Summary Notes designed for the International Baccalaureate Diploma Programme. These notes are detailed yet concise, with all the information to achieve a 7 in IB Biology HL or SL. These notes were made using information from the IB syllabus, Oxford IB Diploma HL Biology Textbook, Bioninja and the B...
Unit 2.1
• Metabolism is the web of all enzyme-catalysed reactions within a cell.
• Condensation reactions are anabolic and release
water (synthesis of molecules)
• Hydrolysis reactions are catabolic and require water
(breakdown of molecules)
• There are two types of glucose, alpha and beta.
• Glucose is a white, crystalline structure that is
soluble.
• Structural isomers are things that have the same molecular formula but
can be drawn in different structures, such as alpha and beta glucose.
• People used to believe in the theory of vitalism, that organic molecules
could not be synthesised from inorganic molecules. The theory was
disproved when urea was synthesised artificially.
Unit 2.2
• Water molecules are polar and hydrogen bonds form between them, which explains its
properties.
• Only polar substances can dissolve in water, such as glucose and amino acids.
• Molecules can be hydrophilic or hydrophobic, meaning they either dissolve or don’t dissolve in
water.
• Properties of water include a high LHV (latent heat vaporisation),
high specific heat capacity, a good solvent and cohesion/
adhesion properties.
• Fats are hydrophobic. To transport them in the blood a
lipoprotein complex is formed, consisting of phospholipids
covering the fats, with their polar heads on the outside.
Unit 2.3
• The general formula for a carbohydrate is CH2O.
• A monosaccharide is a single unit of sugar, with just one carbon ring in its structure.
• Disaccharides consist of two monosaccharides joined together by a condensation reaction to
form a 1,4 glycosidic bond.
• Formation of disaccharides via condensation reaction include:
• glucose + glucose ⇌ maltose + water
• glucose + galactose ⇌ lactose + water
• glucose + fructose ⇌ sucrose + water
, • Polysaccharides are many monosaccharides bonded
together. They provide a slow release of energy and are
used as a long term energy storage. They are also used for
structure and strength.
• The three main polysaccharides are cellulose, starch and
glycogen.
• Cellulose is made by linking together beta glucose
molecules with 1,4 bonds.
• Forms a straight, unbranched chain as every other beta
molecule is flipped.
• Linked molecules form bundles called cellulose microfibrils, which have a high tensile
strength due to H bonds.
• Acts as the base for cell walls to stop cells from bursting.
• Starch is made by linking together amylose and amylopectin, polysaccharides made from alpha
glucose.
• Amylose is unbranched and forms a helix with 1,4 glycosidic bonds.
• Amylopectin is branched, meaning it can form 1,6
glycosidic bonds.
• Starch is useful for energy storage as glucose can easily be
removed and added.
• Glycogen is made by linking together alpha glucose molecules
with 1,4 and 1,6 bonds.
• Insoluble, branched chain.
• Stores sugars and energy.
• Lipids are made up of fatty acids and glycerol.
• A triglyceride consists of 1 glycerol and 3 fatty acids. They are joined by an ester bond via
condensation reaction.
• All fatty acids have a carboxyl group (OH-C=O)
• A phospholipid consists of two fatty acids, one glycerol and one phosphate group.
• There are two types of fat isomers:
• Cis-isomers are common in nature, and are loosely packed as both H’s are on the same side.
Triglycerides formed usually have low melting points.
• Trans-isomers are rare in nature, and are tightly packed as H’s are on opposite ends, forming
a bend in the fatty acid chain. They normally have high melting points.
Carbohydrates Lipids
17KJ of energy released per gram 38KJ of energy released per gram
Easily built up for storage Storage efficiency as they are hydrophobic, water is
not stored.
Easily broken down to release energy quickly Metabolic pathways to build up and break down are
more complex and therefore slower
Glycogen in animals, Starch in plants Converted into fatty acids and glycerol when energy
is required.
Both of these are converted into glucose when These are then converted into acetyl CoA
energy is required
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