6.1- EXCHANGE BETWEEN ORGANISMS AND THEIR ENVIRONMENT Flashcards
Is the internal and external environment of organism the same?
no
What does an organism transfer and between where to survive?
transfer materials between two environments (internal + external)
Where does the exchange of materials from internal + external environments of organism happen?
at exchange surfaces
What does exchanging materials between the two environments involve for an organism?
crossing cell plasma membranes
What is the environment around the cells of a multicellular organism called?
tissue fluid
What is tissue fluid?
environment around cells of multicellular organisms
What is the problem with majority of cells in an organism being too far from exchange surfaces?
diffusion alone cannot supply or remove their tissue fluid with the various materials needed to keep its composition relatively constant
What happens to materials once absorbed into an organism?
rapidly distributed to tissue fluid + waste products returned to exchange surface for removal
What does the process of materials distributed to tissue fluid + waste being removed involved?
mass transport system
What does the mass transport system maintain?
diffusion gradients that bring materials to + from cell-surface membranes
What can affect the amount of each material that is exchanged ? (2)
size
metabolic rate of organism
What does an organism with a high metabolic rate require?
larger surface area to volume ratio
Why does an organism with a high metabolic rate require a larger SA:V?
exchanges more materials
Examples of things that need to be interchanged between an organism and its environment (5)
respiratory gases (oxygen + CO2)
nutrients (glucose, fatty acids, amino acids, vitamins, minerals)
excretory products (urea + CO2)
heat
Except for heat, how can exchange of the 4 substances take place? (2)
passively- diffusion or osmosis
actively- by active transport
What is meant by passive exchange?
no metabolic energy required
What is meant by active exchange?
metabolic energy required
Where does exchange take place in an organism?
surface of an organism
What is the materials absorbed by an organism used by?
cells that mostly make up its volume
For exchange to be effective, what must the exchange surface(s) of an organism be like?
must be large compared with its volume
What do small organism have? (hint: SA)
SA large enough, compared with their volume
What does small organisms having a SA large enough compared with their volume allow?
efficient gas exchange across their body surface
What happens to volume as organisms become larger in comparison to SA?
volume increases at faster rate than their SA
What happens as organisms are larger and volume increases at a faster rate than their SA?
simple diffusion of substances across outer surface can only meet needs of relatively inactive organisms
Even if the outer surface could supply enough of a substance in a larger organism, why is this still not good enough?
still take too long for it to reach middle of organism if diffusion along was method of transport
Organisms have developed one or more of the following features for exchange (2)
flattened shape so no cell ever far from surface (e.g. flatworm or leaf)
specialised exchange surfaced with large areas to increase SA:V (e.g. lungs in mammals, gills in fish)
What features do exchange surfaces show to allow effective transfer of materials across specialised exchange surfaces by diffusion/ active transport? (5)
large SA relative to volume of organism
very thin
selectively permeable
movement of environmental medium
transport system
What does the exchange surface having a large SA relative to volume of organism do?
increases rate of exchange
What does the exchange surface being very thin do?
diffusion distance short so materials cross exchange surface rapidly
What does exchange surface being selectively permeable do?
allow selected materials to cross
What does movement of environmental medium e.g. air do for exchange?
maintain diffusion gradient
What does a transport system do for exchange?
ensure movement of internal medium e.g. blood to maintain diffusion gradient
What is Fick’s law equation?
diffusion ∝
length of diffusion path
As specialised exchange surfaces are thin, what can easily happen to them? (2)
easily damaged + dehydrated
As specialised exchange surfaces are easily damaged + dehydrated, where are they often located?
often located inside organism
Where an exchange surface is located inside the body, what must the organism need to have?
means of moving external medium over surface
What is an example of an organism have a means of moving external medium over the surface?
means of ventilating lungs in mammal
