1. The problem asks which two molecules cross the cell membrane by active transport. 2. Active transport moves substances against their concentration gradient, meaning from low concentration to high concentration inside the cell, requiring energy. 3. From the table: - Molecule 1: Low inside, High outside, moves into cell (against gradient) - Molecule 2: High inside, Low outside, moves out of cell (down gradient) - Molecule 3: Low inside, High outside, moves out of cell (against gradient but direction is out, which is unusual) - Molecule 4: High inside, Low outside, moves into cell (against gradient) 4. Molecules moving against their concentration gradient into the cell are Molecules 1 and 4, indicating active transport. 5. Therefore, the two molecules crossing by active transport are Molecules 1 and 4. Final answer: Molecules 1 and 4