Digestion

• The digestive system is an example of an organ system in which several organs work together to digest and absorb food
• Mechanical digestion: chewing; peristalsis; churning of food which breaks down food into smaller pieces so there is a bigger surface area for enzymes to carry out chemical digestion
• Chemical digestion: Breaking down large, insoluble molecules into smaller soluble ones that can be easily absorbed into the blood
• Chemical digestion uses enzymes, carbohydrases, protease and lipases
• The primary digestive system is one long tube from the mouth to the anus
• The secondary digestive system is not part of the tube but can secrete things into the tube
• The mouth:

  • Contains teeth and salivary glands
  • The teeth break food into smaller pieces so they are easier to swallow
  • Saliva (which contains amylase) is secreted by salivary glands

  The reactant to product is:

  (amylase) carbohydrase -> glucose
• The stomach:

  • Churns food
  • Has HCL which has a low pH and kills any pathogens
  • Secretes protease

  The reactant to product is:

  (protease) protein -> amino acids
• The small intestine:

  • Where a lot of the breakdown of large molecules occurs - then absorbs these molecules into the bloodstream
  • Has a large surface area due to million of villi
  • protease, carbohydrase and lipase produced here

  The reactant to product:

  (protease) protein -> amino acids

  (amylase/carbohydrase) -> carbohydrates -> glucose

  (lipase) fats -> fatty acids + glycerol
• The pancreas:

  • Secondary digestive organ
  • Secretes protease, lipase and carbohydrase

  The reactant to product:

  • protein -> amino acids
  • carbohydrates -> glucose
  • fats -> fatty acids + glycerol
• Liver and bile:

  • Produces bile (turns fat from large globules to small droplets to increase their surface area)
  • Produced bile (which is an emulsifier and alkaline)
  • Bile is not an enzyme
  • Has an area for lipase to digest and provides an optimum pH for lipase to work

  reactant to product:

  • big fat globules -> little fat droplets
• The large intestine absorbs water
• Enzyme: Protease

  Reaction: protein -> amino acids
• Enzyme: Carbohydrase/amylase

  Reaction: carbohydrates -> glucose
• Enzyme: lipase

  Reaction: fats (lipids) -> fatty acid + glycerol
• Bile (NOT AN ENZYME) Emulsifies fats
• Nutrient we are testing for: Protein

  Reagent: Biuret test

  Negative test: Blue

  Positive: Purple
• Nutrient we are testing for: Sugar

  Reagent: Benedict's solution + heat

  Negative test: Blue

  Positive: (From least to most sugar): green, yellow, orange, brick red
• Nutrient we are testing for: Starch

  Reagent: Iodine

  Negative test: Orange

  Positive: Blue black
• Nutrient we are testing for: Starch

  Reagent: Ethanol, shaken THEN water

  Negative test: Transparent

  Positive: Emulsion
• The secondary digestive system

  Not part of the tube but can secrete things into the tube

  • Liver, gall bladder, pancreas
• The primary digestive system

  One long tube from mouth to anus

  • Mouth > oesophagus> stomach> small

  intestine > large intestine > rectum > anus
• The emulsification of fats

  Fats form big globules in water. Our body is full of water. This means that they have a very small surface area, which makes digestion of lipids by the enzyme lipase very slow.

  To try and conquer this problem bile turns the fat into small droplets (emulsification). These have a much bigger surface area so the lipase works faster
• Aerobic respiration takes place in the mitochondria of cells
• Aerobic respiration releases energy, so it is an EXOTHERMIC reaction.
• Organisms need energy for:

  • chemical reactions to build larger molecules

  • movement (muscle contraction)

  • keeping warm (mammals & birds)

  • active transport.
• Oxygen and glucose are needed for aerobic respiration
• The equation for AEROBIC respiration is:

  glucose + oxygen -> carbon dioxide + water

  C6H12O6 + 6O2 -> 6CO2 + 6H2O
• If insufficient oxygen is supplied anaerobic respiration takes place in muscles.
• The incomplete oxidation of glucose causes a build up of lactic acid and

  creates an oxygen debt.

  During long periods of vigorous activity muscles become fatigued and stop contracting efficiently.
• Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
• Anaerobic respiration in muscles is represented by the equation: glucose -> lactic acid
• Anaerobic respiration in plant and yeast cells is represented by the equation:

  glucose -> ethanol + carbon dioxide
• Anaerobic respiration takes place in the cytoplasm of cells
• Anaerobic respiration releases a little bit of energy
• We start to breath faster/deeper & our heart begins to beat faster/stronger to try to provide more oxygen to muscles, but it takes time for the uptake of oxygen to increase, so don’t have enough oxygen & we respire anaerobically as well & produce lactic acid.
• Metabolism - ALL the chemical reactions in our body
• There are 2 types of metabolic reactions – break down & synthesis
• Which type of reactions USE energy?

  ● Synthesis

  How would we describe this type of reaction, because it takes in energy?

  ● Endothermic
• Which type of reactions RELEASE energy?

  ● Breaking down

  How would we describe this type of reaction?

  ● Exothermic