Exchange and transport

• To respire and grow living things need to take up:

  • Oxygen > Respiration
  • Glucose > Respiration (hetrotophis)
  • Water > Everything
  • Carbon dioxide > Photosynthesis
  • Mineral ions > All sorts
• Living things also need to remove by-products and wastes such as:

  • Carbon Dioxide > Respiration
  • Urea > Metabolic waste
  • Oxygen > Respiration (plants) and photosynthesis
• Ficks Law:

  Rate of Diffusion = Surface area x Concentration gradient / Diffusion distance
• Small organisms do not have specialized transport systems as they have a large surface area to volume ratio so they can rely on simple diffusion alone.

  This works through oxygen from the surroundings, which diffuses through the cell surface membrane.
• Large organisms cannot rely on diffusion from the surface for their supplies of oxygen because of:

  • Metabolic demand
  • Diffusion distance
  • Surface area : Volume is low
• All good exchange surfaces have certain features in common:

  • Small diffusion distance
  • Large surface area
  • Blood supply (well ventilated)
• Lung an an organ for exchange:

  A) Trachea

  B) Bronchus

  C) Bronchiole

  D) Intercostal

  
• Avelio:

  A) Ventilation

  B) Moisture

  C) Short

  D) Diffusion Distance

  E) Blood

  
• Adaptations of the Aveoli for efficient gaseous exchange:

  • Surface area > Folded + lots of alveoli
  • Concentration gradient > Good blood supply - Well ventelated
  • Rate of diffusion > O2 in CO2 out
  • Diffusion distance > Squamous cells + Permeable
• Ventilation: The refreshing of the air in the lungs so that there is a higher concentration of O2 in comparison to the blood and a lower concentration of CO2.
• The mechanism of breathing (Inspiration):

  Diaphragm > contracts + flattens

  Rib cage > external intercostal muscles contract, ribs move up and out

  Volume of thorax > increases

  Pressure in lungs > Decrease

  Movement of air > Moves in
• The mechanism of breathing (Expiration):

  Diaphragm > Relaxs + moves up

  Rib cage > external intercostal muscles relax, ribs move down and in

  Volume of thorax > Decreases

  Pressure in lungs > Increases

  Movement of air > Moves out
• Bronchi function in the mammalian gaseous exchange system

  Supported by rings of cartilage and lined by ciliated epithelium cells and goblet cells. Narrower than the trachea and there are two of them, one for each lung. Allow passage of air into the bronchioles
• Surface area to volume ratio is calculated as Ratio = Surface area / Volume
• Trachea function in the mammalian gaseous exchange system

  Wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes. Lined by ciliated epithelium cells which move mucus, produced by goblet cells, towards the throat to be swallowed, preventing lung infections. Carries air to the bronchi
• Multicellular organisms require specialised gas exchange surfaces due to their smaller surface area to volume ratio, which means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism
• Alveoli function in the mammalian gaseous exchange system


  To be continued...
• Features of an efficient gas exchange surface include: 1. Large surface area, e.g. root hair cells. 2. Thin/short distance, e.g. alveoli. 3. Steep concentration gradient, maintained by blood supply or ventilation, e.g. gills
• Bronchioles function in the mammalian gaseous exchange system

  Narrower than the bronchi. Mostly have only smooth muscle and elastic fibres so that they can contract and relax easily during ventilation. Allow passage of air into the alveoli
• Define breathing rate
• Explain how a spirometer works

  1. Used to measure lung volume

  2. A person breathes into an airtight chamber which leaves a trace on a graph showing the volume of the breaths
• Explain the process of expiration and the changes that occur throughout the thorax

  1. External intercostal muscles relax (while internal contract), bringing the ribs down and in

  2. Diaphragm relaxes and domes upwards

  3. Volume of the thorax decreases

  4. Air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance
• Define tidal volume
• Describe the alveoli and their function in the mammalian gaseous exchange system

  1. Mini air sacs, lined with epithelium cells, site of gas exchange

  2. Walls only one cell thick, covered with a network of capillaries, 300 million in each lung, all of which facilitates gas diffusion
• Define vital capacity
• Explain the process of inspiration and the changes that occur throughout the thorax

  1. External intercostal muscles contract (while internal relax), pulling the ribs up and out

  2. Diaphragm contracts and flattens

  3. Volume of the thorax increases

  4. Air pressure outside the lungs is therefore higher than the air pressure inside, so air moves in to rebalance
• Gas exchange in fish

  1. Buccal cavity volume increased to enable water to flow in, reduced to increase pressure

  2. Water is pumped over the lamellae by the operculum, oxygen diffuses into the bloodstream

  3. Waste carbon dioxide diffuses into the water and flows back out of the gills
• Gas exchange in insects

  1. Gases move in and out of the tracheae through the spiracles

  2. A diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out

  3. Contraction of muscles in the tracheae allows mass movement of air in and out
• Countercurrent exchange system


  Maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration. Keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed
• Fish’s gas transport system

  • Gills = located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles
  • Lamellae = at right angles to the gill filaments, give an increased surface area. Blood and water flow across them in opposite directions (countercurrent exchange system)
• Insect’s gas transport system

  • Spiracles = holes on the body’s surface which may be opened or closed by a valve for gas or water exchange
  • Tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse
  • Tracheoles = smaller branches dividing off the tracheae