digestive system

• Properties of enzymes:

  • Is a protein molecule
  • Speeds up chemical reactions without getting used up itself (catalysts)
  • Are specific, will only catalyze one type of reaction
  • pH, concentration and temperature can effect reaction
  • long chain of amino acids
• Lock and key theory - to catalyze a reaction enzyme molecule must collide with its substrate, the place where the substrate fits is called the active site

  
• Effects of temperature and pH on enzymes:

  • Increase in temperature makes particles move faster so they are more likely to collide
  • High temperatures break chemical bonds and change the shape of the enzyme so the substrate no longer fits into its active site. (the enzyme is denatured and cannot work)
  • When the pH is too far or below the enzymes optimum pH it will denature.
• digestion:

  1 - the breakdown of large insoluble molecules into small soluble substances (small enough to pass through the wall of the small intestine into the blood)

  • carbohydrates (amylase) -> glucose
  • fats (lipase) -> fatty acids and glycerol
  • protein (protease) -> amino acids
• Food tests:

  • starch - iodine changes from brown to blue/black
  • glucose - benedicts solution and heat, cloudy, blue to green then orange and finally brick red
  • protein - biurets reagent, pale blue to purple
• errors in calorimetry:

  1. difficult to maintain distance from flame and food, varies heat loss to the environment
  2. difficult to minimize heat loss when transferring burning food to tube
  3. incomplete burning of crisp gives inaccurate measurements of mass burned

  bomb calorimeter improvements

  1. sample in sealed chamber, reduces heat loss to environment
  2. temperature change measured by surrounding chamber of water
  3. burned in pure oxygen to ensure complete combustion
• Fair testing during calorimetry:

  variables kept the same

  • volume of water
  • mass of food
  • distance of the flame from the boiling tube
• Stomach acid:

  • hydrochloric acid
  • kills harmful micro organisms
  • works best in acidic conditions, low pH

  Bile:

  • produced by liver and stored in gallbladder
  • passes down bile duct into small intestine
  • emulsifies fats - breaks down large fat globules into smaller ones to provide a larger surface area for lipase enzymes to work
  • neutralizes stomach acid on food so lipase enzymes work at optimum pH

  Peristalsis:

  • waves of rhythmic muscle contractions
  • pushes the food bolus down the oesphogus
• Absorption:

  the small intestine has millions of villi

  • lining one cell thick allows for easier diffusion
  • increase surface area (folded into finger like projections)
  • good blood supply (each has own capillary)
• Egestion:

  the end of the small intestine and digestion, faeces exit out the anus, the remaining materials consist of:

  • water
  • bacteria
  • cells from gut lining
  • indigestible substances
• 1. Mouth - saliva contains amylase, begins digestion of starch
  2. Oesophagus - pushes the food down by peristalsis
  3. stomach - digestion of protein begins
  4. pancreas - produces hormones and carbohydrase, protease and lipase
  5. liver - produces bile stored into gallbladder
  6. bile duct - transports bile from gall bladder to small intestine
  7. small intestine - duodenum first section, digestion completed, second part ileum absorbs digested food into bloodstream
  8. large intestine - absorbs water, minerals and vitamins
  9. rectum - faeces stored here
  10. anus - defecation, egestion
• breakdown of fats/lipids

  
• breakdown of proteins

  
• breakdown of starch/carbohydrates

  
• Modelling absorption/visking tubing

  1. visking tube is a selectively permeable membrane, has pores
  2. visking tube (small intestine) water (blood)
  3. diffusion allows small molecules through but not large
  4. starch too big but when broken down into glucose it can fit
  5. outside has to be washed to ensure no enzymes or starch on the outside

  
• balanced diet: adequate amount of each of the components required for healthy growth and activity, dependent on age, sex, metabolism, activity and environment
• • Carbohydrates (glucose stored as glycogen in liver)- source of energy
  • proteins - repair and growth of cells
  • lipids - storage, insulation and energy
  • minerals - lots of functions (iron needed to make hemoglobin), lack of can lead to deficiencies such as anemia
  • vitamins - various jobs, lack can cause deficiencies such as scurvy (vitamin C)
  • water - in cytoplasm and body fluids all chemicals in body must be dissolved in water
  • fibre - indigestible provides bulk
• too much sugar - type 2 diabetes, obesity, tooth decay

  too much fat - heart disease, obesity, circulatory disease (stroke)

  too much salt - high blood pressure,
• 1. pour 10 cm3 cold water into a boiling tube
  2. record the starting temperature of the water
  3. record the mass of the food sample
  4. heat the food in a Bunsen flame until it catches fire
  5. heat the water using the flame from the burning food
  6. record the final temperature of the water

  energy in food =

  mass of water (g) x 4.2 J/g x temperature increase 'C

  mass of food (g)