Gas Exchange Flashcards
Which major adaptations do most gas exchange surfaces have in common?
- large SA
- thin (often one layer of epithelial cells) to provide short diffusion pathway
Why do single celled organisms not need an exchange system?
Nevais Ethel have a large SA:V, a thin surface and short diffusion pathways (so oxygen can take part in biochemical reactions as soon as it diffuses into the cell).
Why do fish need special adaptations to get enough oxygen?
Because there’s a lower conc of oxygen in water than in air.
Insects have tracheae. What are these?
Internal air-filled network of tubes, supported by strengthened rings to prevent them from collapsing.
Insect’s tracheae further divide into…
Tracheoles.
What is the function of tracheoles in insects?
They extend throughout all boys tissues of the insect. In this way, the atmospheric air (with the oxygen it contains) is brought directly to the respiring tissues because there’s a short diffusion pathway from tracheole to any body cell.
What are the three ways in which respiratory gases move in and out of tracheae system?
- ALONG DIFFUSION GRADIENT: when cells are respiring, oxygen is used up and so its conc towards the ends of tracheoles falls. This creates diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along trachea, tracheoles into cells.
- MASS TRANSPORT: the contraction of muscles can squeeze the tracheae enabling mass movements of air in and out.
- ENDS OF TRACHEOLES FILLED WITH WATER: during major activity, muscle cells around tracheoles respire and carry out some anaerobic respiration. This produces lactate, which is soluble and so lowers the WP of muscle cells.
Water therefore moves into tracheoles by osmosis, so the water in ends of tracheoles decreases in volume so mor air is drawn into them.
Insects have spiracles. What are they?
These are pores on the body surface. They’re opened / closed by a valve. Insects use rhythmic abdominal movements to move air in and out of spiracles.
When spiracles are open, water vapour can evaporate from the insect. But most of the time they’re closed to prevent this water loss.
Gills of fish are found behind the head. What are they made up of and why?
Gill filaments - these are thin plants which give a large SA for exchange of gases. They’re stacked at right angles to gill lamellae, which increase SA even more.
Outline how the countercurrent system works in fish.
- Water containing O2 enters the mouth, and is forced over the gills (gill filaments and gill lamallae).
- Blood flows through the lamallae in one direction, and water flows in the opposite direction. This maintains large conc gradient between water and blood.
- The conc of oxygen in water is always higher than that in blood, so as much oxygen diffuses into blood as possible.
What would happen in fish if there was no counter current system, and blood and water flowed in the same direction?
The diffusion gradient would only be maintained across part of the length of lamallae, so only 50% (rather than 80%) of available oxygen would be absorbed by the blood.
Most gaseous exchange occurs in leaves of plants. Outline how they’re adapted for rapid diffusion.
- large SA of mesophyll cells.
- many stomata (pores), so no cell is far from a stomp and therefore diffusion pathway is short.
- numerous interconnecting air spaces that occur throughout the mesophyll cells so that air can readily come into contact with mesophyll cells.
What are stomata?
Minute pores found (usually) on underside of leaves
Outline the structure of stomata.
Each stoma is surrounded by a pair of guard cells, which control the opening and closing of stomata - therefore controlling rate of gaseous exchange.
What happens when guard calls are wet?
They become turgid, which opens the stomata pore.
