and others out to maintain cellular homeostasis, create energy, communicate with other cells, and store nutrients. Maintaining a stable internal environment, or homeostasis, is crucial for a cell's proper functioning.
This includes regulating the balance of salts, nutrients, and other substances inside the cell. Cells also need to import essential substances, such as nutrients and oxygen, and export waste products to stay healthy. Additionally, cells need to communicate with other cells to coordinate various processes.