Gas Exchange Systems

Question 1

How do single-celled organisms exchange gas?

Answer 1

They have a large SA:V ratio.

Oxygen = accessed by diffusion from short diffusion pathway from cell to surface.

Question 2

Why can’t insects exchange gases by diffusion?

Answer 2

Increase in surface area conflicts with conserving water as water evaporates from it.

Question 3

What are the tracheae in insects?

Answer 3

Network of tubes supported by rings so that they don’t collapse.

Question 4

Explain how gas is exchanged in insects.

Answer 4

Have a network of tubes called tracheae - they split up into smaller dead-end tubes called tracheoles which extend over all tissues of insect.
Oxygen from atmospheric air = transported to repairing cells from short diffusion path from trachioles to body cells.
Starts at spiracles on body surface. Air in insects has much lower oxygen conc. than atmospheric air, so air transports into insects from atmospher to balance conc.

Question 5

What is the problem with the spiracles.

Answer 5

When open - water evaporates from insect.

Most of the time they are closed by guard cells to reduce water loss.

Question 6

What are the three ways in which gases go in/out of the tracheal system?

Answer 6

1. Along diffusion gradient.
2. Mass transport.
3. End of trachioles filled with water.

Question 7

How do gases go in/out of the tracheal system by a diffusion gradient?

Answer 7

Respiring cells use oxygen .: creates conc. gradient from atmospheric air to respiring cells. Respiring cells produce CO2 as well, .: creates conc. gradient in opposite direction. Diffusion in air = much quicker than in water so .: gas exchange is quick.

Question 8

How do gases go in/out of tracheal system by mass transport?

Answer 8

Contraction of muscles in insects can squeeze trachea = mass movements in/out so speed up exchange in respiratory gases further.

Question 9

How do gases go in/out of tracheal system due to the fact that the end of the trachioles are filled with water?

Answer 9

Muscle cells respire - produces lactate around tracheoles - lowers water potential. .: water moves in by osmosis - decreases volume of travelled so draws gas further into the tracheoles.
Last phase = diffusion pathway = in gas not liquid and diffusion is more rapid however means more evaporation.

Question 10

What are the limitations of gas exchange in insects?

Answer 10

1. Relies mostly on diffusion to exchange gases between environment + cells.
2. For diffusion to be effective - diffusion pathway = short - why insects have to be small.
3. .: Length of diffusion pathway limits size insects can attain.