6.1 -> 6.5 gas exchange

Question 1

diffusion formula

Answer 1

surface area x difference in concentration/ length of diffusion path

Question 2

5 features of specialised exchange surface

Answer 2

1. large SA:volume ratio
2. thin so diffusion distance is short(rapid)
3. selectively permeable
4. movement of environmental medium
5. transport system to ensure movement of internal medium to maintain conc gradient

Question 3

structure of insects

Answer 3

internal network of tubes- tracheae
- supported by strengthened rings to prevent them collapsing

tracheae divide into smaller dead-end tubes called tracheoles

tracheoles extend through entire body tissue

Question 4

How oxygen moves through tracheal system along diffusion gradient

Answer 4

cells respire, oxygen is used up and so the concentration towards end of tracheoles falls so diffusion gradient is created

causes oxygen to diffuse from atmosphere along trachea and tracheoles to cells

Question 5

How CO2 moves through tracheal system along diffusion gradient

Answer 5

co2 is produced by cells during respiration

creates diffusion gradient in opposite direction

causes co2 to diffused along tracheoles and trachea from cells to atmosphere

Question 6

how gases exchange in insects by mass transport

Answer 6

contraction of muscles can squeeze trachea, enabling mass movement of air in and out

Question 7

how gases exchange in insects by water in tracheoles

Answer 7

muscle cells around tracheoles respire to carry out anaerobic respiration, producing lactate

lactate is soluble and lowers water potential of muscle cells

water moves into cells from tracheoles by osmosis

water in the ends of tracheoles decreases in volume and so draws air further into them

final diffusion pathway is in gas not liquid so diffusion is more rapid

increases rate of air moving into tracheoles but leads to greater h20 evaporation

Question 8

spiracles

Answer 8

tiny pores on body surface gases enter and leave trachea in

opened and closed by valve

Question 9

limitations of tracheal system

Answer 9

the small length of diffusion pathway limits size that insects can attain

Question 10

structure of gills

Answer 10

• made up of gill filaments stacked up in a pile
• ## at right angles to the filaments are gill lamellae which increase SA of gills

Question 11

counter-current exchange

Answer 11

1. blood and water flow over gill lamellae in opposite directions so diffusion gradient is maintained along width of lamellae
2. blood that is already well loaded with o2 meets water which has maximum conc of o2. So diffusion of o2 from water to blood takes place.
3. blood with little o2 meets water that has most of o2 removed. so diffusion of o2 from water to blood takes place

Question 12

3 limiting water loss in insects

Answer 12

1. small SA: volume ratio to minimise area water is lost
2. rigid outer skeleton of chitin that is covered with waterproof cuticle
3. spiracles at openings of trachea that can be closed

Question 13

limiting water loss in plants

Answer 13

1. thick cuticle- waterproof
2. stomata in pits or grooves- traps still, moist air next to leaf and reduces wpt gradient
3. small sa:vol ratio
4. hairy leaves- traps still, moist air next to leaf surface which reduces wpt gradient between inside and outside of leaf
5. rolling up of leaves- protects stomata on lower epidermis, trapping still air within rolled leaf, air becomes saturated with water vapour so high wpt so there is no gradient between inside and outside