Gaseous exchange
Part 1 – Recap + other organisms
Microthrombi: A microscopic clump of fibrin, platelets, and red blood cells.
Covid- 19
Breathing
Already in your
book.
• Breathing is also called ventilation.
• It is a mechanical process that is responsible for the movement of air
into and out of the lungs of an organism.
Gaseous Exchange
• Gaseous exchange is a physical process
whereby gases replace each other.
• The movement of the gases occurs by means
of breathing, diffusion and red blood cell
transport.
• In living organisms, gaseous exchange occurs
when oxygen and carbon dioxide are
exchanged.
• This exchange occurs in two areas, namely
between:
• The air that is in contact with the gaseous
exchange surface and the blood
• The blood and the cells of the various
tissues in the body.
Cellular Respiration
Already in your
book.
• Cellular respiration is a chemical process that occurs in all living cells.
• Cellular respiration is the gradual, controlled release of energy,, in the
form of ATP, from an energy-rich fuel molecule, usually glucose, in the
presence of oxygen. Water and carbon dioxide are released as waste
products.
The need for gaseous exchange
Already in your
book.
Gaseous exchange is vital to the survival of all living organisms for the
following reasons:
• It allows oxygen to enter the body of an organism efficiently so that aerobic
cellular respiration can occur.
• It allows the carbon dioxide produced during cellular respiration to be
removed from an organism efficiently.
• In small aquatic organisms, gaseous exchange can occur directly and
efficiently from the surrounding environment to all the body cells through
the body wall of the organism.
• Diffusion, however, is a relatively slow process and larger organisms
therefore need a specialised surface area for diffusion, as well as an
effective transport system for the movement of the respiratory gases
through the body.
Gaseous Exchange in
Different Animals
Requirements of an effective surface for
gaseous exchange
• Large surface – to absorb enough oxygen.
• Thin and permeable surface – for easy diffusion
• Moist – to facilitate diffusion
• Transport system – to bring oxygen to the cells and to take carbon
dioxide away
• Well ventilated –to bring oxygen into contact with the gaseous
exchange surface
• Well-protected – to prevent drying out and mechanical
injury
Already
in your
book.
Dicotyledonous plant
• There is a high surface area to volume ratio because leaves are flat.
• The atmospheric air is in direct contact with the air between the
spongy mesophyll due to the stomata.
Dicotyledonous plant
No need for a
specialised gaseous
exchange surface.
Spongy mesophyll cells have a large surface area
They are thin walled and have air spaces in between them
Stomata are close to the environment to allow the oxygen to enter the air spaces
Earthworm
• Earthworms do not have specialized respiratory organs like we do;
instead, they take in oxygen and expel carbon dioxide directly through
their skin. Oxygen diffuses through the earthworm's body surface and
diffuses inward to the network of capillaries lying just under the body
surface.
Insects
• Insects have air tubes called tracheae and tracheoles
throughout their body.
• The tubes are held open by hard rings of chitin. Insects
don't have a circulatory system, so the tracheoles must
reach every cell in the body as they rely on diffusion to
take in oxygen.
• At the end of each tracheole is a small amount of liquid
which allows gasses to dissolve and then diffuse into
the cells.
• The places where the tubes leave the body are called
spiracles, and these can open and close to control
water loss.
Bony fish
• Water can be actively pumped over the gills even when the fish is
stationary.
• The gill filaments provide a large surface area for gaseous exchange.
• The oxygen-carrying capacity of the blood is increased dramatically
due to the presence of the blood pigment, haemoglobin, present in
the erythrocytes.
Introduction to mammals:
• Air enters the lungs through the trachea,
which splits into two bronchi and then
smaller bronchioles.
• All of these tubes are held open by rings of
cartilage.
• On the bronchioles are alveoli, where gas
exchange takes place. These alveoli greatly
increase the surface area : volume ratio,
increasing the efficiency of gas exchange
and more particles can diffuse at once.
• The alveoli are surrounded by capillaries so
gases can diffuse between the air and blood.
Mammals have a circulatory system, so their
size isn't limited by their gas exchange
system.
Advantages
• Having an internal gas exchange system (lungs) helps to reduce water loss
and maintain a moist gas exchange surface. This allows mammals to inhabit
a greater variety of terrestrial habitats.
• The highly branched structure of the bronchial tree leads to many tiny
alveoli. The large number and small size of the alveoli gives the lungs a
large surface area to volume ratio. This allows mammals to grow to much
larger sizes without the limitations normally imposed by the associated
increase in the size and weight of the gas exchange system. The large
surface surface area of the lungs also helps to meet the high metabolic
demands of these larger, warm blooded animals.
• A transport system (blood vessels) reduces the distance dissolved gasses
have to diffuse. This also enables mammals to grow to larger sizes than
many other animal groups.
Disadvantages
• Does not work under water. Water is denser and more viscous and could not
easily be ventilated (forced in and out of the tracheal tubes).
• Air flow is tidal (in / out) and not all of the air can be forced out of the lungs.
Some oxygen poor air always remains and mixes with fresh air coming into the
lungs, slightly reducing the concentration gradient and making gas exchange less
efficient.
• The gas exchange surface is warm, moist and continuously ventilated, making it a
site of significant water loss (despite being internal). Humans exhale over a cup of
water each day. Most larger mammals rely on reservoirs of fresh water such as
rivers and lakes which may limit their range.
• The gas exchange surface is warm and moist making it prone to infection.
Respiratory illnesses such as cold and flu can also be easily transmitted when fine
droplets containing bacteria / viruses are coughed or sneezed into the air and
then breathed in by others.
Video Time
• Gas Exchange In Different Animals | Physiology | Biology | FuseSchool
(02:53)
• https://www.youtube.com/watch?v=LXGG-HgtJoI