FACT
Because all
compounds contain
more than one
atom, all
compounds are
molecules.
However, not all
molecules are
compounds.FACT
WATCH: simulation
on building a
molecule
See video:
SHORTCODEat
http://www.everythingscience.co.zaatom→molecule→cell→tissue→organ→organism→ecosystem
2.2 Molecules for life
Although life at the macro level is diverse, the chemistry making up that life is remarkably
similar. All living things are made up of basic building blocks calledelements. An element is
a substance that cannot be broken down into simpler substances using chemical means. Car-
bon, oxygen, hydrogen, nitrogen, sulfur, calcium, sodium and iron are examples of elements
you will come across in Life Sciences.
Each element is distinguished by the composition of itsatom. An atom is the basic unit of
matter.Moleculesare formed when one or more atoms are covalently bonded together. The
atoms of a molecule can be identical, such as 02 or H 2 or differ such as H 2 O. A compound
is formed when atoms ofdifferentelements join together.
Compounds are divided intoorganicandinorganiccompounds. Organic compounds al-
ways contain carbon, but not all compounds that contain carbon are organic. A general
rule of thumb is that organic compounds contain carbon, with at least one of these car-
bons bonded to hydrogen atoms. Carbon dioxide is therefore an inorganic compound even
though it contains carbon. The major organic compounds found in living organisms include:
carbohydrates,fats,proteinsandnucleic acids. These will be discussed in detail later in
this chapter.
Substance Percentage
Inorganic
Water 65%
Mineral salts 1%
Organic
Protein 18%
Carbohydrate 5%
Other organic macromolecules 1%Table 2.1: The composition of macromolecules in humans by percentage.2.3 Inorganic compounds
The role of water in the maintenance of life DUMMY
As mentioned in Table 2.1, up to 65% of our bodies are made up of water. Water is an
inorganic compound made up of two hydrogen atoms and one oxygen atom. Its molecular
formula is H 2 O. Water plays an important role in the maintenance of biological systems.
Temperature regulation: in humans, the sweat glands produce sweat which cools the body
as it evaporates from the body surface in a process calledperspiration. In a similar way, plants
are cooled by the loss of water vapour from their leaves, in a process calledtranspiration.
Form and support: water is an important constituent of the body and plays an important role
in providing form and support in animals and plants. Animals, such as worms and jellyfish,
Chapter 2. The chemistry of life 25