Summary AQA Biology Unit 1: Biological molecules full notes
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Course
Unit 1 - Biological molecules
Institution
AQA
Book
AQA Biology A Level Student Book
full notes hitting all areas of specification for unit 1 of AQA A Level biology
consisting from carbohydrates to inorganic ions
with diagrams and definitions
highlighted key information
Monomers and polymers
Monomers are the smaller units from which polymers can be made from, through a
condensation reaction where a polymer and water molecule are products.
Carbohydrates
Carbohydrates consist only of carbon oxygen and hydrogen.
Monosaccharides are single carbohydrate units.
Glucose - which has 2 isomers being alpha glucose and beta
glucose,
Galactose and fructose
They can be tested for using benedict's reagent:
1. Add liquid food sample to test tube
2. Add equal volume benedicts
3. Heat in gently boiling water bath for 5 minutes
4. Solution turns blue to orange brown if reducing sugar
present
Disaccharides are formed by a condensation reaction between two monosaccharide units-
forming a glycosidic bond
Most disaccharides and polysaccharides are non-reducing sugars:
1. Add liquid food sample to test tube
2. Add equal volume benedicts
3. Heat in gently boiling water bath for 5 minutes
4. If colour doesn't change, no reducing sugar present
5. Add HCl to some of food sample
6. Heat in gently boiling water bath for 5 minutes
7. Add NaCO3 to neutralise solution and test with universal indicator
8. Add equal volume benedicts
9. Heat in gently boiling water bath for 5 minutes
10. Solution turns blue to orange brown if reducing sugar present
Polysaccharides are polymers
Starch
- Found in plants in the forms of small grains
- Forms an important component of food and is the major energy source in most diets
- Made up of alpha-glucose monosaccharides linked by glycosidic bonds
- Can be branched and unbranched
- Unbranched chains are wound into a tight coil that makes the molecule very compact
properties
➔ Insoluble = does not affect water potential, water isn't drawn into cells by osmosis
➔ Large + insoluble = does not diffuse out of cells
1
, ➔ Compact = a lot can be stored in a tight space
➔ When hydrolysed it forms a-glucose = easily transported and readily used by
respiration
➔ Branched form has many ends = can be acted on by enzymes simultaneously,
glucose monomers are released very rapidly
Test for starch
1. Add sample to test tube
2. Add iodine solution and shake
3. Blue black shows starch is present
Glycogen
- Found in animals + bacteria
- Shorter chains + more branched than starch
- Major carbohydrate store of animals
- Stored as small granules in liver and muscles
Properties
➔ Insoluble = does not draw water into cells via osmosis
➔ Insoluble = does not diffuse out of cells
➔ Compact = lots can be stored in small space
➔ Highly branched = acted on simultaneously by enzymes >>(more branched than
starch) animals have a higher metabolic and therefore respiratory rate than plants
because they are more active
Cellulose
- Made up of beta-glucose
- Straight unbranched chains which allow hydrogen bonds to form cross-linkages
between adjacent chains
- Cellulose molecules are grouped to form microfibrils which are arranged parallel in
groups to form fibrils
Properties
➔ B-glucose = long straight unbranched chains
➔ Long unbranched chains = form hydrogen crosslinks to add collective strength
➔ Microfibrils = grouped in fibres for more strength
➔
= maximising surface area for photosynthesis
Lipids
Roles of lipids
- Cell surface membrane
- Source of energy = provides more than twice
- Waterproofing = lipids are insoluble in water therefore can be used by insects as a
waxy cuticle and by mammals as an oily secretion
- Insulation = slow conductors of heat when stored. Also
act as electrical insulators in the myelin sheath
- Protection
Triglycerides
Triglycerides are lipids made of one molecule of glycerol and
2
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