AQA A Level Biology: Year 1 - Digestion and Absorption

• Why would damage to the microvilli cause the amino acid concentration of the blood to decrease?

  Decreases surface area of epithelial cellsFewer amino acid actively transported/ absorbed into epithelial cell
• Give an advantage of maltose being in the cell membrane and not secreted in pancreatic juice

  It's a more effective way to absorb the productsEnzymes not lost in gut contents
• Explain why chylomicrons leave the cell by exocytosis

  They are too large to leave by any other method
• Explain how the products of lipid digestion are absorbed

  Micelles move monoglycerides and fatty acids to the epitheliumMicelles constantly break up and reform, releasing the monoglycerides and fatty acidsThese diffuse across the cell membrane
• Explain lipid digestion

  In the small intestine lipase hydrolyses ester bonds Produces monoglycerides, fatty acids and glycerolMonoglycerides and fatty acids form micelles with bile salts
• Explain the role of bile in lipid digestion

  Bile salts emulsify lipids Provide a larger surface area for lipase
• Where does lipid digestion occur?

  The lumen of the small intestine
• Explain how amino acids are absorbed

  Na+ actively transported into the ileum from the epithelial cellsNa+ and amino acids diffuse into cells via sodium-dependent transporter proteins
• Describe how exopeptidases work

  Hydrolyse peptide bonds at the ends of the proteinRemove single terminal amino acids from proteins
• What is the difference in the co-transport of amino acids and the co-transport of glucose?

  With glucose - Na+ are actively transported into the bloodWith amino acids- Na+ are actively transported into the ileum
• Explain the steps in the digestion of a protein to a dipeptide

  Endopeptidases hydrolyse peptide bonds within the proteinExopeptidases hydrolyse peptide bonds at the ends of the protein
• Explain how dipeptides are hydrolysed to amino acids

  Dipeptidases in the cell surface membrane of epithelial cellsHydrolyse peptide bond between 2 amino acids
• How is the small intestine adapted for digestion?

  The lining Is folded into villi which give a large surface areaThe epithelial cells have microvilli which increase the surface area even more
• Explain co transport of glucose and sodium ions

  Na+ actively transported out of epithelial cells into bloodEstablishes concentration gradient for Na+ into epithelial cells from lumenNa+ and glucose move by facilitated diffusion via co-transporter proteins into epithelial cellGlucose diffuses out of the cell into the blood by facilitated diffusion
• Which monosaccharides is lactose hydrolysed to?

  GlucoseGalactose
• Which monosaccharides is sucrose hydrolysed to?

  GlucoseFructose
• Explain how maltose is hydrolysed to alpha glucose

  Maltase (membrane bound disaccharidase)Hydrolyses glycosidic bond in maltose to produce alpha glucose
• Explain how starch is hydrolysed to maltose

  Amylase in the small intestine and mouth hydrolyses the glycosidic bonds
• What is maltose digested to?

  alpha glucose
• What is starch first digested to?

  Maltose
• Why can starch not be absorbed as easily?

  It is a large, insoluble molecule
• What is fat hydrolysed to?

  Fatty acids and glycerolMonoglycerides
• What is starch hydrolysed to?

  alpha glucose
• What are proteins hydrolysed to?

  Amino acids
• Where is bile stored?

  Gall bladder
• Where is bile produced?

  Liver
• What is the role of bile in the digestive system?

  Neutralises HCl (from stomach) to provide alkaline conditions in which small intestine enzymes work bestIt emulsified the fats into smaller fat droplets giving a larger surface area for lipase to act on
• Where is protease secreted?

  Stomach and small intestine
• Where is protease produced?

  Stomach, pancreas and small intestine
• Where is lipase secreted?

  The small intestine
• Where is lipase produced?

  Pancreas and small intestine
• What are enzymes?

  Biological catalysts with a specific shape active site
• What is the role of the liver in the digestive system?

  It produces bile
• What is the function of the stomach in the digestive system?

  It is where digestion occurs. It produces hydrochloric acid
• What is the function of the small intestine in the digestive system?

  It is where some digestion occurs and the absorption of soluble food also occurs
• Name two types of glands in the digestive system

  Pancreatic glandsSalivary glands
• What are the roles of the glands in the digestive system?

  To produce digestive juices
• Where is amylase secreted?

  Mouth and small intestine
• Where is maltase secreted?

  Small intestine(In the epithelial cells of the small intestine)
• Where is maltase produced?

  (In the cell membrane of epithelial cells) Small intestine