This is part of the PowerPoint that covers section 2.2 in the Cambridge Pre-U Biology course. The full PowerPoint covers the following topics: Water, lipids, carbohydrates, proteins and nucleic acids.

1. MAKING SENSE OF
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• The basic unit of life is a cell.
• To really understand how it works you need to know
what it is made from.
• In this topic you will learn about the most important
molecules that are used to make cells and other
important structures in biology.
• This is the chemistry of life!

3. MAKING SENSE OFMAKING SENSE OF
Water
Lipids
Carbohydrates
Proteins
Nucleic Acids
3

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• Life on this planet is dependent on
water.
• It is the medium in which reactions
take place and therefore what is
contained inside cells.
• It is one of the simplest molecules
we know but it has some incredible
properties which living organisms
have been able to take advantage
of.

5. Copyright © 2015 Henry Exham
a) Describe the chemical and physical properties of
water and explain the biological significance of
these properties.

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• H2O
• Seems very basic but due to the
electrons it means water is what
we call a polar molecule.
• This means it is slightly charged.
• The oxygen is a little bit negative
and the hydrogen's are a little
positive.
• This is shown using the letter
delta (δ).
δ+ δ+
δ-
O
HH

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• This may not seem like such a big deal but it means that
water molecules can interact with each other by forming
hydrogen bonds.
δ+ δ+
δ-
δ+δ+
δ-
δ+δ+
δ-
δ+δ+
δ-
δ+δ+
δ- δ+δ+
δ-
δ+δ+
δ-

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• The hydrogen bonds give water some incredible
properties which many forms of life depend on.
• These are outlined on the following slides.

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1. Water is a polar solvent
– This means many substances will
dissolve in it. Therefore chemical
reactions can happen in it and it
can be used for transport.
– In humans the blood plasma is
mostly water.
– In plants water is used to
transport minerals and sugars in
the xylem and phloem.

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2. Water has a high specific heat capacity
– Large bodies of water vary only a little throughout the year
as it takes a lot of energy to heat up water due to the many
hydrogen bonds.
– This makes it a very stable environment for organisms to
live in.

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3. Water has a high latent heat of
vaporisation
– This means it takes a lot of
energy to vaporise water.
– This is important for sweating as
when the sweat evaporates from
the skin it uses a lot of heat
energy.
– This cools the body down.

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4. Cohesion - Surface tension
– The hydrogen bonds mean
that the water at the surface
holds together like a skin.
– This means organisms can live
on the surface easily.
– It also helps water to be
transported up the xylem
vessels in plants.

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5. Maximum density at 4oC
– As water cools below 4oC the
density decreases because the
hydrogen bonding becomes more
regular and keeps the water
molecules further apart.
– This means that when it freezes,
the ice floats on the surface.
– This provides a habitat on top of
water but also maintains the
habitat for the organisms in the
water.

14. MAKING SENSE OFMAKING SENSE OF
Water
Lipids
Carbohydrates
Proteins
Nucleic Acids
14

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• Lipids are used for many different functions in living
organisms.
• They are used as an energy store, to make cell
membranes, insulation, protection and water
proofing.
• They are made of carbon, hydrogen and oxygen like
carbohydrates, but have a much lower proportion of
oxygen.

16. Copyright © 2015 Henry Exham
b) Describe the structures and properties of
triglycerides and phospholipids and explain how
these are related to their roles in living organisms.
c) Describe the formation and breakage of ester bonds
such as those found in triglycerides.
d) Distinguish between saturated and unsaturated
fatty acids.

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• Fats and oils are groups of lipids.
• Fats are solid at room temperature when oils are
liquid.
• They are made from two types of molecules:
FATTY ACIDSGLYCEROL
C
H
OH
C
H
OH
C
H
OH
HH C
H
H
C
H
H
C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C OH
O

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