Form 1:
Nutrition in Plants and Animals

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lipids

These are compounds of carbon, hydrogen and oxygen. However, they contain lesser oxygen but higher hydrogen compared to carbohydrates.

Building units for lipids are fatty acids and glycerol. To synthesize a molecule of lipid, three fatty acids and a glycerol molecule are linked through a condensation reaction.

There is one type of glycerol but numerous fatty acids.

There are different types of fatty acids. The property of a lipid therefore depends on the type of fatty acids that link up with the glycerol.

There are complex lipids such as phospholipids, steroids, waxes and cholesterol. These also form through condensation.

Properties of lipids

Fats easily change to oil when heated while oils easily solidify when cooled.

They are insoluble in water but readily dissolve in organic solvents such as chloroform to form emulsions.

They are inert hence can be stored in tissues of organisms.

Functions of lipids

•They are a source of energy when oxidized. They yield more energy compared to carbohydrates when oxidized per unit weight. However, they are less preferred as source of energy because they require a lot of oxygen to oxidize. In addition, they are insoluble hence not easy to transport to respiratory sites.

• They are a source of metabolic water. When oxidized, they yield a lot of metabolic water. This explains why some desert animals such as camels store large quantities of fat in their bodies.

• Lipids offer protection to internal organs as they are deposited around them to act as shock absorbers.

• Lipids provide heat insulation when stored underneath the skin as they are poor conductors of heat hence do not conduct heat away from the body. Organisms in cold areas tend to be short and plump as they have fatter fat adipose.

•Lipids form structural compounds for instance phospholipids in cell membrane.

• Complex lipids such as waxes in leaves help minimize water loss through transpiration.

• Some lipids mediate communication between cells.

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