Lipids and Carbohydrates
Lipids are a group of substances, which include fats, oils and waxes.
Carbohydrates include sugars, starches, glycogen and cellulose. They
are stored in plants as starches and in animals as glycogen.
There are many differences between carbohydrates and lipids. For
example lipids are insoluble in water whereas carbohydrates are
soluble in water. This is because lipids contain non - polar
hydrocarbon units whereas water contains polar hydrocarbon units. So
when the two are mixed together there is no attraction between
particles so no breakdown is possible. But lipids care soluble in non
- polar solvents, e.g. alcohol. Carbohydrates have polar hydroxyl
groups, so there are able to break down in water.
The structure of each is also different. Carbohydrates form long
chained polymers and lipids form shorter chains of polymers. Also they ...view middle of the document...
They are also an energy store,
since they are insoluble in water and have a high energy content it
makes them ideal for storage. This energy store is used make up for
heat, movement and energy lost by respiration. This energy store is
also useful in plants (e.g. sunflower) because it is needed for seed
dispersion. Lipids can also be used as insulation. Fat insulates the
body because it conducts heat slowly. This type of energy store can be
seen with polar bears, for example. They have a thick layer of fat
beneath their skin for insulation. Some mammals, e.g. whales or
penguins, don't have fur like polar bears do so they need extra
insulation called 'blubber' because there is no fur there to trap air
and to insulate further. The insulating feature of lipids also
protects internal organs. Lipids also store energy useful for
hibernation. Phospholipids are the major components in cell membranes;
they are ideal for this due to their ability to be permeable with some
substances but impermeable to others. Oils and waxes prevent
evaporation through the skin or through the leaves of plants. Another
important function of lipids is that they are waterproof, due to their
insolubility in water. This is important especially with plants
because the waxy layer on the leaves prevent the plant from losing
C. Why do many organisms store lipids rather than carbohydrates?
Carbohydrates supply energy more than store it.
Many organisms store lipids rather than carbohydrates because lipids
can act as insulation, an energy store and supply, and other features
such as its use in cell membranes and their waterproof properties also
make them extremely useful. Organisms also store carbohydrates, but
mainly in cellulose in plants to form cell walls, and glucose is used
as an energy store in respiration. Although carbohydrates are used in
the body, lipids are stored in many organisms rather than
carbohydrates. Other than the functions already mentioned, lipids are
also needed to produce certain hormones. So lipids are stored due to
their many functions in organisms.