Page 31 - Biology Form Two

Biology for Secondary Schools

also be boiled or heated before testing to Inference: It refers to a conclusion that
make them mix thoroughly with reagents is made following the observation. The
used. The solution or mixture, which is conclusion tells whether the type of food
made from food substance, is kept in a tested is present or absent.
container and is referred to as a stock.
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A small portion of solution or mixture, Test for carbohydrates
There are three types of carbohydrates,
which is taken from the stock solution for which are monosaccharide, disaccharides

experiment is termed as a food sample.
and polysaccharides.
Procedure: This involves the steps to be
followed when carrying out the test for Monosaccharides
These are also known as simple sugars
a particular food substance. Steps differ (single sugar). They include glucose,
when testing for one food type from fructose (fruit sugar) and galactose
another. Failure to follow these steps (milk sugar). These sugars dissolve

often results in the wrong conclusion. in water to form sweet solutions. All
Therefore, in each step, the procedures to monosaccharides can reduce copper
be followed should be stated clearly. The in Benedict’s solution from copper II
+
2+
amount of food sample which has been (Cu ) which is blue to copper I (Cu )
taken from the stock solution in a certain which is orange or brick red. Hence,
procedure should be stated together with they are named as reducing sugars.
During the reduction process, the colour
its unit of measurement. The apparatus of Benedict’s solution changes from
used should also be stated clearly. blue, to green, to yellow, and finally to

Observation: This refers to the process orange or brick red, depending on the
of carefully watching, monitoring or concentration of the reducing sugar. If
examining a series of changes that it is high, the colour change can reach
to brick red, but if it is low it can end
occur when carrying out an experiment. up to the intermediate colours that
Different changes are experienced as a have been mentioned. Some examples

person attempts one stage after another. of food sources containing reducing
These changes can involve colour, smell, sugars are onions and carrots.
sound or heat changes. The changes The general formula for monosaccharide

differ from one experiment to another. is (CH O) where n represents the
2
n
During observation, it is important to number of carbon (C) atoms, and has a
make sure the colour of the reagent is value of between 3 and 6. For example,
known to be clear about the new changes. the formula for glucose is C H O .
6 12 6

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