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ICSE Class 10 · Biology · Chapter 5

Absorption by Roots – The Processes Involved

7 topics · 15 questions

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Everything you need, in order

Structure of Root for Absorption

  • Root Hair Zone: Region just behind root tip with numerous root hairs. Primary site of water and mineral absorption.
  • Root Hairs: Unicellular extensions of epidermal cells. Increase surface area for absorption (10-20 times).
  • Structure: Thin-walled, no cuticle, large vacuole with cell sap. Short lifespan (few days to weeks).
  • Root Anatomy: Epidermis → Cortex → Endodermis (Casparian strip) → Pericycle → Vascular tissue (xylem, phloem).
  • Casparian Strip: Waxy band in endodermis. Forces water through cell membrane (selective barrier).
  • Diagram Importance: Root cross-section showing tissues is crucial for ICSE exams.

Osmosis and Water Absorption

  • Osmosis: Movement of water from higher concentration to lower concentration through semi-permeable membrane.
  • Semi-permeable Membrane: Allows water but not solutes. Example: Cell membrane.
  • Direction: Water moves from hypotonic (dilute) to hypertonic (concentrated) solution.
  • In Root Absorption: Soil water → Root hair → Cortex → Xylem by osmosis.
  • DPD (Diffusion Pressure Deficit): Force with which cell absorbs water. DPD = OP - TP.
  • Water Movement: From lower DPD to higher DPD.

Types of Solutions and Cell Responses

  • Isotonic: Same concentration as cell sap. No net water movement.
  • Hypotonic: Lower concentration. Water enters cell → Turgid.
  • Hypertonic: Higher concentration. Water leaves cell → Plasmolysed.
  • Turgidity: Cell full of water. Maintains plant rigidity.
  • Plasmolysis: Cytoplasm shrinks from cell wall in hypertonic solution.
  • Importance: Explains wilting and water absorption mechanisms.

Pathways of Water Movement

  • Apoplast Pathway: Water moves through cell walls and intercellular spaces. Faster but less selective.
  • Symplast Pathway: Water moves through cytoplasm via plasmodesmata. Slower but more controlled.
  • Vacuolar Pathway: Water moves through vacuoles from cell to cell.
  • Endodermis Barrier: Casparian strip blocks apoplast pathway. Water must enter symplast.
  • Significance: Ensures selective absorption and prevents backflow.

Active and Passive Absorption

  • Passive Absorption: Driven by transpiration pull. No energy from roots. Accounts for 98% absorption.
  • Active Absorption: Roots actively absorb water using metabolic energy. Occurs when transpiration is low.
  • Root Pressure: Pressure developed in roots due to active absorption. Causes guttation.
  • Guttation: Loss of water droplets from leaf margins. Occurs at night when transpiration is low.
  • Conditions: Active absorption dominant at night; passive during day.

Mineral Absorption

  • Active Transport: Minerals absorbed against concentration gradient using ATP energy.
  • Carrier Proteins: Specific proteins transport specific minerals across membrane.
  • Selectivity: Roots selectively absorb required minerals, reject harmful ones.
  • Essential Minerals: Macronutrients (N, P, K, Ca, Mg, S) and Micronutrients (Fe, Mn, Zn, Cu, B, Mo, Cl).
  • Nitrogen: For proteins, chlorophyll. Deficiency causes yellowing.
  • Phosphorus: For ATP, DNA. Deficiency causes stunted growth.
  • Potassium: For enzyme activation. Deficiency causes weak stems.

Factors Affecting Absorption

  • Temperature: Optimum 20-30°C. Low temperature reduces absorption (decreased kinetic energy).
  • Oxygen: Required for respiration and active transport. Waterlogged soil reduces absorption.
  • Soil Water: Adequate water needed. Dry soil reduces absorption.
  • Concentration of Soil Solution: High concentration (saline soil) reduces absorption by osmosis.
  • Root System: Extensive root system increases absorption area.
  • Transpiration Rate: High transpiration increases passive absorption.

Formulas

Keep these ready

Formula 01

DPD = OP - TP

Diffusion Pressure Deficit = Osmotic Pressure - Turgor Pressure

Formula 02

TP = WP (in turgid cell)

Turgor Pressure equals Wall Pressure

Quiz

Test your knowledge

Multiple choice

  1. Question 1 of 15Knowledge
    The primary site of water absorption in roots is:
  2. Question 2 of 15Knowledge
    Root hairs increase the surface area for absorption by:
  3. Question 3 of 15Knowledge
    Osmosis is the movement of:
  4. Question 4 of 15Knowledge
    The Casparian strip is found in:
  5. Question 5 of 15Knowledge
    DPD (Diffusion Pressure Deficit) is calculated as:
  6. Question 6 of 15Application
    When a plant cell is placed in a hypotonic solution, it becomes:
  7. Question 7 of 15Comprehension
    Plasmolysis occurs when a cell is placed in:
  8. Question 8 of 15Knowledge
    The pathway where water moves through cell walls is called:
  9. Question 9 of 15Knowledge
    What percentage of water absorption is passive?
  10. Question 10 of 15Comprehension
    Guttation is caused by:
  11. Question 11 of 15Assertion-Reasoning
    Assertion (A): Root hairs are unicellular. Reason (R): They increase surface area for absorption.
  12. Question 12 of 15Knowledge
    Minerals are absorbed by roots through:
  13. Question 13 of 15Knowledge
    Which mineral is essential for chlorophyll formation?
  14. Question 14 of 15Comprehension
    Waterlogged soil reduces water absorption because:
  15. Question 15 of 15Comprehension
    In a turgid cell:

0 of 15 answered