gas exchange in fish (and insects)

Question 1

explain how body surface of a single-celled organism is adapted for gas exchange.

Answer 1

thin/flat shaped and large surface area to volume ratio so theres a short diffusion distance.

Question 2

describe tracheal system of an insect.

Answer 2

spiracles - pores on surface that can open/close for diffusion.
trachea - large tubes full of air that allow diffusion.
tracheoles - smaller branches from trachea, permeable to allow gas exchange.

Question 3

explain how an insects tracheal system is adapted for gas exchange.

Answer 3

• tracheoles have thin walls so short diffusion distance to cells.
• rhythmic abdominal movement which maintain concentration gradient for diffusion.
• high numbers of highly branched tracheoles so short diffusion distance as larger surface area.

Question 4

explain structural and functional aspects in insects that allow efficient gas exchange while limiting water loss.

Answer 4

• thick waxy cuticle so increases diffusion distance so less water loss.
• spiracles can open to allow gas exchange and close to reduce water loss.
• hairs around spiracles trap moist air, reducing WP gradient so less water loss.

Question 5

explain how gills of fish are adapted for gas exchange.

Answer 5

gills made of many filaments covered with lamellae - increases surface area for diffusion.
thin lamellae - short diffusion distance.
lamellae have large number of capillaries - maintains concentration gradient.

Question 6

describe the counter-current flow.

Answer 6

• blood and water flow in opposite directions.
• so oxygen concentration is always higher in water than blood.
• so maintains a concentration gradient of o2 for diffusion along whole length of gill.