2. Gas Exchange

Question 1

gas exchange surfaces adaptations (to increase rate of diffusion/ maintain steep conc gradient)

Answer 1

large surface area

thin - short diffusion pathway

Question 2

how do single celled organism exchange gas

Answer 2

absorb and release gas by diffusion through their outer surface
large surface area a thin surface/short diffusion pathway. (no need for gas exchange system)

Question 3

fish counter current system

Answer 3

1. blood flows through lamellae in one direction
2. water flows in opposite direction
3. maintains large concentration gradient between water and blood
4. concentration of oxygen in water always higher than in blood = as much O2 diffuses as possible

Question 4

fish

gills are made of `

Answer 4

1. thin plates called gill filaments
   give big surface area
2. filaments covered in tiny structure called lamellae - SA increased
3. lamellae have lots of blood capillaries and thin surface layer of cells

Question 5

gas exchange in insects

Answer 5

1. air moves into trachea through pores on surface (spiracles)
2. O2 travels down conc gradient towards cells
3. trachea branch off into tracheoles which have thin permeable walls and go to individual cells
4. CO2 from cells moves down conc gradient towards spiracles and released
5. use abdominal movements to move air in and out of spiracles

Question 6

interesting fact about insect gas exchange

Answer 6

direct to cells

circulatory system doesn’t transport O2

Question 7

Gas exchange in plants

Answer 7

1. need CO2 for photosynthesis which produces O2 as waste
   need O2 for repiration which produces CO2 as waste
2. main gas exchange surface is surface of mesophyll cells (large surface area)
3. gases move in and out through pores in epidermis called stomata
4. stomata open to allow gas exchange. close to prevent loss of water
5. guard cells control opening and closing of stomata

Question 8

how insects control water loss

Answer 8

close spiricales using muscles
waxy waterproof cuticle
tiny hairs around spiricals = reduced evaporation

Question 9

how plants control water loss

Answer 9

1. stomata kept open during day = gas exchange
   water enters guard cell -> turgid -> stomata open
2. plants dehydrated -> guard cells loose water and flaccid -> pore closes

Question 10

e.g xerophyte adaptations
(warm dry windy habitat, water loss a problem)
5 points

Answer 10

1. stomata sunk pits = traps moist air reducing conc gradient between leaf and air. less evaporation
2. layer of hair on epidermis- trap moist air around stomata
3. curled leaves with stomata inside - protects from wind (wind increases rate of diffusion and evaporation)
4. reduced number of stomata (fewer places for water to escape
5. waxy, waterproof cuticles- reduces evaporation