gas exchange in other organisms

• Bony fish

  • use gills in order to absorb oxygen dissolved in water and release carbon dioxide into the water
  • oxygen concentration will be found much lower than found in air
  • most bony fish has 5 pairs of gills which are covered by a bony plate called an operculum
  • each gill consits of 2 rows of gill filament (primary lamellae) attached to a bony arch

  →filaments are very thin, and their surface is folded into many secondary lamellae (or gill plates) ; providinmg LSA

  • blood capillaries carry deoxygenated blood close to the surface of the secondary lamellae where exchange takes place
• Investigation :

  1. find the operculum
  2. lift the operculum and observe gills (note colour)
  3. cut away one operculum to view the gills (note the gill slits or spaces between the gills)
  4. carefully cut out one gill (note bony support and soft gill filaments that make each gill) and draw the gill
• Countercurrent flow

  Blood flows along the gill arch and out along the filaments to the secondary lamelllae

  • the blood then flows through capillaries in opoosite directions to the flow of water over the lamellae → this arrangement creates a countercurrent flow that absorbs the maximum amount of oxygen from the water
• Insects

  do not transport oxygen in blood as they have an open circulatory system; circulation is slow and can be affected by body movements

  • insects possess an air-filled tracheal system whuch supplies air directly to all respiring tissues
  • air enters via a pore in eachs egment, called a spiracle
  • the air is transported through a series of tubes called tracheae (plural) and these divide into smaller tubes called tracheoles
• Insects 2

  • the ends of the tracheoles are open and filled with tracheal fluid
  • gaseous exchange occurs between the air in the tracheole and the tracheal fluid

  →some exchanges occur across thin wall of the tracheoles

  • many insects are very active and need a good supply of oxygen
  • when tissues are active, the tracheal fluid can be withdrawn into the body fluid in order to increase the surface area of the tracheole wall exposed to air meaning more oxygen can be absorbed when insect is active
• ventilation in insects

  • in many insects, sections of the tracheal system are expanded and have flexible walls. These act as air sacs which can be squeezed by the action of the flight muscles; repetitive expansion and contraction of these sacs ventilate
  • in some insects, movements of the wings alter the volume of the thorax and as the thorax volume, the air in the tracheal system is put under presure and is pusged out of the tracheal system. When thorax increases in volume, the pressure inside drops and air is pushed into the tracheal system from outside
• ventilation in insects 2

  • some insects have developed this ventilation even further as locusts can alter the volume of their abdomen by specialised breathing movements. These are coordinated with opening and closing valves in the spiracles. As the abdomen expands, spiracles at the front end of open and air enters the tracheal system. As the abdomen reduces in volume, the spiracles at the end of the body open and air can leave the tracheal system
• Ventilation in bony fish

  • bony fish can keep water flowing over the gills by using a buccal-operculum pump
  • the buccal cavity (mouth) can change volume
  • the floor of the mouth opens and draws water into buccal cavity
  • the mouth closes and floor is raised again pushing water through gills
  • movements of the operculum are coordinated with the movements of the buccal cavity
  • as water is pushed from buccal cavity, the operculum moves outwards
  • this movement reduces pressure in the operculum cavity (space under operculum), helpinmg water to flow through gills