The table below shows the concentrations of four different solutes inside a mammalian proximal convoluted tubule (PCT) cell and in the surrounding glomerular filtrate within the tubule lumen:
| Solute | Concentration in lumen (mmol dm−3\text{mmol dm}^{-3}mmol dm−3) | Concentration inside PCT cell (mmol dm−3\text{mmol dm}^{-3}mmol dm−3) |
|---|---|---|
| Sodium ions (Na+\text{Na}^+Na+) | 140 | 15 |
| Glucose | 4.5 | 12.2 |
| Urea | 5.0 | 5.0 |
| Chloride ions (Cl−\text{Cl}^-Cl−) | 115 | 40 |
Which solute requires active transport to be absorbed from the tubule lumen into the PCT cell?
Sodium ions (Na+)\text{Sodium ions } (\text{Na}^+)Sodium ions (Na+)
Glucose\text{Glucose}Glucose
Urea\text{Urea}Urea
Chloride ions (Cl−)\text{Chloride ions } (\text{Cl}^-)Chloride ions (Cl−)