Topic 2 - Human Nutrition

• What are the 3 biological molecules

  carbohydrates, proteins, lipids
• Carbohydrates structure


  1. Monosaccharides:

  - simple sugar

  eg. glucose or fructose

  
  

  2. Disaccharide:

  - 2 monosaccharides join together

  eg. maltose is formed from 2 glucose and sucrose is formed from 1 glucose + 1 fructose

  
  

  3. Polysaccharide:

  - large and complex carbohydrates

  - formed by lots of monosaccharides in LONG CHAIN

  - insoluble -> used as storage molecules

  eg. starch, glycogen, cellulose
• Chemical elements in Carbohydrates

  carbon, hydrogen, oxygen
• Chemical elements in proteins

  carbon, hydrogen, oxygen, nitrogen
• Chemical elements in lipids (fats)


  carbon, hydrogen, oxygen
• Lipids (fats) structure


  - formed by one glycerol molecule chemically bonded to 3 fatty acid chains

  - lipids that are solid at room temp are FATS

  - lipids that are liquid at room temp are OILS
• Structure of protein


  - formed from long chains of amino acids

  - amino acids can be arranged in any order, resulting in many different combinations + protein types

  - diff order/shape of amino acids = different protein formed

  eg. Enzymes, haemoglobin
• PRACTICAL: Food Tests


  Identify the type of biological molecule a sample contains. You first need a food sample:

  - food broken using pestle and mortar

  - food into beaker + distilled water added

  - give mixture good stir to dissolve food

  - filter solution using funnel lined with filter paper to get rid of solid bits
• Benedicts solution test


  Test = glucose

  Positive test = brick red

  Practical:

  1. add solution to food sample in test tube

  2. heat in water bath for 5 mins
• Iodine test


  Test = starch

  Positive test = blue-black

  Practical:

  1. add drops to food sample

  2. shake gently
• Biurets solution test


  Test = protein

  Positive test = purple

  Practical:

  1. add drops to foods sample

  2. shake gently
• Ethanol test


  Test = lipids

  Positive test = cloudy/milky

  Practical:

  1. mix food sample with 4cm^3 ethanol and shake

  2. allow time for sample to dissolve in ethanol

  3. strain ethanol solution into equal volume of COLD distilled water
• Balanced diet


  1. Carbohydrates

  function: source of energy

  sources: bread, cereal, pasta, rice

  
  

  2. Proteins

  function: repair and growth

  sources: fish, meats, eggs, nuts

  
  

  3. Lipids / fats

  function: insulation and energy storage

  sources: butter, oil, nuts

  
  

  4. Minerals (2)

  function of calcium: strong teeth and bones (deficiency = osteoporosis)

  function of iron: make haemoglobin or blood (deficiency = anemia)

  sources of calcium: milk, cheese, eggs

  sources of iron: red meat, leafy green vegies

  
  

  5. Water

  function: chemical reactions to take place in cells

  sources: fruits, juices, water

  
  

  6. Vitamins

  f+s vit a: vision, skin + hair healthy -> liver, dairy, eggs

  f+s vit d: calcium absorption -> oily fish, dairy, sunlight

  f+s vit c: collagen protein (deficiency = scurvy) -> citrus fruit

  
  

  
  

  7. Dietary fibre

  function: builds roughage for intestines to push food through

  sources: wholemeal bread, fruit
• Understand how energy requirements vary


  AGE: amount of energy required increases as age increase towards adulthood for growth and muscle development. Then, development into elderly ages, energy requirements decrease.

  
  

  ACTIVITY LEVELS: amount of energy required increases as activity levels increase because more energy is needed for muscle movements/contractions and faster/more respiration during exercise.

  
  

  PREGNANCY: amount of energy required increases during pregnancy as the mother is now feeding and needs to support the growth for the developing feotus. Also the mother needs to carry around a large mass.
• Digestion definition


  Breakdown of large, insoluble molecules to simpler, smaller chemical compounds that can be absorbed into the blood stream + delivered to cells in the body
• Digestive enzymes


  break down big insoluble molecules into smaller ones

  
  

  Analyse, maltase, proteases, lipases
• Amylase converts starch into

  maltose
• maltASE converts maltose into

  glucose
• Proteases convert proteins into

  amino acids
• Lipases convert lipids into


  glycerol and fatty acids
• Alimentary Canal Structure (mouth, oesophagus, stomach)


  Mouth:

  Mechanical digestion: teeth chew food to increase surface to volume ratio. food shaped into bolus by tongue and lubricated in saliva.

  Chemical digestion: amylase enzyme breaks down starch into maltose

  
  

  Oesophagus:

  Muscular tube connecting the mouth to stomach. Food bolus enters. Wave like contractions push bolus down

  
  

  Stomach:

  Mechanical digestion: pummels food with muscular walls, churning action

  Chemical digestion: PROTEASE enzymes (pepsin) start to mechanically digest proteins + HYDROCHLORIC acid produced to kill bacteria and give optimum pH for protease enzymes to work
• Alimentary Canal Structure (small intestine, large intestine, pancreas)


  Small intestine:

  Duodenum:

  - where food coming out of stomach finishes being digested by enzymes

  - enzymes are added into the duodenum by the pancreas in the form of a liquid called pancreatic juice.

  - these include: amylase, trypsin, lipase

  - bile is also added at this stage

  Ileum:

  - by this stage, the food has broken down fully into small enough molecules to be absorbed into the blood.

  - the ileum is well ADAPTED for this process:

  - has a very large SA due to the villi and microvilli.

  Each villus contains a network of blood vessels and lacteal.

  - Lacteals help absorb fatty acids + glycerol to take away to rest of the body (lymph capillary).

  - the blood capillary network maintains the concentration (good blood supply)

  - Short diffusion distance --> villis wall is only 1 cell thick.

  - Wall made of cells NOT cell wall.

  
  

  Large intestine:

  - first part of the large intestine absorbs water (colon job)

  - faeces stored in rectum and removed through anus

  
  

  Pancreas:

  - releases enzymes into the intestines which breaks down carbohydrate (amylase), proteins (protease), lipids (lipase) in food

  - secretes enzymes in alkaline fluid into duodenum for digestion to raise pH of fluid coming out of stomach
• Alimentary Canal Structure (liver, gall bladder)

  Liver:

  - produces bile to emulsify fats (break large droplets into smaller = larger SA for enzyme lipase to work) --> MECHANICAL DIGESTION

  - bile also neutralises hydrochloric acid from stomach as enzymes in small intestine work best in alkaline conditions

  - amino acids that are not used are broken down here to produce urea

  
  

  Gall bladder:

  - stores bile before released into small intestine
• Peristalsis


  Food is moved through the gut via peristalsis.

  - controlled by circular and longitudinal muscles that contract to reduce diameter + length of section in oesophagus/small intestine

  - Wave like contractions squeeze bolus through gut
• Assimilation


  movement of digested food molecules into cells of body where they are used
• Egestion


  passing of not digested/absorbed food through anus in form of faeces