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Biology Essay : Importance of Diffusion in Organisms (25 marks)
Diffusion is the movement of particles from an area of high concentration to an area of low
concentration down the concentration gradient and it is a passive process so it doesn't
require any energy for it to occur
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The first is with action potentials
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Diffusion is also very important during
depolarization because this is where voltage gated sodium channels open and sodium ions
rapidly diffuse into the cell and significantly increases the membrane potential
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The next process which involves diffusion and is essential in living organisms is synaptic
transmission
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This allows a new action potential to form in the
postsynaptic neuron
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Synaptic transmission is useful for different processes such as gaseous exchange in
organisms
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This states that the higher the surface area, the steeper the concentration
gradient and the shorter diffusion distance gives the highest rate of Diffusion
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gradient
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Another organism which have effective gaseous exchange system are insects, this is where
oxygen enters the system via diffusion through the spiracles which are holes which can open
and shut and then it diffuses down the tracheal system
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Humans also have a very efficient gaseous exchange system as air enters through the nasal
passage or the mouth via diffusion then moves through the trachea, bronchi and the

bronchioles to the alveoli
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This is effective because there is a
high surface area due to there being millions of alveoli throughout the human body, there is a
short diffusion pathway as they are surrounded by capillaries which are 1 cell thick and
constant ventilation allows the concentration gradient to remain steep
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Inspiration is
where the external intercostal muscles contract, the diaphragm moves down and the ribcage
expands upwards and outwards so there's a larger volume for the incoming diffusion of
oxygen and there's far more pressure on the thoracic cavity so air is forced in via diffusion
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Linking to gaseous exchange, respiration is another process in organisms that is heavily
related to diffusion
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Linking these stages to diffusion is that there is Internal
respiration - this is the movement in the internal tissues between cells and capillaries, and
External respiration - when gas is exchanged between the alveoli and lung capillaries
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Alveoli are perfused by capillaries
so the diffusion of oxygen and carbon dioxide can take place
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Photosynthesis consists of 2 main stages: the light
dependent stages and the light independent stage; light dependent - this is where light is
absorbed by the chlorophyll molecules causes photo ionisation and NADPH and ATP is
produced
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Sticking on the topic of plants another process linked to diffusion is transpiration and this is
the evaporation of water from the leaves through the stomata where it diffuses into the
environment
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This
ensures the plant recieves the water needed or the cella will shrink and shrivel causing cell
death
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The phloem is
involved in Translocation and this is the process involved to move the nutrients by the mass
flow hypothesis, at the source this is where the sugars made pass through the companion
cells by diffusion down their concentration gradient into the sieve tube elements
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Moving away from plants, in humans and animals mass transport is linked to diffusion with
haemoglobin, this is where oxygen must diffuse from the alveoli to the red blood cells where
it binds to the haemoglobin to form oxyhaemoglobin and this has many uses for the body
such as being able to readily associate with oxygen at the surface where gas exchange to
take place and readily dissociate from oxygen at the tissues requiring it
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gradient due to the increased amounts
of solutes such as urea and CO2
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