3. Gas Exchange Flashcards
What happens to the s.a. and volume when the length of sides of a cuboidal cell increases?
- s.a. + vol ↑ exponentially
- vol ↑ at a ↑ rate than s.a.
- s.a. : vol ↓ exponentially
Calculate s.a. for spheres
4πr²
Calculate volume of sphere
4/3πr³
Environment around the cells of multicellular organisms
Tissue fluid.
What causes spiracles in an insect to open during movement?
↑ level of CO2
Suggest an advantage of spiracle movements to a terrestrial insect.
- helps conserve water
- ∵ spiracles x open continuously
- ∴ water x diffuse out continuously
State similarities between gas exchange in a plant leaf and in a terrestrial insect.
- diffusion in gas phase
- diffuse air thru pores in outer covering (opening & closing √ controlled)
- all living cells close to external air
- prevent water loss
State differences between gas exchange in a plant leaf and a terrestrial insect.
Insects:
1. create mass air flow vs X
2. ↓ sa : vol than plants
3. X interchange gases between resp & phots vs √
State one modification to reduce water loss that is shared by plants and insects.
- cuticle- waterproof
- ability to close openings of gas exchange system
Explain two reasons why plants growing on sand dunes need to have xerophytic features even though there is plentiful rainfall.
- rain rapidly drains out of reach of roots
- sand dunes- in windy situations- ↓ Ψ - ↑ Ψ gradient- ↑ water loss
Water flow over fish gills is one-way, whereas the flow of air in and out of the lungs is two-way.
Suggest why one-way flow is an advantage to fish.
- ↓ energy required
- ∵ flow x reversed (water is dense & diff. to move)
Explain 3 features of leaves of xerophytes to increase the uptake of water.
- deep extensive root system
– maximises water uptake (esp. during dry periods) - accumulation of solutes in the roots
– ↓ Ψ in root hair cell
– ↑ Ψ gradient from soil to root cells - some shallow roots
– absorb dew condensed on soil at night
+ immediately after rain
Features of specialised exchange surfaces
- ↑ s.a.
– ↑ rate of exchange - v. thin
– ↓ diffusion distance–>↑ rate of diffusion - selectively permeable
– √ selected materials to cross - movement of environmental medium
– maintains conc. gradient - transport system
– movement of internal medium (eg. blood) –> maintains diffusion gradient
Features of a single-celled organism
- ↓ diffusion pathway
– gases only have to pass plasma mem
–> ↓ distance to middle of cell - ↑ s.a. : vol
– vol small enough for s.a. to supply sufficient exchange of substances (eg. ants vs humans) - ↑ conc. gradient
– O2 continually used + CO2 produced in resp.
–> conc. gradient for each
Why do fish need exchange surfaces for gas exchange?
- water has ↓ dissolved O2 conc (1%)
- ↑ water needs to pass over fills–> enough O2
