Gas Exchange - Plants and Animals

Question 1

Gas Exchange surfaces

Answer 1

have large surface area
thin = short diffusion pathway
constant steep concentration gradient

Question 2

Single-cell organisms

Answer 2

absorb and release gases by diffusion through their outer surface
have relatively large SA:V ratio, thin surface & short diffusion pathway
=>O2 takes part in biochemical reactions as soon as it diffuses into cell
NO NEED FOR GAS EXCHANGE SYSTEM

Question 3

Fish

Answer 3

Counter Current system
water enters mouth=>exits through gills
every gill has many gill filaments = big SA
every gill filament has many lamellae = bigger SA
lamellae have many blood capillaries and thin surface = faster diffusion

Question 4

Counter current

Answer 4

Blood flows in lamellae in opposite direction to water flowing over lamellae
maintains steep conc grad
O2 conc is always higher in water than blood => maximum O2 levels diffuse from water to blood

Question 5

Insects

Answer 5

tracheae = air filed pipes
air moves into tracheae via pores on surface = spiracles
tracheae => tracheoles
tracheoles have thin permeable walls and go to individual cells
O2 travels down conc grad towards cells and diffuses directly into respiring cells
CO2 from cells moves down conc grad towards spiracles to be released
Use rhythmic abdominal movements to move air in/out of spiracles

Question 6

Plants

Answer 6

Dicotyledonous plants use Mesophyll Cells
main gas exchange surface is mesophyll cells surface in leaf = Large SA
gases move in and out of leaf through pores in epidermis = STOMATA
guard cells control opening and closing of stomata (regulates water loss)

Question 7

Controlling water loss - insects

Answer 7

insects:
close spiracles
waterproof waxy cuticle REDUCE EVAPORATION
tiny hairs around spiracles

Question 8

controlling water loss - plants

Answer 8

stomata usually open during the day = allows gas exchange
water enters guard cells = turgid = OPEN pore
dehydration = guard cells lose water = flaccid = CLOSE pore

Question 9

Xerophytic adaptations

Answer 9

sunken stomata = traps moist air = reduces water conc grad between leaf and air = lower diffusion rate out of leaf
hairs on epidermis = traps moist air around stomata
curled leaves w/ stomata inside = protects them from wind
reduced no. stomata = fewer water escapes
waxy waterproof cuticles on leaves and stems = reduces evaporation