Summary Complete notes on AS/A level Biology B with the Pearson Edexcel exam board- Topics 1 to 3
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Edexcel A level Biology B Student Book 2 ActiveBook
This includes the perfect and complete summary notes from Topics 1 to 3 for the Biology B AS/A level exam using the Pearson Edexcel exam board. These notes are written following the Pearson Edexcel Specification, including all the necessary requirements according to the specification. They also in...
Complete notes on Topic 2 Biology- Pearson Edexcel
Complete notes on AS/A level Biology B Pearson Edexcel
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Topic 1: Biological Molecules
1.1 Carbohydrates
- General formula: Cx(H2O)n
- Made up of elements; Carbon, Hydrogen, Oxygen
- Made up of sugar units called saccharides
1. Monosaccharides; Monomers of one sugar unit
- General formula: (CH2O)n - (n= from 3 to 7)
Triose sugars - Three carbon atoms (n=3)
(C3H6O3) - Mitochondria- broken down from glucose into triose sugars during respiration
Pentose sugars - Five carbon atoms (n=5)
(C5H10O5) - Ribose and deoxyribose
- Making genetic material- nucleic acids (DNA and RNA)
Hexose sugars - Six carbon atoms (n=6)
(C6H12O6) - Highly soluble in water
- Isomers; same chemical formula but different structure
1. Glucose; main substrate for respiration (cardiac tissues)
- Carbon atom always bonded to oxygen atom in a stable closed chain
- Isomers; a-glucose and B-glucose
- BUT in B-glucose; H and OH swap in C1
2. Galactose; production of glycolipids and glycoproteins
- Not as soluble
3. Fructose; sweet and very soluble
- Source of energy in respiration
Condensation Reactions Hydrolysis reactions
- Monosaccharides join to form disaccharides and - Disaccharides and polysaccharides split
polysaccharides - Water molecule is added to break glycosidic bond
- Formation of glycosidic bond - covalent bond - Used to digest polysaccharides in the gut (starch,
- One molecule of
water +
+H2O
+ formed/released
glycogen, cellulose
+H2O per bond
2. Disaccharides; Two monosaccharides
- Form 1,4-glycosidic bond (C-O-C)
Disaccharide Source Monosaccharide
Sucrose Stored in plants (sugar cane) a-glucose + fructose
, 3. Polysaccharides; Chains of 11+ monosaccharide units
- Not sugars; do not contain the sweet taste
- Starch and Glycogen;
1. Form compact molecules; large numbers can be stored
2. Glycosidic bonds easily broken; rapid release of glucose for cellular respiration
3. Insoluble; do not cause osmotic water movements/change water potential of cell
4. Flexible
Starch - Plant storage of glucose
(plant) - Long chain of a-glucose units
- Mixture of two polysaccharides;
1. Amylose
- Helix shape
- Longer unbranched polymer of a-glucose molecules
- Joined by 1,4-glycosidic bonds
- Releases glucose slowly over a long period of time
2. Amylopectin
- Helix shape with branches
- Shorter branched polymer of a-glucose molecules
- Joined by 1,4 and branches with 1,6-glycosidic bonds
- Releases glucose rapidly- easily hydrolysed and digested
Glycogen - Animal storage of glucose
(animals - Branched chain of a-glucose units
and fungi) - Joined by 1,4 and branches with 1,6-glycosidic bonds
- Large surface area as it is very branched- contains many 1,6-glycosidic bonds
- Hydrolysed quickly as it forms many bonds- rapid release of energy
Cellulose - Plant structure- component of cell wall; gives strength and structural support
(plant) - Long, straight, unbranched chains of inverted B-glucose units
- Joined by inverted 1,4-glycosidic bonds
- Alternating unit inversion causes cross-linking; hydrogen bonds form between the partially positive
hydrogen atoms of the hydroxyl (-OH) group and the partially negatively oxygen atoms
- Hydrogen bonds hold the chain in strong, rigid threads; microfibrils- they increase tensile strength to
withstand osmotic pressure
- Insoluble
- Permeable
- Hard to digest
Test for reducing sugars; all monosaccharides and some disaccharides (maltose
and lactose)
- Benedict's solution; chemical test
- Contains copper(II) ions which are reduced to copper(I) ions when heated
- Change in colour; increasing concentration
(blue - green - yellow - orange - brick red)
Test for non reducing sugars (do not react with Benedict's solution); sucrose
- Heat sucrose with a few drops of hydrochloric acid to hydrolyse the
glycosidic bonds and allow it to cool
- Neutralise solution with sodium hydrogen carbonate- produces the
monosaccharide unit the sugar
- It will now give a positive Benedict's test
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