plant physiology

• Roots absorb water from the soil through root hair by osmosis and diffusion
• Water is transported by the cortical cell and xylem vessels to different parts of the plant under the influence of various forces/pressure
• Soil water contains inorganic salts such as nitrates, sulphates, phosphates, chlorides, carbonates, etc. of potassium, calcium, sodium, magnesium, iron, manganese
• Essential elements for plants include: K, Ca, Mg, Fe, C, H, O, N, S and P
• Trace essential elements for plants include: Mn, Zn, Cu, Mo and B
• Water constitutes more than 80% of the cell protoplasm, essential for normal cell functioning
• Water is needed for processes like photosynthesis, transpiration, transportation of food
• Water is a universal solvent, essential for enzyme production, transport, and activity
• Water provides turgidity to cells, necessary for seed radicals to penetrate the soil
• Root adaptations for water absorption:
• Roots are positively geotropic, growing deeper towards gravity and water source
• Roots have a large surface area due to abundant root hair for increased water and mineral absorption
• Roots contain concentrated cell sap and have thin walls in root hairs for easy water absorption
• Factors affecting water absorption:
• Soil temperature affects the rate of water absorption
• Concentration of soil solution affects water absorption balance
• Well-aerated soil facilitates more water absorption by root hairs
• Processes of water and mineral absorption by root hairs:
• Diffusion, osmosis, imbibition, and active transport
• Diffusion is the movement of molecules from higher to lower concentration
• Osmosis is the passage of solvent molecules through a semipermeable membrane
• Osmosis helps in water absorption, maintaining plant structure, and cell-to-cell water movement
• Types of solutions:
• Isotonic solution: equal concentration, no net movement of water molecules
• Hypotonic solution: higher water concentration outside the cell, lower solute concentration
• Hypertonic solution: lower water concentration outside the cell, higher solute concentration
• Endosmosis is inward diffusion of water in less concentrated solution, exosmosis is outward diffusion in more concentrated solution
• Turgidity is the outward pressure on the cell wall by cell contents, important for maintaining plant shape and growth
• Turgidity helps in opening and closing of stomata and movements of plant organs
• Flaccidity occurs when a plant cell loses water content, leading to wilting
• Imbibition is the absorption of water by cells due to hygroscopic constituents in the cell wall
• Active transport is the passage of substances from lower to higher concentration using cell energy
• Root pressure is the pressure exerted by root cortex cells, forcing liquid contents into xylem vessels for upward movement in the stem
• Ascent of sap is the movement of sap from roots to aerial parts of the plant
• Forces responsible for ascent of sap:
• Root pressure in small herbaceous plants
• Capillary force from xylem capillaries
• Cohesion and adhesion of water creating a continuous column from roots to leaves
• Transpirational pull aiding in sap ascent in tall trees
• cell membranes are semi-permeable - only certain substances can pass through them