3.3 describe the tests for glucose and starch

Chemical test	Food	Procedure	Positive result
Iodine	Starch Found in: bread, pasta	Add a few drops of iodine to food This test works on solid food but for accuracy, crush solids in water.	Blue-black
Benedict’s	Glucose Found in naturally sweet foods Glucose is a reducing sugar; this food test involves reducing an alkaline solution of copper sulfate into copper oxide.	Add Benedict’s solution to food, put in water bath of around 70ºC. Solid foods should be crushed in water beforehand	Brick red
Biuret solution	Protein Found in: meat, fish, egg, milk Biuret solution potassium hydroxide + copper sulfate.	Add Biuret reagent to food Solid foods should be crushed in water beforehand	Light purple
Ethanol and water Emulsion	Lipids Found in oil, butter, margarine, avocado, salmon Fats are insoluble in water but dissolve in ethanol	Add ethanol to food, shake Then add water to food, shake For solid foods, filter after shaking.	Milky and cloudy

External links:

http://biology-igcse.weebly.com/-food-test-3---emulsion-ethanol-test-for-fats.html

3.2 describe the structure of carbohydrates, proteins and larger molecules made up from smaller basic units: starch and glycogen from simple sugars, proteins from amino acids, lipids from fatty acids and glycerol

~         Biological molecules: carbohydrates

-       Body’s main ‘fuel’ for supplying cells with energy

-       Starch is a large insoluble molecule. Starch is manufactured in the green leaves of plants from excess glucose produced during photosynthesis and serves the plant as a reserve food supply/ storage carbohydrate. Some plants that store glucose as starch: e.g. rice, barley, potato, wheat. Starch is made from a long chain of glucose molecules joined together. It is called a polymer of glucose. Monomer of starch: glucose. Starch is only found in plant tissues, but animal cells sometimes contain a very similar carbohydrate called glycogen, found in tissues where it acts as a store of energy.

-       Monosaccharaide: basic monomer units of carbohydrates. ‘Single’ sugars such as glucose and fructose are called monosaccharaides. 

-       Disaccharide: consist of 2 monosaccharaides joined by a glycosidic bond. Sucrose (table sugar) is made from 2 monosaccharaides (glucose and fructose) and is called a disaccharide. Lactose is also a disaccharide of glucose joined with a monosaccharaide galactose. Maltose is a disaccharide of glucose and glucose.

-       Polysaccharides: consist of thousands of monosaccharaides (monomers) linked by glycosidic bonds to form long chains. Polymers of monosaccharaides, e.g. starch and glycogen. 

~         Biological molecules: Lipids (fats and oils) 

-       Two types of molecule lipids are made of:glycerol and fatty acids

~         Biological molecules: proteins

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- The amino acids are linked together in long chains, usually folded up or twisted into spirals.

-       Monomers of proteins: Amino acids.

-       The shape of a protein is very important in allowing it to carry out its function. The order of amino acids and the number of amino acids in each protein decides the shape. As there are 20 different types of amino acids and the order and number of structures varies, there are thousands of different proteins in organisms.

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3.1 identify the chemical elements present in carbohydrates, proteins and lipids

Carbohydrates contain 3 elements: carbon, hydrogen and oxygen (CHO). The ratio of hydrogen atoms to oxygen atoms is always 2:1. e.g. sucrose: C₁₂ H₂₂ O₁₁

Lipids contain the same 3 elements as carbohydrates: carbon hydrogen and oxygen (CHO). However, the proportion of oxygen in a lipid is much lower.

Proteins contain 4 elements: carbon, hydrogen, oxygen and nitrogen (CHON). Proteins are made of chains of amino acids. There are about 20 different amino acids, two of these also contain sulphur.

External links:
http://alevelnotes.com/Biological-Molecules/38
http://lesiuk-biology.wikispaces.com/Unit+C+-+Biological+Molecules
http://ibguides.com/biology/notes/digestion