Download 2.1b Transport & gaseous exchange

Mass transport systems
• Move substances to & from excahnge
surfaces
• Substances are dissolved or suspended in
fluid
• Fluid travels in vessels
• Prevents accumulation of waste
• Mass flow transport occurs within larger
organisms and more active organisms
because their SA:VOL can never be large
enough to provide all the cells with the
necessary metabolites.
• Pressure differences within the organism
move the materials from and area of high
concentration, called the source, to an
area of lower concentration, called the
sink.
Gas exchange
in flowering plants & mammals
• It is necessary to supply all cells with
oxygen for respiration and to excrete
carbon dioxide.
• Gas exchange surfaces are specialised to
maximise the rate of gas exchange:
– Large surface area
– Moist surface for respiratory gases to dissolve
– Diffusion gradients for both O2 & CO2
– Permeable to both O2 & CO2
– Short diffusion path
• Fick’s Law expresses the relationship
between the rate of diffusion, surface area,
concentration gradient & membrane
thickness.
RATE
Surface area x difference in concentration
=
OF
Membrane thickness
DIFFUSION
A good exchange surface needs
to be adapted to allow
a high rate of diffusion.
It needs to have:
• large SA
• method to maintain a high conc. gradient
• short diffusion distance
• e.g alveoli in the lungs to pick up oxygen and
remove carbon dioxide, root hair cells to take
up minerals such as nitrates by AT, leaf for gas
exchange for photosynthesis.
A poor exchange surface needs
to be adapted to reduce the rate
of diffusion.
It needs to have:
• small SA
• method to reduce a high conc. gradient
• large diffusion distance
• e.g leaf to reduce transpiration
• Mammals have highly specialised
exchange surfaces because they have a
small surface area to volume ratio and an
impermeable body covering.
• The alveolar wall forms the gas exchange
surface.
Adaptations of the lung surface
• Thin respiratory surface creates a short
diffusion distance
– Single layer of squamous epithelium of the alveoli
– Single layer of squamous endothelium of blood
capillary wall
The capillaries sit tight against the alveoli and
the capillaries are so narrow that the red blood
cells )erythrocytes) must squeeze through,
ensuring contact with the endothelial wall and
reducing the diffusion pathway
Squamous epithelium lining the
alveoli
lumen of alveolus
squamous endothelium lining blood capillary wall.
Adaptations of the lung surface
• Large surface area provided by alveoli
– Approximately 700 million alveoli with a surface
area of 75m2, 30 times larger than the surface of
the body.
• Moist outer surface of alveoli
Adaptations of the lung surface
Steep concentration gradients are created by
• Mass flow of air to the respiratory surface i.e.
ventilation
– Brings oxygen into the lungs and removes carbon
dioxide
• Rich vascular supply through the capillaries
– Brings carbon dioxide rich blood to the alveoli and
removes oxygen rich blood
Together these maintain a steep diffusion gradient of
oxygen from the alveoli into the blood and carbon
dioxide from the blood into the alveoli.
Diffusion gradient for O2
•Breathing movements ensure that there is always a
high concentration of O2 in the alveoli
•Good blood supply constantly removes O2 (which
combines with haemoglobin in RBC) ensuring the
concentration is low
•Large difference between O2 concentration creates
steep concentration gradient for efficient gas exchange
Adaptations of the lung surface
• Moist outer surface of alveoli, deep inside the
body to reduce water loss by evaporation
– gases dissolve for diffusion across the surfaces
• Surfactant in the moisture layer of alveoli
reduces surface tension
– This prevents the alveoli collapsing which would
reduce the SA for gas exchange
• Macrophages
– Protect against infection by digesting
microorganisms by phagocytosis
Diffusion gradient for CO2
• Breathing movements ensure that there is
always a low concentration of CO2 in the alveoli
• Good blood supply constantly brings CO2
(released in cell respiration) from the body
ensuring the concentration is high
• Large difference between CO2 concentration
creates steep concentration gradient for efficient
gas exchange
Concentration gradient
circulation
diffusion
Lungs
Large SA
for gas
exchange
diffusion
Blood transports
gases and
metabolites
circulation
Deoxygenated
Oxygenated
Respiring
cell
Large SA
for gas
exchange
Lung surfactant
• The watery film lining the lungs creates a
surface tension which would cause the alveoli
to collapse and stick together when air is
exhaled.
• Surfactant is a mixture of phospholipid
molecules found between the watery film on
the inner surface of the alveoli and the air
inside them
• It reduces the surface tension so that the
alveolar surfaces do not stick together, they
remain open for gas exchange
• IMPORTANT AT BIRTH. First breath very difficult,
but causes surfactant to line alveoli; subsequent
breaths easier. Premature babies do not have
sufficient to keep alveoli open.
Air exhaled
Hydrophobic head
immersed in water
next to alveolar wall
Walls of the alveolus
drawn inwards
Surfactant prevents
alveolar membranes
sticking together
Hydrophobic tail
in air space
Water lining the
inner surface of
alveolus
Past paper essay question
• Give an account of the features of the gas
exchange surface in a mammal and
explain how these result in efficient gas
exchange. (13 marks)
breathing
• The term used to describe the processes
involved in ventilating the lungs and the
alveoli.
https://pbs.twimg.com/tweet_video/B30NonUAAER7Yf.mp4
The respiratory system
The breathing mechanism
Breathing involves the alternate increase and decrease
of air pressure in the lungs relative to that outside.
A fall in air pressure in the thorax causes inspiration
A rise in air pressure in the thorax causes expiration
Inspiration/inhalation (breathing in)
ACTIVE PROCESS
•
external intercostal muscles contract & internal intercoastal muscles relax
– ribs and sternum move up and out
– width of thorax increases front to back and side to side
•
diaphragm contracts
– diaphragm moves down, flattening
– depth of thorax increases top to bottom
•
volume of thorax increases.
•
pressure between the pleural surfaces decreases.
•
air pressure in alveoli is less than atmospheric pressure.
•
air is forced in by the higher external atmospheric pressure
•
lungs expand to fill thoracic cavity.
expiration (breathing out)
PASSIVE PROCESS
• External intercostal muscles relax internal intercostal muscles contract
ribs and sternum move down and in
width of thorax decreases front to back and side to side
• diaphragm relaxes
diaphragm moves up & returns to a dome shape
depth of thorax decreases top to bottom. So the …
• volume of thorax decreases.
• pressure between the pleural surfaces increases.
• lung tissue recoils from sides of thoracic cavity
• air pressure in alveoli is more than atmospheric pressure.
• air is forced out.
The effects of smoking
Use class text books to BRIEFLY outline the
following conditions
•Lung cancer
•Emphysema
•Cilia damage
•Bronchitis
PRACTICALS:
The respirometer
The J tube