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Edexcel Biology A: Topic 1 - Lifestyle,Health and Risk
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Topic 1: Lifestyle, Healthand Risk
By Dr Elilan Somaskantharajah
,Circulatory Systems
1.1:Understand why many animals have a heart and circulation (mass transport to
overcome limitations of diffusion in terms of meeting the requirements of organisms)
Mammals especially need a heart and circulatory system to function because mass
transport is needed to overcome the diffusion limitations to meet the requirements
of the organism. Substances need to be circulated throughout their body as large
organisms have a low surface area to volume ratio while smaller organisms have a
large surface area to volume ratio which means they don’t need a circulatory
system to meet the demands of their body
, Water
1.2: Understand the importance of water as a solvent in transport, including its dipole nature
Hydrogen bonds within water cause stability, so a large amount of energy is required to raise the temperature of
water. This means that oceans and lakes provide a stable environment in which organisms can live. This also
means that a large amount of heat is required to evaporate water, so it is very useful in cooling, for when animals
sweat to cool down.
Cohesion is the tendency of molecules within a substance to 'stick together'. Water has a high cohesion because
of hydrogen bonding. This is important as transport of water in the xylem in plants relies on water being pulled up.
Cohesion also gives the water a high surface tension
Water is less dense as a solid rather than a liquid, allowing it to float on water. This is due to the regular
arrangement of fixed bonds when frozen forming a semi crystalline structure. As a result, water is insulated
beneath ice, allowing organisms in the liquid water to survive
Water is a good solvent for polar molecules and for ionic substances. This means that is the perfect medium for
allowing metabolic reactions to take place and also as a transport vehicle
, Blood Vessels
6.3: Understand how the structures of blood vessels (capillaries, veins and arteries)
relate to their function
ARTERY - Pulmonary artery transports deoxygenated blood from the right ventricle to the
lungs. Systemic arteries transport oxygenated blood from left ventricle to body.
They have elastic fibres - as the artery increases in diameter due to high pressure, the pressure reduces
and the arteries give as the elastic fibres recoil inwards causing the pressure to fall and the artery
decreases in diameter, increasing the pressure again. This process produces a smoother blood flow
They have smooth layer of endothelial cells - to adapt to the high pressure of blood, friction needs to be
reduced in order for the blood to flow smoothly. This is why the endothelium is smooth
They have thick muscular walls - needs to withstand the high pressure that comes from the blood being
pumped out of the heart. As a result the lumen is quite narrow
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