Answer: There are several
1: The degree of hydrophobic vs polar properties of the molecule will determine if it needs a protein transporter or can diffuse across the membrane.
2: The concentration of the molecule will determine the direction of transport. If the molecule must be transported against its concentration gradient, energy is required.
3: For molecules needing a protein transporter, whether the cell actually makes that transporter will determine if that molecule can be transported.
Explanation: N/A