1. Explain why it is necessary for food to be digested in order to be absorbed into our body.
Answer
Food particles need to be hydrolysed into smaller molecules so that they can pass across cell membranes and dissolve into the blood stream.
2. Digestion of carbohydrates occurs in two parts of the digestive system. Describe the role of enzymes in digesting starch into glucose.
Answer
Starch is hydrolysed by amylase (either in the mouth or small intestines) into maltose. Maltose is then hydrolysed by maltase into glucose.
3. Describe the role played by endopeptidases, exopeptidases and dipeptidases in the digestion of proteins.
Answer
Endopeptidases hydrolyse peptide bonds within the middle of the proteins, causing them to break into smaller polypeptides. Exopeptidases hydrolyse these polypeptides further into dipeptides. Dipeptidases then hydrolyse the peptide bonds between the two amino acids of a dipeptide causing them to become single amino acids.
4. Explain the role played by sodium ions in the movement of amino acids from the gut lumen into the blood capillaries.
Answer
Na+ concentration is higher in the lumen than the epithelial cell. Concentration gradient is maintained by Na+ being actively transported out of the epithelial cell. Na+ move into epithelial cell by co-transport bringing amino acids into the epithelial cell. Amino acids then move through facilitated diffusion into the blood.
5. Explain the effect a respiratory inhibitor would have on amino acid absorption.
Answer
Stops active transport of sodium ions out of cell, so no concentration gradient of sodium ions to allow cotransport of amino acids into cell.
6. Snakes can kill prey by producing venom. Snake venom consists of proteins that act as toxins and enzymes. Snake venom kills prey when it is inserted directly into the bloodstream or tissues. Ingesting or swallowing snake venom is not harmful. Suggest why.
Answer
Toxins and enzymes from the venom are denatured by hydrochloric acid in the stomach. Protein-digesting enzymes then hydrolyze the venom. The toxins are no longer functional and therefore not harmful.
7. The figure below shows the human digestive system. Complete the table with the relevant letter(s).
Answer
8. Some people have their gall bladder removed because of medical problems. After surgery they may be advised to avoid very high fat foods. Suggest why.
Answer
With less bile available (or no bile storage), fats are not emulsified as effectively. This results in a lower surface area for lipase activity. Consequently, fats are digested less efficiently and may not be fully absorbed. As a result, more fat is present in the faeces, which can lead to complications such as diarrhoea.
9. Coeliac disease is a condition that causes damage to the villi. The villi are significantly reduced in size and some may disappear completely. People who develop coeliac disease may experience fatigue and unexpected weight loss. Explain why.
Answer
Reduced surface area for absorption means fewer nutrients (such as glucose, amino acids, and fatty acids) are absorbed. This leads to a lower respiration rate and reduced metabolism, as well as fewer nutrients available to maintain and repair tissues.