|
Digestion
II
Joanna
George-Johnson, Contributor
 |
| A
teacher from Greater Portmore High School uses a sun visor to shelter from the
rain during an ISSA/Pepsi/Digicel Manning Cup match between his school and Denham
Town High in Portmore, St. Catherine, recently. - Anthony Minott/Freelance Photographer |
Chemical
digestion: this
involves the use of enzymes. Enzymes facilitate the breakdown of complex molecules
which are too large to pass through the walls of the alimentary canal, into smaller
molecules which will readily do so. Recall
that enzymes are specific in nature, and because of this, different enzymes are
needed for each type of food in the diet. See
table below The
major differences between chemical and mechanical digestion are: - In
chemical digestion, the food substances are broken down to their basic molecules,
whereas in mechanical digestion, the food substances are broken down into smaller
pieces.
- No
enzymes are involved in mechanical digestion but there are always enzymes in chemical
digestion.
| Where
the enzyme | Name
of enzyme | Where
it works | Function
of Enzyme | | Enzyme
is made | | | | | Salivary
gland | amylase | mouth | starch
maltose | | Stomach
wall | pepsin | stomach | protein | | | | | polypeptides | | Pancreas | amylase | small
intestine | starch
maltose | | | trypsin | small
intestine | protein | | | | | polypeptides | | | lipase | small
intestine | fats
fatty acid | | | | | and
glycero | | Wall
of intestine | maltase | small
intestine | maltose
| | | | | glucose | | | peptidase | small
intestine | polypeptides
| | | | | amino
acids |
What
is Digested? In
humans, the only food types that can be digested are proteins, carbo-hydrates
(starch) and lipids (fats). The reason is that they are macromolecules, that is,
they are large and, therefore, cannot pass through the walls of the alimentary
canal unless they are broken down into their constituent units. Vitamins,
minerals and water, that are also essential to our nutrition, can be absorbed
directly. Their molecules are small enough to pass through the walls of the stomach.
Starch breaks down to become glucose molecules. Protein breaks down to become
amino acids. Lipids (fats) are broken down to become fatty acids and glycerol.
Lab
exercise Here
is an activity that you can try at home. 1.
Get a small piece of water cracker. 2.
Chew the cracker for five minutes. 3.
Keep it in your mouth for as long as possible. 4.
Make observations on: the taste, after one, three and five minutes. 5.
Compare the texture of the cracker before chewing and after five minutes of chewing.
Questions
1.
Explain why the enzyme pepsin works only in the stomach of the alimentary canal.
2. From
the experiment above, explain why the cracker starts to taste sweet after five
minutes in the mouth? Joanna
George-Johnson teaches at Ardenne High School.
Email: Masterbio@gmail.com.
| 
