3.1.1g Gas Exchange in Insects Flashcards
Why do insects need an effective gaseous exchange system
Many insects are very active during parts of their life cycles. They are mainly land-dwelling animals with relatively high oxygen requirements.
What is the issue with insects and gas exchange
- They have a tough exoskeleton through which little or no gaseous exchange can take place
- They do not usually have blood pigments that can carry oxygen
They need a diff way of exchanging gases
The gaseous exchange system of insects has evolved to…
…deliver the oxygen directly to the cells and to remove the CO2 in the same way
What are spiracles
Along the thorax and abdomen of most insects are small openings known as spiracles. Air enters and leaves through the spiracles, but water is also lost
What do mammals and insects need to ensure their exchange system does
Just like mammals, insects need to maximise the efficiency of gaseous exchange, but minimise the loss of water
What are sphincters
The spiracles can be opened and closes by sphincters. The spiracle sphincters are kept closed as much as possible to minimise water loss
When are the spiracles in insects usually closed
When an insect is inactive and oxygen demands are very low, the spiracles will all be closed most of the time
When are the spiracles in insects usually opened
When the oxygen demand is raised or the CO2 levels build up, more of the spiracles open
What are the tracheae (plural for trachea)
- Leading away from the spiracles are the tracheae.
- These are the largest tubes of the insect respiratory system, up to 1mm in diameter, & they carry air into the body.
- They run both into & along the body of the insect. The tubes are lined by spirals of chitin (which keep them open if they are bent or pressed)
What is significant about the tracheae being lined with chitin
Chitin is the material that makes up the cuticle. It is relatively impermeable to gases & so little gaseous exchange takes place in the trachea
What are the tracheoles
- The tracheae branch to form narrower tubes until they divide into the tracheoles - minute tubes of diameter 0.6-0.8pm.
- Each tracheole is a single, greatly elongated cell w NO chitin lining so they are freely permeable to gases
- Bc of their very small size they spread throughout the tissues of the insect, running between individual cells. This is where most of the gaseous exchange takes place between the air & the respiring cells
By what process does air reach all tissue in insects
Air moves along the tracheae and tracheoles by diffusion alone, reaching all the tissues
Features of tracheoles that make them effective exchange surfaces
- The vast no. of tiny tracheoles give a very large SA for gaseous exchange.
- Moist walls of the tracheoles causes oxygen to dissolve into the walls and diffuse into the surrounding cells
- Towards the end of tracheoles, there is tracheal fluid, which limits the penetration of air for diffusion
What happens when oxygen demands build up in insects
When oxygen demands build up - when the insect is flying for eg, a lactic acid build up in the tissues results in water moving out of the tracheoles by osmosis. This exposes more SA for gaseous exchange
How is all the oxygen needed by the cells of an insect supplied to them
all the oxygen needed by the cells of an insect is supplied to them by the tracheal system
What controls the extent of gas exchange in most insects
The extent of gas exchange in most insects is controlled by the opening and closing of the spiracles
Alternative methods of increasing the level of gaseous exchange INTRODUCTION
Some insects (eg, larger beetles, locusts, grasshoppers, bees, wasps, flies) have very high energy demands. To supply the extra oxygen they ned, these insects have alternative methods of increasing levels of gaseous exchange
Alternative methods of increasing the level of gaseous exchange: Mechanical ventilation of the tracheal system
Air is actively pumped into the system by muscular pumping movements of the thorax & abdomen. These movements change the volume of the body & this changes the pressure in the tracheae & tracheoles. Air is drawn into the tracheae & tracheoles, or forced out, as the pressure changes
Alternative methods of increasing the level of gaseous exchange: Collapsible enlarged tracheae or air sacs
Collapsible enlarged tracheae or air sacs, whcih act as air reservoirs - these are used to increase the amount of air moved through the gas exchange system. They are usually inflated & deflated by the ventilating movements of the thorax & abdomen
Exam Q: Outline structures of the insect gaseous exchange system (6)
SPIRACLES:
- open & close by sphincters, to allow gas in and out
- pores on the tough exoskeleton (impermeable) to allow gas exchange
TRACHEAE:
- leads away from the spiracles into the body cavity
- lined with chitin, creating rigid structure, preventing collapse
TRACHEOLES:
- many branches - increased SA
- highly permeable
- tracheal fluid
How do insects use the Tracheae to exchange gases (steps)
- Insects have microscopic air-filled pipes called tracheae which they use for gas exchange
- Air moves into the tracheae through pores on the insects surface called spiracles
- Oxygen travels down the concentration gradient towards the cells. CO2 from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere
- The tracheae branch off into smaller tracheoles which have thin, permeable walls & go to individual cells. They also contain tracheal fluid, which oxygen dissolves in
- The oxygen then diffuses from this fluid into body cells. CO2 diffuses in the opposite direction
- Insects use rhythmic abdominal movements to change the volume of their bodies & move air in & out of the spiracles. When larger insects are flying, they use their wing movements to pump their thoraxes too
