uptake and transport2

UPTAKE & TRANSPORT SYSTEM IN PLANTS BIO 240: Plant Physiology

Overview

  • Understanding plant transport systems is critical for comprehending how plants efficiently manage internal resources.

Outline of Key Concepts

  • Review terms related to transport in plants:

    • Importance of transport mechanisms.

    • Transpiration: the process of water movement through plants and its evaporation from aerial parts, primarily leaves.

    • Transport of Water: primarily through the xylem.

    • Routes through which water moves through plant tissues:

      • Apoplast Pathway: Movement through the cell wall space.

      • Symplast Pathway: Movement through the cytoplasm connected by plasmodesmata.

      • Vacuolar Route: Movement through the vacuoles of cells.

Review of Transport Terms

  • Diffusion: Movement of molecules from an area of higher concentration to an area of lower concentration.

  • Osmosis: Movement of water across a semi-permeable membrane due to solute concentration differences.

  • Water potential: A measure that combines solute potential and pressure potential.

  • Solute Potential (ΨS): The effect of dissolved substances on the direction of water movement.

  • Pressure Potential (ΨP): The pressure exerted by the fluid on the membrane.

  • Active Transport: The movement of ions against their concentration gradient, requiring energy.

Osmosis and Plant Cells

  • Key organelles and structures in plant cells include:

    • Mitochondria, Nucleus, Chloroplasts, Vacuole, Cell Wall, Cell Membrane.

  • Diagrams are used to illustrate cell structure, highlighting the functions of these components.

New Terms

  • Apoplast pathway: Movement of water around cells.

  • Symplast pathway: Movement of water through living cell cytoplasm.

  • Endodermis: Innermost layer of the cortex, regulating water and solute uptake.

  • Casparian Strip: A waxy barrier in the endodermis that prevents water from freely moving through cell walls.

  • Transpiration: Evaporation of water vapor from leaves.

  • Cohesion and Adhesion: Forces that allow water to move through plants due to molecular attraction.

  • Capillarity: The ability of water to rise in small tubes due to cohesion and adhesion forces.

  • Translocation: Movement of sugars through the plant.

Importance of Transport

  • Multicellular organisms, including plants, require efficient transport systems to ensure successful distribution of nutrients and removal of waste:

    • Supplies of oxygen, carbon dioxide, organic nutrients, inorganic ions, and water are crucial for plant growth and metabolism.

Transpiration

  • Definition and process:

    • Loss of water vapor through leaves, driven by energy from the sun.

    • It creates a gradient that helps pull water from roots to leaves through the xylem.

  • Mechanism:

    • Changes in water potential lead to the passive movement of water via transpiration pull.

    • Structure of mesophyll allows for efficient water vapor saturation in leaf interiors.

Transpiration Sites

  • Stomata are the primary site of transpiration (accounting for 90% of water loss).

  • The cuticle and lenticels also contribute to water loss.

Conditions for Transpiration

  • Occurs primarily under conditions where:

    • Stomata are open.

    • Humidity outside is lower than inside the leaf, creating a water potential gradient.

Water Potential Gradient

  • Water moves from areas of high water potential to low water potential, with various measurements depending on environmental conditions:

    • Different water potentials are observed in atmospheric air, leaves, roots, and soil, influencing water movement.

Factors Influencing Water Potential

  • Two main factors:

    • Solute Potential (ΨS): Affects water movement via osmosis.

    • Pressure Potential (ΨP): Influences water movement due to pressure.

Osmosis in Plant Cells

  • Osmosis leads to movements of water, with predictions regarding cell behavior in different solution types (hypotonic, isotonic).

  • Plant cells resist bursting due to cell walls, unlike animal cells that may burst in hypotonic solutions.

Water Transport Mechanisms

Cohesion-Tension Theory

  • Describes the pull mechanism of water ascent in plants.

    • Water molecules are cohesive and adhere to xylem walls, allowing for efficient upward transport.

Root Pressure

  • Water movement driven by osmotic pressure due to solutes being actively transported into xylem.

Capillary Action

  • Water can move short distances due to adhesion and capillary forces, although limited in reaching tall plants like redwoods.

Summary of Root to Leaf Transport

  • Transport from roots to leaves involves:

    • Pushing action from root pressure.

    • Pulling action due to transpiration and cohesion-tension.

Mechanisms for Ion Absorption

  • Active and selective processes of nutrient uptake in roots.

  • Strategies for ion movement via diffusion and mass flow, requiring energy.

Pathways in Water Movement

  • Illustrates apoplast and symplast pathways and their roles in transporting water from the soil to the vascular system.

Role of the Casparian Strip

  • Functions as a barrier that regulates water entry into the vascular system, preventing harmful substances from entering.

Ascent of Water in the Xylem

  • Water movement occurs via mass flow influenced by:

    • Cohesion-tension, capillarity, and root pressure from active solute secretions.

Importance of Sugar Transport (Translocation)

  • Essential for plant nutrition, moving sugars from production sites (sources) to usage sites (sinks).

  • The pressure flow hypothesis explains how sugars move through the phloem by pressure gradients created during loading and unloading.

Conclusion

  • Understanding these mechanisms provides insight into plant physiology and adaptations for survival in various environments.