exchange

what is the external environment different from

the internal environment found with an organism and within its cells

what must organisms do in order to survive

transfer materials between the two environments

where does transfer take place

at exchange surfaces

what does transfer always involve

crossing cell plasma membranes

what is tissue fluid

the environment around the cells of multicellular organisms

the majority of cells are too far from exchange surfaces for diffusion alone to....

supple or remove their tissue fluid with the various materials needed to keep its composition relatively constant

therefore once absorbed materials are rapidly distributed to the tissue fluid and the waste products returned to the exchange surface for removal

what does a mass transport system do

maintains the diffusion gradients that brings materials to and from the cell surface membranes

what affects the amount of each material that is exchanged

- size

- metabolic rate

what do organisms with a higher metabolic rate do in terms of exchange

exchange more material

if an organism exchanges more material and has a high metabolic rate then what does it require

a larger surface area to volume ratio

examples of things that need to be interchanged between an organism and it's environment

- respiratory gases

- nutrients

- excretory products

- heat

example of respiratory gases in exchange

- oxygen

- carbon dioxide

examples of nutrients in exchange

- glucose

- fatty acids

- amino acids

- vitamins

- minerals

example of excretory products in exchange

- urea

- carbon dioxide

two ways heat exchange can take place

- passively (no metabolic energy required) by diffusion and osmosis

- actively (metabolic energy required) by active transport

exchange takes place at the ______ of an organism

surface

materials absorbed are used by the cells that...

mostly make up it's volume

what must happen for exchange to be effective

the exchange surfaces of the organism must be large compared with its volume

small organisms have a surface area that is...

large compared to their volume in order to allow efficient exchange across their body surface

as organisms become larger what happens to surface area and volume

their volume increases at a faster rate than their surface area

what happens as a result of surface area to volume ratio decreasing as organisms become larger

- simple diffusion of substances across the outer surface can only meet the needs of relatively inactive organisms

- even if the outer surface could supply enough of a substance it would still take too long for it to reach the middle of the organism if diffusion alone was the method of transport

organisms have evolved one or more of which features

- a flattened shape so that no cell is ever far from the surface (eg a leaf)

- specialised exchange surfaces with large areas to increase the surface area to volume ratio (eg lungs in mammals or gills in fish)

surface area of sphere calculation

4 pi r^2

volume of a sphere calculation

4/3 pi r^2

what characteristics do exchange surfaces show to allow effective transfer of materials across specialised exchange surfaces by diffusion or active transport

- a large surface area relative to the volume of the organism which increases the rate of exchange

- are very thin so that the diffusion distance is short and therefore materials cross the exchange surface rapidly

- selectively permeable to allow selected material to cross

- movement of environmental medium for example air to maintain a diffusion gradient

- a transport system to ensure the movement of the internal medium for example blood in order to maintain a diffusion gradient

diffusion is proportional to

surface area x difference in concentration/ length of diffusion path

as a result of being thin what happens to specialised exchange surfaces

they are easily damaged and dehydrated and located inside an organism

where an exchange surface is located inside the body....

the organism needs to have a means of moving the external medium over the surface (eg ventilating the lungs in a mammal)

area of a cylinder calculation

disc : pi r ^2

external surface area of an enclosed cylinder: 2pi r h + 2pi r^2

as single celled organisms are small what do they have

a large surface area to volume ratio

gas exchange in a single celled organism

-oxygen absorbed by diffusion across their body surface which is covered only by a cell surface membrane

- in the same way, carbon dioxide from respiration diffuses out across their body surface which

where a living cell is surrounded by a cell wall...

this is no additional barrier to the diffusion of gases

what have insects evolved mechanisms for

to conserve water

in insects what does the increase in surface area required for gas exchange conflict with

conserving water because water will evaporate from it

what is tracheae

an internal network of tubes supported by strengthened rings to prevent them from collapsing

what have insects evolved for gas exchange

an internal network of tubes called tracheae

what are the tracheoles

smaller deadend tubes that extend throughout all the body tissues of the insect

what do the tracheae divide into

smaller dead end tubes called tracheoles

what happens through the tracheae and tracheoles in insects

atmospheric air with the oxygen it contains is brought directly to the respiring tissues as there is a short diffusion pathway from a tracheole to any body cell

what are the three ways respiratory gases move in and out of the tracheal system

- along a diffusion gradient

- mass transport

-the ends of the tracheoles are filled with water

how do respiratory gases move in and out of the tracheal system along a diffusion gradient

- when cells are respiring oxygen is used up and its concentration towards the ends of the tracheoles falls

- this creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the tracheae and tracheoles to the cells

- carbon dioxide is produced by cells during respiration creating a diffusion gradient in the opposite direction

- this causes gaseous co2 to diffuse along the tracheoles and tracheae from the cells to the atmosphere

- as diffusion in air is much more rapid than in water, respiratory gases are exchanged quickly by this method

how do respiratory gases move in and out of the tracheal system by mass transport

- the contraction of muscles in insects can squeeze the tracheae enabling mass movements of air in and out

- this further speeds up the exchange of respiratory gases

how do respiratory gases move in and out of the tracheal system by the ends of the tracheoles filling with water

- during periods of major activity the muscle cells around the tracheoles respire carry out some anaerobic respiration

- this produces lactate which is soluble and lowers the water potential of the muscle cells

- water moves into the cells from the tracheoles by osmosis

- the water in the ends of the tracheoles decreases in volume and in doing so draws air further into them

- this means the final diffusion pathway is in a gas rather than a liquid phase and therefore diffusion is more rapid

- this increases the rate at which air is moved in the tracheoles but leads to greater water evaporation

how do gases enter and leave the tracheae

through tiny pores called spiracles on the body surface

what are spiracles

tiny pores on the body surface

how do spiracles open and close

by a valve

what happens when spiracles are open

water vapour can evaporate from the insect

what do insects do most of the time to prevent water loss

keep their spiracles closed

what do insects do periodically

open their spiracles to allow gas exchange

limitations of the tracheal system

- relies mostly on diffusion to exchange gases between the environment and the cells

- for diffusion to be effective the diffusion pathways needs to be short which is why inspects are of a small size, as a result the length of the diffusion pathway limits the size that insects can attain

insects are one of the most_____groups of organisms on earth

successful

what kind of outer covering to fish have

a waterproof and therefore gas tight outer covering

as fish are relatively large what do they have

a small surface area to volume ratio

why did fish need to evolve

their body surface is not adequate to supply and remove their respiratory gases as they have a small surface area to volume ratio

what have fish evolved for efficient exchange of respiratory gases

gills

are gills an internal or external gas exchange surface

internal

where are gills located

in the body of the fish behind the head

what are gills made up of

gill filaments

how are gill filaments arranged

they are stacked up in a pile

what are at right angles to the gill filaments

gill lamellae

what do gill lamellae do

increase the surface area of the gills

what is the counter current flow

- water is taken in through the mouth and forced over the gills and out through an opening on each side of the body

- the flow of water over the gill lamellae and the flow of blood within them are in opposite directions

what is counter current important for

- ensuring that the maximum possible gas exchange is achieved

- if the water and blood flowed in the same direction far less gas exchange would take place

what is the essential feature of the countercurrent system

blood and water flowed over the gill lamellae in opposite directions

as water flows over the gill lamellae in the opposite direction to blood, what does this arrangement mean

- blood that is already well loaded with oxygen meets water which has its maximum concentration of oxygen, therefore diffusion of oxygen from the water to the blood takes place

- blood with little oxygen in it meets water which has had most but not all of its oxygen removed, again diffusion of oxygen from the water to the blood takes place

what happens as a result of the counter current

- a diffusion gradient for oxygen uptake is maintained across the entire width of gill lamellae

- in this way about 80% of the oxygen available in the water is absorbed into the blood of the fish

-if the flow of water and blood had been in the same direction

- the diffusion gradient would only be maintained across part of the length of the gill lamellae and only 50% of the available oxygen would be absorbed by the blood

what do plant cells require during respiration

oxygen

what do plants produce in respiration

carbon dixoide

when it comes to ______ plant and animal cells are different

gas exchange

what causes gas exchange in plants to be different

some plant cells carry out photosynthesis

how does photosynthesis change gas exchange

- during photosynthesis plant cells take in co2 and produce o2

- at times the gases produced in one process can be used for the other

- this reduces gas exchange with the external air

- overall meaning that the volumes and types of gases that are being exchanged by a plant leaf change depending on the balance between the rates of photosynthesis and respiration

exchange when photosynthesis is taking place

- even though some co2 comes from respiration of cells

- most is obtained from the external air

- in the same way some o2 from photosynthesis is used in respiration but most of it diffuses out of the plant

exchange when photosynthesis is not occurring eg in the dark

- oxygen diffuses into the leaf because it is constantly being used by cells during respiration

- in the same way co2 produced during respiration diffuses out

how is gas exchange in plants similar to that of insects

- no living cell is far from the external air therefore there's a source of o2 and co2

- diffusion takes place in the gas phase (air) which makes it more rapid than if it were in water

in plants there is a _______ diffusion pathway

short and fast

what do the air spaces inside a leaf do for plants

they have a large surface area compared with the volume of living tissue

there is no specific transport system for gases as....

they simply move in and through the plant by diffusion

adaptations of leaves for rapid diffusion

- many small pores called stomata

- numerous interconnecting air spaces

- large surface area of mesophyll cells

what does the stomata allow for gas exchange

so that no cell is far from a stoma and therefore the diffusion pathway is short

what does having interconnecting air spaces allow for gas exchange

so that gases can readily come in contact with mesophyll cells

what does the large surface area of mesophyll cells allow for gas exchange

for rapid diffusion

what are stomata

minute pores that occur mainly but not exclusively on the leaves especially on the underside

what is each stoma surrounded by

a pair of special cells called guard cells

what do guard cells do

they can open and close the stomatal pore to control the rate of gaseous exchange

how are guard cells and stomata important

- terrestrial organisms lose water by evaporation

- plants have evolved to balance the conflicting needs of gas exchange and control of water loss

- they do this by closing stomata at times when water loss would be excessive

in terrestrial organisms like plants and insects, problems arise from...

- the opposing needs of an efficient gas exchange system

- the requirement to conserve water

the features that make a good gas exchange system are the same features that increase....

water loss

in order to survive terrestrial organisms must limit their water loss without....

compromising the efficiency of their gas exchange systems

the gas exchange surfaces of terrestrial organisms are ________ the body

inside

the air at the exchange surface is more or less 100% saturated with water vapour....

meaning there is less evaporation from the exchange surface

what does it mean if most insects are terrestrial

they live on land

what is the problem for all terrestrial organisms

water easily evaporates from the surface of their bodies and they can become dehydrated

terrestrial organisms have evolved adaptations to....

conserve water

what does an efficient gas exchange require

a thin permeable surface with a large area

what does having a thin permeable surface with a large area conflict with

the need to conserve water

as a terrestrial organism, what does the insect have to balance

the opposing needs of exchanging respiratory gases with limiting water loss

what adaptations have insects evolved to reduce water loss

- small surface area to volume ratio

- waterproof coverings

- spiracles

how does a small surface area to volume ratio reduce water loss in insects

minimises the area over which water is lost

how does a waterproof covering reduce water loss in insects

in the case of insects this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle

how do spiracles reduce water loss in insects

- they are openings of the treacheae at the body surface and these can be closed to reduce water loss

- this conflicts with the need for oxygen and so occurs largely when the insect is at rest