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Food and Digestion (Digestive system (Process (Sphincter muscle relaxes,…
Food and Digestion
Digestive system
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Mouth, stomach and duodenum break down food using enzymes
–> either made in the gut wall or by glands eg. pancreas
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Large intestine absorbs water out of the remains and stores the waste products before they are removed
Enzymes:
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Lipases: break down, you guessed it, lipids
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Process
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Lump of food mixed with saliva, KA a bolus, passes along the oesophagus to the stomach
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Sphincter muscle relaxes, releasing food into the duodenum
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Several digestive enzymes – amylase, maltase, trypsin, peptidase, lipase
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Green liquid which emulsifies fat – increases the surface area of the lipid so enzymes can break it down more easily
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Absorption in the ileum
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Blood vessels join up to form a large blood vessel KA the hepatic portal vein, which leads to the liver
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Assimilation – soluble food molecules absorbed from the blood into cells of tissues and are used to build new parts of cells
Large intestine
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Waste material consists mainly of cellulose and other indigestible remains, water, dead and living bacteria and cells lost from gut lining
1st part: colon – absorbs most of the remaining water, leaving semi-solid waste KA faeces
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PRACTICAL: Food Tests
Test for Starch
- Place a bit of starch on a spotting tile
- Add a drop of yellow-brown iodine solution to the starch
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Test for Glucose
- Place a small spatula measure of glucose into a test tube
- Add a little water to the tube and shake to dissolve the glucose
- Add several drops of Benedict's solution (copper (II) sulfate) to the tube, enough to colour the mixture blue
- Prepare a water bath by half-filling a beaker with water and heating on a tripod and gauze
- Place test tube in beaker and allow water to boil
Result: clear blue solution gradually changes colour, forming a brick red precipitate of Copper (I) Oxide
*glucose is a reducing sugar, as are all other single sugars and some double sugars (eg. lactose). Table sugar (sucrose) will stay blue
Test for Protein
- Place powdered protein in test tube and add 2cm depth of water
- Shake tube to mix powder with water
- Add an equal volume of dilute potassium hydroxide solution and shake again
- Add two drops of 1% copper sulfate solution
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*AKA the 'biuret' test as sometimes the two solutions are mixed together, KA 'biuret solution'
Test for Lipid
- Use a pipette to place one drop of oil (lipid) in the bottom of a test tube
- Add 2cm depth of ethanol and shake the tube to dissolve the oil
- Pour solution into test tube that is 3/4 full with cold water
Result: white cloudy layer forms on the top of the water
–> ethanol dissolves in the water, leaving the lipid behind as a suspension of tiny droplets KA an emulsion
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Digestion
Digestion is the chemical and mechanical breakdown of food. It converts large soluble molecules into small soluble molecules, which can be absorbed into the blood
Chemical digestion: the breakdown of food by enzymes, eg. amylase
Mechanical digestion: the physical breakdown of food, eg. teeth cutting
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Energy from food
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Different energy needs
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Men have, on average, a larger body mass => more food
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