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Summary AQA a level biology year 1 mark points for every topic £8.48
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Summary AQA a level biology year 1 mark points for every topic
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A document with every past mark point for every topic in all of AQA a level biology year 1. Made using mark schemes for all the exam papers from 2016 (new spec), 4 different textbooks, using resources from exam pro and assistance from examiners for the 2024 papers.

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  • April 17, 2024
  • 49
  • 2023/2024
  • Summary

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A level biology

Year 1

Carbohydrates

Monosaccharides:
 Glucose (C6H12O6)
 Galactose
 Fructose

Structures:




Made of carbon, hydrogen and oxygen.

Monosaccharides are monomers.

Monomer
 Single repeating unit that makes up a polymer.

Polymer
 Many monomers joined together to make a larger molecule.



Disaccharides:
 Glucose + glucose = maltose
 Glucose + galactose = lactose
 Glucose + fructose = sucrose

Disaccharide – 2 monosaccharides joined together via a condensation reaction, forming a glycosidic
bond.

Condensation reaction – a reaction that results in the loss of a small molecule, usually water.

Glycosidic bond – bond that holds monosaccharides together.

,Example:




Loss of water molecule (H2O).




Forms glycosidic bond on oxygen.

Hydrolysis is the reverse of condensation reactions, breaks the glycosidic bonds.

Hydrolysis – using water to split a larger molecule into its constituent monomers.


Polysaccharides:

Polysaccharides – many (more than 2) monosaccharides joined together via condensation
reactions.

Starch:

Carbohydrate store of plants

Made of:
 Amylose, long unbranched chains, 1-6 glycosidic bonds, coiled into spirals (80%)
 Amylopectin, long branched chains, 1-4 and 1-6 glycosidic bonds (20%)

Features of starch
 Insoluble, so it does not affect water potential.
 Coiled structure, makes molecule compact for storage.
 Polymer of alpha glucose, when hydrolysed it provides energy for respiration.
 Branched ends, can be hydrolysed faster.
 Large molecule, so can't diffuse out of the cell / cross cell membrane.

,Test for starch
 Add sample to test tube or spotting tile.
 Add 2-3 drops of iodine solution.
 If starch is present, there will be a colour change from brown to blue/black.

Glycogen:

Energy store in animals and bacteria.
Polysaccharide of alpha glucose.
Stored in the liver, and as granules in muscles as muscles are active so will need respiratory
substrates readily available.
Shorter, more branched chains than starch.

Features of glycogen:
 Insoluble, so it does not affect water potential.
 Large molecule, so can’t diffuse out of cells.
 Coiled structure, makes molecule compact for storage.
 Polymer of alpha glucose, when hydrolysed it provides energy for respiration.
 Highly branched / more highly branched than starch, (1-4 and 1-6 glycosidic bonds) makes it
easier to hydrolyse into alpha glucose monomers due to a larger surface area.

Fast hydrolysis of glycogen is important for animals as they are more active than plants so need to
do more respiration.

Metabolism – all the chemical reactions that take place inside of a cell.


Cellulose:

Major component of plant cell walls.

Features of cellulose
 Straight, long and unbranched chains of beta glucose.
 Every other beta glucose is rotated 180 degrees so hydroxyl groups are adjacent.
 Chains run parallel to each other, linked by hydrogen bonds to make microfibrils.
 Microfibrils link together to provide strength and rigidity for plant cell wall.

, Singular hydrogen bonds are weak forces, but many hydrogen bonds provide strength.


Chemical tests:

All monosaccharides as well as lactose and maltose are ‘reducing sugars’.
Sucrose is a ‘non reducing sugar’.

Test for reducing sugar:
 Add sample to a test tube.
 Add equal volume of Benedict’s reagent.
 Heat mixture gently in water bath for 5 minutes and observe colour change.
 Positive test result is blue to red.

Test results vary depending on concentration of reducing sugar.
Order of concentration from lowest to highest goes:
Blue, green, yellow, orange, red

Test for non-reducing sugar:
 Test for reducing sugar as normal, if no change is observed then your sample must contain a
non-reducing sugar.
 Add sample to new test tube.
 Add dilute hydrochloric acid (HCl) and heat mixture gently in water bath for 5 minutes, HCl
will hydrolyse glycosidic bonds in sucrose forming glucose and fructose.
 Add sodium hydrogen carbonate to neutralise the acid.
 Add Benedict’s reagent.
 Observe colour change.
 Positive result, blue to red.

Both tests can be made quantitive by using a colorimeter rather than observing colour change:
 Increases accuracy as it is not subjective.
 Standardises the test method.

Other potential method of testing is:
 Filter and dry precipitate formed.
 Weigh dry mass.


Lipids

Are a good source of energy.
Can be used as protection for vital organs.
Provide waterproofing.
Provide insulation.

Triglycerides:
 Made of 3 fatty acids and a glycerol.
 Hydrophobic tails.
 Formed via condensation reactions.
 Produces ester bonds which holds lipids together.

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