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Chapter 1.1 Transport around the body
Diffusion Movement of particles in a liquid or a gas down a concentration gradient from an area
where they are at a relatively high concentration to an area where they are at a relatively low
The surface area to volume The bigger the The distance from
ratio of an organism largely organism the smaller outside the organism
determines whether diffusion the surface area to to the inside gets
alone will allow substances to volume becomes. longer.
move in and out of the cell.
So it takes longer for There is less surface for
substances to diffuse substance to enter
Large organisms are made up of billions of cells. Substances need to travel long distances to reach
the cytoplasm of the cells. Nutrients and oxygen could reach the inner cells by diffusion, but not fast
enough to sustain the process of life.
Humans have a mass transport system consisting of the heart and circulatory system and the blood
flowing through it. Substances are transported in the flow of fluid, to individual cells through,
osmosis and active transport.
Each water molecule is polarised. This means it has a very slightly negative part (oxygen atom) and
very slightly positive parts (hydrogen atoms). The separation of charge is called a dipole and the tiny
charges are represented as and ¯. The slightly negative oxygen atom attracts the slightly positive
hydrogen atoms in a weak electrostatic attraction called a hydrogen bond. Although each hydrogen
bond is weak, there are lots of them, so water has high melting and boiling points because it takes
more energy to overcome the attractive forces of all the hydrogen bonds.
The water has a dipole so many ionic substances (E.g. sodium chloride) which are made up of
positive and negative ions, will dissolve in to it. The positive and negative ions separate and become
surrounded by water molecules which keep them in solution.
Polar molecules (compounds with covalent bonds but with the small charges on different parts of
the molecule) don't usually dissolve in organic solvents, but they will dissolve in water. However
water can also carry non-polar substances (chemicals that don't form ions).
Emulsions Formed by insoluble particles Tiny droplets of one liquid suspended in another liquid.
Suspensions Formed by insoluble particles A solid mixed with a liquid in which the particles will
separate out if the mixture is not constantly moved or stirred.
Blood is suspensions of cells and platelets in the plasma. Fats may be transported in the blood as
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Surface tension is a property of liquids when they behave as if the surface is covered by a thin elastic
skin. Water has a high surface tension because water molecules form hydrogen bonds, which tend to
pull them together.
The water molecule is amphoteric. It can act both as an acid (forms H ions and is a proton acceptor)
and as a base (forms OH¯ ions and is a proton acceptor).…read more
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Transportation of Oxygen
The haemoglobin molecules When blood enters the lungs, Oxygen moves into the cells
transport oxygen. Each the concentration of oxygen from the air in the lungs by
molecule can hold 4 in the red blood cells is low. diffusion.
molecules of oxygen.…read more
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Birds and mammals have a double circulation because they use up a lot of energy whilst maintaining
a constant body temperature.
The systemic circulation carries oxygenated blood from the heart to the cells of the body, and
carries deoxygenated blood back to the heart.
The pulmonary circulation carries deoxygenated blood from the heart to the lungs to be oxygenated
and carries the oxygenated blood back to the heart.
Arteries carry oxygenated blood away from the heart and towards the body.…read more