Exchange between organisms and their environment

Question 1

what are the features of a specialised exchange surface

Answer 1

• Large SA to vol ratio
• Short diffusion pathway (thin)
• Selectively permeable
• Movement of environmental medium
• Concentration gradient

Question 2

How does gas exchange occur in single celled organisms

Answer 2

because single celled organisms only have a cell surface membrane and no cell wall they can…

• oxygen is absorbed by diffusion across their body surface
• Carbon dioxide diffuses out across their body surface

Question 3

How does gas exchange occur in insects

Question 4

How are insects adapted for gas exchange

Answer 4

Insects have developed an internal network of tubes called trachea for respiratory gas exchange, the gases move in and out of the tracheal system in 3 ways..

• Along a diffusion gradient, respiring cells are extremely close to the ends of tracheoles therefor concentration near the ends is low and so oxygen diffuses along a concentration gradient from the air into the tracheoles, this occurs similarly with CO2 but in the opposite direction
• Mass transport, contraction of muscles squeezes trachea enabling mass movement of air
• Tracheole ends filled with water, Anaerobic respiration produces lactate which causes diffusion to occur in a liquid not gas and therefor increases the rate of diffusion