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AQA AS Biology MS Nadat 2009

Unit 1 Revision notes
Topic 2


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…

Page 2

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AQA AS Biology MS Nadat 2009

o prevents the concentration of glucose itself becoming so high that it exerts an
osmotic effect on the cell (lowers water potential so water diffuses in and cells
o or does not produce a diffusion gradient for glucose to diffuse out of the…

Page 3

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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.

Saturated fatty acids
Every carbon atom is bonded to as many hydrogen atoms as possible no more can
be added, hence `saturated (with…

Page 4

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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…

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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…

Page 6

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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.
· the substrate ­ which has a shape complimentary to the active site - fits into the…

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AQA AS Biology MS Nadat 2009

Rates of enzyme-catalysed reactions
Rate can be measured as amount of substrate broken down or amount of product produced
in a set time
Rate will initially be high when there is lots of substrate. But rate slows over time as amount
of substrate decreases…

Page 8

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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)

Fluid mosaic model of the structure of cell membranes

Methods of transport across membranes.

Diffusion: small lipid soluble molecules move from high to low…

Page 9

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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…

Page 10

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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…


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