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Summary AQA Alevel year 12 notes ( topics 1-4)
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This document contains all content from topics 1-4 (content learned in year 12). It is colourful and contains many detailed images .
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AQAA-level biology
Year 12 AS
content
Topics 1-4
,Topic 1 –
biological
molecules
,Carbohydrates:
The general formula of a carbohydrate – (CH20)n
Carbohydrates are only made of carbon, oxygen and hydrogen (CHO)
Monosaccharides
Simple sugars that act as the monomers for larger carbohydrates
They are soluble and are quickly absorbed into the bloodstream
Glucose, galactose and fructose
They taste sweet
Alpha and beta glucose are structural isomers- they are di erent structures made from
the same building blocks
Alpha Glucose Beta Glucose
The hydroxide (OH) on carbon 1 points in The hydroxide (OH) on carbon 1 points in
the same direction (down) as the OH on the opposite direction as the OH on the
carbon 4. carbon 4 .
Disaccharides
Condensation reaction between 2 monosaccharides (OH on carbon 1 and 4)=
glycosidic bond (oxygen)+ water
Disaccharide Monosaccharide units
Maltose Alpha glucose+ alpha glucose
Sucrose Alpha glucose + fructose
Lactose Alpha glucose + galactose
Soluble
Hydrolysis of disaccharides forms the monosaccharides
Polysaccharides
A chain of alpha glucose forms starch in plants and glycogen in animals
Starch Glycogen
Polymer of alpha glucose Polymer of alpha glucose
Slightly branched Highly branched
Forms a helix Circular granules
Insoluble (doesn’t affect water Lots of ends of branches = higher
potential) surface area =more enzyme activity
Too large to diffuse through Too large to diffuse through
membrane membrane
Insoluble (doesn’t affect water
potential)
, Glycogen has a higher surface area so enzymes can work more e iciently to
have faster hydrolysis so glucose is readily available for respiration. This is
required to support animals faster metabolic rate.
Cellulose-
Polymer made of beta glucose monomers
Unbranched, perfectly straight
Every second beta glucose is flipped to allow the formation of a glycosidic bond
Microfibril- layers of cellulose chains which form hydrogen bonds between
The microfibrils weave together
The high number of hydrogen bonds give the cellulose a lot of strength
Biochemical tests for sugars and starch
Reducing sugars are monosaccharides (and some disaccharides) that can give away electrons
to substances that will accept them, meaning they can be oxidized, reducing something else in
the process (REDOX) .
Maltose is the only disaccharide that is a reducing sugar.
In the reducing sugars test, the sugar gives its electrons (reduces) benedict’s reagent. Non-
reducing sugars don’t have this ability.
Reducing sugars test Non-reducing sugars test Starch test
1. Take sample of liquid Acid hydrolysis- 1. Add iodine
food and place in a 1. If the original sample 2. Positive result will be brown
boiling tube remains blue, take a to blue black
2. Add an equal volume of fresh sample and add
benedicts reagent dilute HCl.
3. Heat tube in a hot water 2. Boil sample for 5
bath minutes in a water bath.
4. Positive result = color 3. Cool and slowly add
change from blue to alkali (sodium hydrogen
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