Surface Area:Volume Ratio & Gas Exchange

Question 1

what is gas exchange like in single-celled organisms?

Answer 1

they rely on diffusion for the exchange of oxygen and carbon dioxide down their concentration gradient
large surface area:volume ratio

Question 2

why do large multicellular organisms need specialised exchange surfaces/transport systems?

Answer 2

they have a small surface:area ratio so they have to transport substances such as oxygen around the body

Question 3

what adaptations has the body made for more efficient gas exchange?
(6 points)

Answer 3

lots of alveoli - larger surface area:volume ratio
alveolar epithelium is 1 cell thick - short diffusion distance
alveolar walls are elastic - stretches during inspiration and recoils during expiration which maintains the concentration gradient
lots of capillaries - maintains a large concentration gradient
ventilation - maintains the concentration gradient by expiring carbon dioxide and inspiring oxygen
capillary endothelium is 1 cell thick - short diffusion distance

Question 4

what is gas exchange like in insects?

Answer 4

occurs via the tracheal system which can transport oxygen directly into respiring cells
ventilation creates a mass movement of air in and out of the tracheae from outside the insect via the spiracles

Question 5

what is gas exchange like in fish?

Answer 5

counter-current flow system - blood flows in one direction and water flows in the other direction maintaining the concentration gradient along the whole length of the lamellae

Question 6

what is gas exchange like in plants?

Answer 6

stomata on the lower epidermis of the leaves open and close allowing carbon dioxide to enter and oxygen to leave the plant

Question 7

what is gas exchange like in humans?

Answer 7

oxygen is inspired which diffuses into the blood from the alveoli and carbon dioxide diffuses into the alveoli from the capillaries to be expired

Question 8

how do insects limit water loss?
(3 points)

Answer 8

waterproof covering
small surface area:volume ratio
spiracles which open and close

Question 9

how have xerophytic plants adapted to hot, dry conditions?

Answer 9

reduced number of stomata
hairs to trap water
rolled leaves
spines instead of leaves
thick waxy cuticle - limit water loss