exchange surfaces Flashcards
how can single celled organisms exchange substances
- with the external environment by diffusion through the cell surface membrane
- they can do this due to short diffusion distances
why is diffusion through the cell surface membrane enough for single celled organisms
- metabolic activity is usually relatively low
- surface area to volume ratio is large
- these mechanisms are enough to supply a single cell with everything it needs to survive
example of a single celled organism
ameoba
why can’t multi cellular organisms solely rely on diffusion of substances across the body surface to the cells in order to survive ?
- diffusion would be too slow as they are larger
- higher metabolic rate
- surface area to volume ratio is much smaller
- environment is a lot further away from the organisms centre
why do animals need specialised transport systems
- they are very active and have high metabolic demands
- bigger SA:V ratio as they are bigger
- many molecules are produced in one part of the body but are needed in another part
- food is digested in digestive system but products of this is needed all over the body
- all cells produce waster products which must be transported to excretory organs
how do you calculate surface area to volume ratio
surface area/volume :1
give common exchange surfaces present in most animals
- increased surface area
- thin layers
- good blood supply
- ventilation to maintain diffusion gradient
increased surface area -
provides the area needed for exchange and overcomes the limitations of SA:V ratio of larger organisms
- e.g villi, root hair cells
thin layers -
diffusion distances are short
making process fast and efficient
- e.g alveoli in lungs
good blood supply -
steeper concentration gradient, the faster diffusion takes place
good blood supply ensures substances are constantly delivered to and removed from exchange surfaces
maintaining steep concentration gradient
ventilation to maintain diffusion gradient
for gases in a ventilation system, helps to maintain concentration gradient
makes process more efficient
e.g alveoli in lungs, gills of fish
as the size of an organism increases, what happens to SA:V ratio
decreases
why does the SA:V ratio decrease when organism size increases
- the distances substances need to travel from the outside to reach the cells at the centre of the body get longer
- making it hard for cells to absorb enough O2 through the available SA to meet needs of the body
if exchange surfaces are thin and permeable enough what molecule is able to be let across
water
why could water being able to cross exchange surfaces be a negative
- there is a risk of organisms losing water to the environment as it could evaporate from gas exchange surface
in mammalian exchange systems, why do we keep the lungs deep inside of our body
so a much lower concentration gradient of water evaporates out of the body
why are mammalian gas exchange surfaces moist ?
so O2 dissolves in the water before diffusion into body tissues
however these conditions are also good for evaporation of water
why do mammals need an exchange system
- they are big an have a small SA:V ratio
- have a large volume of cells
- high metabolic rate
- maintain a constant body temperature independent of their environment
- need lots of O2 for respiration and removed CO2 from the lungs
site of mammalian gas exchange
lungs
lungs
inflatable sacs lying in the chest cavity
how are lungs protected
ribcage
how are ribs held together
intercostal muscles
what do the intercostal muscles and diaphragm do
help to produce breathing movements
name parts of the mammalian gas exchange system
nasal cavity
trachea
bronchus
bronchioles
alveoli
nasal cavity adaptations (just name)
- large SA with good blood supply
- hairy lining
- moist surfaces
nasal cavity - large SA with good blood supply - explain
warms the air to body temperature
nasal cavity - hairy lining - explain
secretes mucus to trap dust and bacteria
this protects delicate lung tissue from irritation and infection
nasal cavity - moist surfaces - explain
increases humidity of incoming air
this reduces evaporation from exchange surfaces
trachea
main airway carrying clean, warm air from the nose to the chest
trachea - structure
wide tube supported by incomplete rings of strong, flexible cartilage
- walls of smooth muscle
- elastic fibres
trachea - why is the cartilage useful
- supports trachea and stops it from collapsing
why are cartilage rings incomplete
to allow food to move down
what is the trachea lined with
ciliated epithelium and goblet cells
cilia
- hair like structures
- they beat the mucus secreted by goblet cells away from the alveoli to the throat where it is swallowed
- preventing lung infections
goblet cells
- secrete mucus trapping microorganisms and dust particles in the inhaled air
- stops them reaching alveoli
bronchus
- in chest cavity, trachea divides forming left and right bronchus
bronchus structure
similar to trachea - with some rings of cartilage, except smaller
- walls of smooth muscle
- elastic fibres
bronchioles
- bronchi divide to form bronchioles
bronchioles structure
- no cartilage rings
- walls of smooth muscle
- elastic fibres
smooth muscle
- controls diameter of walls
- when smooth muscle walls contract, structures constrict
- when smooth muscle walls relax, structures dilate
- controlling air volume of the lungs
elastic fibres
- aids process of breathing out
- when breathing in, elastic fibres stretch
- when breathing out, the fibres recoil to help push air out
- stretch and recoil mechanism
alveoli
tiny air sacs which are the main gas exchange surfaces of the body
alveoli - structure
- each alveolus has a diameter of 200-300 micrometres
- consists of a layer of thin, flattened epithelial cells along with some collagen and elastic fibres
what do the collagen and elastic fibres surrounding alveoli help them to do
stretch as air is drawn in
squeeze air out when they return to their normal size
= elastic recoil of the lungs
alveoli adaptations
- large SA
- thin layers
- good blood supply
- good ventilation
- inner surfaces covered in thin layers of water salts and lung surfactant
alveoli - explain - large SA
- the alveoli provides an average surface between the lungs of around 50-72 m2
= HUGE - provides area needed for exchange and overcomes limitations of SA:V ratio
alveoli - thin layers - explain
- only 1 epithelial cell thick = short diffusion path
alveoli - good blood supply - explain
- around 280 million capillaries surround alveoli = transports O2 and CO2 maintaining a steep concentration gradient between air in the alveoli and blood in capillaries
alveoli - good ventilation - explain
- breathing moves air in and out of the alveoli = steep concentration gradient of oxygen and CO2 from air in lungs and blood in capillaries
- constantly refreshes oxygen supply
alveoli - inner surfaces covered in thin layer of water salts and lung surfactants - explain
- allows alveoli to stay inflated
- O2 dissolves into H20 before it goes into the blood, and water evaporates
ventilation
when air is moved in and out of the lungs as a result of pressure changes in the thorax brought about by breathing movements
pleural membrane
lines the thorax surrounding the lungs
pleural cavity
space between the lungs and pleural membrane, contains lubricating fluid so membrane slides easily
rib cage
provides a semi rigid case within which the pressure can be changed with respect to the air outside it
diaphragm
broad, domed sheet of muscle which forms the floor of the thorax
inspiration
taking air in
inspiration: active or passive
active
inspiration - step by step
1- external intercostal and diaphragm muscles contract
2- causes ribcage to move upwards and outwards and the diaphragm to flatten, increasing volume of the thorax
3- as volume of thorax increases, pressure decreases
4- air flows to lungs
active process
requires energy
expiration
process of breathing out
expiration - active or passive
passive
expiration - step by step
1- external intercostal and diaphragm muscles relax
2- ribcage moves downwards and inwards and diaphragm becomes curved again
3- thorax volume decreases causing air pressure to increase
4- air is forced out of the lungs
passive
does not require energy
when can expiration be active
when forced, e.g blowing out birthday candles
what happens during forced expiration
internal intercostal muscles contract, to pull ribcage down and in
asthma effects
airways sensitive to everyday triggers, e.g house dust mites, pollen etc
what happens to exchange surfaces during an asthma attack ?
- cells lining in bronchioles release histamines
- as a result airways narrow and fill with mucus making breathing difficult
histamines - what do they do
- make epithelial cells inflamed and swollen
- stimulate goblet cells to make excess mucus and smooth muscle walls in bronchioles contract
relivers
give relief to symptoms (of asthma)
what do relivers do
- they are chemicals similar to adrenaline
- attach to active sites of surface membranes of smooth muscle cells in bronchioles making them relax and dilating the airways
preventers (for asthma attacks)
often steroids
taken everyday to reduce sensitivity of the lining in the airways
what happens to the bells jar model when the rubber sheet is pulled down
- volume of bell jar increases
- decreasing pressure in bell jar
- causing pressure in bell jar to be less than the atmospheric pressure
- so air from the atmosphere is forced into the glass tube
- causing the balloons in the bell jar to inflate
how can the volume of air which is drawn in and out of the lungs be measured
peak flow meter
vitalograph
spirometer
peak flow meter
rate at which air can be expelled from lungs
vitalograph
more sophisticated peak flow meter
spirometer
measures different aspects of lung volumes, as well as to investigate breathing patterns
what does a spirometer produce
a trace showing different aspects of lung volume
steps of how a spirometer works
1- person breathes in and out through their mouth via mouthpiece
2- air is trapped between enclosed chamber between the float and the water
3- when breathing in, the volume of air in the chamber decreases and the float drops
4- when breathing out, the volume of air inside the chamber increases and float rises
in the spirometer what is the float attached to
a pen, which writes on paper on the revolving drum, recording breathing movements
if soda lime is used in spirometry, what happens
the carbon dioxide breathed out into the mouthpiece is absorbed so does not reach the chamber
tidal volume
volume of air in each breath
(usually 0.4 dm3)
vital capacity
maximum volume of air that can be breathed in and out in one breath
breathing rate
how many breaths taken per unit of time
oxygen uptake
rate at which a person uses up oxygen
(e.g, number of dm3 used/minute)
residual volume
the remaining air left in the lungs after the maximum amount of air has been forcibly expelled from the body
why is there always air left in the lungs
to prevent the lungs from collapsing
what rules should we follow when using a spirometer
- use a healthy volunteer
- block their nose
- make sure they are breathing in and out of their mouth normally
Inside the spirometer there is pure oxygen, why ?
aerobic respiration
why does the reading from the spirometer gradually decrease over time
oxygen is being used up
revolving drum
records movements of pen
inner chamber
filled with oxygen
rises and falls when air enters/leaves the chamber
canister
filled with soda lime
valves
maintain direction of flow
how do we calculate breathing rate on the spirometer
peak to peak = 1 breath
count the number of these per minute
how is oxygen uptake calculated
work out the gradient of the trace
what happens to the gradient of oxygen uptake during exercise
it gets steeper
how do we calculate the rate of reaction on a spirometer trace
x/y
how do we calculate pulmonary ventilation
tidal volume x breathing rate
how do we calculate ventilation rate
tidal volume x breathing rate
why do the participants need to wear a nose clip
so no air escapes the nose
so breathing can be measured and measurements are more valid and accurate
how would we use a spirometer to calculate someones tidal volume
- get subject to take normal breaths through the mouthpiece
- minimum of 3 breaths
- calculate mean
- use trace to measure volume 0f air breathed in and out
relationship between tidal volume, breathing rate and oxygen uptake
- ventilation rate = tidal volume of air breathed in x number breaths/min
- oxygen uptake is linked to this as the more air moved into the lungs = more oxygen uptake
what difficulties are there in trying to gain oxygen from water rather than air
- water is 1000 x denser than air
- water is 1000 x more viscous than air
- water has a lower oxygen concentration = smaller concentration gradient across exchange surface
what is the issue with water being more viscous than air
it can’t move in and out of the lungs without using lots of energy
what gas exchange surface to fish use
gills
why do fish need a very efficient gas exchange mechanism
- they are very active - swimming
- high oxygen demands
- lots of carbon dioxide to get rid of
how many gills do fish have
4, on each side of their head
gils adaptations
- large SA
- good blood supply
- thin surface
where are gills found
within a gill cavity
covered by a flap called operculum
what does the operculum help to do
maintain a 1 way flow of water over the gills
- bringing in water with fresh oxygen
- carrying away water with carbon dioxide
gills - structure
- each gill is made up of 2 rows of gill filaments
- attached to bony gill arch
how do gills achieve a large surface area
- each gill filament is very thin
- surface is folded into gill lamellae
where does gas exchange take place in fish
gill lamellae
fish - counter-current system
- blood flows through gill plates in 1 direction
- water flows over in the opposite direction
how does the counter-current system ensure a steep concentration gradient is maintained between water and the blood
- water with relatively high oxygen concentration always flows next to blood with a lower oxygen concentration
- maximising diffusion
fish use their mouth and operculum flap to maintain a flow of water over their gills at all times, the tips of adjacent gill filaments overlap - how is this good
- increases resistance to the flow of water
- slows down water movement
- allowing more time for gas exchange
ventilation in bony fish - step by step - fish opening mouth
- fish opens their mouth
- lowering floor of buccal cavity
- increases volume of buccal cavity
- lowering pressure of buccal cavity
- water is then drawn into the buccal cavity due to pressure gradient
ventilation in bony fish - step by step - fish closing their mouth
- fish closes mouth
- floor of buccal cavity is raised
- volume inside buccal cavity falls
- pressure inside buccal cavity increases
- water is forced over gill filaments
- gas exchange occurs
- pressure forces open the flaps over operculum so water leaves gills
dissecting fish gills - step by step
1- place fish on dissection tray
2- push back operculum
3- use scissors to remove the gills
4- cut each gill arch through the bone at the top and bottom
5- gill filaments should be visable
why do insects have high oxygen demands
they are very active (flight)
why can’t gas exchange occur across insects body surface
they have a hard exoskeleton
what type of circulatory system do insects have
open circulatory system
open circulatory system
no blood or blood vessels
oxygen is delivered directly to cells
spiracles
small opening where air enters and leaves the insect
trachae
tube which carries air into the body
what is trachae lined with
rings of chitin
tracheoles
smaller tubes
elongated single cell with no chitin
tubes lead directly to insect tissues
site of gas exchange
insect pathway of air
- air enters through spiracles
- oxygen diffuses down concentration gradient along the trachea
- trachea branches into trachae then tracheoles
- tracheoles have thin walls which lead directly into insect tissues, where oxygen diffuses into
in insects, what helps to maintain a high concentration gradient
ventilation
chitin
similar function to cartilage
provides support
keeps tubes open even if they are bent or pressed
how are tracheoles adapted for insects
single celled
thin
short diffusion distance
tracheoles adaptations insects
- branches
- gives large SA
- greater surface for gases to diffuse from
- large number of these
towards the end of each tracheole there is tracheal fluid - why is this bad
prevents air getting to the very ends of tracheoles, near the cells
how can insects overcome tracheal fluid
- when they are active
- because respiration rate increases
- some anaerobic respiration happens, producing lactic acid in body cells
how can lactic acid produced by insects during anaerobic respiration reduce the volume of tracheal fluid in tracheoles
- water moves out by osmosis
- exposing more surface area for gas exchange
what do sphincter muscles do
surround the spiracles of an insect
causes them to open and close
why are sphincter muscles important
- to control extent of gas exchange
- and maximise this whilst minimising water vapour loss from gas exchange surface
when inactive, sphincter muscles close spiracles - why
- to save water
when active - sphincter muscles open spiracles - why
- to allow more oxygen in
- however some water vapour will leave
how is water loss reduced in insects
they are covered in waxy cuticle to reduce evaporation
insects can close their spiracles
ventilation in insects helps to maintain a steep concentration gradient, how ?
- large insects = by moving body can ventilate tracheal system
- sections of tracheal system can be expanded and have flexible walls which act as air sacs which can be squeezed by the action of the flight muscles
- movements of wing alters thorax volume
some insects such as Locusts can alter volume of abdomen - how does this aid ventilation
- as abdomen expands, spiracles at front end of body open and air enters tracheal system
- as abdomen reduces in volume spiracles at rear end open and air leaves tracheal system
