Digestion and absorbtion

• Describe digestion of carbohydrates

  -teeth breaks down carbohydrate into smaller pieces (mechanical breakdown)

  -Amylase found in salivary gland hydrolyses glycosidic bonds in starch to maltose

  -Any starch left over is broken down to maltose in pancreas and small intestine

  -In the ileum maltose a membrane bound enzyme hydrolyses maltose to 2 glucose molecules which are then absorbed into the blood stream
• Describe absorption of glucose/amino acid in ileum

  • Na+ ions leave epithelial cell and enter blood;-(Transport out is by) active transport / pump / via carrier protein using ATP;
  • So, Na+ conc. in cell is lower than in lumen (of gut);
  • Sodium/Na+ ions enter by FACILITATED diffusion;
  • Glucose absorbed with Na+ ions against their concentration/diffusion gradient / glucose absorbed down an electrochemical gradient;
• Describe digestion of proteins

  • endopeptidases- hydrolyse peptide bonds between amino acids in the central region of the protein forming smaller polypeptides
  • dipeptidases- hydrolyse the peptide bonds between two amino acids = into single amino acids
  • exopeptidases- hydrolyses the peptide bonds on the terminal amino acids so released dipeptides and amino acids
• Describe digestion of lipids

  -large droplets of monoglycerides and fatty acids are emulsified by bile salts into many droplets called micelles

  -this increases the surface area that lipase enzymes can work on so speeds up the reaction

  The ester bonds in triglycerides are hydrolysed forming 3 fatty acids and a glycerol molecule
• Describe absorption of lipids

  • monoglyceride and fatty acids combine with bile salts to form micelles
  • when micelles come into contact with epithelial cells they break down to monoglycerides and fatty acids
  • as these are non-polar they diffuse through the membrane
  • Once inside they're transported to endoplasmic reticulum are are recombined to form triglycerides
  • The they go to Golgi apparatus to form chylomicrons
  • they move out of the cell via exocytosis into the lymphatic vessels and then into the bloodstream.
• Cells lining the illum of mammals absorb the monosaccharide glucose by co-transport with sodium ions explain how

  • Sodium ions actively transported from ilium cell to blood
  • Maintains diffusion gradient for sodium to enter cells from God and with it glucose
  • Glucose enters by facilitated diffusion with sodium ions
• Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidizes on their own


  • Endopeptidases hydrolyse internal peptide bonds and exopeptidases remove amino acids at the end
  • More ends increase in surface area for exopeptidases  
• The addition of a respiratory inhibitor stops the absorption of amino acids in the ilium why

  • No slash less ATP produced so no active transport
  • So sodium ions not moved into/out of cell
  • This means there's no diffusion / concentration gradient for sodium to move into cell with amino acid
• Describe how you would use a microscope to find a mean diameter of triglycerides on a slide  

  • Measure with eyepiece graticule / scale
  • Calibrate with stage micrometer
  • Repeat and calculate the mean