3.1.1 exchange surfaces Flashcards
why does an amoeba (single-celled organism) not need a specialised gas exchange system, but a mammal/fish/insect does?
- smaller organisms have a large SA compared to their volume (SA : volume ratio).
- This makes exchange across their surface
by DIFFUSION fast - larger organisms have a smaller SA : volume ratio, this makes exchange across their surface by DIFFUSION slow. They also
have more cells that require O2
– single celled organisms have a much lower metabolic rate / are less active. They have lower demands for oxygen & produce less
carbon dioxide to get rid of
Why do multicellular organisms need specialised exchange systems?
- some cells are deep within the body so there is a big distance between them and the outside environment
- larger animals have a smaller surface area to volume ratio
- multicellular organisms have a higher metabolic rate so they use glucose and oxygen up faster
surface area of a sphere
4pi r squared
volume of a sphere
3/4 pi r cubed
as the size of an organism increases what happens to the SA: V ratio?
decreases
examples of a big surface area give an effective exchange surface?
- lots of tiny alveoli collectively give a big SA
- intestine cells have microvilli for absorption of digested food
- root hair cells increase SA to absorb water / mineral ions
examples of a thin exchange surfaces.
shorter diffusion pathway (shorter distance for diffusion to occur)
e.g. alveoli have very thin walls around them – made of squamous epithelium
examples of a big concentration gradient in exchange surfaces
- very good blood supply
- this ensures that O2 is constantly moved away from the alveoli to the cells and CO2 is returned to the alveoli to maintain the diffusion gradient
- ventilation
- breathing air in/out delivers oxygen & removes carbon dioxide to/from alveoli in mammals
how does permeability to gases provide an effective exchange surface?
necessary if oxygen and carbon dioxide have to move in/out
If gas exchange surfaces are thin and permeable enough to let gases cross, what will also allowed to pass through? why is this bad?
water molecules. there is a risk of organisms losing water to the environment – it can
evaporate from the gas exchange surface
how is the fact that exchange surfaces being thin overcome?
lungs of mammals are DEEP INSIDE THE BODY, further away from the
air outside, so a much lower concentration gradient for water to evaporate out
describe the gaseous exchange system in mammals
- air passes into the lungs through the nose and along the trachea, bronchi and bronchioles
- air reaches the tiny sacs called alveoli
-lungs are protected by ribcage - ribs held together by intercostal muscles
- diaphragm helps to produce breathing movements
what does it mean to have a high metabolic rate?
high cell respiration rate, to produce ATP fast enough to supply the cells with enough energy to carry out active processes.
features of nasal cavity
- large SA with good blood supply, warms air to body temp
- hairy lining, which secretes mucus to trap dust and bacteria protecting lung tissue from damage
- moist surfaces, to increase humidity of air, reducing evaporation
goblet cells
secrete mucus to trap unwanted microorganisms and dust and stop them from reaching alveoli
ciliated epithelium
beat the mucus secreted by the goblet cells upwards to the throat
where are goblet and ciliated epithelium found?
inner layer of wall
elastic fibres
help process of breathing out.
- elastic fibres stretched when breathing in and recoil when breathing out to push air out
- with every breath
- not cells
smooth muscle
- controls diameter
- smooth muscle relaxes during exercise, making the tubes wider, so there is less resistance to airflow, air can move in and out of the lungs more easily.
- contract and relax
- not with every breath
- depends on activity level
where are elastic fibres found?
middle layer of wall of the trachea, bronchi, bronchioles and alveoli
where is smooth muscle found?
middle layer of wall of the trachea, bronchi and bronchioles (except the smallest ones)
cartilage
- rings of cartilage in walls of trachea and bronchi provide support.
- strong but flexible
- stops trachea and bronchi collapsing when you breathe in and the pressure drops
where is cartilage found?
outer layer of wall
Why do smokers often develop long-term coughs?
The substances in cigarette smoke stop cilia beating, so mucus cannot be brought up to the back of the throat. It may remain in the airways,
sometimes with pathogens trapped in it – causing infection and irritation.
Why does the amount of cartilage reduce as we move from the trachea to the bronchi to the bronchioles?
The airway tubes become smaller in diameter and do not need the same
amount of support to hold them open
Why do cilia & goblet cells disappear deeper down in the airways?
- already done their job higher up in the airways – produced
mucus to trap pathogens and swept it up to back of throat. - cilia would take up too much space in the lumen of very small
bronchioles, could obstruct the air flow
why is the cartilage incomplete?
It would be too rigid if it was complete – need to allow a little bit of flexibility to allow food to
be swallowed down the oesophagus, which runs behind the trachea
what does cartilage on the outer wall of the trachea look like?
c shaped
what does cartilage on the outer wall of the bronchi look like?
patches
how are the alveoli adapted for effective gas exchange? (5 points)
- The walls of the alveoli are made from squamous epithelium cells which are thin and flat., giving a short diffusion pathway for oxygen to diffuse from the alveolus into the blood, and carbon dioxide to diffuse the other way
- inner surface of each alveolus is coated with a secretion called SURFACTANT. helps to keep the alveoli inflated & stops them from collapsing and sticking together
- Each alveolus has a network of blood capillaries wrapped around the surface. The walls of these are one cell thick (ENDOTHELIUM), giving a
short diffusion pathway for gas diffusion. the blood is constantly moving, it brings carbon dioxide TO the alveoli and carries
oxygen AWAY from the alveoli, maintaining the CONCENTRATION GRADIENT - millions of tiny alveoli in each lung, collectively giving a huge surface area for gas exchange
- Ventilation (breathing) brings fresh oxygen to the alveoli and takes away carbon dioxide away – maintains the concentration gradient for O2 to enter the blood & CO2 to leave.
is inspiration active or passive?
active
describe process of inspiration
-breathing in
- external intercostal and diaphragm contract
- so ribcage moves upwards and outwards
-diaphragm flattens, increasing volume of the thorax
- so lung pressure drops below atmospheric pressure
- causes air to flow into lungs
- active
describe process of expiration
- external intercostal and diaphragm muscles relax
- ribcage moves downwards and inwards
- diaphragm becomes curved again
- decreasing volume of thorax
- so air pressure increases above atmospheric pressure
- air is forced out of the lungs
- normal expiration is passive
describe forced expiration
- internal intercostal muscles contract to pull ribcage down and in
ventilation rate
volume of air taken into lungs per min
how to measure ventilation rate
VR = breathing rate x tidal volume
what is tidal volume?
volume of air in each breath
how does a spirometer work?
- person breathes in and out through their mouth via the mouthpiece
- air is trapped between the enclosed chamber between the float and the water
- when breathing in, the volume of air in the chamber decreases and the float drops
- when breathing out, the volume of air in the chamber increases and the float rises
- the float is attached to a pen which writes on the paper on the revolving drum, recording breathing movements
what can you do about the CO2 in the chamber?
soda lime can be used to absorb the CO2
vital capacity
max volume of air that can be breathed in and out in 1 breath
breathing rate
breaths taken per min
oxygen uptake
rate at which a person uses up oxygen
residual volume
even when you have pushed out as much air as possible from the lungs, some still remains, as lungs never completely collapse
why does a spirometer trace slope downwards overtime?
- O2 removed from the chamber and is used up in resp. by the person and is not returned
- lose gas in chamber overtime
- CO2 exhaled does not enter the chamber, it is absorbed by the soda lime
why is gaining oxygen from water harder than air?
- water is denser than air so it would not be possible to move it in and out of the lungs without using lots of energy
-water has a lower oxygen content than air, which means there is a smaller concentration gradient across the gas exchange surface
what is the gas exchange surface of fish?
gills
why do fish need a very efficient gas exchange mechanism?
they are very active as they need lots of energy to swim so have high O2 demands and lots of CO2 to remove
structure of the gills
- 4 gills on each side of head
- each gill made up of 2 rows of thin gill filaments attached to a bony gill arch
- gill filament surface is folded into gill lamellae (gill plates)
- GIVES BIG SURFACE AREA
how are the gills adapted for gas exchange?
-large surface area, good blood supply and thin surface
- found within gill cavity covered by a flap called the operculum
use of the operculum
helps to maintain one way flow of water over the gills, bringing water in with fresh O2 and carrying water away that has picked up CO2
describe the counter-current system
- blood flows over the gill plates in one direction and water flows in the opposite direction
- so water with high O2 conc always flows next to the blood with lower O2 conc
- giving a steep conc gradient between water and blood
- so as much as possible O2 diffuses from water to blood
how do fish gills have a short diffusion pathway?
blood capillaries are very close to surface of gill plates, the gill plates are very thin. so as water floes over gill plates it is very close to blood
how do fish gills have a big S.A?
- 4 gills on each side of head
- each gill made of 2 stacks of gill filaments
- each filament is covered with gill plates (lamellae- site of gas exchange)
how do fish gills have a good/ big conc gradient?
- rich blood supply brings blood rich in CO2 INTO the gill and blood rich in O2 OUT of the gill and back into the body of the fish
- ventilation: the fish opens and closes it’s mouth as it swims to force water over the gills and out. so more O2 is delivered and more CO2 is removed.
- counter-current mechanism: blood flows over the gill plates in one direction and water flows in the opposite direction
what do fish use to maintain the flow of water over their gills at all times?
mouth and opercuclum
what allows more time for gas exchange in fish?
tips of gill filaments overlap, increasing resistance to the flow of water and slowing down the water movement
describe ventilation in bony fish
- fish opens mouth
- lowers floor of buccal cavity inside mouth
- increasing volume of buccal cavity
- pressure in buccal cavity decreases
- water is drawn into buccal cavity due to pressure gradient (higher outside)
THEN:
- fish closes mouth
- floor of buccal cavity raises
- volume inside buccal cavity decreases
- so pressure increases
- water forced over gill filaments- gas exchange occurs
- pressure forces open the flaps over the operculum, so water can leave the gills
why do insects need efficient gas exchange systems?
- high O2 demands
- very active (flight)
- hard exoskeleton which stops gas exchange across their body surface
what does it mean by insects have a open circulatory system?
there is no blood or blood vessels, O2 directly delivered to cells and CO2 removed by cells
explain gas exchange in insects
- along thorax and abdomen are spiracles (small openings where enters and leaves insects)
- which lead into tubes called tracheae, carrying air into the body
- tracheae have rings of chitin around them
- which lead into tracheoles, which are single elongated cells with no chitin
- trachelole walls are fully permeable to gases and are thin
- lead into insect tissues
- O2 diffuses in moisture at the end of the tracheoles and diffuses into the cells
role of rings of chitin
flexible support- keeps tubes open even if they are bent or pressed
what are spiracles?
small openings where enters and leaves insects
what are tracheoles?
- single elongated cells with no chitin
- fully permeable walls to gases
- very thin
- site of gas exchange
how is the insect gas exchange system adapted to have a big S.A?
- lots of tiny tracheoles leading directly to the body cells
how is the insect gas exchange system adapted to have a short diffusion pathway?
tracheole walls are very thin and close to body cells
how is the insect gas exchange system adapted to have a big conc gradient?
cells are respiring, using O2 and producing CO2 so O2 keeps diffusing into cells and CO2 keeps diffusing the other way
limits to diffusion of oxygen in insects
- tracheal fluid at end of tracheoles near to cells
- slows down diffusion
how is tracheal fluid overcome?
when insect is very active.
when activity increases, cell respiration rate increases, some anaerobic resp occurs, producing lactic acid in body cells.
how does lactic acid reduce the volume of tracheal fluid in tracheoles?
- lowers the water potential of the cells, drawing water from the tracheoles into cells by osmosis
- less fluid left in tracheoles, increasing the SA for gas exchnage.
use of sphincter muscles around spiracles of an insect?
so they can open and close
why do spiracles need to be able to open and close?
- to maximise gas exchange whilst minimising water vapour loss
- when inactive, insects can close spiracles to save water
- when active, insects can open them to allow more O2 in, but some water vapour will be lost
- spiracles open and close according to activity level
ventilation in larger insects
- larger insects also ventilate by body movement
1. sections of tracheal system expand + have flexible walls. act as air sacs which squeeze which can be squeezed by action of flight muscles
2. wing movement changes volume in thorax. if volume decreases, air in the tracheal system is under pressure and forced out. if vol increases, pressure decreases, air enters tracheal system
3. locusts change volume in abdomen. opening and closing valves in spiracles. abdomen expands, causing spiracles at front and end of body to open to air enters. abdomen decreases in volume, spiracles at end of body open, air leaves.
