Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.
What is the name for the [whole] tube in which these processes take place?
the gut or alimentary canal
What are the main causes for:
a) the physical breakdown of food? [clue - there are usually 20-32 of them]
b) the chemical breakdown of food into simpler substances?
What carries the simpler substances around the body?
> blood / bloodstream
What is the biological name for the final waste product of the process?
Why is it likely that dietary fibre will be part of this?
> it is not soluble / unable to be digested
Name some classes of food substances or ingredients which do not need to be broken down (into simpler subunits) before they can be taken in:
> minerals / vitamins / (simple) sugars
Measure the distance between your seat and your mouth, using a metre rule: ?70 cm Using this and the figure from the book, make an estimate of how many times your gut is coiled.
> about 10 times
Explain why even this is likely to be an underestimate.
[clue: What main regions of the body does the gut pass through? Is there much space there?]
> oesophagus (gullet) goes straight through the chest
Complete the table below, summarising the effects of different sorts of enzymes. These terms can be general(*) or specific(@) - see the examples already added to the top 2 lines below.
It should be useful to refer back to work on the main classes of foods.
|Class of FOOD:||broken down into SIMPLER SUBUNITS called :||by ENZYMES called:|
@ e.g. starch
|- simple sugars e.g. glucose
- maltose (2 glucose units, joined)
amylases (see later work)
|Fats and oils||>fatty acids and glycerol||>lipases|
Enzymes are sometimes called biological catalysts because they speed up reactions, and only small amounts are required. Digestive enzymes speed up the breakdown of complex food substances into simpler subunits. The breakdown of food in digestion is actually caused by water chemically splitting the complex food molecules, a process called hydrolysis (but this is not the same as simply dissolving).
Please note that digestive enzymes do not break foods down into the elements they are made of, and they do not release any energy from the food. This happens when the simpler food substances are respired in the individual cells.
Name some food substances which are almost entirely composed of starch:
> rice > bread > potatoes, pasta etc
Molecules of starch are built up from molecules of what simpler substances? (2 possible answers )
> glucose > maltose
What 2 structures will small molecules have to pass through in order to enter the blood stream?
> gut wall > blood capillary
Digestion is shown if the product disintegrates. This is more than just getting soggy!
Fill in the results at the appropriate time in the table below:
|Final results of demonstration - appearance of Quavers placed in|
|totally broken down||just extremely soggy!|
|slightly broken down||just soggy!|
> amylase and warmth must both be present