Plant Nutrition and Transport

Plant Nutrition and Transport

Plant Nutrients

  • Essential Elements for Growth

    • Plants require elements for various physiological functions.

  • Macronutrients: Required in large amounts

    • Examples: Carbon (C), Oxygen (O), Hydrogen (H).

    • Main components of all biological molecules.

    • Abundant in air (CO₂) & water (H₂O).

  • Soil Macronutrients: Include

    • Nitrogen (N), Phosphorus (P), Sulfur (S)

    • Essential for proteins & nucleic acids.

    • Potassium (K), Calcium (Ca)

    • Important for cell signaling.

    • Magnesium (Mg)

    • Central component of chlorophyll.

  • Soil Micronutrients:

    • Include Chlorine (Cl), Iron (Fe), Boron (B), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mo).

    • Many act as enzyme cofactors essential for enzyme function.

Mineral Uptake

Passive Transport

  • Soil Composition:

    • Contains mineral particles from rock weathering, decomposing organic matter (humus), and air & water spaces.

  • Soil Particle Size:

    • Sand: ~1mm, Silt: much smaller, Clay: even finer.

    • Each has different effects on soil properties.

  • Properties of Clay:

    • Enhances soil quality by holding water & nutrients but excessive amounts can impair soil aeration.

  • Benefits of Sand & Silt:

    • Loosen soil and improve oxygen availability but retain less water and nutrients.

  • Loam: Ideal soil composition that balances sand, silt, and clay with high organic matter content.

  • Soil Horizons:

    • Topsoil is the uppermost layer rich in organic matter, supporting most plant roots.

  • Leaching:

    • Nutrient removal due to water movement, most prominent in sandy soils.

  • Soil Erosion:

    • Loss of soil due to wind, water, or ice exacerbated by lack of vegetation.

Root Adaptations for Nutrient Uptake

Passive and Active Transport

  • Osmosis:

    • Water moves into roots due to solute concentration differences.

  • Water Movement:

    • Flows from the epidermis through the cortex into the vascular cylinder without entering cells.

  • Endodermis & Casparian Strip:

    • Endodermis surrounds the vascular cylinder; the Casparian strip controls water and solute movement into the vascular system, requiring water to pass through endodermal cells.

  • Transport Proteins:

    • Needed for mineral ion uptake, as ions cannot pass through the lipid bilayer. Specific proteins control ion movement.

  • Mycorrhizae Relationship:

    • Mutualism between plant roots and fungi; provides enhanced nutrient uptake in exchange for sugars.

  • Nitrogen-fixing Bacteria:

    • Convert nitrogen gas (N₂) into usable ammonia (NH₃), hosted in root nodules of certain plants.

Movement of Water in Plants

Xylem Dynamics

  • Structure of Xylem:

    • Composed of dead cells; provides structural support through lignin.

  • Water Flow:

    • Flows upward through xylem and laterally between tubes via pitted walls.

  • Types of Xylem Tubes:

    • Vessel elements (more efficient in angiosperms) and tracheids (found in gymnosperms).

  • Cohesion-tension Theory:

    • Describes how water is pulled through plants via evaporation (transpiration) and cohesion between water molecules.

  • Transpiration Mechanism:

    • Evaporation creates negative pressure, facilitating water movement from roots to leaves.

  • Stomata Function:

    • Regulated openings on leaves that facilitate gas and water exchange controlled by guard cells.

Movement of Organic Compounds in Plants

Phloem Functionality

  • Structure of Phloem:

    • Composed of sieve tubes (living cells) and companion cells (provide metabolic support).

  • Translocation:

    • Movement of sugars; occurs from source (photosynthesis site) to sink (storage or utilization site).

  • Mechanism of Pressure Flow:

    • Differences in turgor pressure push sugar from source to sink through sieve tubes, with water following by osmosis, thereby regulating the pressure levels in the phloem.