3a (exchange/transport) Flashcards
do bigger or smaller animals have a larger surface area to volume ratio?
smaller organisms
what is fick’s law?
rate of diffusion = (surface area x conc diff) / thickness of membrane
how do you work out surface area to volume ratio?
surface area/volume
how do single celled organisms exchange substances? is this fast or slow?
diffusion directly into or out of cell across the cell surface membrane
fast rate due to short diffusion pathway
dont have gas exchange system
why is diffusion across the outer membrane in multicellular organisms too slow? how is this combated?
some cells are deep in the body so big distance to the outside environment
larger animals have smaller sa:v and its hard to exchange enough substances to supply a large volume animal across a small outer surface
so, instead of just diffusion, multicellular organisms have exchange organs and mass transport systems
what is a mass transport system? what is this in animals and plants
a efficient system to carry substances to and from cells
mammals- circulatory system
plants- xylem and phloem
factors affecting heat exchange
body size- rate of heat loss depends on sa:vol (larger sa;vol means heat lost more easily so smaller organisms need faster metabolic rate to generate enough heat to stay warm.)
body shape- compact shape means small sa:vol so minimised heat loss from surface. vice versa. if animal is compact or nor depends on temperature of its environ (eg arctic fox has smaller sa:vol than african bat-eared fox)
behavioural and physiological adaptations to aid exchange
animals w high sa:v lose more water so some small desert animals have kidney structure adaptations - produce less urine
to support high metabolic rates, small animals in cold places eat high energy food
some smaller mammals have thick layer of fur/ hibernate in cold
larger organisms in hot places have larger ears to increase sa to lose more heat/ spend lots of time in water
3 major adaptations of gas exchange surfaces
large surface area
thin walls- short diffusion pathway
also maintain conc grad
gas exchange in fish
counter current flow
1. water enters mouth and out gills
2. blood flows through lamellae one way and water the other- maintains large conc gradient between water and blood (always higher conc of oxygen in water so as much amount of oxygen diffuses into blood as possible
what is the structure of gills?
made of lots of thin plates called gill filaments which provide large sa
gill filaments covered in lamellae which increase sa more
lamellae have lots of blood capillaries and thin surface layer of cells to increase diffusion rate
pictures on page 60 of revision guide
check book
gas exchange in insects
microscopic air filled pipes called tracheae (supported by strengthened rings) which are used for gas exchange
air moves into them through spiracles (pores on surface)
oxygen travels down conc gradient to cells
trachea branch into tracheoles which have thin permeable walls and go to individual cells- oxygen diffuses directly into respiring cells
co2 moves down conc gradient to spiracles to be released into atmosphere
rhythmic abdominal movements to move air in and out spiracles
fluid at end of tracheoles drawn into anaerobically respiring muscles (low water pot as has lactic acid) so vol of tracheoles increase so pressure decrease so air is drawn further into tracheoles
why are insects small?
rely mostly on diffusion to exchange gases so need small pathway so size of growth is limited
gas exchange in plants
main exchange surface is the surface of mesophyll cells- large sa
air spaces- gases come into contact often with mesophyll cells- conc grad
mesophyll cells are inside leaf, gases move in and out of leaf through stomata in epidermis short diffusion pathway
stomata opened and closed by guard cells to get balance between loss of water and exchange of gases
structure of leaf
waxy cuticle
upper epidermis
palisade mesophyll
spongy mesophyll and xylem and phloem
lower epidermis with stomata and guard cells
waxy cuticle
