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Q9:
How is the mycorrhizal association helpful in absorption of water and minerals in plants?
Solution :
1. Definition and Biological Basis of Mycorrhiza
Mycorrhiza is a symbiotic, mutualistic association between the mycelium of a fungus and the roots of higher plants. In this biological system, the fungus provides nutrients to the plant, while the plant provides carbohydrates (products of photosynthesis) to the fungus [Reference: Mutualistic Symbiosis Theory].
2. Morphological and Physiological Adaptations
The efficiency of mineral and water absorption is significantly enhanced by the physical structure of the fungal hyphae. Fungal filaments (hyphae) have a much smaller diameter ($< 10 \mu m$) compared to the finest root hairs of the plant. This structural difference enables the following mechanisms:
- Increased Surface Area: The extensive network of hyphae (extramatrical mycelium) creates a massive surface area-to-volume ratio, reaching into soil pores that are inaccessible to root hairs [Per the Principle of Nutrient Diffusion].
- Soil Penetration: The hyphae act as extensions of the root system, effectively extending the depletion zone of nutrients around the plant root.
3. Mechanism of Nutrient and Water Acquisition
The association facilitates the uptake of specific elements, most notably phosphorus, which has low mobility in soil:
| Mechanism | Biological/Physical Process |
|---|---|
| Phosphorus Uptake | Fungi secrete organic acids (e.g., oxalates) that solubilize mineral-bound phosphorus (like calcium phosphate), making it bioavailable for transport [Per Chelation Principles]. |
| Water Potential Gradient | By actively accumulating minerals, the hyphae lower the solute potential ($\Psi_s$) within the fungal tissues, thereby lowering the total water potential ($\Psi_w$), inducing a gradient that draws water from the soil into the hyphae [Per the Water Potential Equation: $\Psi_w = \Psi_s + \Psi_p$]. |
4. Visual Representation of Mycorrhizal Interaction
5. Summary of Functional Benefits
The mycorrhizal association is essential for survival in nutrient-poor conditions because:
- Solubilization: It converts insoluble minerals into soluble ionic forms ($PO_4^{3-}$, $NH_4^{+}$).
- Transport Efficiency: The high-affinity transport systems in fungal membranes are more efficient at gathering dilute nutrients than standard root epidermal cells.
- Pathogen Defense: The physical mantle formed by fungi around roots acts as a mechanical barrier against soil-borne pathogens.
Final Solution: The mycorrhizal association provides a vastly increased surface area for absorption, utilizes highly specialized transport proteins to acquire immobile ions like phosphorus, and establishes a steep water potential gradient to increase moisture uptake beyond the capabilities of the root system alone.
More Questions from Class 11 Biology Transport in Plants EXERCISES
- Q1: What are the factors affecting the rate of diffusion?
- Q2: What are porins? What role do they play in diffusion?
- Q3: Describe the role played by protein pumps during active transport in plants.
- Q4: Explain why pure water has the maximum water potential.
- Q5(a): Differentiate between the following: (a) Diffusion and Osmosis
- Q5(b): Differentiate between the following: (b) Transpiration and Evaporation
- Q5(c): Differentiate between the following: (c) Osmotic Pressure and Osmotic Potential
- Q5(d): Differentiate between the following: (d) Imbibition and Diffusion
- Q5(e): Differentiate between the following: (e) Apoplast and Symplast pathways of movement of water in plants.
- Q5(f): Differentiate between the following: (f) Guttation and Transpiration.
- Q6: Briefly describe water potential. What are the factors affecting it?
- Q7: What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution?
- Q8(a): (a) With the help of well-labelled diagrams, describe the process of plasmolysis in plants, giving appropriate examples.
- Q8(b): (b) Explain what will happen to a plant cell if it is kept in a solution having higher water potential.
- Q10: What role does root pressure play in water movement in plants?
- Q11: Describe transpiration pull model of water transport in plants. What are the factors influencing transpiration? How is it useful to plants?
- Q12: Discuss the factors responsible for ascent of xylem sap in plants.
- Q13: What essential role does the root endodermis play during mineral absorption in plants?
- Q14: Explain why xylem transport is unidirectional and phloem transport bi-directional.
- Q15: Explain pressure flow hypothesis of translocation of sugars in plants.
- Q16: What causes the opening and closing of guard cells of stomata during transpiration?
CBSE Solutions for Class 11 Biology Transport in Plants
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Cell – The Unit of Life
- Biomolecules
- Cell Cycle and Division
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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