Modelling digestion

Digestion in action at Latymer Upper School This demo is sufficiently high in the urghh factor to make it memorable to the students. It is also good for stimulating discussion – in some ways the model is an accurate representation of the digestive process, in others it isn’t.

Apparatus and materials per group
Beakers or plastic cups. 2 large
Pop socks
Zip-lock plastic bag. large
Plastic cutlery
Small bowl

Rice crispies
Banana

Coloured water, as follows:
‘saliva’ (clear)
‘stomach acid’ (yellow); add citric acid to make acid
‘bile’ (green)
‘pancreatic juice’ (red); add sodium hydrogen carbonate to make basic
‘intestinal juice’ (blue)

Apparatus and materials

Procedure

1 Provide students with a small bowl half-filled with rice crispies, and one-third of a banana.

2 Using plastic cutlery (mechanical digestion) students mush the banana and cereal together, and then add a small volume of water (‘saliva’). Mix these together.

4 Place the mixture in a zip-lock plastic bag. Squeeze excess air out of the bag. Add a small quantity of yellow coloured water (‘stomach acid’, acidified with citric acid if you like) then zip it closed. Squish the bag contents together by squeezing with the hands.

5 Holding the bag over a beaker, cut off one of the bottom corners and allow the contents of the stomach to pass into the beaker (you might need to squeeze here). Add small volumes of green coloured water (‘bile’), red coloured water (‘pancreatic juice’, made basic with sodium hydrogen carbonate if you like), and blue coloured water (‘small intestine juice’).

6 Put the stretchy top of a pop sock (Primarks sell 5 pairs for a pound) over the mouth of the beaker or plastic cup. Hold the pop sock in place, then invert the first beaker over a second beaker so the foot of the pop sock falls into the second beaker, and the gut contents fall into the pop sock.

7 Allow the liquid (‘digested food particles’) to drain out into the second beaker – squeezing the pop sock helps.

8 Once the liquid stops draining freely, take the pop sock off of the mouth of the beaker. Hold the pop sock over a paper plate, cut off a small part of the toe and squeeze the contents onto the plate (defaecation).

Last updated: 31 March 2008