Gaseous Exchange in Insects & Fish Flashcards
Why is gaseous exchange difficult for insects?
They have a tough exoskeleton through which very little to no gas exchange can take place.
They also do not usually have haemoglobin which carries oxygen.
What are spiracles?
Small openings along the insect’s thorax and abdomen through which air enters and leaves. Some water is also lost.
How are spiracles controlled?
They are opened and closed by sphincters - kept closed as much as possible to limit water loss.
They open more when Oxygen demand is raised or when Carbon Dioxide builds up.
What are the tracheae?
The largest tubes of the insect’s respiratory system (up to 1mm in diameter) which carry air into the body. They run both into and along the body of the insect.
How are the tracheae supported?
They are lined by spirals of chitin which keep the tracheae open - chitin is relatively impermeable to gases meaning little gaseous exchange takes place in the tracheae.
What do the tracheae divide into?
The tracheae branch into narrower tubes until they divide into tracheoles.
Tracheoles are single, greatly elongated cells with a diameter of 0.6 - 0.8 micrometers.
How are the tracheoles adapted for gaseous exchange?
- They have no chitin lining which makes them freely permeable to gases.
- The vast number of tracheoles provides a large surface area.
- Their small size allows them to spread throughout insect tissue, between cells.
What is tracheal fluid and why is it withdrawn?
Tracheal fluid is found towards the end of the tracheoles. They limit the penetration of air for diffusion and are therefore withdrawn during anaerobic respiration to allow a larger surface area for exchange.
How is SA in the tracheoles increased during high oxygen demand?
A lactic acid build up in the tracheoles during anaerobic respiration, resulting in tracheal fluid moving out by osmosis, exposing more area for gaseous exchange.
How else do insects increase their gaseous exchange?
- Mechanical Ventilation
- Collapsible enlarged tracheae / air sacs
How was mechanical ventilation work?
Air is actively pumped into the system by the muscular pumping of the thorax and abdomen.
As a result of this, the volume and pressure changes inside the body, and air rushes in or is forced out.
How do collapsible enlarged tracheae / air sacs work?
They act as air reservoirs and are used to increase the amount of air being moved. They are usually inflated / deflated by the movements of the thorax and abdomen.
What are the main parts of the fish involved in water flow?
- mouth
- buccal cavity (inside of the mouth)
- gills
- opercular cavity (space behind gills)
- operculum (opening)
How does “inhalation” work in bony fish?
- The opercular cavity expands and the mouth opens. The operculum is closed and the floor of the buccal cavity is lowered.
- The volume of the buccal cavity increases.
- The pressure in the opercular cavity decreases below the pressure in the surrounding water.
- Water flows into the buccal cavity.
How does “exhalation” work in bony fish?
- The opercular cavity decreases in size and the mouth closes. The operculum is opened and the floor of the buccal cavity rises.
- The volume of the buccal cavity decreases.
- The pressure in the opercular cavity increases above the pressure in the surrounding water.
- Water is forced over the gills and out of the operculum.
