6.2 Gas exchange in single-celled organisms and insects Flashcards
How does gas exchange occur in single celled organism
Single-celled organism are small and therefore have a large surface area to volume ratio. Oxygen is absorbed by diffusion across their body surface, which is covered only by a cell-surface membrane
What have insects evolved mechanisms to conserved water caused
A conflict with conserving water
What system do insects have for gas exchange
An internal netwrok of tubes called traceae
Describe the overall structure of the tracheal system
There is an internal network of tubes called tracheae. These are supported by strengthened rings to prevent collpase. The tracheae divide into smaller dead end tubes called tracheoles.
What are the three ways respiratory gases move in and out of the tracheal system
- Along a diffusion gradient
- Mass transport
- The ends of the tracheoles are filled with water
How do respiratory gases move in and out of the tracheal system via a diffusion gradient
When cells are respiring, oxygen is used up and so its concentration towards the ends of tracheoles falls.
This creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the tracheae and tracheoles to the cells
How do respiratory gases move in and out of the tracheal system via mass transport
The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out. This further speeds up the exchange of respiratory gases
How do the water filled ends of tracheoles assist in the movement of respiratory gases in the tracheal system
During periods of major activity, the muscle cells around the tracheoles respire and carry out some anaerobic respiration. This produces lactate, which is soluble and lowers the water potential of the muscle cells. Water therefore moves into the cells by osmosis
The water in the tracheole ends decreases and in doing so draws in air. This means the final diffusion pathway is in a gas rather than a liquid, and therefore diffusion is more rapid.
How do gases enter and leave tracheae
Through tiny pores called spiracles
What are the limitations of the tracheal system
It relies on diffusion to exchange gases, and for diffusion to be effective the diffusion pathway must be short, therefore this limits the size insects can achieve.
