BIO C05

• Gas exchange


  Process of getting oxygen from air (or water) and releasing carbon dioxide wastes
• Plant gas exchange


  • Involves photosynthesis

  
• Plant tissues


  • Dermal
  • Ground
  • Vascular
• Dermal tissue


  • On external surfaces that serves a protective function
• Ground tissue


  • Forms several different internal tissue types and can participate in photosynthesis, serve a storage function, or provide structural support
• Vascular tissue


  • Conducts water and nutrients
• Guard cells


  Paired sausage-shaped cells that flank a stoma (pl. stomata) - epidermal opening which is a passageway for oxygen, carbon dioxide, and water vapor
• How a stoma opens


  1. Abscisic acid (ABA) initiates a signaling pathway to close stomata in drought

  2. Opens K+ and Cl- and malate channels

  3. Water loss follows, making guard cells flaccid
• Abscisic acid (ABA)


  A plant hormone that plays a central role in regulating stomatal movement, particularly in response to environmental stress and water availability
• Scarce water = ABA is synthesized = prevents stomatal opening
• Also affecting stomatal opening


  • Close when CO2 concentrations are high
  • Open when blue wavelengths of light promote uptake of K+ by the guard cells
  • Close when temperature exceeds 34°C and water relations unfavorable
  • Crassulacean acid metabolism (CAM) plants conserve water in dry environments by opening stomata and taking in CO2 at night
• Lenticel


  Small, corky pores or openings in the bark of woody stems and roots of plants that facilitate gas exchange between the internal tissues of the plant and the external environment
• Respiration


  The sequence of events that results in gas exchange between the body's cells and the environment
• Components of respiration


  • Ventilation
  • External respiration
  • Internal respiration
• External respiration


  Gas exchange between the air and the blood within the lungs
• Internal respiration


  Gas exchange between the blood and the tissue fluid (interstitial)
• Gas exchange by diffusion


  • Gas-exchange regions must be moist, thin, and large in relation to body size
  • Effectiveness of diffusion is enhanced by vascularization (presence of many capillaries)
  • Delivery to cells is promoted by respiratory pigments (for example, hemoglobin)
• It is more difficult for animals to obtain O2 from water than from air
• Hydra


  • Simple diffusion - lacks specialized respiratory structures like gills or lungs
  • Oxygen from the water diffuses through the moist epidermis of Hydra and enters the cells of the ectoderm
  • Carbon dioxide, produced as a byproduct of cellular respiration, diffuses out of the cells and across the epidermis into the surrounding water
• Earthworm


  • Cutaneous respiration - exchange of gases through the skin
  • Moisture is crucial - Oxygen from the air dissolves in the thin layer of moisture on the skin and diffuses into the bloodstream
  • Highly vascularized skin - extensive network of blood vessels
• Vertebrate respiratory structures


  • Gills
  • Trachea
  • Lungs
• Gills


  • Finely divided, vascularized outgrowths of the body surface or the pharynx
  • Gills of bony fishes are outward extensions of pharynx
  • Ventilation is brought about by combined action of the mouth and gill covers (opercula)
• Concurrent flow


  Oxygen-rich water passing over gills would flow in the same direction as oxygen-poor blood in vessels and results in 50% oxygen extraction
• Countercurrent flow


  The two liquids flow in opposite directions and results in 8 to 90% oxygen extraction
• Tracheal system of insects

  • Internal organs lie within the hemocoel cavity, which contains both blood and lymph
  • Circulation is inefficient
  • Respiratory system consisting of branched tracheae overcomes inefficiency of blood flow
  • Tracheae are tiny air tubes, 0.1 µm in diameter
  • Oxygen enters tracheae at spiracles
  • Tracheae branch until they end in tracheoles that are in direct contact with almost all body cells
  • O2 can flow more directly from a tracheole to a mitochondrion, where cellular respiration occurs
• Spiracles


  Openings on the insect's body that allow air to enter and exit
• Trachea


  Main respiratory tubes
• Tracheoles


  Smallest branches of the tracheal system
• Air sacs


  Store and regulate the movement of air within the tracheal system
• Lungs


  • Air moving through the upper respiratory system is filtered to free it of debris by hairs and cilia, warmed, and humidified
  • Air reaching lungs is at body temperature, and is saturated with water
• Diffusion


  Movement of molecules from a region with high concentration to a region with low concentration, rapid only in very small distances
• Osmosis


  Water can diffuse down its concentration across a plasma membrane
• Aquaporins


  Membrane water channels that speed up water movement across a membrane, but do not change its direction
• Plant tissues


  • Dermal
  • Ground
  • Vascular
• Xylem


  • Moves water and minerals from the roots to the leaves
  • Strong-walled, nonliving cells, gives trees much needed internal support
  • Dead cells upon maturation
  • Consists of vessel elements and tracheids
• Vessel elements


  Long tubular with perforation plates at each end
• Tracheids


  Narrower and have a substantial role in structural support
• Xylem transport


  1. The aqueous solution that passes through the endodermal cells moves into the tracheids and vessel elements of the xylem

  2. As ions are actively pumped into root or move via facilitated diffusion, their presence decreases the water potential

  3. Water then moves into the plant via osmosis, causing an increase in turgor pressure
• Water uptake


  1. Water is absorbed by the roots from the soil through a process called osmosis

  2. Most of the water absorbed by the plant comes in through the region of the root with root hairs

  3. Surface area further increased by mycorrhizal fungi
• Root pressure


  • Caused by the continuous accumulation of ions in the roots at times when transpiration from leaves is low or absent
  • Causes water to move into plant and up the xylem despite the absence of transpiration