Plant Transport

Photosynthesis & Pesticide Effects

• NADP+ Reductase Enzymes:

  • Inhibited by pesticides.

  • Key role: Reduces NADP+ to NADPH in Photosystem I.

  • Effects on Photosynthesis:

  1. Directly Affected Stage: Calvin cycle.

  2. **Impact on Other Stages: **

     • Without NADPH, the Calvin cycle cannot occur, resulting in no G3P molecules. G3P is a precursor for glucose.

     • No regeneration of NADP+ or ADP for the light reactions.

Phloem Structure & Function

• Cell Types:

  • Phloem Cells: Alive at functional maturity; lack organelles for efficient sugar transport.

  • Sieve Cells: Present in seedless vascular plants like ferns and gymnosperms (e.g., pine trees).

  • Sieve-Tube Elements: Present in angiosperms, transported in chains of cells.

  • Sieve Plates: End walls between sieve-tube elements; have pores for fluid flow.

  • Companion Cells: Non-conducting; assist sieve-tube elements and are connected via plasmodesmata.

Types of Plant Tissues

Ground Tissue

• Definition: Not dermal or vascular, specialized for storage, photosynthesis, support, and transport.

• Components::

  • Pith: Ground tissue internal to vascular tissue.

  • Cortex: Ground tissue external to vascular tissue.

  • Cell Types:

  • Parenchyma Cells:

    • Perform metabolic functions; photosynthesis occurs here in chloroplasts.

    • Role: Storage (e.g., starch in roots).

  • Collenchyma Cells:

    • Support young plant parts; flexible cell walls.

  • Sclerenchyma Cells:

    • Rigid support; thick secondary walls with lignin.

Plant Tissue Systems

• Dermal Tissue System: Complex tissues including epidermal cells, guard cells, trichomes, and root hairs.

• Ground Tissue System: Consists of parenchyma, collenchyma, and sclerenchyma.

• Vascular Tissue System:

  • Xylem: Conducts water/nutrients; contains dead tracheids and vessel elements.

  • Phloem: Conducts sugars and organic products; includes sieve-tube elements and companion cells.

Meristems and Growth

• Differentiation: Cells specialize during development; plants grow throughout life—indeterminate growth.

• Indeterminate Growth: Most plants continue growth after reaching a size; contrast with determinate growth in animals.

• Meristems: Key for continuous growth, they are undifferentiated tissues that divide.

Apical and Lateral Meristems

• Apical Meristems:

  • Cause primary growth (length).

  • Located at root and shoot tips; responsible for new leaves and flowers.

• Lateral Meristems:

  • Cause secondary growth (width).

  • Located at cambium; produce bark in trees.

Primary Growth Mechanisms

Shoots and Roots

• Shoots: Youngest differentiated cells at the top; undergo elongation and complexity.

• Roots: Youngest differentiated cells at the bottom; root hairs facilitate absorption (70-90% surface area).

Water and Sugar Transport in Plants

Chapter Overview

• Topics: Adaptations for acquiring resources; transport types; mechanisms of transport; transpiration and sugar transport.

Stomatal Functionality

• Role: Gas exchange and evapotranspiration; affected by light, water, and temperature.

• Vulnerability: Stomata loss impacts CO2 intake, affecting photosynthesis.

Water Potential and Movement

• **Definitions: **

  1. Water Potential (Ψ): Predicts water flow direction; measured in megapascals (MPa).

  2. Solute Potential (ΨS): Indicates water movement tendency by osmosis due to solute concentration.

  3. Pressure Potential (ΨP): Movement tendency of water due to physical pressure.

Transport Mechanisms

• Xylem Transport: Water and minerals upwards, driven by negative pressure from transpiration.

• Phloem Transport: Sugars pushed towards sinks, working in both directions; relies on positive pressure from sugar sources.

Mechanisms of Transport

• Transport Pathways: Apoplast (external to living cell membranes) vs. Symplast (internal, living cell pathways).

Long-Distance and Short-Distance Transport

• Short-Distance: Diffusion and active transport across plasma membranes.

• Long-Distance: Bulk flow driven by pressure gradients in xylem and phloem.

Root Architecture

• Mutualism with Mycorrhizae: Enhances surface area for water/mineral absorption.

Stomata Regulation

• Guard Cells: Open/close stomata to regulate transpiration based on environmental conditions.

Transpiration Processes

• Cohesion-Tension Theory: Explains how water moves via negative pressure generated as water evaporates.

• Cavitation: Risks posed during drought or freezing due to disruption in water chain.

Sugar Transport via Phloem

• Sources and Sinks:

  • Sucrose is actively moved from sources (e.g., mature leaves) to sinks (e.g., fruits, roots).

  • Phloem Loading: Sucrose must enter sieve-tube elements against concentration gradient; typically involves active transport.

Mechanisms of Phloem Unloading

• Involves diffusion or active transport, depending on sink location.

• Water follows sucrose into the sink, maintaining pressure flow mechanism.

Summary of Concepts

• Xylem vs. Phloem Transport:

  • Xylem: passive, treansport driven by transpiration (negative pressure).

  • Phloem: active, transport driven by turgor pressure variations (positive pressure).

Important Definitions and Concepts to Memorize:

1. Water Potential Equation: $( ext{Ψ} = ext{Ψ}<em>{S} + ext{Ψ}</em>{P})$

2. Pressure Flow Hypothesis: Phloem sap moves from high to low-pressure levels, highlighting flow dynamics.

3. Cohesion and Adhesion: Water's unique properties that enable transpiration and sap movement within plants.

Practice Questions and Concepts

• Identify the roles of xylem and phloem in resource transport.

• Explain how stomata facilitate photosynthesis and transpiration concurrently.

• Discuss the cohesion-tension model of water transport in plants.

• Define active vs passive transport and their implications for plant physiology.

Maple Syrup Production as an Example

• Maple Sap: Primarily xylem sap, produced in late winter; boiling reduces water content to create syrup.

• Conversion Ratio: Approximately 40-43 gallons of sap yield 1 gallon of syrup.