Digestion & digestive system

• what is the need for digestion?

  Biological molecules are important in organisms to build structures and for use in metabolic reactions
• what are the main biological molecules?

  • fats - glycerol & fatty acids carbohydrates - made up of simple sugars proteins - made up of amino acids
• why does digestion occur?

  Digestion is the breakdown of large insoluble molecules of food into smaller soluble molecules.
• why is the breakdown of large molecules during digestion important?

  • Large molecules are too big to be absorbed and ensures molecules can be transported into the bloodstream
• what are the 3 digestive enzymes?

  carbohydrases, proteases, and lipases
• function of enzyme carbohydrase?

  • Catalyse the breakdown of carbohydrates into simple sugars
• location of enzyme carbohydrase?

  Mouth, pancreas, small intestine
• function of enzyme proteases?

  • Catalyse the breakdown of proteins into amino acids
• location for enzyme protease?

  Stomach, small intestine
• function of enzyme lipase?


  Catalyse the breakdown of fats into glycerol and fatty acids
• location of enzyme lipase?

  Pancreas, small intestine
• what is peristalsis?

  • process by which food moves through the digestive system. It is a wave of muscle contractions in the gut wall which forces food down the gut.
• bile?


  Bile (a liquid secreted by the liver) aids the digestion of lipids in the small intestine
• how does bile aids the digestion of lipids in small intestine?

  • ● Neutralising acid from the stomach to provide optimum conditions for enzymes. Emulsifying lipids to provide a greater surface area for lipases
• why is there adaptations in small intestine?

  • adapted for the absorption of food molecules into the bloodstream
• adaptations of small intestine?

  • Surrounded by a network of capillaries which supply a good blood supply and many villi in the walls of the small intestine to increase surface area
• how can you model the gut?

  visking tubing (permeable, plastic tubing)
• limitations of using visking tubing to model the gut?

  • Non-living cells so no active transport, Contains pores, Smaller surface area as no villi
• what nutrients does the body require to mantain a balanced diet?

  carbohydrates, proteins, lipids, minerals, vitamins, fibre, water
• function - carbohydrates?


  ● Broken into smaller sugars e.g. glucose and Sugars used in respiration to release energy or are stored
• function - proteins

  • Joined in long chains to form new proteins which are used for growth
• function - lipids?


  Broken into fatty acids and glycerol
• function - minerals?


  Range of different functions e.g. iron required for the synthesis of haemoglobin in red blood cells
• function - vitamins?


  Range of different functions
• fibre - function?


  Provides bulk which aids the movement of food via peristalsis
• water - function?


  ● Main component of cells ● Enables chemical reactions to take place within cells
• implications of a diet high in sugar?

  obesity, type 2 diabetes, tooth decay
• health implications with diet high in salt?

  high blood pressure, cardiovascular disease
• health implications with diet high in fat?

  obesity, cardiovascular disease, type 2 diabetes, cancer
• food test - Glucose


  Add an equal volume of test solution and Benedict’s reagent to a boiling tube. Heat in a boiling water bath for five minutes. Remove the boiling tube and observe the colour of the precipitate formed.
• what is the positive result for food test - Glucose?


  Colour change from green to yellow to orange to brown to brick red
• food test - Protein?

  Add an equal volume of test solution and Biuret reagent to a boiling tube. Shake gently to mix. Observe colour change.
• what is the positive test for food test - Protein?

  Colour change from pale blue to purple
• Food test - starch ?


  Add some test solution to a test tube. Add two drops of iodine solution, gently mix. Observe colour change
• what is positive result for starch

  Colour change from yellow-brown to blue-black