2 - HUMAN NUTRITION 

Alimentary canal 

Mouth - 

- Salivary glands in the mouth produce amylase in saliva 

- Teeth break down food mechanically 

Oesophagus - 

- Muscular tube 

- Connects mouth and stomach 

Liver - 

- Produces bile 

Gall bladder - 

- Stores bile 

Stomach - 

- Pummels food with muscular walls 

- Produces pepsin (protease enzyme) 

- Produces HCl - kills bacteria, right pH for proteas enzyme (pH 2) 

Pancreas - 

- Produces protease, amylase, lipase 

- Releases enzymes into small intestine 

Small intestine -

- Produces protease, amylase, lipase 

- Nutrients absorbed into body 

- Contains villi 

Large intestine - 

- Excess water absorbed by blood 

Peristalsis - 

• Muscular tissue all the way down alimentary canal 
• Squeeze boluses through gut 
• Squeezing action - waves of circular muscle contractions 

Digestive process - 

1. Ingestion 

• Putting food in mouth 

2. Digestion 

• Break-down of large, insoluble molecules to small, soluble molecules 
• Mechanical - teeth and stomach muscles 
• Chemical - enzymes and bile 

3. Absorption 

• Process of moving molecules through the walls of the intestines into the blood 
• Digested food molecules absorbed in small intestine 
• Water mainly absorbed in large intestine 

4. Assimilation 

• Digested molecules have been absorbed, moved into body cells - become part of cells (assimilation) 
• eg: amino acids used by cells to make cellular proteins 

5. Egestion 

• Undigested materials form faeces 
• Egested 

Villi (small intestines) - 

• Small intestine - adapted for absorption of food 
• Very long - time to break down and absorb all food 
• Large surface area for absorption - covered in millions of villi 
• Each cell on surface of villi has microvilli - increase surface area further 
• Villi - single permeable layer of surface cells, very good blood supple for quick absorption 

2 - HUMAN NUTRITION 

Digestive enzymes 

• Break down big molecules into smaller ones 
• Starch, proteins and fats are too big to pass through walls of digestive system and insoluble 
• Sugars, amino acids, glycerol and fatty acids are smaller, soluble and can pass through walls of digestive system 

Amylase - starch to maltose 

Maltase - maltose to glucose 

Protease(s) - proteins to amino acids 

Lipase(s) - lipids to glycerol and fatty acids 

Bile - 

• Produced in liver, stored in gall bladder, released into small intestine 
• Neutralises stomach acid 
• Emulsifies fats 
• HCl in stomach makes pH too acidic for enzymes in small intestine - bile neutralises/makes conditions alkaline 
• Emulsifies fats - breaks fats into tiny droplets (bigger surface area for lipase to break down - speeds up digestion) 

2 - HUMAN NUTRITION 

Balanced diet 

• Gives all essential nutrients in right proportions 
• Carbohydrates, proteins, lipids, vitamins, minerals, water 
• Fibre

Carbohydrates - 

• Pasta, rice, sugar 
• Provide energy 

Lipids (fats and oils) - 

• Butter, oily fish 
• Provide energy 
• Act as energy store 
• Provide insulation 

Proteins - 

• Meat, fish 
• Growth and repair of tissue 
• Provides energy in emergencies 

Vitamins -

1 - Vitamin A 

• Liver 
• Improves vision 
• Keeps skin and hair healthy 

2 - Vitamin C  

• Oranges 
• Prevents scurvy 

3 - Vitamin D 

• Eggs 
• Calcium absorption 

Mineral ions - 

1 - Calcium 

• Milk, cheese 
• Makes bones and teeth 

2 - Iron 

• Red meat 
• Makes haemoglobin 
• Healthy blood 

Water - 

• Food, drink 
• Most bodily functions 
• Homeostasis 
• Replaces water lost through urinating, breathing and sweating etc 

Dietary fibre - 

• Wholemeal bread 
• Movement of food through gut 

Energy requirements - 

• Activity level - active people need more energy 
• Age - children/teenagers need more energy than older people - growth, generally more active 
• Pregnancy - pregnant women need more energy - provide energy baby needs for development 

2 - HUMAN NUTRITION 

Biological molecules 

Carbohydrates - 

• Made up of simple sugars 
• Contain carbon, hydrogen and oxygen 
• Starch and glycogen are large, complex carbohydrates - made up of many smaller units (eg: glucose or maltose molecules) joined in a long chain 

Proteins - 

• Made up of long chains of amino acids 
• Contain carbon, nitrogen, hydrogen and oxygen 

Lipids - 

• Fats and oils 
• Made up of fatty acids and glycerol 
• Contain carbon, hydrogen and oxygen 

Testing for glucose (Benedict's reagent) - 

• Add Benedict's reagent (blue) to a sample (an excess) 
• Heat - do not boil 
• Positive = coloured precipitate (blue-green-yellow-orange-brick red) 
• The higher the concentration, the further the colour change goes - can compare 

Testing for starch (iodine test) - 

• Add iodine solution (iodine dissolved in potassium iodide solution - brown/orange) 
• Present = blue/black 
• No starch = stays brown/orange