Topic 3C: Digestion And Absorption Flashcards
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. [5]
- Micelles contain bile salts, fatty acids and monoglycerides;
- Make fatty acids and monoglycerides soluble (in water);
- Fatty acids and monoglycerides absorbed by diffusion;
- Triglycerides reformed (in cells);
- Vesicles move to cell membrane.
Explain the advantages of lipid droplet and micelle formation. [3]
- Droplets increase surface areas;
- (So) fast(er) hydrolysis (of triglycerides);
- Micelles carry fatty acids and monoglycerides to (intestinal epithelial) cells
How is the Golgi apparatus involved in the absorption of lipids? [3]
- Modifies triglycerides;
- Combines triglycerides with proteins;
- Forms vesicles
Describe the role of micelles in the absorption of fats into the cells lining the ileum. [3]
- Micelles include bile salts and fatty acids;
- Make fatty acids (more) soluble in water;
- Carry fatty acids to lining (of the ileum);
- Fatty acids (absorbed) by diffusion.
Describe the complete digestion of starch by a mammal. [4]
- Hydrolysis;
- (Of) glycosidic bonds;
- (Starch) to maltose by amylase;
- (Maltose) to glucose by disaccharides/maltase;
- Membrane-bound (disaccharidase/maltase)
Describe the role of enzymes in the digestion of proteins in a mammal. [4]
- Hydrolysis of peptide bonds;
- Endopeptidase acts in the middle of polypeptide;
- Exopeptidase acts at the end of polypeptide;
- Dipeptidase acts on dipeptide.
Describe the mechanism for the absorption of amino acids in the ileum. [4]
- Sodium ions actively transported from cell to blood;
- Creating sodium ion concentration gradient;
- Co-transport of amino acids with sodium ions (into cell);
- Facilitated diffusion of amino acid into blood.
Name the three enzymes involved in the hydrolysis of proteins. [1]
- Endopeptidase, exopeptidase, dipeptidase
Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own. [2]
- Endopeptidases hydrolyse internal (peptide bonds);
- More ends (for exopeptidases)
Describe the structure of glycogen. [2]
- Polysaccharide of alpha glucose;
- (Joined by) glycosidic bonds
Suggest how glycogen acts as a source of energy. [2]
- Hydrolysed to (glucose);
- Glucose used in respiration.
Suggest and explain two ways the cell-membranes of epithelial cells may be adapted to allow rapid absorption. [2]
- Membrane folded so larger surface area;
- Lots of protein channels for facilitated diffusion;
- Lots of protein carriers for active transport;
- Lots of protein (channels/carriers) for co-transport
Respiratory inhibitors prevent the absorption of amino acids.
Suggest why. [3]
- No/less ATP produced;
- Sodium ions not moved (into/out of cell);
- No concentration gradient for sodium ions
Explain why amylase is unable to digest cellulose even though starch and cellulose are both polymers of glucose. [3]
- Amylase has an active site only complementary to starch so can (only) form enzyme-substrate complexes with starch;
- Starch contains alpha glucose but cellulose contains beta glucose;
- Starch is helical, cellulose is straight.
The concentration of glucose in the blood rises after eating a meal containing carbohydrates. The rise is slower if the carbohydrate is starch rather than sucrose.
Explain why. [3]
- Starch digested to maltose (by amylase);
- Maltose digested to glucose (by maltase);
- Digestion of sucrose is a single step.
Suggest one advantage if using a pH meter rather than a pH indicator. [1]
- Numerical reading / not subjective / gives quantitative data;
- Greater accuracy
Explain why the pH decreases when lipase is added to milk. [1]
- Fatty acids produced
Name the part of a cell that produces enzymes. [1]
Ribosomes
Trypsin is an endopeptidase. It is produced in an inactive form inside some of the cells of the pancreas. Suggest the advantage of producing trypsin in an inactive form. [2]
- Does not digest protein inside cells;
- So (pancreatic) cell not damaged
Explain how competitive inhibitors stop enzymes from working. [3]
- Inhibitor is a similar shape to the substrate.
- (Inhibitor) is complementary to the active site;
- Substrate can’t bind to active site
Describe how bacteria divide. [2]
- Binary fission;
- Replication of (circular) DNA;
- Division of cytoplasm to produce 2 daughter cells;
- Each with single copy of (circular) DNA
Suggest and explain one advantage to a bacterium of secreting an extracellular protease in its natural environment. [2]
- To digest protein;
- (So) they can absorb amino acids for growth
Describe the action of membrane-bound dipeptidases and explain their importance. [2]
- Hydrolyse (peptide bonds) to release amino acids;
- Amino acids can cross (cell) membrane
Explain how digestion of starch in the gut (small intestine) leads to an increase in the concentration of glucose in the blood. Details of co-transport are not requires. [3]
- Hydrolysed by enzymes;
- Produces glucose (in the gut);
- Small enough to cross the gut walk (into the blood)
Describe the difference between the structure of a triglyceride molecule and the structure of a phospholipid molecule. [1]
- In phospholipids, one fatty acid replace by a phosphate group
Describe how you would test for the presence of a lipid in a sample of food. [2]
- Add ethanol then add water and shake;
- White/milky emulsion
Maltose is hydrolysed by the enzyme maltase.
Explain why maltase only catalyses this reaction. [3]
- Active site complementary to maltose;
- (Only) maltose can bind;
- To form enzyme substrate complex
