Page 56 - Biology_F5

Cytology

Terpenes: They are essential oils in plants this reason, they are functional parts of the
and they are particularly found in conifers, nerve cells and skin sub-cutaneous layer.
citrus trees and some insects. They are used
for formation of aroma into medicine, Biochemical test for lipids
such as aromatherapy, perfume and food Lipids are non-polar and do not dissolve
additives. They include certain fat-soluble in polar solvents, such as water. They
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vitamins, such as vitamins A, E, and K. only dissolve in non-polar solvents, such
as benzene, ether, absolute alcohols, and
Carotenoids: These are widely distributed chloroform. This property makes the
in both plants and animals. They are lipids to be tested effectively by adding
exclusively of plant origin. Due to the non-polar dye, which can easily be
presence of many conjugated double bonds, absorbed by a non-polar lipids. Lipids
they are coloured red or yellow. Examples can be tested using several methods,
of carotenoids are lycopene, carotenes, including that which involves the use of
and xanthophyll (oxygenated derivatives Sudan III solution, the grease spot test and
of carotenes). emulsification test (Table 1.5).

Properties of lipids The basis for lipid tests
Lipids are either liquids or non-crystalline Fat globules are stained red with Sudan III
solution. Being less dense than water and
solids at room temperature. Pure fats or oils insoluble in water, a red stained oil layer
are colourless, odourless, and tasteless.
They are less dense than water and are floats on the surface of water. In addition,
esters of alcohols and acids. Simple lipids, with grease spot test, fats or oil droplets
such as fats are esters of fatty acids and create a translucent spots on the paper on
glycerol. Lipids are insoluble in water, warming. Given that lipids are immiscible
but soluble in organic solvents such as with water, therefore, an addition of water
ether, toluene and chloroform. They can to a solution mixture of lipids and ethanol
be hydrolysed by alkaline compounds results into emulsion of tiny droplets in the
into their constituent components by the water, which reflect light, giving a white
process known as saponification. Simple opalescent appearance. Emulsification
process is permanent and complete in the
lipids, such as fats and oils are hydrolysed presence of emulsifying agents, such as
by the lipase enzyme into fatty acids and bile salts, soap and protein. This process is
glycerol. Lipids contain either saturated
or unsaturated hydrocarbon chains and important in fat digestion in the intestine,
have a high calorific value due to the as the emulsifying agents (bile salts) lower
surface tension of the lipids and increase
presence of large number of hydrogen the surface area, hence easily acted by
atoms in their hydrocarbon chains. They digestive enzymes.
are poor heat and electric conductors. For

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