Biology Paper 1

• Digestion


  The hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes
• Carbohydrate digestive enzymes


  • Amylase in mouth
  • Maltase, sucrase, lactase in membrane of small intestine
• Carbohydrate digestion


  1. Amylase → starch into smaller polysaccharides

  2. Maltase → maltose into 2 x glucose

  3. Sucrase → sucrose into glucose and fructose

  4. Lactase → lactose into glucose and galactose
• Lipid digestion


  Occurs in the small intestine
• Lipid digestion


  1. Bile salts emulsify lipids

  2. Lipase hydrolyses the ester bond between monoglycerides and fatty acids
• Protein digestive enzymes


  • Endopeptidases break between specific amino acids in the middle of a polypeptide
  • Exopeptidases break between specific amino acids at the end of a polypeptide
  • Dipeptidases break dipeptides into amino acids
• Co-transport


  Mechanism by which certain molecules are absorbed into the ileum despite a negative concentration gradient
• Molecules requiring co-transport


  • Amino acids
  • Monosaccharides
• Co-transport mechanism


  1. Sodium ions (Na+) are actively transported out of the cell into the lumen, creating a diffusion gradient

  2. Nutrients are then taken up into the cells along with Na+ ions
• Fatty acids and monoglycerides

  Do not require co-transport as they are nonpolar and can easily diffuse across the membrane of the epithelial cells