6 - Exchange

Question 1

features of specialised exchange surfaces

Answer 1

large SA:V ratio to increase rate
thin to decrease diffusion distance/path
selectively permeable to allow specific substance across
maintained concentration/diffusion gradient
effective transport system (to maintain conc. gradient)

Question 2

gas exchange in insects

Answer 2

need high SA:V to gain oxygen but don’t want to dehydrate from water loss
have exoskeleton with waterproof cuticle to reduce water loss
internal network of tracheae and tracheoles
gases enter and leave through spiracles

Question 3

gas exchange in fish

Answer 3

large volume of water must pass over gills to supply oxygen
large SA and lots of blood supply to give good diffusion surface
water flows opposite direction to blood flow - COUNTERCURRENT FLOW - maintains concentration gradient

Question 4

countercurrent flow

Answer 4

water flows opposite direction to blood flow

at each point water has a higher concentration of oxygen than in the blood

Question 5

stomata

Answer 5

minute pores on underside of leaves
surrounded by two guard cells which control opening and closing
control rate of gaseous exchange and prevent water loss

Question 6

water loss is reduced in plants by

Answer 6

a thick cuticle
rolling up of leaves
hairy leaves
stomata in pits/grooves
(all above trap still moist air, reduces the water potential gradient and reduce water loss)
reduced SA:V ratio

Question 7

goblet cells

Answer 7

cells in the trachea and bronchi which secrete mucus

ciliated epithelial cells beat and remove the mucus containing microbes

Question 8

alveoli

Answer 8

minute air sacs
one cell thick to give short diffusion path
have a high SA:V ration
good blood supply to maintain a concentration gradient

Question 9

mechanism of inhalation

Answer 9

external intercostal muscles contract
ribs pulled up and out
diaphragm contracts and flattens
volume of thorax increases and pressure decreases
air forced into lungs

Question 10

mechanism of exhalation

Answer 10

internal intercostal muscles contract
ribs pulled down and in
diaphragm relaxes
volume of thorax decreases and pressure decreases
air forced out of lungs