Chapter 3

• Water is an essential component of all body tissues
• 70% of our body weight is water
• Why water is essential

  • Is a solvent in which chemical reactions take place
  • Is essential for photosynthesis
  • Keeps cells turgid or firm
  • Helps in the transport of mineral salts in plants
  • Regulates body temperature
  • Helps to transport dissolved substances around the body
• Types of Nutrients

  • Carbohydrates
  • Fats
  • Proteins

  
• Carbohydrates


  Organic molecules made up of carbon, hydrogen and oxygen, with a hydrogen to oxygen ratio of 2:1
• Types of Carbohydrates

  • Single sugars
  • Double sugars
  • Complex carbohydrates

  
• Single Sugars

  Basic unit of carbohydrate, small enough to pass through cell membranes

  
• Common single sugars

  • glucose (C6H12O6)
  • fructose (C6H12O6)

  
• Double Sugars

  Formed when two single sugars are joined together
• Common double sugars

  • maltose
  • sucrose

  
• Maltose

  Consists of two glucose molecules bonded together

  
• Sucrose

  Consists of one glucose molecule and one fructose molecule bonded together

  
• Splitting double sugars

  Can be split into two single sugar molecules in the presence of an enzyme
• Reducing Sugars

  Glucose, fructose and maltose are examples of reducing sugars (because they can undergo redox reactions)

  
• Sucrose is NOT a reducing sugar
• Benedict's Test for reducing sugars

  1. Add 2 cm3 of Benedict's solution to 2 cm3 of food sample in a test-tube

  2. Shake the mixture

  3. Heat the contents in a boiling water bath for 2–3 minutes
• Benedict's Test Observations

  Green, yellow or red precipitate is formed if reducing sugar is present in trace, moderate or large amounts, respectively
• Complex Carbohydrates

  Made up of many molecules of single sugar joined together

  
• Examples of complex carbohydrates

  • starch
  • cellulose
  • glycogen

  
• Types of Complex Carbohydrates

  • Starch: Storage form of carbohydrates in plants
  • Cellulose: Makes up cell walls to protect plant cells, serves as dietary fibre
  • Glycogen: Storage form of carbohydrates in animals

  
• Double sugars

  • Insoluble in water, do not affect water potential of cells
  • Large molecules that cannot diffuse through cell membranes
  • Easily hydrolysed to glucose when needed
  • Made of molecules that have compact shapes, so they occupy lesser space

  
• Breakdown of starch

  1. Amylase will digest starch into maltose molecules

  2. Maltase will then digest maltose into glucose molecules

  
• Iodine Test for starch

  Add a few drops of iodine solution to a food sample
• Iodine Test Observation

  If starch is present, the iodine solution turned from yellow-brown to blue-black
• Functions of Carbohydrates


  • Act as an immediate source of energy for cell activities
  • To form supporting structures (e.g. cell wall)
  • For conversion into other organic compounds (e.g. amino acids and fats)
  • To form nucleic acids (e.g. DNA)
  • To synthesise lubricants
  • To synthesise nectar in flowers

  
• Fats


  Organic molecules made up of carbon, hydrogen and oxygen, containing much less oxygen in proportion to hydrogen
• Structure of a Fat Molecule

  Made up of glycerol and fatty acid chains
• Breakdown of Fats

  Fats can be broken down into fatty acids and glycerol by the enzyme lipase
• Sources of Fats

  • Butter
  • Corn oil
  • Olives, nuts and their oils
• Functions of Fats

  • Long-term source and store of energy
  • Act as an insulating material to prevent excessive heat loss
  • Solvent for fat soluble vitamins and some hormones
  • Form the main part of cell membranes
  • Help reduce water loss from skin surface
• Ethanol Test for Fats

  Add a few drops of ethanol to a food sample
• Fats can be broken down into simpler compounds by an enzyme called lipase
• Breakdown of Fats


  Fats are broken down into fatty acids and glycerol
• Sources of Fats


  • Butter
  • Corn oil
  • Olives, nuts and their oils
• Functions of Fats

  • Are a long-term source and store of energy
  • Act as an insulating material to prevent excessive heat loss
  • Are a solvent for fat soluble vitamins and some hormones
  • Form the main part of cell membranes
  • Help reduce water loss from skin surface
• How Can We Test for Fats?

  1. Add 2 cm3 of ethanol to 2 cm3 of food sample to a clean test-tube

  2. Shake the contents of the tube vigorously

  3. Add 2 cm3 of water into the test-tube and shake the mixture
• Expected Observation: A cloudy white emulsion is formed if fats are present
• Proteins are organic molecules made up of the elements: carbon, hydrogen, oxygen, nitrogen
• In certain cases, proteins may also contain sulfur
• Amino acids

  The smaller basic units that make up each protein molecule