exchange surfaces and breathing

• what are the 3 main factors that affect the need for an exchange system

  • size
  • SA:Volume
  • level of activity
• size

  • small organisms such as single celled organisms - cytoplasm is close to the environment they live in therefore short diffusion pathway, diffusion will supply enough oxygen to keep the cells alive and active
  • multicellular organisms - longer diffusion pathway, too slow to enable sufficient supply to the innermost cells
• surface area: volume

  • small organisms have large SA : vol, SA is large enough to supply all their cells with sufficient O2
  • large organisms have a small SA: vol
• level of activity

  • some organisms are more active than others
  • metabolic activity uses energy from food and requires oxygen to release the energy in aerobic respiration
  • active organisms need a good supply of nutrients and oxygen to supply the energy for movement
  • need for energy eg mammals to keep them warm
• what are the features of a good exchange surface

  • a large surface area
  • thin membrane
  • good blood supply
• large surface area

  • provide more space for molecules to pass through , often achieved by folding the walls and membranes involves eg root hair cells
• thin barrier/membrane

  • shortens the diffusion pathway
  • barrier must be permeable to the substance that is being exchanged
• a good blood supply

  • bring fresh supply to keep [] high of remove molecules to keep [] low
  • important to maintain steep [] gradient so that diffusion can occur rapidly
• gaseous exchange in the blood

  • occurs in the alveoli of mammalian lungs
• how are the lungs adapted

  • large surface area
  • thin barrier to reduce diffusion distance
  • many blood vessels
  • ventilation
• 1. large surface area

  • caused by the vast number and shape of the alveoli
• 2. thin barriers to reduce diffusion distance


  - walls of alveoli's and capillaries only one cell thick, close to each other

  • capillaries are so narrow that red blood cells are forced against its walls
• 3. many blood vessels

  • alveoli are surrounded by thousands of capillaries which constantly take away the O2 and deliver CO2 , maintaining steep [] gradient
• 4. ventilation

  • breathing removes air in rich CO2 replacing it with O2
  • maintain stee [] gradient for rapid diffusion
• surfactants

  • inside of the alveoli are coated in a thin layer of water.
  • pulls of this waters surface tension and cohesive forces could cause the alveoli to collapse
  • surfactants are present which reduces these forces
• inspiration

  • breathe in, external intercoastal muscles contract to lift the ribs upwards and outwards
  • diaphragm contracts and moves down
  • vol increases, pressure decreases
  • air rushes into lungs
• expiration

  • breathe out, external intercoastal muscles relax
  • ribs move down and in
  • diaphragm relaxes and moves up
  • vol decreases and pressure increases
  • causes air to rush out
• forced expiration

  • internal intercoastal muscle contracts when forcing air out of lungs
• the airways

  • trachea, bronchi and bronchioles allow the passage of air into lungs
  • large enough to allow sufficient air to flow without obstruction
  • be supported to prevent collapse when air pressure is low during inspiration
  • be flexible in order to allow movement
• what are the airways lined by?

  • ciliated epithelium , contributes to keeping the lungs healthy
  • goblet cells - release mucus traps pathogen
• trachea and bronchioles

  • bronchioles are much narrower than the bronchi
  • walls are compromised of smooth muscles and elastic fibres
  • smooth muscles can contract constricting the airways to control the air flow
  • elastic fibres allow the tubes and alveoli to 'recoil' pushing the air out
  • small bronchioles end in clusters of alveoli
• how does a spirometer work

  1. person breathes in air through tube from a container of O2 that floats in a tank of water
  2. floating container rises and falls as the person breathes out and in respectively
  3. container is attached by an arm to a pen that also rises and falls as the person breathes
  4. since O2 is being used up at each breath, the vol in chamber slowly reduces and is shown on the trace produced
  5. the extent of this rise and fall reflects the vol of O2 taken out of or into lungs at each breath
• continued

  6. air passes through a chamber containing soda lime before it is passed back into the O2 container , removes CO2 other wise it would be rebreathed=person to faint
• what are some precautions that must be taken when using a spirometer

  1. subject should be healthy and be free from asthma
  2. fresh and functioning soda lime
  3. no air leaks in the apparatus, would give invalid result
  4. mouthpiece should be sterilised
  5. water chamber must not be overfilled
• tidal volume

  • volume moved in and out with each breath
• residual capacity/volume

  • volume of that always remains in the lungs after forced exhalation
• functioning residual capacity

  • total of residual capacity and expiratory reserve volume
• vital capacity

  • maximum volume of air that can be moved in 1 breath
• total lung volume

  • whole thing
• bony fish are very active and therefore require...., and what do they use to exchange gases with water

  • large amount of O2 for respiration
  • they use gills to exchange gases with water
• • bony fish have 5 pairs of gills that are covered by a bony plate called the operculum, each gill consists of 2 stacks of gill filament are folded into gill lamella which have a rich blood supply and a very large SA- gaseous exchange happens here
• what happens when the mouth is open

  • the buccal cavity lowers, which increases the volume but decreases the pressure
  • causes water to rush into the buccal cavity down the pressure gradient
  • operculum remains closed
• what happens after water has entered the mouth?

  • once buccal cavity is full of water the mouth opening closes, the floor of the buccal cavity rises
  • volume decreases and pressure increases
  • operculum opens
  • forcing the water through the gills
• examples of cartilaginous fish

  • such as sharks and rays, they do not have an operculum so they rely on constant movement to force water over the gills
  • shunt ventilation : they have to move
• counter current flow

  • in bony fish the blood and water flow in opposite direction , ensures a steep [] gradient of O2 and CO2 are maintained throughout the gills
• how does air enter an insect?

  • via a small opening in their exoskeleton called spiracles, run along side of the abdomen and thorax
  • spiracles can be opened or closed using rings of muscles called spcinters
• once air has entered through the spiracles what happens next

  • air then flows through tubes called trachea, which divide to form smaller tracheoles
  • the ends of tracheoles are filled with tracheal fluid
• between what and what does gas exchange in insects occur

  • between the trachea fluid and tracheoles
  • the fluid spreads and surrounds the respiring tissues supplying them with O2 and removing CO2
• ventilation in insects

  • air normally diffuses into the insect but if they are more active and have higher O2 demand for aerobic respiration and can increase air flow in the following ways
  • -- by having sections of the tracheal system with flexible walls that act as air sacs, these can be pumped by the contraction of small bands of muscles
  • -- mechanical pumping of the thorax using muscles or wing movement
  • -- opening and closing the spiracles can build up pressure differentials increasing the efficiency of ventilation