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Heterotrophic
nutrition (cont'd)
Monacia
Williams, Contributor
Diet
LAST
WEEK, we looked at dentition, that
is, the structure of teeth and their
uses. Teeth are used in the mechanical
digestion of food. In order for food
to be properly digested, a second
type of digestion must take place.
This is known as chemical digestion
and involves the use of enzymes. We
will need to talk about enzymes later
but, before we do that, we need to
learn something about the food that
we eat.
The
type and quantity of the food that
is eaten constitute the diet. An individual's
diet is made up of nutrients. These
nutrients can be grouped in two ways
as:
1.
Macro and micro nutrients
2.
Organic and inorganic nutrients.
In
the first grouping, macronutrients
are those which are required by the
body in large amounts and include:
- Carbohydrates
- Proteins
- Lipids
Micronutrients
include:
In
the second grouping, organic nutrients
include:
- Carbohydrates
- Proteins
- Lipids
- Vitamins
Minerals
would then be the sole inorganic nutrients.
A
diet must also include two other components
water and roughage. In order for individuals
to remain healthy, they must consume
a balanced diet. This is one which
has all the nutrients in the correct
proportions needed to maintain good
health.
Let
us now take a closer look at these
nutrients.
Carbohydrates
These
are large organic molecules containing
the elements carbon, hydrogen and
oxygen. The ratio of carbon to hydrogen
to oxygen is 1:2:1. The 2:1 ratio
of hydrogen to oxygen is the same
as it is in water, hence the hydrate
portion of the name. Some carbohydrates
are known as macromolecules because
of their large size, for example,
starch, glycogen and cellulose. The
simplest carbohydrates belong to a
group of molecules known as monosaccharides,
that is, simple sugars with one 'ring'.
An example of this is glucose.
More
complex carbohydrates are made up
of monosaccharide units joined together
by bonds. When two monosaccharides
are joined together, a disaccharide
unit is formed; the prefix 'di' means
two. Disaccharides are known as complex
sugars. Many monosaccharide units
join together to form a polysaccharide.
The macromolecules, starch, glycogen
and cellulose are all examples of
polysaccharides.
Please
note: You need to pay attention
to how these reactions take place
because how they form helps to determine
how they are broken down, and this
is part of the underlying principles
of digestion.
When
two monosaccharides join together,
a special bond known as a glycosidic
bond is formed between them. During
the formation, one molecule of water
is lost (see equation below). This
type of reaction is known as a dehydration
synthesis reaction or a condensation
reaction because the water molecule
is removed. The corresponding reaction,
where the water molecule is replaced
and the constituents or reactants
are reformed, is known as hydrolysis.
C6H12O6
+ C6H12O6 ? C12H22O11 + H2O
Characteristics
and functions of carbohydrates
monosaccharides
- Simple
sugars
- Sweet
to taste
- Soluble
in water
- All
are reducing sugars*
- The
major source of energy in living
organisms
Disaccharides
- Complex
sugars
- Soluble
in water
- Sweet
to taste
- Source
of energy in living organisms
Polysaccharides
- Insoluble
- Not
sweet
- Starch
is the storage compound of plants.
- Cellulose
is a major constituent of cell walls.
- Glycogen
is the storage carbohydrate in animals.
Next
week we will discuss why monosaccharides
are reducing sugars and we will also
continue our study of the other nutrients.
Monacia
Williams teaches at Glenmuir
High School.
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