exchange Flashcards
what are the two different environments
we have both external and internal environments
the internal environment within an organism and within its cells is different form the external environment
what must organisms do in order to survive
to survive, organisms transfer materials between the two environments
where does this transfer of materials take place
this transfer of material takes place at exchange surfaces and always involves crossing cell plasma membranes ( including membranes within internal organelle of cells )
what is the environment around the cells called
the environment around the cells of multicellular organisms is called tissue fluid
why can’t diffusion be the only source of transport for materials
the majority of cells are too far from exchange surfaces for diffusion alone to supply 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 - this involves a mass transport system
It is this mass transport system that maintains the diffusion gradient that bring materials to and from cell - surface membranes
how will size and metabolic rate of an organism affect the amount of each material that is exchanged
organisms with a high metabolic rate exchange more materials and so require a larger surface area compared to the volume ratio
this reflects the type of exchange surface and transport system that evolved to meet the requirements of each organisms
what are some examples of things that need to be interchanged between an organism and its environment
- respiratory gases (oxygen and carbon dioxide)
- nutrients (glucose, fatty acids, amino acids, vitamins, minerals)
- excretory products (urea and carbon dioxide)
- heat
except for heat, these exchanges can take place in two ways:
- passively by diffusion and osmosis
- actively by active transport
what must happen in order for exchange to be effective
for exchange to be effective,
the exchange surfaces of the organism must be large compared with its volume
what is the surface area of small organisms like
small organisms have a surface area that is large enough, compared with their volume
to allow efficient exchange across their body surface
what happens to the organism as it gets larger
as an organisms become larger, their volume increases at a larger rate than their surface area
because of this, simple diffusion 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
what have organisms done to increase the surface to volume ratio ( to reduce the volume relative to the surface area)
organisms have evolved one or more of the following feature:
- a flattened shape so that no cell is ever far from the surface (e.g. flatwom or a leaf)
- specialised exchange surfaces with large area to increase the surface area to volume ratio (e.g. lungs in mammals, gills in fish)
what are some of the features of exchange surfaces
To allow effective transfer of materials across specialised exchange surfaces by diffusion or active transport, exchange surfaces show the following characteristics:
- large surface area relative to the volume of the organism which increases the rate of exchange
- very thin so that the diffusion distance is short and therefore across the exchange surface rapidly
- selectively permeable to allow selected materials to cross
- movement of the environment medium, e.g. air to maintain a diffusion gradient
- a transport system to ensure the movement of the internal medium, e.g. blood, in order to maintain a diffusion gradient
what is diffusion proportional to
diffusion ∝ surface area x differences in concentration/ length of diffusion path
why is the exchanged surfaces being thin a disadvantage
being thin, specialised exchange surfaces are easily damaged and dehydrated
This is why an exchange surface is located inside the body
Since the exchange surfaces is located inside the body,
the organisms needs to have a means of moving the external medium over the surface, e.g. a means of ventilating the lungs of a mammal
how is gas exchange in a single celled organism
single celled organisms are small and therefore have a large area to volume ratio
Oxygen is absorbed by diffusion across body surface, which is only covered by a cell surface membrane
CO2 (from respiration) diffuses out across their body surface
furthermore, living cells are surrounded by a cell wale - single celled organisms do not have this additional barrier therefore, it has a short pathway of diffusion
describe gas exchange in insects
insects have evolved an internal network of tubes called trachea
The trachea is supported by strenghthend rings to prevent them from collapsing. The trachea is divided into smaller dead - end tubes called tracheoles
The tracheoles extend throughout all the body tissue of the insect
In this way, atmospheric air with the oxygen it contains, is brought directly to the respiratory tissues, as there is a short diffusion pathway from a tracheole to any body cell
Gas enters and leaves the trachea through tiny pores, called spiracles on the body surface
what are the three ways that respiritory gases move in and out of the tracheal system
- Along a diffusion gradient
- mass transport
- the end of the tracheoles are filled with water
how do insects maintain a concentration gradient
when cells are respiring, oxygen is used and so its concentration towards the ends of the tracheoles falls
This creates a concentration gradient that causes gaseous oxygen to diffuse from the atmosphere along the trachea and tracheous to the cells
CO2 is produced by cells during repiration
This creates a concentration gradient in the opposite direction and causes the CO2 to diffuse along the tracheoles and tracheae from the cells to the atmosphere
As diffusion in the air is much more rapid than in water, respiratory gases are changed quickly by this method
how does mass transport speed up the exchange of respiratory gases/abdominal pumping
the contraction of muscles in the abdomen in insects can squeeze the trachea enabling mass movement of air in and out
This further speeds up the exchange of respiratory gases
how does the ends of the tracheoles being filled with water speed up the rate of gas exchange
during periods of major activity, exercise for example, the muscle cells around the tracheoles carry out some anaerobic respiration
This produces lactate, which is soluble and lowers the water potential of the muscle cells
Water therefore moves into the cells from the ends of the tracheoles decreases in volume and 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 trachea but leads to greater water evaporation/ loss
why must the spiracles control when they open and close
gas enters and leaves the trachea through tiny pores, called spiracles on the body surface
The spiracles may be open and closed by a valve
When the spiracles are open, water vapour can evaporate from the insect
Therefore, much time, insets keep their spiracles closed to prevent waters and they open periodically
what are the limitations of the tracheal system
The tracheal system is efficient but:
- it relies mostly on diffusion to exchange gases between the environment and cells
For diffusion to be effective, the pathway needs to be short which is why insects are small
As a result, the length of the diffusion pathway limits the size that insects can attain
why do fish need specialised exchange surfaces to exchange gases
fish are waterproof, and therefore a gas - tight outer covering
They are also relatively large, they also have a small surface area to volume ratio
Their body surface is therefore not adequete to supply and remove their respiratory gases and so, like insects and humans, they have evolved a specialised internal gas exchange surface: the gills
what is the structure of the gills
the gills are located within the body of the fish head
the gills are made up of filaments
The gill filaments are stacked up in a pile , rather like the pages in a book - increases the surface area of the gill
From the gill lamellae sit at right angles increasing SA
what is the passage of water in a fish
water is taken in through the mouth and forced over the gills and out through an opening on each side of the body
what is the flow of water in relation to the flow of blood
The flow of water over the gill lamelae and the flow of blood over the gill lamellae are in opposite directions
This is known as a countercurrent flow
what is the essential feature of the countercurrent exchange
this that flow water over goes over the gill lamellae do so in opposite directions of the blood
This arrangement means that:
1. 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 the most, but not all, of its oxygen removed.
Again, diffusion of oxygen from the water to blood
As a result, a diffusion gradient for oxygen uptake is maintained across the entire width of the gill lamealle
In this way, about 80% of the oxygen available in the water is absorbed into the blood of the fish
what would the uptake of water into the blood would be if the the flow was in the same direction
if the flow of water had been parallel ( in the same direction), the diffusion gradient would only be maintained across part of the length of the gill lamelae and 50% of the available oxygen would be absorbed by the blood
do plants undergo respiration
like animal cells, all plant cells require oxygen and carbon dioxide during respiration
what is the difference between plants and animals in gas exchange
some plant cells carry out photosynthesis
during photosynthesis plant cells take in carbon dioxide and produce oxygen
At times the gases produced in one process can be used for the other
The benefits of this is that it reduces gas exchange with external air
at times, the gases produced in one process can be used for the other, what does this depend on
This depends on the balance between the rates of the photosynthesis and respiration:
- when photosynthesis is taking place, although some CO2 comes from respiration of the cells, most of it is obtained from the external air. In the same way, some oxygen from photosynthesis is used in respiration but most of it diffuses out of the plant
2) when photosynthesis is not occurring, e.g. 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
what are the similarities between plant and insects gas exchange
- no living cells is far from external air, and therefore a source of oxygen and carbon dioxide
- diffusion takes place in the gas spaces (air) which makes it more rapid than if it were in water
Overall, therefore, there is a short, fast diffusion pathway
In addition, the air spaces inside a leaf have a very large surface area compared with the volume of living tissue
what are some adaptions of leaves for efficient gas exchange
most gaseous exchange occurs in the leaves, which show the following adaptations for rapid diffusion:
- many small pores, called stomata, and so no cell is far from a stomata and therefore the diffusion pathway is short
- numerous interconnecting air - spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
- large surface area of mesophyll cells for rapid diffusion
what is the stomata
the stomata are minature pores that occur mainly, but not exclusively, on the leaves especially the underside
what is the stoma surrounded by
each stomas surrounded by a pair of special cells (guard cells)
how do guard cells control the rate of gaseous exchange
guard cells can open and close
This controls the rate of gaseous exchange
This is important because terrestrial organisms lose (water by evaporation)
how do the guard cells control the rate of water loss
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
why does the body need oxygen
all aerobic organisms require a constant supply of oxygen to release energy in the form of ATP during respiration
why must CO2 be constantly removed
the CO2 produced from respiration must be constantly removed as build - up could be harmful to the body
why is the volume of O2 abosrbed and the volume of CO2 removed large in mammals
- they are relatively large organisms with a large volume of living cells
- they maintain a high body temperature which is related to them having high metabolic and respiratory rates
as a result, mammals have evolved specialised surfaces called lungs to ensure efficient gas exchange between the air and the blood
what are lungs
lungs are the site of gas exchange in mammals
They are lobed structures made up of a series of highly branched tubules called bronchioles which end in tiny air sacs called the aveloli
why are lungs located within the body
- air not dense enough to support and protect these delicate structures
- the body as a whole would lose great deal of water and dry out
what structure protects and supports the lungs
the lungs are supported and protected by a bony box called the ribcage
the ribs can be moved by the muscles between them
how are the lungs ventilated
the lungs are ventilated by a tidal stream of air
This ensures that the air within them is constantly replenished
what is the trachea
it is a flexible airway that is supported by a ring of cartilage
the tracheal walls are made up of muscle, lined with cilrated epithelium and goblet cells
why is the trachea supported by cartilage
cartilage prevents the trachea collapsing as the air pressure inside falls when breathing in
what are the bronchi
the bronchi are two divisions of the trachea, each leading to one lung
They are similar in structure to the trachea and, like the trachea, they also produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat
The larger bronchi are supported by cartilage, the amount of cartilage is reduced as the bronchi get smaller
what are the bronchioles
the bronchioles is a series of branching subdivisions of the bronchi
Their muscle allows them to constrict so that they can control the flow of air in and out the alveoli
what are the alveoli
small/ minute air - sacs with a diameter of between 100 μm and 300 μm, at the end of the bronchioles
Between the alveoli, there are some collagen and elastic fibres
The alveoli are lined with epithelium
why does the alveoli have collagen and elastic fibres between them
the elastic fibres allow the alveoli to stretch as they fill with air when breathing
They then spring back during breathing out in order to expel the CO2 rich air
what is the gas exchange surface in the alveoli
the alveolar membrane is the gas exchange surface
what is ventilation
to maintain a diffusion gradient across the alveolar epithelium, air is constantly moved in and out of the lungs
This is called ventilation
what is inspiration
when the air pressure of the atmosphere is greater than the air pressure inside the lungs, air is forced into the lungs
This is called inspiration (inhalation)
what is expiration
when the air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs
This is called expiration
how does the pressure change inside the lungs
the pressure changes are bought about by the movement of three sets of muscle:
- the diaphragm
- external the intercostal muscles
- internal the intercostal muscles
what is the diaphragm
it is a sheet of muscles that separates the thorax from the abdomen
what do the external intercostal muscles contractions lead to
the external intercostal muscles contractions leads to inspiration
what do the internal intercostal muscles contractions lead to
the internal intercostal muscles contractions leads to expiration
what are the different processes involved in inspiration
breathing in is an active process ( it uses energy) and occurs as follows:
- external intercostal muscles contract, while the internal intercostal muscles
- the ribs are pulled upwards and outwards, increasing the volume of the thorax ( the thorax is the front part of the ribcage)
- the diaphragm muscles contract, causing it to flatten, which increases the volume of the thorax
- the increased volume of the thorax results in reduction of pressure in the lungs
- atmosphere pressure is now greater than pulmonary pressure and so air is forced into the lungs
what are the different processes involved in expiration
breathing in is a passive process ( it does not use energy) and occurs as follows:
- internal intercostal muscles contract, while the external intercostal muscles relax
- the ribs are pulled downwards and inwards, decreasing the volume of the thorax ( the thorax is the front part of the ribcage)
- the diaphragm muscles relax, and so it is pushed up against the contents of the abdomen that were compressed during inspiration.
The volume of the thorax therefore decreases - the decreased volume of the thorax results in increase of pressure in the lungs
- the pulmonary pressure is now greater than that of the atmosphere and so air is forced out of the lungs
what is the pulmonary ventilation rate
to know how much air is taken in and out of the lungs in a given time,we use a measure called pulmonary ventilation rate
what is pulmonary ventilation
the total volume of air that is moved into the lungs during 1 minute
how do we calculate the pulmanory ventilation rate
we use this equation:
pulmonary ventilation = tidal volume x breathing rate
what is the tidal volume
the tidal volume is the volume of air that is normally taken out at each breath when the body is at rest
this is usually around 0.5dm3
what is the breathing rate
breathing/ ventilation rate is the number of breaths taken in in 1 minute ( normally 12 - 20 breaths in a healthy adult)
the unit is min-1
what is the unit for PV rate
dm3 min-1
what is the site of gas exchange in mammals
the site of gas exchange om mammals is the epithelium of alveoli
what are alveoli
alveoli are minute air sacs 100 - 300 micrometres in diameter and situated in the lungs
what must the body do to ensure a constant supply of oxygen
to ensure a constant supply of oxygen to the body, a diffusion gradient must be maintained at the alveolar surface
what are the features of an efficient exchange surfaces
- thin
- partially
- have a large surface area
what must the body do to maintain a diffusion gradient of gases
to maintain a diffusion gradient, there also has to be movement of both the environment medium
e.g. air and the internal medium (e.g. blood)
how do mammals move the external medium (air) over the exchange surface
as the exchange surface in mammals are on the inside of the body, the organism has some means of moving the external medium over the surface, e.g. a means of ventilating the lungs in a mammal
This is because diffusion alone is not enough to maintain adequate transfer of oxygen and CO2 along the trachea, bronchi and bronchioles
-Breathing is basically a form of mass transport
how many alveoli are there in the lungs
there are about 300 million alveoli in each human lung
what is the surface area of the alveoli in the lungs
their total surface area us around 70m2 - about half the area of a tennis court
what are each alveolus lined with
each is lined with epithelial cells only 0.5 to 0.3 micrometres thick
what is around each alveolus
around each alveolus is a network of pulmonary capillaries, so narrow (7-10 micrometres) that red blood cells are flattened against the thin capillaries have walls that are only a single layer of cells thick (0.04 -0.02) micrometres)
why is diffusion of gases between the alveoli and the blood very rapid
- red blood cells are slowed as they pass through pulmonary capillaries, allowing more time
- the distance between the avleor air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
- the walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is very short
- alveoli and pulmonary capillaries have a very large total surface area
- breathing movements constantly ventilate the lungs and the action of the heart constantly circulates blood around the alveoli
Together, these ensure that a steep concentration gradient of the gases to be exchanged is maintained - blood flow through the plumonary capillaries maintains a concentration gradient
why is the diffusion pathway short
the diffusion pathway is short because the alveoli have only a single layer of epithelial cells and blood capillaries have only a single layer of endothelial cells
how do organisms lose water while gas - exchange
the features that make a good gas - exchange system are the same features that increase water loss
e.g. in terrestrial organisms like insects and plants problems arise from the opposing needs of an efficient gas - exchange system and the requirement to conserve water
what must organisms do in order to survive - limit water loss
in order to survive, terrestrial organisms must limit their loss without compromising the efficiency of their gas exchange systems
what is the problem with terrestrial organisms
most insects are terrestrial (live on land)
The problem for all terrestrial organisms is that water easily evaporates from the surface of their bodies and they can become dehydrated
- they have evolved adaptions conserve water
why do insects have to balance the needs of exchanging respiratory gases limiting water loss
efficient gas exchange requires a thin, permeable surface with a large area
These features conflict with the need to conserve water
Therefore, the insect has to balance the opposing needs of exchanging respiratory gases with limiting water kiss
what have insects done to reduce water loss
insects have evolved the following adaptations that reduce water loss
- SMALL SURFACE AREA TO VOLUME RATIO
- WATERPROOF COVERING
- SPIRACLE CLOSE WHEN INSECT IS AT REST
These features mean that insects cannot use their body surface to diffuse respiratory gases in the way a single - celled organism does. Instead they have an internal network of tubes called tracheae that carry air containing oxygen directly to the tissue
how does having a surface area to volume ration reduce water loss in insects
- SMALL SURFACE AREA TO VOLUME RATIO to minimise the area over which water is lost
how does having waterproof covering reduce water loss in insects
- WATERPROOF COVERING over their body surfaces. In the case of insects this covering is a rigid outer skeleton that as covered with a waterproof cuticle
how does the spiracles opening and closing reduce water loss in insects
- SPIRACLES are the opening of the trachea at the body surface and those can be closed to reduce water loss
This conflicts with the need for O2 and so occurs largely when the insects are at rest
