features of a specialised exchange surface Flashcards
what do large multicellular organisms have
evolved specialised systems for the exchange of the substances they need and the substances they need to remove
why is an increased surface area important for exchange surfaces
it provides the area needed for exchange. it overcomes the limitations of the SA:V ratio of larger organisms
how is an increased surface area achieved
by folding the walls and membranes for e.g. root hair cells in plants and villi in small intestine
greater surface area = …
… = higher diffusion rate
what is the root hairs at the tip of the root adaped for
increasing the surface area
- adapted for taking up water and mineral ions by having a large surface area to increase the rate of absorption
- contains lots of mitochondria which release energy from glucose during respiration in order to provide the energy needed for active transport
what does the rate of diffusion also depend on
the difference in the concentration gradient
what is a concentration gradient
difference in concentration of a substance between two areas
steeper gradient = …
…. = faster rate of diffusion
what happens if there is a higher concentration of molecules outside
there is a net rate of diffusion into the cell
if there is an equal concentration of particles inside and outside the cell what does this mean
there is a lower rate of diffusion
how do the thin layers make exchange of gases more efficient
there is a shorter diffusion distance
thicker membrane = …
…= greater diffusion distance
thinner membrane = …
…= shorter diffusion distance
give examples of where there are thin layers to minimise the diffusion pathway
the alveoli in lungs and villi of the small intestine
what must the barrier be
permeable to the substances being exchanged
describe the walls of the alveoli
the walls of the alveoli are one cell thick. the barrier between the blood and the air is just 0.3µm. they have a thin permeable barrier giving them a shorter diffusion distance
what does a good blood supply provide
ensures the substances are constnatly delivered to and removed from the exchange surface. this maintains a steep concentration gradient for diffusion
how does a good blood supply maintain the concentration gradient
they can bring fresh supplies of molecules to one side keeping the concentration high or remove molecules from the demand side to keep the concentration low
give examples of places with a good blood supply
alveoli of the lungs, fish gills, and villi of small intestine
good blood supply = …
…= steeper concentration gradient
steeper concentration gradient = …
… = faster diffusion rate
why is ventilation important
helps maintain concentration gradients making the process more efficient. for e.g the alveoli and gills of a fish where ventilation means a flow of water carrying dissolved gases.
how does ventilation maintain the concentration gradient
brings fresh supplies of molecules to one side (supply side). keeps the concentration high or may remove molecules from the demand side to keep the concentration low.
why is it important to maintain a steep concentration gradient
so diffusion occurs rapidly
where does ventilation occur in fish
gills
how does ventilation occur in fish gills
flowing water carries dissolved gases. water flows over the gills in a counter current direction
what does the countercurrent flow of blood and water in fish gills ensure
diffusion occurs along the length of the lamellae
what does countercurrent mean
the current/flow of water flows in the opposite direction
list the features of a specialised exchange surface
- increased surface area
- thin walls
- concentration gradient
- good blood supply
- ventilation
