Diet, enzymes, digestion (pg. 15-18)

• Digestive enzymes break down big molecules into smaller ones.
• Starch, proteins and fats are big, insoluble molecules. They can't pass through the walls of the digestive system.
• Sugars, amino acids, glycerol and fatty acids are smaller, soluble molecules. They can easily pass through the walls of the digestive system.
• Amylase converts starch into maltose. Then, maltase converts maltose into glucose.
• Proteases convert proteins into amino acids.
• Lipases convert lipids into glycerol and fatty acids.
• Bile neutralises the stomach acid and emulsifies fats.
• Bile is produced in the liver and stored in the gallbladder before it's released into the small intestine.
• The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile neutralises the acid and makes conditions alkaline, allowing for the enzymes to work better.
• Bile emulsifies fats: it breaks the fat down into tiny droplets. This gives a much bigger surface area of fat for the lipase enzyme to work on which makes digestion faster.
• Food is moved through the gut through peristalsis.
• There's muscular tissue throughout the whole alimentary canal.
• The muscular tissue in the alimentary canal's job is to squeeze boluses through your gut. Otherwise it would get clogged up with bits of old food.
• Peristalsis is waves of circular muscle contractions.
• Mouth.

  1. Salivary glands in the mouth produce amylase enzyme in the saliva.
  2. Teeth break down the food.
• Oesophagus.

  The muscular tube that connects the mouth and stomach.
• Stomach.

  1. It churns the food with its muscular walls.
  2. It produces the protease enzyme, pepsin.
  3. It produces hydrochloric acid for two reasons:

  • To kill bacteria.
  • To give the optimum pH for the protease enzyme to work (pH - 2).
• Liver.

  Where bile is produced.
• Gallbladder.

  Where bile is stored.
• Pancreas.

  Produces protease, amylase and lipase enzymes. It releases these into the small intestine.
• Small intestine.

  1. Produces protease, amylase and lipase enzymes.
  2. Where the nutrients are absorbed out of the alimentary canal into the body.
  3. Three parts: the duodenum, the jejunum and the ileum.
• Large intestine.

  1. Also called the colon.
  2. Where excess water is absorbed from the food.
• Rectum.

  1. The last part of the large intestine.
  2. Where the faeces (made up mainly of indigestible food) are stored before being excreted through the anus.
• Villi in the small intestine help with absorption.
• The walls of the small intestine are covered in millions and millions of tiny little projections called villi. Each cell on the surface of a villus also has its own microvilli. These give a large surface area for absorption.
• Villi have a single permeable layer of surface cells and a very good blood supply to assist quick absorption.
• Carbohydrates are found in pasta, rice, sugar. Their function is to provide energy.
• Lipids (fats and oils) are found in butter, oily fish. Their function is to provide energy, act as an energy stored and provide insulation.
• Proteins are found in meat and fish. They're needed fro growth and repair of tissue, and to provide energy in emergencies.
• Vitamin A is found in liver. Its function is to improve vision and keep your skin and hair healthy.
• Vitamin C is found in fruit (for example, oranges). It's needed to prevent scurvy.
• Vitamin D is found in eggs. It's needed for calcium absorption.
• Calcium (a mineral ion), is found in milk, cheese. It's needed to make bones and teeth.
• Iron (a mineral ion) is found in red meat. It's needed to make haemoglobin for healthy blood.
• Water is found in foods and drinks. Every bodily function requires water, so we need a constant supply to replace water lost through urinating, breathing and sweating.
• Dietary fibre is found in wholemeal bread, fruit. Its function is to aid the movement of food through the gut.
• The six essential nutrients: carbohydrates, lipids, proteins, vitamins, minerals and water.
• Energy requirements vary in different people depending on...

  1. Activity level.
  2. Age.
  3. Pregnancy.
• Calorimetry experiment:

  1. Choose a food that burns easily (something dry like pasta).
  2. Weigh the sample of food and then skewer it on a mounted needle.
  3. Add a set volume of water to a boiling tube .
  4. Measure the temperature of the water, then set fire to the food using a Bunsen Burner flame.
  5. Immediately hold the burning food under the boiling tube until it goes out. Then relight the food and hold it under the tube. Repeat this until the food won't catch fire again.
  6. Measure the temperature of the water again.
• energy in food = mass of water * temperature change of water * 4.2

  (The 4.2 in the formula is the amount of energy in joules needed to raise the temperature of 1g of water by 1ºC)