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Q3:
Describe the role played by protein pumps during active transport in plants.
Solution :
Definition and Theoretical Framework
In biological systems, specifically within plant cells, active transport is defined as the movement of molecules or ions across a cell membrane against their concentration gradient (from a region of low concentration to a region of high concentration). This process is non-spontaneous and requires the expenditure of metabolic energy, typically in the form of Adenosine Triphosphate (ATP) [Per the Chemiosmotic Hypothesis].
Role of Protein Pumps
Protein pumps are integral transmembrane proteins that function as molecular machines. Their roles are categorized as follows:
- ATP Hydrolysis: The pump possesses an active site that binds to ATP. Upon binding, the protein acts as an ATPase, catalyzing the reaction: $ATP \rightarrow ADP + P_i + \text{Energy}$ [Per the Enzymatic Catalysis Principle].
- Conformational Change: The energy released from ATP hydrolysis induces a shape change (allosteric shift) in the protein pump, allowing it to move specific solutes across the lipid bilayer.
- Gradient Establishment: In plant cells, the most significant pump is the Proton Pump ($H^+$-ATPase). It actively extrudes protons ($H^+$ ions) from the cytosol into the apoplast or the vacuole [Per the Electrochemical Gradient Theory].
Diagrammatic Representation: Proton Pump Mechanism
Biological Significance in Plants
| Function | Mechanism |
|---|---|
| Secondary Active Transport | The $H^+$ gradient generated by the pump creates a proton motive force ($PMF$) that drives the uptake of sugars and amino acids via symport or antiport systems [Per the Co-transport Model]. |
| Nutrient Uptake | Plants utilize the electrochemical gradient to facilitate the influx of nitrate ($NO_3^-$) and phosphate ($H_2PO_4^-$) against their respective concentration gradients. |
| Turgor Maintenance | Pumping ions into the vacuole (via the tonoplast) lowers the water potential, causing water to enter the cell by osmosis, thus maintaining turgor pressure necessary for plant structural integrity. |
Summary of Thermodynamic Logic
The protein pump effectively converts chemical energy into an electrochemical potential difference ($Δ\mu_{H^+}$). Mathematically, this is expressed as: $$\Delta\mu_{H^+} = RT \ln \frac{[H^+]_{out}}{[H^+]_{in}} + zF\Delta\psi$$ Where $R$ is the gas constant, $T$ is temperature, $z$ is the charge, $F$ is Faraday's constant, and $\Delta\psi$ is the membrane potential. Protein pumps maintain this non-equilibrium state, ensuring the plant remains physiologically active.
Final Solution: Protein pumps serve as the primary drivers of active transport in plants by hydrolyzing ATP to move protons across membranes, thereby generating an electrochemical gradient that acts as a secondary energy source for the uptake of essential nutrients and the maintenance of cellular turgor.
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?
- 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.
- Q9: How is the mycorrhizal association helpful in absorption of water and minerals in plants?
- 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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