Gas exchange in single-celled organisms and insects

Question 1

Gas exchange in single-celled organisms

Answer 1

-Small. ∴ have a large SA to V ratio
-O is absorbed by diffusion across their body surface. CO2 diffuses out of body surface.

Question 2

Gas exchange in insects

Answer 2

-For gas exchange, insects have evolved an internal network of tubes
=Tracheae
-Supported by strengthened rings to prevent collapse.
-The tracheae are further divided into smaller dead end tubes
=Tracheoles
-The tracheols extend throughout the body tissues ses.
-∴ Oxygen is brought directly brought to the respiring tissues ∵ there is a short diffusion pathway.
-Gasses enter and exit through tiny pores= Spiracles.. They open and close by a valve.
-When opened water vapour can evaporate.

Question 3

Ways respiratory gases move in and out of the tracheal system.

Answer 3

+Along a diffusion gradient
-When O is used up, it lowers the concentration of it in tracheoles. ∴ O diffuse along the tracheae from the atmosphere to cells.
-When CO2 is produced within cells, it creates a high concentration of CO2 in cells. ∴ CO2 diffuses from the cells to the atmosphere.
-Exchange of gasses occur quickly in air than water.

+Mass transport
-The contraction of muscles in insects can squeeze the tracheae enabling mass movements of air in and out. ∴ it further speeds up exchange of gasses.

+The ends of the tracheoles are filled with water
-During high activity, cells carry out anaerobic respiration.
-This produces lactate which is soluble and lowers the water potential in muscles cells.
-∴ water moves from the tracheoles into cells through osmosis.
-∴ the water in the tracheoles reduce in volume and draws air further into them.
- This means that the final pathway is in a gas rather than a liquid. ∴ diffusion is more rapid.