bio

• Complex sugars (starch and glycogen)

  • Provide short-term storage of energy
  • Can be digested into glucose for respiration
• Cellulose


  • Structural component of plant cell walls
• Functions of carbohydrates


  1. Provide immediate source of energy

  2. Form cell structures

  3. Form supporting structures

  4. Synthesise important molecules
• Carbohydrates


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


  • Can be classified as single sugars, double sugars or complex carbohydrates
• Carbohydrates


  • Glucose
  • Sucrose (cane sugar)
• Fats


  A type of lipid, organic molecules made up of carbon, hydrogen and oxygen, but with much less oxygen in proportion to hydrogen compared to carbohydrates
• Fats


  • Can be animal fats or plant fats, commonly used as a store of energy
• Breaking down fats


  Fats can be broken down into fatty acids and glycerol using enzymes
• Foods rich in fats

  • Butter
  • Cheese
  • Fatty meat
  • Olives
  • Nuts
  • Peas
  • Beans
  • Seeds of castor oil and palm oil
• Functions of fats


  • Source and long-term storage of energy
  • Insulating material to prevent heat loss
  • Solvent for fat-soluble vitamins and other substances
  • Essential part of cell membranes
  • Reduce water loss from skin
• Animals like seals and polar bears have a thick layer of fat (blubber) beneath their skin which helps reduce heat loss
• Proteins


  Organic molecules made up of the elements carbon, hydrogen, oxygen and nitrogen. Another element, sulfur, may also be present.
• Proteins


  • Always present in all cells
  • Their molecules are the largest and most complicated of all the food substances
  • Commonly found in the meat of animals
• Amino acids


  • Simpler compounds that a protein molecule is built up from
  • Made up of an amino group (-NH), an acidic group (-COOH) and a side chain (denoted by R, which may sometimes contain sulfur)
• Formation of proteins


  1. Many amino acid molecules are joined in a linear manner to form a polypeptide

  2. Polypeptides in turn may be linked up to form an even longer chain of amino acids

  3. A protein molecule is made up of one or more such chains folded together
• Sources of proteins


  • Animal foods: Milk, eggs, seafood, meat (chicken, lean beef)
  • Plant foods: Soya beans, nuts, grains, vegetables (French beans)
• Functions of proteins


  • Synthesis of new cytoplasm, for growth and repair of worn-out body cells
  • Synthesis of enzymes and some hormones
  • Formation of antibodies to combat diseases
• Testing for proteins


  1. Add biuret solution to a sample

  2. Shake and observe colour change

  3. Reddish-violet colour indicates the presence of proteins
• Vegetarians choose not to eat meat and instead consume more dairy or soy products as alternative sources of protein
• Proteins are essential nutrients and alternative sources of protein must be consumed to ensure a healthy and balanced diet
• Digestion


  Breaking down large food molecules into smaller soluble molecules that can be absorbed into the body cells
• Digestion


  • Involves physical digestion and chemical digestion
• Physical digestion


  1. Mechanical break-up of food into small particles

  2. Occurs in the mouth, stomach, and small intestine

  3. Increases surface area-to-volume ratio for digestive enzymes
• Chemical digestion

  1. Breaking down large molecules in food into small soluble molecules that can be absorbed

  2. Enzymes break down proteins, starch, and fats
• Processes in the mouth


  1. Food stimulates salivary glands to secrete saliva

  2. Saliva contains amylase enzyme that digests starch

  3. Chewing breaks food into smaller pieces

  4. Tongue rolls food into bolus

  5. Bolus swallowed and passed to oesophagus
• Peristalsis in oesophagus


  Pushes bolus of food down into stomach
• Processes in the stomach


  1. Food stimulates gastric glands to secrete gastric juice

  2. Peristalsis churns and breaks up food

  3. Gastric juice contains hydrochloric acid, mucus, and protease enzyme

  4. Protease digests proteins into polypeptides

  5. Mucus protects stomach wall

  6. Food liquefies into chyme

  7. Chyme passes into duodenum
• Food normally remains in the stomach for about three to four hours
• Without the stomach, a person may not feel hungry
• Peristalsis


  Rhythmic, wave-like muscular contractions in the wall of the alimentary canal
• Peristalsis


  1. Mixes food with digestive juices

  2. Pushes or propels the food along the gut
• Peristalsis


  • Circular muscles contract to constrict the lumen
  • Longitudinal muscles contract to shorten and widen the lumen
  • Circular and longitudinal muscles are antagonistic
• Circular muscles contract


  Longitudinal muscles relax
• Longitudinal muscles contract


  Circular muscles relax
• The wall of the gut constricts when the circular muscles contract and the longitudinal muscles relax
• The gut dilates when the longitudinal muscles contract and the circular muscles relax
• Antagonistic muscles


  Work in opposite directions
• Pancreas


  • Gland lying in the loop of the duodenum
  • Connected to the duodenum by the pancreatic duct
  • Bile duct joins the pancreatic duct before opening into the duodenum
• Pancreatic juice


  Contains digestive enzymes: amylase, lipase and protease