How Water Enters a Plant

• Entry of Water Into a Plant

  • each root hair comes into close contact with surrounding soil solution
  • thin film of liquid surrounding each soil particle is a dilute solution of mineral salts
  • cell sap has lower water potential than soil solution. cell sap and soil solution are separated by partially permeable cell membrane of root hair cell, water enters by osmosis, diluting cell sap
  • cell sap of the outer root hair cell has higher water potential than next cell, water passes by osmosis from root hair cell into inner cell, continuing until water enters xylem vessels and moves up plant

  
• How root hairs absorb ions or mineral salts

  • when the concentration of ions in the soil solution is lower than that in the root hair cell sap, the root hairs absorb the ions against the concentration gradient by active transport
  • cellular respiration in the root provides energy for active transport
  • when the concentration of ions in the soil solution is higher than the root hair cell sap, ions diffuse down the concentration gradient and are absorbed by diffusion
• Root hair cell adaptations

  • Has a long and narrow extension which increases surface area to volume ratio, increasing rate of absorption of water and mineral salts by the root hair cell
  • cell membrane prevents the cell sap from leaking out. The cell sap contains sugars, amino acids and salts, and thus has a lower water potential than the soil solution so water can enter the cell by osmosis
  • contains many mitochondria to provide energy for active transport, energy is produced by aerobic respiration