3.3.2 Gas exchange Flashcards
Why do fish need gills as a specialised internal gas exchange surface?
- Gas tight outer covering
- Small surface area to volume ratio
Explain the counter current gas exchange mechanism in fish
- Water and blood flow in opposite directions
- So water with a higher oxygen concentration meets blood with a lower oxygen concentration
- This maintains a constant favourable concentration and diffusion gradient
- Across the entire length of the gill filament
- And equilibrium is never reached so there is a constant diffusion of oxygen
- more oxygen diffuses into blood
Describe how an insect is able to obtain oxygen and limit water loss?
- Body covered with waterproof waxy layer/cuticle
- So insects have spiracles which are able to close
- Air enters through open spiracles
- Down diffusion gradient
- Into trachea
- Tracheae associated with all cells
- Oxygen diffuses into cells
- Ventilation replacing air in tracheae
Why is there a conflict in insects between the need to reduce water loss and to exchange gas?
- Waterproof coverings - cover whole body surface and prevent water being lost through skin (or insect exoskeleton)
- A smaller surface area to volume ratio (for insect) - less area to lose water from
Describe 2 ways respiratory gases move in and out of an insect’s tracheal system?
- Diffusion down concentration gradient - oxygen used during respiration and carbon dioxide produced during respiration
- Mechanical ventilation (abdominal pumping) - muscle movement causes mass air movements in and out of tracheae
What are the limits of the tracheal system?
Limits size of an insect because it relies on diffusion for exchange and diffusion needs a short diffusion pathway
Why is diffusion exchange only possible in very small organisms? (2)
- Large surface area to volume ratio
- All parts of cell only a small distance from the exchange surface (short diffusion pathway)
How do insects respire when spiracles are closed and all oxygen has been used up?
Anaerobic respiration
What is tidal volume?
Volume of air normally taken in at each breath when the body is at rest
What is the ventilation rate?
Number of breaths taken in one minute
What is the equation for pulmonary ventilation rate?
Pulmonary ventilation rate (dm^3 min^-1) = tidal volume (dm^3) X ventilation rate (min^-1)
Describe features of alveoli (and capillaries) that make them an efficient gas exchange surface
- Large surface area of alveoli and pulmonary capillaries
- short diffusion pathway
- thin walls of alveoli
- thin walls of capillaries
- Red blood cells are flattened against capillary walls
- more time for diffusion:
- red blood cells slow while passing through pulmonary capillaries
- steep concentration gradient of gases to be exchanged
- breathing constantly ventilates lungs
- blood circulates through capillaries around alveoli
How are alveoli able to stretch and recoil?
Contain elastic tissue (elastin)
Explain how cells lining the trachea and bronchus protect the alveoli from damage
- goblet cells produce mucus that traps particles of dirt and bacteria in the breathed air
- the cilia on the epithelial cells ‘waft’ the debris up the trachea and down the oesophagus into the stomach, away from the alveoli
- The dirt/bacteria cause damage/infection in alveoli
Why is the volume of oxygen that has to be absorbed so large in humans?
Humans are large organisms with a large volume of cells so they have a high metabolic and respiratory rate because they maintain a high body temperature
