6.1 Exchange between organisms and their environment Flashcards
What are exchange surfaces
The places on an organism adapted to exchange substances with the environment eg oxygen and CO2
It always involves passing a plasma membrane
What is tissue fluid and what do they do
The environment around around the cells of multicellular organisms
Most cells are too far from exchange surfaces for diffusion to supply their tissue fluid with substances.
Therefore, once absorbed into blood, the materials are rapidly distributed to the tissue fluid and the waste products return to exchange surface for removal
This involves a mass transport system which can maintain the concentration gradient to bring materials to and from cell membranes
What adaptation do organisms that have a high metabolic rate have
They exchange more materials so require a larger surface area to volume ratio
What materials/substances are interchanged between an organism and its environment
oxygen, carbon dioxide, nutrients eg glucose, excretory products eg urea
How does surface area to volume ratio differ between organisms of different sizes
Smaller organisms have a larger surface area to volume ratio to allow efficient exchange across their body surface.
However as organisms get larger, this ratio decreases as their volume increases at a faster rate than their surface area
This means simple diffusion of substances across the outer surface membrane can only meet the needs of inactive organisms,
as even if the outer surface could supply enough of a substance, it would take too long to diffuse to the middle of the organism
What two features have organisms adapted to help diffusion of substances
. A flattened shape so no cell is too far from the surface, eg a leaf or flatworm
. Specialised exchange surfaces with large areas to increase surface area to volume ratio eg lungs in mammals or gills in fish
How would you calculate surface area to volume ratio if a cell was the shape of a sphere that is 10qm in diameter
. To find surface area of sphere, the equation is 4πr2
So do 4 x 3.14x 25 which is 314qm2
To find volume of sphere, the equation is 4/3π r3
so do 4/3 x 3.14 x 125 which is 523. 33
Find the ratio of these two where the volume is 1: …
so sa:v is 0.6:1
What do exchange surfaces do
Allow the transfer of materials across specialised exchange surfaces by diffusion or active transport
What are the characteristics of exchange surfaces
. Large surface area relative to the volume of the organism which increases rate of gas exchange
. Very thin so the diffusion distance is short so materials cross the exchange surface rapidly
. Selectively permeable to allow certain materials to cross
. Movement of the environmental medium eg air to maintain a diffusion gradient
. A transport system to ensure the movement of the internal medium eg blood in order to maintain a diffusion gradient
Why are exchange systems usually located inside an organism and not outside
. They are very thin so are easily damaged and dehydrated
. Where an exchange surface is located inside a body, the organism needs to have a means of moving the external medium over the surface, eg ventilating the lungs of a mammal
What is diffusion directly proportional to
(surface area x difference in conc)
———————————————- or ÷
Length of diffusion path
