Biology AS AQA Unit 1 Notes

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AQA AS Biology MS Nadat 2009
Unit 1 Revision notes
Topic 2
Carbohydrates
Monosaccharides
Glucose, fructose and galactose are all monosaccharides
all have the molecular formula C6H12O6
have 6 carbon atoms, so are called hexose sugars
Carbon atoms joined together to form rings
atoms associated with hydroxyl groups ­ OH
hydroxyl groups and H atoms joined to the carbon atoms project above and below
the plane of the carbon atom ring
Examples of disaccharides
Maltose glucose+glucose Sucrose glucose+fructose Lactose glucose+galactose
Glycogen Storage form of glucose in animals found in liver and muscles
Starch Storage form of glucose in plants
Relationship between structure of starch/glycogen and their function.
These are large molecules made from lots of glucose monomers allowing storage of large
amounts of energy;
they can pack lots of glucose molecules into a small space for efficient storage so cells
can store large amounts of energy.
insoluble so will not diffuse out of the cell.
storing glucose as an insoluble polymer rather than as free glucose
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AQA AS Biology MS Nadat 2009
Types of fatty acid determine the type of triglyceride
Saturated fats contain saturated fatty acids
Unsaturated fats contain unsaturated fatty acids.…read more

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AQA AS Biology MS Nadat 2009
· There are 20 different types of amino acid commonly found in the proteins in living
organisms. It is only the R group which differs in each case
· Amino acids are linked together by condensation reactions
This process can be repeated many times with amino acids being added at either end of the
chain to produce polypetide chains which may contain thousands of amino acids.…read more

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AQA AS Biology MS Nadat 2009
· some of these bonds are weak, such as hydrogen bonds (can be broken by increased
vibrations if molecule is heated up or in acid conditions)
· others are very strong and help to maintain the tertiary structure, such as disulphide bridges
which form between the R groups of certain sulphur-containing amino acids.
· if any of these bonds are broken (e.g.…read more

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AQA AS Biology MS Nadat 2009
How enzymes work as catalysts.
Lock and key hypothesis
· enzyme and substrate are constantly moving around in solution and there will be random
collisions between them.…read more

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AQA AS Biology MS Nadat 2009
Structure of the cell membrane
Components of a cell membrane
Globular proteins
Carbohydrates chains attached to proteins (called glycoproteins)
Phospholipids
Fluid mosaic model of the structure of cell membranes
Methods of transport across membranes.
Diffusion: small lipid soluble molecules move from high to low concentration through
phospholipid bilayer (so not ions, glucose etc); passive, no energy needed, no carriers.…read more

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AQA AS Biology MS Nadat 2009
Topic 4
Gas exchange
Gas exchange is the transfer of gases (oxygen and carbon dioxide) by diffusion between the
organism and the environment.
It takes place simply by diffusion.
It occurs at a specific gas exchange surface (the ultimate gas exchange surface is a cell
membrane)
In mammals gas exchange takes place in the lungs
The efficiency of gas exchange depends on the surface area:volume ratio.…read more

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AQA AS Biology MS Nadat 2009
Topic 5
Why many animals have a heart and circulation.
Small organisms such as flatworms do not need a circulatory system because:
· they have a large surface area to volume ratio so sufficient oxygen can diffuse in across
the entire surface
· they are thin enough and small enough for sufficient materials to diffuse fast enough to
and from every cell
In large organisms, with larger bodies, diffusion is too slow to move materials ­ oxygen,
food etc.…read more

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