Edexcel iGCSE Biology-3.5B Absorption of Water by Root Hair Cells- Study Notes- New Syllabus

Water Absorption by Root Hair Cells

📝 Introduction

Plants need water for photosynthesis, transport, cooling, and maintaining turgidity.
Water enters plants through root hair cells, which are specialised for absorption.

🔑 Structure of Root Hair Cells

• Long, thin extensions from root epidermal cells → provide a large surface area for absorption.
• Very thin cell wall → short distance for diffusion/osmosis.
• Direct contact with moist soil particles.

💧 Process of Water Absorption

• Higher Water Concentration in Soil
  Soil water (with dissolved minerals) usually has a higher water potential than the cytoplasm of root hair cells.
• Osmosis into Root Hair Cells
  Water moves by osmosis (from high water potential → low water potential) through the partially permeable membrane of root hair cells.
• Movement to Xylem
  After entering root hair cells, water moves:
  • Cell to cell through the cytoplasm (symplast pathway).
  • Or through the cell walls (apoplast pathway).
  Finally, water reaches the xylem vessels in the root.
• Transport Upwards
  Xylem carries the absorbed water upwards to the stem and leaves.

📊 Key Points

⚡ Quick Recap 
Root hair cells absorb water by osmosis.
Adaptations → long projection, thin walls, large SA.
Water potential gradient: soil → root hair cell → cortex → xylem → leaves.
Essential for photosynthesis, cooling, transport, and turgidity.