6.2 Gas exchange in insects and single celled organisms Flashcards
How can gas exchange occur in single cell organisms
They are very small so have a large surface area to volume ratio
This means oxygen is absorbed by diffusion across their body surface which is covered by a cell membrane
Carbon dioxide released from respiration can also diffuse out across their body surface
Why do insects need to have the right balance of surface area to volume ratio
Insects need to be able to preserve water as well as doing gas exchange.
A large surface area means more water will evaporate from it
What are tracheae found in insects
What smaller thing do these divide into
An internal network of tubes
These tubes can divide into tracheoles that have dead ends
What helps support tracheae to stop them collapsing
There are strengthened rings of chitin around them
Where do the tracheoles extend to in insects and why is this good for gas exchange
The tracheoles can extend throughout all the body tissues of the insect
In this way, the atmospheric air containing oxygen is brought directly to respiring tissues
Adaptations of trachea in insects for good gas exchange
. Thin walls of tracheoles for short diffusion distance to cells
. Large numbers of tracheoles which are highly branched for large surface area
. Fluid in the ends of tracheoles that move into cells during exercise so oxygen can diffuse down them quicker as there is a larger surface area.
. Abdominal stomach muscles can contract and relax to push air down the tracheoles
Why is it easy for oxygen to diffuse from tracheoles to the cells
There is a short diffusion pathway
How can respiratory gases move in and out of the tracheal system
Along a diffusion gradient?
When cells respire they use up oxygen so its concentration towards the end of the tubes is low
This creates a diffusion gradient that causes the gaseous oxygen to diffuse from atmosphere along the tracheae and tracheoles to the cells.
It also works with carbon dioxide produced by cells as it causes the CO2 to diffuse from the cells through the tracheoles and tracheae to the atmosphere.
How do respiratory gases move in and out of the tracheal system by
Mass transport
The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out
As insects inhale, abdominal muscles relax so pressure decreases so gas moves in through the spiracles
As insects exhale, the abdominal muscles contract which increases the pressure in them so gases move out through spiracles
How do respiratory gases move in and out of the tracheal system by
Water filling tracheoles
The ends of tracheoles are filled with water, and during periods of major activity, muscle cells around tracheoles respire by some anaerobic respiration.
The product of this is lactate, which is soluble and so lowers the water potential of muscle cells
Water therefore moves into the cells from the tracheoles by osmosis, so there is less water in the tracheoles which draws more air into them
As a result the final diffusion pathway is in a gas rather than a liquid phase so therefore diffusion is more rapid
This increases rate of air moving into the tracheoles but leads to greater water evaporation
What are spiracles
Tiny pores on the body surface that let gases enter and leave the trachea.
These spiracles can be opened and closed by a valve
Why do insects keep their spiracles closed most of the time
When the valves are opening the spiracles, water vapour can evaporate from the insect
So the valves are kept shut to reduce this water loss, however they have to periodically open them for gas exchange.
Limitations of the tracheal system for gas exchange
Why is it good that insects are small
. It relies mostly on diffusion to exchange gases between the environment and cells
. For diffusion to be effective, the pathway must be short which is why insects are small
As a result, this diffusion pathway limits the size that insects can attain
What is the exoskeleton of insects made of
hard fibrous protein called chitin for protection
And a lipid layer for preventing water loss
