E&T: Gas Exchange in Insects Flashcards
What two things do most gas exchange surfaces have in common?
- Large surface area
- Thin - often just one layer of epithelial cells - providing a short difusion pathway across surface.
How do single-celled organisms absorb and release gases?
Diffusion through their outer surface.
In single-celled organisms, why is there no need for a gas exchange system?
- Have a relatively large surface area, thin surface and short diffusion pathway.
- Means oxygen can take part in biochemical reactions as soon as it diffuses into the cell.
How do insects exchange gases?
Through an evolved internal network of tubes called tracheae.
What are the tracheae supported by?
Strengthened rings of cartilage.
What do the tracheae divide into in insects?
Tracheoles
Tracheae.
Microscopic air-filled pipes.
Tracheoles.
Smaller, dead end divisions of the tracheae.
What do tracheoles extend through?
All the body tissues of the insect.
Spiracles.
Pores on the surface of the insect.
Microscopic air-filled pipes.
Tracheae.
Smaller, dead end divisions of the tracheae.
Tracheoles.
Pores on the surface of the insect.
Spiracles.
How do respiratory gases move in and out of the tracheal system?
- Along a diffusion gradient.
- Mass transport.
- Osmosis.
Describe how respiratory gases move in and out of the tracheal system by moving along a diffusion gradient:
- Cells respire, oxygen is used up and the concentration gradient at the end of the tracheaeoles falls.
- Creates diffusion gradient.
- Gaseous oxygen diffuses from atmosphere along tracheae and tracheoles to cell.
- Carbon dioxide is produced during respiration.
- Creates diffusion gradient in other direction.
Describe how respiratory gases move in and out of the tracheal system by mass transport:
- Contraction of muscles in insects can squeeze the trachea, enabling mass movement or air in an out.
- Speeds up exchange of gases.
Describe how respiratory gases move in and out of the tracheal system by osmosis:
- Ends of tracheoles are filled with water.
- Major activity - muscle cells around tracheoles respire anaerobically.
- Produces lactate - insoluble and lowers water potential of muscles.
- Water moves into cells from tracheoles by osmosis.
- Water in ends of tracheoles decreases in volume and so more air is drawn in.
- So final diffusion pathway is in a gas, not a liquid and is more rapid.
What is an issue with respiratory gases being moved in and out of tracheoles via osmosis?
Leads to greater water evaporation/water loss.
How are spiracles opened and closed?
By a valve.
When the spiracles are open …
What does this mean?
… water can evaporate from the insect.
Means most of the time spiracles are shut to prevent water loss, and opened periodically for gas exchange.
What is a limitation of the tracheal system?
- Relies on diffusion - so diffusion pathway must be short.
- Limits the size insects can attain.
What system do fish use for gas exchange?
Counter-current system
Why do fish need adaptions to get enough air?
Lower concentration of oxygen in water than in air
Describe gas exchange in fish:
- Oxygenated water enters fish through mouth and passes through gills.
- Gill filaments are covered in lamellae.
- Blood flows through lamellae in one direction and water flows over in the opposite.
- Maintains concentration gradient between water and blood.
- Concentration of O2 always higher in water than in blood, so as much O2 diffuses into blood.
What is each gill made of?
Thin plates called gill filaments which give a big surface area.
What are gill filaments covered with?
How are these adapted?
Tiny structures called lamellae which increase SA even more.
These also have lots of blood capillaries and a thin surface layer of cells to speed up diffusion
Where do dicotyledonous plants exchange gases?
Why is fish gas exchange knwon as a counter current system?
How does this aid gas exchange?
Blood flows through lamellae in one direction and water flows over in the opposite direction.
Maintains large concentration gradient between water and blood.
Describe how stomata open
Become turgid and open
Describe how stomata close
Become flaccid and close
What also needs to be considered with gas exchange?
Water loss
How are insects adapted to control water loss?
- Close spiracles using muscles.
- Waterproof, waxy cuticle all over their body and tiny hairs around spiracles - reduce evaporation
How do plants reduce water loss?
- Stomata controlled by guard cells.
- Water enters guard cells - turgid - opens stomatal pore.
- If dehydrated, guard cells lose water - flaccid - closes stomatal pore.
Xerophytes
Plants specifically adapted for life in warm, dry or windy habitats where water loss is a problem.
Give examples of xerophyte adaptions:
- Stomata sunk in pits - traps moisture, reduces concentration gradient and thus diffusion.
- Hairs on epidermis - again traps moisture.
- Curled leaves with stomata inside - protects from wind which increases diffusion and evaporation.
- Reduced number of stomata - less water can leave
- Waxy, waterproof cuticles - reduce evaporation.
