IGCSE Biology 0610: Organs of the Alimentary Canal and Peristalsis

Karim eats a mouthful of rice. Below are three events that happen to this mouthful as it moves along his alimentary canal.

Event 1: Saliva, which contains an enzyme that begins digesting the starch in the rice, is mixed with the food as Karim chews it.

Event 2: The chewed food is pushed by a wave of muscular contraction down a narrow muscular tube in the neck and chest, before it reaches the stomach.

Event 3: After most digestion of the rice is complete, water is reabsorbed from the remaining undigested material, producing semi-solid faeces.

(a) Name the organ in which each event mainly takes place. [3]

(b) Name the process by which the food is pushed along the tube described in Event 2, and describe how the muscles in the wall of this tube bring about this movement. [2]

(c) Suggest one problem Karim would experience if the muscles surrounding this tube stopped contracting properly. [1]

(d) Explain why the reabsorption of water described in Event 3 is important, and suggest what would happen to Karim's faeces if this organ failed to reabsorb water normally. [2]

Part (a): Naming the organs

Event 1. Salivary glands

Saliva, containing the enzyme salivary amylase, is produced by the salivary glands and mixed with food in the mouth as it is chewed.

Event 2. Oesophagus

The oesophagus is the narrow muscular tube in the neck and chest that connects the mouth (via the throat) to the stomach, and along which chewed food is pushed by muscular contraction.

Event 3. Large intestine

The large intestine is the region of the alimentary canal, after the small intestine, in which water is reabsorbed from the remaining undigested material to form semi-solid faeces.

Part (b): Peristalsis

The process is called peristalsis. The wall of the oesophagus contains circular and longitudinal muscles. Behind the ball of food, these muscles contract, narrowing the tube, while just ahead of the food they relax, widening the tube. This coordinated wave of contraction and relaxation passes along the oesophagus, squeezing the food forward towards the stomach.

Part (c): Effect of failed peristalsis

If the muscles surrounding the oesophagus stopped contracting properly, food would not be pushed down effectively and could become stuck in the tube, causing Karim to have difficulty swallowing or even to choke.

Part (d): Importance of water reabsorption

Reabsorbing water in the large intestine is important because it prevents the body from losing too much water in the faeces, and it converts the watery undigested material into semi-solid faeces that can be egested (removed from the body) in a controlled way. If the large intestine failed to reabsorb water normally, the material passing through would remain watery, so Karim’s faeces would be runny rather than semi-solid, causing diarrhoea.

Final answers

(a) Event 1: salivary glands; Event 2: oesophagus; Event 3: large intestine.
(b) Peristalsis; circular and longitudinal muscles contract behind the food and relax ahead of it, producing a wave that pushes food forward.
(c) Food could become stuck, causing difficulty swallowing or choking.
(d) Water reabsorption prevents excessive water loss and produces semi-solid faeces; without it, the faeces would remain watery, causing diarrhoea.