animal organisation digestion

• Carbohydrates


  Food belonging to the food group consisting of sugars, starch and cellulose. Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess. In plants, carbohydrates are important for photosynthesis.
• Proteins


  Organic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair.
• Lipids


  Fat or oils, composed of fatty acids and glycerol. (or fats) are major nutrients that we need in large quantities. We get these by eating them. They are broken down first and then reassembled into our own carbohydrates, proteins and lipids.
• Most of the molecules in food are too large to pass through the absorbing surface of the gut wall
• The carbohydrates, proteins and lipids are reassembled in the form required, rather than other animal or plant versions
• Nutrients


  • Carbohydrates
  • Proteins
  • Lipids
• Carbohydrates


  Source of energy, glucose is the main respiratory substrate
• Major sources of carbohydrates

  • Starch: potatoes, rice and wheat products, bread, cereals and pasta
  • Sugars: fruit, smoothies, fizzy drinks, chocolate and sweets
• Proteins


  Growth and repair
• Major sources of proteins

  • Meat, eggs, cheese, beans, nuts and seeds
• Lipids


  Energy, make up part of cell membranes so essential for normal growth
• Major sources of lipids


  • Butter and margarine, meat and processed meat, plant oils, oily fish, nuts and seeds
• Carbohydrates in our diet

  • Sugars
  • Starches
• Glucose molecule


  Small enough to be absorbed directly through the walls of the digestive system
• Starch


  Polymer of glucose, must be broken down into glucose molecules as it is too large to pass through the gut
• Cellulose


  Made up of glucose molecules, makes up plant cell walls, fundamental part of our diet, cannot be broken down by the digestive system, so is egested from the gut
• What happens to glucose molecules once absorbed by the body


  1. Transported to cells

  2. Used for respiration

  3. Reassembled into the storage form of carbohydrate in animals - glycogen
• Plant metabolism


  Glucose produced by photosynthesis is converted into starch for storage, and cellulose, for cell wall synthesis
• In humans and animals glucose is stored in glycogen, it is not converted into starch
• Proteins


  Made up of amino acids, big molecules that are too large to pass through the gut wall, must first be broken down into amino acids
• What happens to amino acids once inside the body

  1. Reassembled into the proteins the individual requires - the process of protein synthesis

  2. Excess amino acids are broken down in the liver
• Lipids


  Esters of fatty acids and glycerol, lipid molecules are too large to pass through the gut wall and must be digested first
• Lipids


  • In a lipid, there may be 1, 2 or 3 fatty acids combined with glycerol, fatty acids 1, 2 and 3 may be the same, or different
• What happens to lipids in the body's cells

  They are reassembled into the lipids the cell needs, for instance, for the cell membranes
• Qualitative tests for foods


  Tests that can be used to detect the presence of food chemicals, but not how much is present
• Test for sugars


  1. Benedict's test

  2. Heat in a water bath

  3. Observe colour change (green, yellow, orange, red or brown)
• Reducing sugars


  Sugars that will react with Benedict's solution on heating for a few minutes (e.g. glucose)
• Reducing sugars with Benedict's solution


  • Give a red-brown precipitate
  • Precipitate takes a while to settle, more likely to see a red or brown colour
  • If little glucose, final colour may be green or yellow, or orange if a little more
• Wear safety goggles for Benedict's test
• Benedict's solution is an irritant
• Avoid contact with skin and eyes for Benedict's test
• Test for starch


  1. Add iodine solution

  2. Foods containing starch will turn blue-black
• Iodine test can also be used with a microscope to stain starch grains in plant cells
• Wear safety goggles for iodine test
• Iodine solution is an irritant
• Avoid contact with skin and eyes for iodine test
• Test for proteins


  1. Biuret test

  2. Add 1 cm3 biuret solution A to food solution

  3. Mix

  4. Add 1 cm3 biuret solution B and shake
• Wear safety goggles for biuret test
• Biuret solution A is corrosive
• Biuret solution B is an irritant