Brown's GCSE/IGCSE/O Level KS4 science-CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
12. Natural Molecules - carbohydrates - sugars - starch
What happens when we cook
potatoes? This page describes the
classification and molecular structure of carbohydrates e.g. sugars like
monosaccharides e.g. pentoses like ribose and hexoses like glucose and fructose,
disaccharides like sucrose, maltose and lactose and polysaccharides like
starch, glycogen and cellulose. Carbohydrates are important sources of energy
for many living organisms and their formation in plants via photosynthesis
is the basis of many food chains. Why can we digest starch? Why can't we digest
Index of KS4 Science GCSE/IGCSE
Chemistry Oil & Organic Chemistry Pages: 1.
Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3.
ALKANES - saturated hydrocarbons and combustion : 4.
Pollution, carbon monoxide, nitrogen oxides, what
makes a good fuel?, climate change-global warming :
5. Alkenes - unsaturated hydrocarbons :
6. Cracking - a problem of supply and demand, other products :
7. Polymers, plastics, uses and problems :
8. Introduction to Organic Chemistry - Why so many series of
organic compounds? : 9. Alcohols - Ethanol
- properties, reactions, biofuels :
10. Carboxylic acids and esters : 11. Addition
polymers and condensation polymers :
12. Natural Molecules - carbohydrates - sugars
- starch : 13. Amino acids, proteins,
enzymes & chromatography : 14. Oils, fats,
margarine and soaps :
15. Vitamins, drugs-analgesic medicines & food
additives and aspects of cooking chemistry! : 16. Ozone, CFC's and free
radicals : 17. Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice and Gap-Fill Quizzes:
m/c QUIZ on Oil Products (GCSE/IGCSE easier-foundation-level)
m/c QUIZ on Oil Products (GCSE/IGCSE harder-higher-level) :
IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry
3 Easy linked GCSE/IGCSE Oil Products word-fill worksheets
Naturally Occurring Molecules from plants
Molecules like glucose ==>
Polymers = Macromolecules like starch
Carbohydrates (this page),
Oils-Fats are the
main nutrient constituents of food.
occurring molecules are based on the elements carbon, oxygen and
hydrogen, together with smaller proportions of nitrogen, phosphorus,
sulfur (sulphur) and sometimes metal ions like iron (in the haemoglobin
molecule) and magnesium (in the chlorophyll molecule).
important sources of energy for many living organisms and their
formation in plants via photosynthesis is the basis of many food chains.
Initially this is
formed as glucose, but this is converted to glycogen and
starch for 'storage'.
carbon dioxide +
water + sunlight energy ==> glucose + oxygen
+ 6H2O ==> C6H12O6
are a whole series naturally occurring molecules based on the elements
carbon, hydrogen and oxygen.
- They are an important source of
chemical energy in our diet.
- e.g. the respiration reaction
- Carbohydrates like glucose and fructose are
used as sweeteners in food as well as sweets themselves.
- Historically the name 'carbohydrate' comes
from the fact that all their formulae seemed to be based on Cx(H2O)y
(see key above) BUT this is not the way to think of their formula.
- They range from relatively small molecules
called monosaccharide (means one basic unit), or disaccharide
(two basic units combined) to very large natural polymers or
macromolecules called polysaccharides (many units combined). A
summary of them is shown in the key diagram above along with some familiar
names from biology.
is one of the simpler sugar molecules (a monosaccharide). The structural formula is
shown on the left and you should be able to see that there are 4 bonds
to each carbon, 2 to each oxygen and just 1 bond to each hydrogen atom.
The right-hand 'shorthand' skeletal formula version uses short
straight lines to represent bonds. Most H's and their bonds are not
shown, and at AS-A2 level it is assumed you can interpret these
structures 'back to' a full structure!, but they are handy for
describing large 'biochemical' molecules (see polysaccharide below)
is a disaccharide
made from combining two monosaccharide molecules, glucose and
fructose by the elimination of a water.
- On hydrolysis sucrose
reforms the glucose and fructose.
<=> C12H22O12 + H2O
- The formation of complex carbohydrates:
- These are made of smaller carbon,
hydrogen and oxygen based molecules combining together e.g. the
polysaccharides starch and
cellulose are formed from glucose, molecular formula C6H12O6.
- Their formation can be described
in terms of a
large number of sugar units joined together by condensation polymerisation
- e.g. the 'box' diagram below shows 4 units of a natural carbohydrate polymer
- Note: Condensation polymerisation means
the joining together of many small 'monomer' molecules by eliminating an
even smaller molecule between them to form the linkage.
- e.g. HO-XXXXX-OH
+ HO-XXXXX-O-XXXXX-OH + H2O
- n C6H12O6 ==>
+ nH2O (where
n is a very large number to form the natural polymer)
- The XXXXX or the [rectangles] below, represent the rest of the carbon chains in each unit (more detail
in the 3rd diagram below).
many H2O etc.
This diagram of starch
or cellulose is in 'skeletal formula'
style and both are polymers of glucose - can you see the connection
between each 'unit' and the structure of glucose
The resulting natural polymer is
called a polysaccharide.
Acid hydrolysis of complex
carbohydrates (e.g.. starch) gives simple sugars.
The hydrolysis products
from polysaccharides can be
paper chromatography as in
the case of amino acids.
We can digest long molecules
like starch, though they have to be broken down by enzyme action before the
smaller molecules like glucose can be used in respiration.
However, we cannot digest
cellulose because we don't have the enzymes to effect this process.
What happens when potatoes are
Potatoes are a good source
of carbohydrates, hence a good source of energy for the body.
Raw potato is not easily
digested but cooking partially breaks the structure of potato down so
that we can digest it AND cooking also improves the texture and taste of
the potato to make it more palatable to eat.
In the cooking process the
plant cell walls of cellulose are softened and this allows hot water to
penetrate the cells.
Further cooking causes the
starch granules to swell and gelatinize as they absorb hot water.
This eventually causes the
cells to separate producing the soft texture of well-cooked digestible
Mash with milk, butter and
salt to suit taste! Cheap and yummy!
Multiple Choice Quizzes and Worksheets
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry
3 linked easy Oil Products gap-fill quiz worksheets
ALSO gap-fill ('word-fill') exercises
originally written for ...
... AQA GCSE Science
Useful products from
crude oil AND
... OCR 21st C GCSE Science
Worksheet gap-fill C1.1c Air
pollutants etc ...
... Edexcel 360 GCSE Science
Crude Oil and its Fractional distillation
... each set are interlinked,
so clicking on one of the above leads to a sequence of several quizzes
Level Organic Chemistry revision notes
Revise KS4 Science GCSE/IGCSE/O level
Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel
GCSE Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science WJEC/CBAC
GCSE science-chemistry CCEA/CEA GCSE science-chemistry
(and courses equal to US grades 8, 9, 10)
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