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Biology
The Need for Transport Systems in Larger Organisms
Why We Need Transport Systems:
All organisms need to exchange substances with their internal and external
environments, in order to take in needed molecules and to expel waste
...
Unlike unicellular organisms which can exchange substances
with their environment simply by diffusion, active transport and osmosis, all cells in a
multi-cellular organism do not necessarily have contact with the external environment
and therefore there is a need for transport systems, to supply all cells with the
substances they need, to keep working
...
However, not all organisms have such complex systems as we do
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We produce large amounts of waste which need to be removed – and
this is, therefore, all achieved by our complex transport systems
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In humans, the heart pumps
blood around the body through the blood vessels
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We have a double circulatory system: the blood is transported
from the heart to the lungs, to collect oxygen, then back to the heart – the systemic
circulation; the blood is then pumped to the rest of the body (before returning to the
heart for the cycle to repeat) - the pulmonary circulation
...
g
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We have three main types of blood vessels
– each adapted to suit their purpose
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These subdivide into microscopic
vessels called capillaries which carry blood through the organs, and then join up to
form veins
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Arteries: - Have a thick wall compared to the diameter of their lumen
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Arteries have a small lumen
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This
stretches the folded endothelial tissue and elastic walls
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Arterioles - are narrower than arteries
and have a higher proportion of smooth muscle fibres and a lower proportion of
elastic tissue
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Arterioles can control
the amount of blood flowing to a particular organ
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Substances are
transferred between the blood in the capillary and the cells
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Veins: - The pressure of the blood is
much lower in the veins than the arteries
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They allow blood to flow through and prevent the backflow of blood as they
have ‘watch-pocket’ valves
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The Cardiac Cycle: - This is the sequence of events that occurs during one heartbeat
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An electric pulse is passed
from the SA node (Sino-Atrial node) to the AV node (Atrio-Ventricular node) causing
the atria to contract (atrial systole)
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The electric pulse travels along the bundle of hiss to the
purkinje fibres which cause the ventricles to contract (ventricle systole) so the blood
passes from the left ventricle through the aortic valve into the aorta and to the rest of
the body and from the right ventricle through the pulmonoric valve to the lungs and
the cycle restarts
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Respiratory System:
The respiratory system is the set of organs that combine together in order to allow an
organism to breath
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We need oxygen for all the cells in our body to respire and keep working
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So, when we breathe
in the oxygen is passed into the blood and then around the body to each organ (every
cell) to keep them working/respiring
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Then, as we
breathe out, we expel the unwanted carbon dioxide
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The lungs are
connected to the trachea (windpipe) – a tube which is kept in shape by the rings of
cartilage
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These then split into bronchioles which branch into
smaller bronchioles
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This is
where gaseous exchange takes place
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Their
suitable shape gives them a large surface area to volume ratio therefore more
diffusion can take place
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g
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Diffusion is faster when there is a bigger difference of
concentrations between the two regions
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The opposite
is true for carbon dioxide
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Oxygen and carbon dioxide can, therefore, pass easily through the
membranes of the epithelial cells
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