2.3: Carbohydrates &
Lipids
Carbohydrates
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EVERYTHING you know…
Investigating starch
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Complete experiment
HWK
Evaluate the method using the IB marking criteria.
Comparing the energy storage
of carbohydrates & lipids
Polysaccharides
Three examples, all formed from glucose.
Starch
Glycogen
Cellulose
Formed from alphaglucose.
Condensation between
C-1 and C-4.
Each alpha glucose is in
the same position.
Results in a curved
structure
Forms a helix, using
hydrogen bonds.
Formed from alphaglucose.
Condensation between
C-1 and C-4.
Very similar to starch, but
the chains form
branches, resulting in a
globules.
Formed from betaglucose.
Condensation between
carbon-1 and carbon-4.
Each beta glucose added
to the chain is 1800 to the
previous one.
Results in a straight
chain.
Form bundles, using
hydrogen bonds.
Storage in plants
Animals & some fungi,
stored in the liver &
muscles.
Very strong, plant cell
walls
Lipids
Triglycerides are formed from the condensation between three fatty
acids and one glycerol.
Triglycerides are present in adipose tissue (fat in humans) and oils in
sunflower seeds.
Fats are liquid at body temperature, solid at room temperature.
Oils are liquid at both temperatures.
See fig. 7, pg. 78 for diagram of condensation reaction.
The bond between an acid (fatty acid) and the OH- (glycerol) is an
ester.
Useful for energy storage. Energy can be released by aerobic
Energy storage
Lipids = long term storage
Carbohydrates = short term storage
Why?
1. Lipids release twice as much energy per gram
2. Lipids have secondary roles e.g. insulation, shock absorber
Glycogen is the short term energy store of
carbohydrate.
Glycogen can be rapidly broken down into glucose and transported in
the blood. Glucose can then be used for aerobic or anaerobic
respiration.
Fatty acids
Can be saturated, monounsaturated or even
polyunsaturated
Most fatty acids have between 14 – 20 carbon atoms.
See fig. 12, pg. 82 for a diagram showing the three forms
of fatty acids.
The two forms of unsaturated fatty
acids
Cis-fatty acids, hydrogen atoms on the
same side of the carbon atoms either
side of the double bond.
Trans-fatty acids, hydrogen atoms on
opposite sides of the carbon atoms
either side of the double bond.
Cis
Bend in the hydrocarbon means
cis-fatty acids cannot be ‘packed’
so easily  lower melting point.
Liquid at room temp. = oils
Trans
No bend, so can be tightly
packed together  high melting
point.
Solid at room temperature = fats.
Read Health risks of fats, pg. 83 - 85
Evaluate the evidence and the methods used to
obtain evidence for health-claims made about
lipids.
Complete data-based questions.