Edexcel A Level Biology B full syllabus summary notes for Year 12-13 students.
I am Tiffany who graduated from Wycombe Abbey School, UK in 2022. My typed notes has compressed two years of notes into a 127 pages long concise single file. Started in 2020, this document has been completed in 2022.
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Reducing sugars Reducing sugars except sucrose Not reducing sugars
e.g. glucose, e.g. maltose (glucose + glucose) Starch
galactose, lactose (glucose + Glycogen
fructose galactose) Cellulose
sucrose (glucose + fructose)
Draw -glucose
Draw -glucose
Draw pentose ribose (C5H10O5)
- Ribose (form RNA) and deoxyribose (form DNA) make nucleotides which form nucleic acid
Draw formation of maltose
Starch
- Mixture of two molecules: Amylose and amylopectin
Amylose Amylopectin
-glucose -glucose
1,4- glycosidic bond 1,4-glycosidic bond within chains
1,6-glycosidic bond between chains
Unbranched, helical molecule Shorter and branched molecule
Why can branched chain be broken down more rapidly?
More ends available for enzymes to work on, can be broken down more quickly
Why are glycogen and starch a good storage molecule?
- Made of many glucose hence can be broken down to release energy during respiration
- Insoluble and large hence won’t have osmotic effect
- Compact a lot of glucose can be packed inside this small space
- Large molecule hence cant diffuse
Glycogen
1
,Structure similar to amylopectin also branched
Cellulose
Why can cellulose perform a structural role? (4 marks)
glucose has to invert to be able to react, hence
- It is a polymer of beta glucose with 1,4 glycosidic bonds in between
1. The resultant molecule is straight, neither coiling nor branching.
2. The long molecules line up next to each other in parallel and form hydrogen bonds between them
3. arranged of microfibrils in parallel
4. Hence have a high tensile strength allowing it to be used as cell walls
Test
Starch: Iodine brown to blue black
Reducing sugar (including monosaccharides + maltose)
1. Heat with Benedict solution
2. Blue (solution) to green to yellow to brick red precipitate
( This is quantitative. The more sugar the darker the colour
Can be improved by filtering out the precipitate and measure its mass or measuring the colour of the
filtrate by colorimeter)
Non-reducing sugar
1. Heat with Benedicts (this is to prove no reducing sugar is present
2. With a new sample and boil with acid (this hydrolysis the glycosidic bonds)
3. Cool and neutralize with alkali
4. Heat with Benedicts solution (Blue to red)
The reducing sugar present must have come from a hydrolysed non reducing sugar
Biuret solution (protein)
From. Blue to lilac
1. Put protein solution in
2. Add drops of biuret solution
Emulsion (droplets of one liquid in test for oil
- fats dissolve in ethanol
- But ethanol is hydrophilic
- Why milk cant have a emulsion test? It is already cloudy before the test.
2
, Lipid
Lipids (C, H, O)
- Non polar and insoluble but can dissolve in organic solvents
How are triglycerides formed?
- Triglycerides are esters formed by condensation between 3 fatty acid molecules and one glycerol
molecule. (this kind of condensation is called esterification)
- The carboxyl group of fatty acid molecule reacts with the hydroxyl group of a glycerol molecule
Draw formation of triglyceride (an example of lipid)
Difference between saturated and unsaturated lipids.
- Saturated fats are made up of saturated fatty acids that only contains C-C single bonds (solid)
- Unsaturated fats are made up of unsaturated fatty acids that only contains C=C double bonds
Roles of Lipid
Energy storage
- Compact can store more (energy ) in a small space
- Insoluble hence won’t have osmotic effect
Waterproofing
- It is waterproofing as hydrocarbon tails of fatty acids are hydrophobic hence will repel water
Insulation
- As fat are poor conductor of heat Buoyancy to the aquatic mammals
- Lipid is less dense than water
Phospholipid
- Ester composed of one glycerol molecule, two fatty acids molecular and a polar phosphate group
- Polar group + glycerol molecule -> hydrophilic head
- Fatty acid chain –> hydrophobic tail
- If phospholipids submerged in water they form micelle
Extra:
Why different fatty acids have different melting temperature? (saturated fatty acids vs unsaturated fatty
acids)
- For unsaturated fatty acids there is presence of C=C double bonds
- Which produce a kink and prevent the fatty acids from lining up
- Fatty acids don’t pack closely together
- Weaker intermolecular forces between adjacent fatty acid
- Less energy is needed to separate the fatty acid molecules
3
, Proteins (C,H,O,N and sometimes S)
- Polymers of amino acids
- There are 20 different types of amino acids
General formula of protein:
NH2RCHCOOH
Draw a diagram of amino acid
What is the pH of amino acid when dissolves in water?
The amino group has basic properties and the carboxylic group is acidic and hence when dissolved in water
it becomes neutral.
How to form dipeptide?
By a condensation reaction between the amino group of one amino acid and the carboxylic group of another.
A peptide bond is formed and water molecule is remove.
Draw a diagram of formation of dipeptide
Polypeptide VS protein
A polypeptide is a linear sequence of amino acids joined together by peptide bonds.
Protein consists of one or more unbranched polypeptide chains coiled and folded into a 3D shape.
Primary structure
The number, type and sequence of the amino acids in a polypeptide chain.
Secondary structure
The formation of repeating structures called alpha-helixes and beta-pleated sheets within the polypeptide
which shape is maintained by hydrogen bonds between the NH and C=O groups of different animo acids in
the same chain.
Tertiary structure
Is the further bending and coiling of the polypeptide chain to form a 3D shape. This is caused by bonds
forming between the R groups of amino acid in the chain. The bonds are hydrogen, ionic ( between +ve and
-ve R groups) or disulfide bridges (between sulfur containing R groups of the amino acid cysteine). Also,
there is hydrophilic and hydrophobic interactions which is when amino acids with hydrophobic R groups
tend to group together in the middle of the molecule and hydrophilic ones on the outside.
Quaternary structure
When more than one polypeptide chain linked together by bonds between the R groups of the amino acids
from each chain.
Fibrous and globular proteins
Fibrous proteins
- Have little or no tertiary structure (mainly secondary structure)
- Made up of long, thin,straight parallel polypeptide chains
- Strong and insoluble and have structural roles
4
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