H.
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
Assignment 10A: Biomolecules
Water
Figure 1 – Diagrams of the structure of
water and the bonding in water
Water is an essential biomolecule that has the
molecular formula, H2O, showing that it has 2
hydrogen atoms per 1 oxygen atom and therefore
a ratio of 2:1 (hydrogen to oxygen). The impact on
having a 2:1 ratio of hydrogen to oxygen atoms on
the properties of water is that water can form
hydrogen bonds with other water molecules,
allowing water be cohesive. Also, the 2:1 ratio of
hydrogen to oxygen atoms impacts the polarity of
water as the more hydrogen atoms there are
compared to oxygen leads to a large difference in
electronegativity, therefore making water a polar
molecule. They hydrogen atoms and oxygen atoms
are covalently bonded in water as they share
electrons – see Figure 1. The element, hydrogen, is
in group 1 and has 1 electron in its outer shell,
whereas the element, oxygen, is in group 6,
consisting of 6 electrons in its outer shell. The
hydrogen atoms share their 1 outer electron with
oxygen and oxygen shares 1 of its outer electrons
with the hydrogen atoms, completing the outer
shell and therefore forming a covalent bond.
In terms of intermolecular forces, water displays Van der Waals, permanent
dipole-dipole interactions, and hydrogen bonding – this has an impact on its
properties, e.g. cohesion. Van der Waals forces are present in water due to the
constant movement of electrons within the shells (refer to Figure 1), causing an
uneven distribution of electrons within the water molecule, resulting in the
formation of a temporary dipole. The formation of a temporary dipole induces
another temporary dipole forming in a molecule that is in close proximity,
resulting in a weak force of attraction – Van der Waals forces (also known as
London forces). In addition to this, permanent dipole-dipole interactions are also
found within a water molecule due to the large difference in electronegativity
between the oxygen atom and hydrogen atoms - electronegativity is the ability
of an atom to attract an electron pair in a covalent bond. This large difference in
electronegativity classifies water as a polar molecule as electrons are unevenly
distributed within the molecule and therefore water is not symmetrical. A partial
negative charge is formed on the oxygen atom due to the unshared negative
electrons on the oxygen atom while the hydrogen atoms have a partial positive
charge as a result of the shared negative hydrogen electrons being pulled
towards the oxygen atom. Oxygen has a higher electronegativity than hydrogen,
so electrons will be more attracted to the oxygen atom when forming a water
molecule. A permanent dipole forms due to the large difference in
electronegativity between oxygen and hydrogen, resulting in the formation of a
weak force of attraction between the oppositely charged ends of a water
molecule - a permanent dipole-dipole interaction. More importantly, hydrogen
1
, H.
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
bonds occur in a water molecule as the partial negative charge on the oxygen
atom attract the partial positive charges on hydrogen atoms of other water
molecules. This force of attraction is referred to as hydrogen bonding and has a
large impact on the many properties of water.
Water has many useful properties which make it an essential component to living
organisms and therefore life itself. Firstly, it plays a major role in many metabolic
reactions, especially condensation and hydrolysis reactions, making it a
metabolite (a substance formed/necessary for metabolism). In condensation
reactions, a water molecule is released to form a bond whereas, in hydrolysis
reactions, a water molecule is required to break a bond. For example,
monosaccharides are joined together to form disaccharides and polysaccharides
via condensation reactions. Secondly, the hydrogen bonding in water causes the
water molecules to stick together which is known as cohesion. This property of
water enables water to flow, especially through xylem vessels in plants, as well
as acting as a transporter for substances. These strong cohesive forces in water
also mean that water has a high surface tension when come into contact with air,
allowing it to act like skin to support small substances. For example, pondskaters
have a high surface tension so can ‘walk’ on the surface of a pond.
Additionally, water has a high specific heat capacity (amount of heat required to
raise/lower 1g of a substance by 1˚C) as it needs a lot of energy to heat up. The
hydrogen bonding in water causes this high specific heat capacity as it allows
molecules to stick together (cohesion) and therefore water absorbs a relatively
large amount of heat before its temperature changes. This resistance against
changes in temperature shows how water acts a buffer and this is useful for
living organisms as it provides a good habitat for aquatic organisms. For
example, lakes, as the temperature is more stable than land. Also, living
organisms are composed mainly of water therefore it helps them to maintain a
constant internal body temperature – this is an important property to have as
temperature affects enzyme activity. Another useful property of water is how it
can act as a solvent due to the polarity of water. Water is a polar molecule that
has a partially positive and partially negative end so the positive end of a water
molecule will be attracted to a negative ion while the negative end of water
molecule will be attracted to a positive ion. For example, water can dissolve
NaCl, an ionic compound, as the positive end of a water molecule will be
attracted to the negative ion (Cl-) and the negative end of a water molecule will
be attracted to the positive ion (Na+). The importance of this property is that it
can dissolve other substances like inorganic ions, allowing water to act as a
medium for metabolic reactions. Water also acts as a transport medium, e.g. in
xylem to transport nitrates that are required to make amino acids. In addition to
these properties, water also has a high latent heat of vaporisation (amount of
energy required to convert 1g of a substance from liquid to a gas). This property
is caused by the hydrogen bonding in water as it means that a lot of energy is
needed to evaporate/vaporise 1g of water. As a result, water can absorb a lot of
energy before the hydrogen bonds break and eventually evaporate/vaporise.
This is important for living organisms as it means when water evaporates, e.g.
sweat, it is an efficient form of cooling (cooling effect) since it removes a lot of
heat at the same time. Also, it allows organisms to maintain a constant internal
body temperature as a result.
Carbohydrates
2
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
Assignment 10A: Biomolecules
Water
Figure 1 – Diagrams of the structure of
water and the bonding in water
Water is an essential biomolecule that has the
molecular formula, H2O, showing that it has 2
hydrogen atoms per 1 oxygen atom and therefore
a ratio of 2:1 (hydrogen to oxygen). The impact on
having a 2:1 ratio of hydrogen to oxygen atoms on
the properties of water is that water can form
hydrogen bonds with other water molecules,
allowing water be cohesive. Also, the 2:1 ratio of
hydrogen to oxygen atoms impacts the polarity of
water as the more hydrogen atoms there are
compared to oxygen leads to a large difference in
electronegativity, therefore making water a polar
molecule. They hydrogen atoms and oxygen atoms
are covalently bonded in water as they share
electrons – see Figure 1. The element, hydrogen, is
in group 1 and has 1 electron in its outer shell,
whereas the element, oxygen, is in group 6,
consisting of 6 electrons in its outer shell. The
hydrogen atoms share their 1 outer electron with
oxygen and oxygen shares 1 of its outer electrons
with the hydrogen atoms, completing the outer
shell and therefore forming a covalent bond.
In terms of intermolecular forces, water displays Van der Waals, permanent
dipole-dipole interactions, and hydrogen bonding – this has an impact on its
properties, e.g. cohesion. Van der Waals forces are present in water due to the
constant movement of electrons within the shells (refer to Figure 1), causing an
uneven distribution of electrons within the water molecule, resulting in the
formation of a temporary dipole. The formation of a temporary dipole induces
another temporary dipole forming in a molecule that is in close proximity,
resulting in a weak force of attraction – Van der Waals forces (also known as
London forces). In addition to this, permanent dipole-dipole interactions are also
found within a water molecule due to the large difference in electronegativity
between the oxygen atom and hydrogen atoms - electronegativity is the ability
of an atom to attract an electron pair in a covalent bond. This large difference in
electronegativity classifies water as a polar molecule as electrons are unevenly
distributed within the molecule and therefore water is not symmetrical. A partial
negative charge is formed on the oxygen atom due to the unshared negative
electrons on the oxygen atom while the hydrogen atoms have a partial positive
charge as a result of the shared negative hydrogen electrons being pulled
towards the oxygen atom. Oxygen has a higher electronegativity than hydrogen,
so electrons will be more attracted to the oxygen atom when forming a water
molecule. A permanent dipole forms due to the large difference in
electronegativity between oxygen and hydrogen, resulting in the formation of a
weak force of attraction between the oppositely charged ends of a water
molecule - a permanent dipole-dipole interaction. More importantly, hydrogen
1
, H.
BTEC L3 EXTENDED DIPLOMA IN APPLIED SCIENCE
Unit 10: Biological Molecules and Metabolic
Pathways
bonds occur in a water molecule as the partial negative charge on the oxygen
atom attract the partial positive charges on hydrogen atoms of other water
molecules. This force of attraction is referred to as hydrogen bonding and has a
large impact on the many properties of water.
Water has many useful properties which make it an essential component to living
organisms and therefore life itself. Firstly, it plays a major role in many metabolic
reactions, especially condensation and hydrolysis reactions, making it a
metabolite (a substance formed/necessary for metabolism). In condensation
reactions, a water molecule is released to form a bond whereas, in hydrolysis
reactions, a water molecule is required to break a bond. For example,
monosaccharides are joined together to form disaccharides and polysaccharides
via condensation reactions. Secondly, the hydrogen bonding in water causes the
water molecules to stick together which is known as cohesion. This property of
water enables water to flow, especially through xylem vessels in plants, as well
as acting as a transporter for substances. These strong cohesive forces in water
also mean that water has a high surface tension when come into contact with air,
allowing it to act like skin to support small substances. For example, pondskaters
have a high surface tension so can ‘walk’ on the surface of a pond.
Additionally, water has a high specific heat capacity (amount of heat required to
raise/lower 1g of a substance by 1˚C) as it needs a lot of energy to heat up. The
hydrogen bonding in water causes this high specific heat capacity as it allows
molecules to stick together (cohesion) and therefore water absorbs a relatively
large amount of heat before its temperature changes. This resistance against
changes in temperature shows how water acts a buffer and this is useful for
living organisms as it provides a good habitat for aquatic organisms. For
example, lakes, as the temperature is more stable than land. Also, living
organisms are composed mainly of water therefore it helps them to maintain a
constant internal body temperature – this is an important property to have as
temperature affects enzyme activity. Another useful property of water is how it
can act as a solvent due to the polarity of water. Water is a polar molecule that
has a partially positive and partially negative end so the positive end of a water
molecule will be attracted to a negative ion while the negative end of water
molecule will be attracted to a positive ion. For example, water can dissolve
NaCl, an ionic compound, as the positive end of a water molecule will be
attracted to the negative ion (Cl-) and the negative end of a water molecule will
be attracted to the positive ion (Na+). The importance of this property is that it
can dissolve other substances like inorganic ions, allowing water to act as a
medium for metabolic reactions. Water also acts as a transport medium, e.g. in
xylem to transport nitrates that are required to make amino acids. In addition to
these properties, water also has a high latent heat of vaporisation (amount of
energy required to convert 1g of a substance from liquid to a gas). This property
is caused by the hydrogen bonding in water as it means that a lot of energy is
needed to evaporate/vaporise 1g of water. As a result, water can absorb a lot of
energy before the hydrogen bonds break and eventually evaporate/vaporise.
This is important for living organisms as it means when water evaporates, e.g.
sweat, it is an efficient form of cooling (cooling effect) since it removes a lot of
heat at the same time. Also, it allows organisms to maintain a constant internal
body temperature as a result.
Carbohydrates
2
