Sample Qs-Digestive system

1. Describe the digestive actions that take place in the
(i) mouth
(ii) stomach
(iii) small intestine

Explain the roles of the glands secretion and enzymes involved in these digestive process.
(10 marks)

Suggested Answer:

Mouth
· Food is chewed and broken up into smaller pieces by the teeth.
· The small pieces of food have a larger surface area for the saliva (enzyme) to act upon.
· Salivary gland secretes saliva (that is alkaline and )contains salivary amylase (ptyalin).
· ( After the food has been thoroughly chewed and mixed with saliva) the tongue starts the process of swallowing by pushing the bolus (small mass of chewed food).
· Saliva also softens and increases the water content of the food.
· In mouth, only starch is digested.
- Starch is hydrolysed by amylase into maltose.
(Starch + Water .....Amylase ....... Maltose ) [ any 3 points]

Stomach
-Secretes gastric juices contains hydrochloric acid and enzyme (rennin and pepsin)
-Hydrochloric acid kills microorganisms and stops the activity of salivary amylase, (which functions optimally at the near-neutral pH of saliva )
- and promotes the activity of pepsin.
-Pepsin is a (hydrolytic ) enzymes that acts on protein to produce peptides
( Protein + Water .... pepsin .... Peptone + polypeptide )
- Rennin changes caseinogens to casein.
- Casein is then digested by pepsin

Ileum (small intestine) :
· There are some digestive glands on small intestine.
-All these enzymes need an alkaline medium function
· There are 5 types of enzymes produced :
1. Erypsin (peptidase) – hydrolysis of peptide to amino acids
2. Sucrase - hydrolysis of sucrose to fructose and glucose
3. Maltase - hydrolysis of maltose to glucose
4. Lactase - hydrolysis of lactose to glucose and galactose
5. Entrokinase – Activates trypsinogen to trypsin in the
duodenum.
Any of the above enzymes reaction - 4 marks