Digestion Flashcards
Definition of digestion
Enzymes hydrolyse large, insoluble molecules to small, soluble moelcules.
Definition of absorption (3 points)
- Products of digestion are transported through the epithelial cell lining the small intestine.
- Using channel/carrier proteins.
- Transported into the blood.
Definition of ingestion
Food is taken into the mouth, chewed and mixed with saliva and swallowed.
Describe how carbohydrates are digested in the mouth (3 points)
- Via sailvary amylase.
- Hydrolyses alternate glycosidic bonds in starch to maltose.
- Optimum pH for amylase is neutral.
Describe how carbohydrates are digested in the stomach
Conditions are acidic which dentaures salivary amylase and prevents further hydrolysis of starch.
Describe how carbohydrates are digested in the small intestine (5 points)
- Remaining starch mixed with the secretion from the pancreas called pancreatic juice (contains pancreatic amylase and alkaline slats).
- Pancreatic amylase continues the hydrolysis of any remianing starch to maltose.
- Alkaline salts maintain the pH at around neutral so that the amylase can function.
- Epithelial cells contain membrane-bound disaccharidase maltase.
- The maltase hydrolyses the maltose into alpha-glucose, which is small enough to cross the ileum wall into the blood by co-transport.
Describe how proteins are digested (3 points)
- Endopeptidase- hydrolyses the peptide bond between amino acids in the central region of a protein molecule forming smaller polypeptide molecules.
- Exopeptidase- hydrolyses the peptide bond at terminal ends of the polypeptide to remove amino acids.
- Dipeptidases- hydrolyse the peptide bond between the two amino acids of a dipeptide. They are membrane-bound being part of the cell-surface membrane of the epithelial cells lining the ileum.
Describe lipid digestion (7 points)
- Most lipid/triglyceride digestion occurs in the small intestine.
- Lipids/triglycerides form a suspension of large droplets.
- Lipids/triglycerides are spilt up into smaller droplets by bile salts, which are produced by the liver.
- This process is called emulsification and increases the surface area for lipase action.
- So faster hydrolysis of lipids/triglycerides.
- Lipases are produced in the pancreas and they hydrolyse the ester bonds found in triglycerides to form fatty acids and glycerol/monoglycerides.
- The fatty acids and glycerol/monoglycerides are carried to the epithelial cells lining the small intestine in the form of micelles.
Describe the method to investigate the effect of bile salts and lipase on the digestion of triglycerides in milk (4 points)
- 2cm^3 of milk was added to 5 labelled test tubes.
- 2cm^3 of phenolphthalein was also introduced to these 5 tubes and were incubated at 40 degrees for 5 minutes.
- 1cm^3 of lipase, water, bile salts, boiled lipase or boiled bile salts were added to each tube. Solutions added to tubes: lipase and water, bile salts and water, lipase and bile salts, boiled lipase and bile salts, lipase and boiled bile salts.
- The time taken for the indicator to turn from pink to colouress was recorded.
Explain how the villi having thin walls increases efficiency of absorbancy
Reduces the distance over which the diffusion takes place.
Explain how the villi containing muscle increases efficiency of absorbancy (3 points)
- Helps maintain diffusion gradients because the movement mixes the contents of the ileum.
- As the products of digestion are absorbed from the food adjacent to the villi.
- New materials rich in the products of digestion replaces it.
Explain how the villi having microvilli increases efficiency of absorbancy
These are finger-like projections of the cell-surface membrane that further increase the surface area for absorption.
Explain how amino acids and glucose are absorbed by co-transport (5 points).
- Absorption of glucose and amino acids occurs in the small intestine by facilitated diffusion and active transport.
- Glucose and amino acids move from the lumen of the ileum to the blood.
- There are carrier proteins called co-tranpsort proteins in the cell-surface membranes of the epithelial cells lining the ileum.
- To maintain a steep gradient, sodium ions are actively transported out of the epithelial cell into the blood using a sodium-potassium pump.
- The glucose or amino acids then move out of the epithelial cells into the blood via facilitated diffusion.
Describe how triglycerides are absorbed (3 points).
- At the epithelial cells, micelles break down to release glycerol/monoglycerides and fatty acids.
- Glycerol/monoglycerides and fatty acids diffuse directly across cell-surface membrane phospholipid bilayer into epithelial cells because they are non-polar molecules.
- They are transported to the smooth endoplasmic reticulum where they recombine to form triglycerides and are places in a vesicle.
