Lecture 21

Resource Overview

• Reading assignments:

  • Chapters 42.1-3 and 36.2-3, 36.5

Housekeeping

• Reminder: Quiz 7 (L18-20) due Wednesday, March 12, by 11:59 PM

• Complete Dynamic Study Modules: 8 & 9

• Focus topics:

  • Chapter 36: Resource acquisition and transport in Vascular Plants

  • Chapter 42: Circulation and Gas Exchange

Key Concepts

• Material Movement

  • Organisms transport materials within and between cells and tissues.

  • Diffusion is sufficient for organisms with 1-2 cells; complex organisms require transport systems.

  • Animal transport systems are metabolically powered.

  • Open circulatory systems use less energy and constrain body size.

  • Double circulation systems are more energy-efficient and support higher blood pressures and flow rates.

  • Plant transport systems are solar and metabolically powered.

• Transport Mechanics

  • Transpiration in xylem is driven by solar energy.

  • Phloem sap movement is metabolically powered, especially the movement of sucrose against the concentration gradient.

Transportation Mechanisms

• Overview of Transportation

  • Organisms can transport materials over substantial distances within and between cells.

Selective Permeability of Membranes

• Membrane Characteristics

  • Polar and charged molecules cannot pass through lipid membranes without transmembrane proteins.

  • Nonpolar molecules (e.g., O2, CO2) can freely diffuse through the membrane.

  • Types of permeability:

    • Freely permeable: Nonpolar molecules (O2, CO2, N2)

    • Slightly permeable: Small uncharged polar molecules (H2O, glycerol)

    • Impermeable: Large uncharged polar molecules (glucose, sucrose) and ions (H+, Na+, etc.)

Transport Processes

• Passive Transport

  • No energy required; solutes diffuse from high to low concentration.

  • Includes co-transport mechanisms.

• Active Transport

  • Requires energy to move solutes against their concentration gradient.

Cellular Level Transport

• Proton Pump

  • Establishes pH gradient, utilizing ATP to transport H+ ions, impacting membrane potential and contributing to solute transport.

• Cotransport Mechanisms

  • Plant cells use energy from H+ gradients to cotransport ions and solutes through specific transport proteins.

  • Common cotransport examples: H+/NO3- and H+/sucrose cotransporters.

• Ion Channels

  • Plant cell membranes contain specific ion channels that regulate the passage of certain ions.

Multicellular Level Transport

• Short Distance Transport

  • Diffusion is effective through a few cell layers for adjacent cell supply.

• Long Distance Transport

  • Utilizes transport systems that reduce the distance between exchange surfaces (e.g., gas, nutrients).

Animal Circulatory Systems

• System Components

  • Parts include fluid, vessels, and a pump to increase fluid pressure for circulation.

  • Fluid moves from areas of high to low pressure through vessels.

• Circulatory System Types

  • Open Circulatory System:

    • Circulatory fluid bathes organs directly;

    • Found in arthropods and most molluscs, utilizing hemolymph.

  • Closed Circulatory System:

    • Blood confined to vessels, present in octopi, annelids, and vertebrates.

    • Efficient exchange occurs in capillaries, which are thin-walled structures that facilitate the transfer of substances between blood and cells.

• Capillary Function

  • Capillaries enable the supply of O2 and nutrients while removing CO2 and waste products from cells.

Circulatory Pathways

• Single Circulation

  • Blood passes through the heart once per circuit; oxygenation happens in gills, followed by deoxygenation in body capillaries.

• Double Circulation

  • Blood passes through two circuits powered by two pumps; deoxygenated blood goes to the lungs for oxygenation, while oxygenated blood is supplied to body tissues.

Plant Transport Systems

• Water Movement

  • In plants, water moves via bulk flow through vascular tissues: xylem (upward transport) and phloem (downward transport).

  • Xylem transports water and minerals from roots to shoots.

  • Phloem moves sugar water from production sites to usage sites (source to sink).

Xylem Characteristics

• Contains tracheids and vessel elements, which are dead at maturity and provide structural support through thick cell walls hardened with lignin.

Phloem Characteristics

• Composed of sieve-tube elements, which are alive at maturity and rely on companion cells for functionality, facilitating water and nutrient flow.

Water Potential in Plants

• Water Potential (Ψ)

  • Defined as the potential energy of water, expressed in pressure units (MPa).

  • Comprises solute potential (Ψs) and pressure potential (Ψp).

  • Water moves from areas of high potential to low potential.

Transpiration and Water Movement

• Transpiration Process

  • Driven by solar energy, the cohesion-tension hypothesis explains how water moves from roots to leaves.

Phloem Transport Mechanism

• Sucrose Transport

  • Sucrose loading in phloem lowers solute potential, resulting in water uptake by osmosis and creating pressure gradients for transport. Unloading is also active, effectively recycling water back to the xylem.

Test Your Knowledge (Sample Questions)

1. Active transport involves all of the following except… (options provided).

2. Blood returning to the mammalian heart in a pulmonary vein first drains into… (options provided).

3. Phloem transport of sucrose is often described as going from source to sink; which would not normally function as a sink? (options provided).

4. Which statement about xylem is incorrect? (options provided).

5. What is likely to be found in organisms with a distinct circulating body fluid? (options provided).

Next Class

• Topic for next class: Thermal Relations

• Reading assignments: Chapters 40.2-3 and 36.4.