* Concentration Gradient: The concentration of mineral salts is generally higher in the soil solution than inside the root cells. This means diffusion alone wouldn't be sufficient to move the salts into the cells.
* Energy Requirement: Active transport requires energy to move substances against their concentration gradient. Root cells use energy from ATP (adenosine triphosphate) to power protein pumps that actively transport mineral ions into the cell.
* Selective Uptake: Plants have specific transporter proteins in their root cells that can bind to and transport particular mineral ions. This allows for selective uptake of essential nutrients, even if their concentration in the soil is low.
While diffusion can play a minor role in the movement of mineral salts across the cell membrane, it's not the primary mechanism. Active transport is essential for plants to acquire the necessary nutrients from the soil, regardless of their concentration.