Answer:
Roots have specialized cells called root hair cells that are responsible for absorbing water and mineral ions like nitrates from the soil. These cells have long thin projections that stick out into the soil.
For plants to take up mineral ions, ions are moved into root hairs, where they are in a higher concentration than in the dilute solutions in the soil. This movement of ions from a low concentration in the soil to a higher concentration in the plant is achieved through a process called active transport. Active transport is a process that is required to move molecules against a concentration gradient. This means that substances are moved from a low concentration to a high concentration, which is the opposite of what would happen naturally. The process requires energy.
In the case of root hair cells absorbing nitrate ions from soils with low nitrate concentrations, active transport allows the plant to take in the ions it needs from the soil around it. The energy required for this process is produced by respiration.