**Category:** Plant Physiology  
**Subtype:** Nutrient Uptake  
**Problem:** Determine the method of ion absorption by plants based on concentration gradients.

**Summary:** The problem presents a scenario where the concentration of magnesium ions (\(\mathrm{Mg}^{2+}\)) in the soil is \(0.01\%\) and in the root hair cells of the plant is \(0.03\%\). The task is to identify how the plant absorbs \(\mathrm{Mg}^{2+}\) ions given the difference in concentration.