Page 57 - Biology_F5

Biology for Advanced Level Secondary Schools

Table 1.5: Biochemical test for lipids
Food sample to be Procedure Observation Inference
tested
Lipid (fat or oil) Sudan III test A red- stained oil Lipids are
Put 2 ml of a solution containing layer separates on present
lipid in a clean and dry test tube the surface of the
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solution
Add 3 drops of Sudan III solution
and shake vigorously. Then allow the
mixture to settle for 1 minute

Grease spot test A permanent Lipids are
Rub a drop of the sample containing translucent spot on present
lipids on to a piece of paper the paper is formed
Allow time for any water to
evaporate. Warm gently in order to
speed up the process or reaction

Emulsification test Lipids become Lipids are
Put 2 ml of absolute ethanol in a finely divided present
clean and dry test tube, and then add and are dispersed
2 ml of lipids in water. When
shaken with water
Shake vigorously to dissolve the
lipids. Then add equal volume of they form a cloudy
cold water white suspension
(emulsification)

Functions of lipids (e) Since lipids are less dense than water,
(a) They are structural component of they aid in buoyancy in aquatic
membranes. Examples: phospholipids animals, such as sharks.
and glycolipids. (f) They are precursors of important body

(b) They insulate the body against heat requirements, such as vitamin D and
loss. For example, fats found in the sex hormones.
sub-cutaneous layer of the skin are an (g) They protect internal vital organs such
insulating blanket. as heart and kidneys.
(c) They are a source of energy; (h) They form protective layers that
therefore, they are used as an prevent water loss. For example,
alternative respiratory substrate waxes in plants prevent water loss.
when carbohydrates are completely
exhausted. (i) They facilitate fast conduction of
nerve impulses, as they are an integral
(d) They are sources of metabolic water, part of myelinated nerve fibres.
especially for animals found in arid (j) They are components of some enzyme
and semi-arid areas, such as camels. systems.

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