Module 3 (Exchange and Transport) Revision Notes
How do Microorganisms Obtain Nutrients & Remove Waste?
by exchange via their surface
nutrients (e.g. glucose, oxygen) move in by diffusion via their surface
waste (e.g. carbon dioxide) move out by diffusion via their surface
Why are Microorganisms able to perform exchange via their surface?
have a large surface area to volume ratio
have a short diffusion distance
have low demand
Why can't Animals/Plants perform exchange via their surface?
have a small surface area to volume ratio
multicellular (large diffusion distance and high demand)
impermeable surface (prevent pathogens entering and reduce water loss)
therefore, require specialised Exchange & Transport systems
exchange system = increases rate of diffusion of nutrients in and wastes out
transport system = deliver nutrients and remove waste from all cells
Why do Fish have Specialised Gas Exchange Systems?
multicellular organism so has a small surface area to volume ratio, large diffusion
distance, high demand & body surface impermeable
therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they
require a specialised gas exchange system called Gills
Structure of Gills in Fish?
many gill filaments and gill lamellae = large surface area
gill lamellae have a thin wall (short diffusion distance) and are permeable
ventilation brings in pure water (high oxygen, low carbon dioxide) and circulation
brings in deoxygenated blood (low oxygen, high carbon dioxide), the water and blood
pass over in opposite directions (countercurrent flow), which maintains concentration
gradient all the way along the gill lamellae
Why do Insects have Specialised Gas Exchange Systems?
multicellular organism so has a small surface area to volume ratio, large diffusion
distance, high demand & body surface made of exoskeleton (impermeable barrier
to reduce water loss)
therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they
require a specialised gas exchange system called Tracheal System
Structure of Tracheal System in Insects?
, starts with openings on body surface called Spiracles
spiracles contain valves, open = gas exchange, closed = prevent water loss
spiracles connect to Trachea
trachea connect to Tracheoles
tracheoles connect directly to Respiring Cells (delivering oxygen, removing
carbon dioxide)
How does Gas Exchange occur in Tracheal System of Insects?
at rest = down a concentration gradient, oxygen moves in & carbon dioxide moves
out by simple diffusion
when active = by ventilation, air inhaled for mass flow of O2 in & air exhaled for
mass flow of CO2 out
Function of Lungs? site of gas exchange in mammals
(oxygen into blood – used in cells for respiration,
carbon dioxide out of the blood – toxic waste product of respiration)
What is Lungs made up of? Trachea, Bronchi, Bronchioles, Alveoli (+ capillaries)
Function of trachea, bronchi, bronchioles? transport of air and filter air, (bronchioles also
controls amount of air
reaching alveoli)
Structure of trachea/bronchi?
wall made of c-shaped cartilage
cartilage is strong so trachea/bronchi do not collapse
cartilage is c-shaped to give flexibility
lining made of goblet cells and ciliated epithelial cells
goblet cells make mucus, which traps pathogens/particles
ciliated epithelial cells have cilia, which pushes mucus up and out of lungs
Structure of bronchioles?
wall made of smooth muscle
smooth muscle contracts, lumen narrows, bronchiole constricts
(occurs when surrounded by noxious gases – reduces amount reaching alveoli)
lining made of goblet cells and ciliated epithelial cells
Adaptation of alveoli?
millions of tiny alveoli that are folded (large surface area)
thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
elastic tissue in wall (stretches when breathing in to increase surface area, recoils
when breathing out to push the air out)
ventilation maintains concentration gradient (high oxygen, low carbon dioxide)
Adaptation of capillaries?
