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Question:

Biological Molecules- structures, functions and movement

by | Jun 5, 2022 | fresh

Write an essay on the structures, functions and movement of biological molecules. In your assignment you should start by comparing the structures of carbohydrates including glucose, starch and cellulose (1.1) Then go on to describe the plasma membrane. Discuss ways molecules move through the membrane including diffusion; osmosis; facilitated diffusion; and active transport (2.1). Relate how the phospholipid bilayer and membrane proteins affect the movement of molecules through the membrane (2.2). Next use the lock and key and induced fit hypotheses to explain how enzymes work (3.1). Explain how all the following factors affect the rate of enzyme-catalysed reactions: enzyme concentration, substrate concentration, temperature, pH and enzyme inhibitors (3.2). Finally, describe how disruption of an enzyme’s function can lead to health problems e.g. lactose intolerance (3.3)The essay should be approximately 1500 words (+/– 10%) In preparing your essay consider the following: 

Your essay should be concise and written in a suitable scientific style. 
Make good use of appropriate scientific terms
Have an extensive reference list used selectively and appropriately within the text. 
Have an introduction that sets the scene.
Have a conclusion that summarises the main points covered.
Each section or paragraph covering each point should be clearly referenced (i.e. in text citation). 
All figures and tables used in your essay should be in the scientific format 
The essay should demonstrate the ability to use the mechanics and conventions of written English including proper use of paragraphs. 
As this is an essay, there should be no bullet points or subheadings. 

LO1: Explain properties of important biological molecules 1.1 Compare the structures of glucose, starch and celluloseLO2: Relate key structures in the plasma membrane to their functions 2.1 Describe the ways molecules move through the membrane to include: · diffusion · osmosis · facilitated diffusion · active transport 2.2 For the following components, relate how they affect movement of molecules through the membrane Phospholipid bilayer plasma proteinsLO3: explain the structure, function and significance of enzymes in the body. 3.1 use lock and key and induced fit hypotheses to explain how enzymes work. 3.2 explaine how all the following factors affect the rate of enzyme-catalysed reactions: · enzyme concentration · substrate concentration, · temperature, · pH and · enzyme inhibitors 3.3 Describe how disruption of an enzyme’s function can lead to health problems e.g. lactose intolerance
UK SOURCE(2018) Essential Cell biology(2013) Essential Cell BiologyBoyle & Senior – Collins Educational – 2008(2015) AQA A level Biology: Student Book 1(2015) AQA A level Biology Year 1 Student book(2015) Advanced Biology for you (2nd Edition), Nelson Thorne(20140) Ross & Wilson Anatomy and Physiology in Health & Illness (121st edition), Churchill Livingstonehttp://www.rsc.org/Education/Teachers/Resources/cfb/enzymes.htm http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html http://www.sumanasinc.com/webcontent/animations/content/enzymes/enzymes.html

Cambridge International AS and A Level

Jones, Fosbery,
G

regory and Taylor
C

am
b

rid
ge International A

S
and

A
Level

B
io

lo
g

y
C

ourseb
ook

Biology
Coursebook

Fourth Edition

Mary Jones, Richard Fosbery,
Jennifer Gregory and Dennis Taylor

Mary Jones, Richard Fosbery,
Jennifer Gregory and Dennis Taylor

Cambridge International AS and A Level

Biology
Coursebook

Fourth Edition

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iii

5 The mitotic cell cycle 93
Chromosomes 94
Mitosis 97
The significance of telomeres 102
Stem cells 103
Cancer 103
End-of-chapter questions 106

6 Nucleic acids and protein synthesis 110
The structure of DNA and RNA 111
DNA replication 113
Genes and mutations 118
DNA, RNA and protein synthesis 118
End-of-chapter questions 123

7 Transport in plants 126
The transport needs of plants 127
Two systems: xylem and phloem 128
Structure of stems, roots and leaves 128
The transport of water 134
Transport of mineral ions 146
Translocation 146
Differences between sieve tubes and

xylem vessels 151
End-of-chapter questions 153

8 Transport in mammals 157
Transport systems in animals 158
The mammalian cardiovascular system 158
Blood vessels 160
Blood plasma and tissue fluid 164
Lymph 164
Blood 166
Haemoglobin 168
Problems with oxygen transport 171
The heart 173
The cardiac cycle 175
Control of the heart beat 177
End-of-chapter questions 179

How to use this book vi

Introduction viii

1 Cell structure 1
Why cells? 3
Cell biology and microscopy 3
Animal and plant cells have features in common 5
Differences between animal and plant cells 5
Units of measurement in cell studies 6
Electron microscopy 6
Ultrastructure of an animal cell 13
Ultrastructure of a plant cell 19
Two fundamentally different types of cell 21
End-of-chapter questions 23

2 Biological molecules 27
The building blocks of life 28
Monomers, polymers and macromolecules 29
Carbohydrates 29
Lipids 36
Proteins 39
Water 46
End-of-chapter questions 49

3 Enzymes 53
Mode of action of enzymes 54
Factors that affect enzyme action 57
Enzyme inhibitors 61
Comparing the affinity of different enzymes for

their substrates 62
Immobilising enzymes 64
End-of-chapter questions 66

4 Cell membranes and transport 72
Phospholipids 73
Structure of membranes 74
Cell signalling 77
Movement of substances into and out of cells 79
End-of-chapter questions 89

Contents

Cambridge International AS Level Biology

iv

9 Gas exchange and smoking 185
Gas exchange 186
Lungs 186
Trachea, bronchi and bronchioles 187
Alveoli 189
Smoking 190
Tobacco smoke 190
Lung diseases 190
Short-term effects on the cardiovascular system 193
End-of-chapter questions 195

10 Infectious diseases 198
Worldwide importance of infectious diseases 200
Cholera 200
Malaria 202
Acquired immune deficiency syndrome (AIDS) 205
Tuberculosis (TB) 209
Measles 212
Antibiotics 213
End-of-chapter questions 219

11 Immunity 222
Defence against disease 223
Cells of the immune system 224
Active and passive immunity 232
Autoimmune diseases – a case of

mistaken identity 237
End-of-chapter questions 242

P1 Practical skills for AS 246
Experiments 247
Variables and making measurements 247
Estimating uncertainty in measurement 255
Recording quantitative results 255
Constructing a line graph 256
Constructing bar charts and histograms 258
Making conclusions 259
Describing data 259
Making calculations from data 259
Explaining your results 261
Identifying sources of error and suggesting

improvements 261
Drawings 262
End-of-chapter questions 264

12 Energy and respiration 267
The need for energy in living organisms 268
Work 269
ATP 270
Respiration 272
Mitochondrial structure and function 276
Respiration without oxygen 277
Respiratory substrates 278
Adaptations of rice for wet environments 281
End-of-chapter questions 283

13 Photosynthesis 286
An energy transfer process 287
The light dependent reactions of photosynthesis 288
The light independent reactions of

photosynthesis 290
Chloroplast structure and function 290
Factors necessary for photosynthesis 291
C4 plants 293
Trapping light energy 295
End-of-chapter questions 297

14 Homeostasis 299
Internal environment 300
Control of homeostatic mechanisms 301
The control of body temperature 302
Excretion 304
The structure of the kidney 305
Control of water content 312
The control of blood glucose 315
Urine analysis 319
Homeostasis in plants 320
End-of-chapter questions 325

15 Coordination 329
Nervous communication 330
Muscle contraction 344
Hormonal communication 349
Birth control 351
Control and coordination in plants 353
End-of-chapter questions 358

Cambridge International AS and A Level Biology

v

Contents

16 Inherited change 364
Homologous chromosomes 365
Two types of nuclear division 367
Meiosis 368
Genetics 374
Genotype affects phenotype 374
Inheriting genes 375
Multiple alleles 378
Sex inheritance 378
Sex linkage 379
Dihybrid crosses 380
Interactions between loci 382
Autosomal linkage 383
Crossing over 384
The χ2 (chi-squared) test 386
Mutations 387
Gene control in prokaryotes 389
Gene control in eukaryotes 391
End-of-chapter questions 393

17 Selection and evolution 397
Variation 398
Natural selection 402
Evolution 404
Artificial selection 409
The Darwin–Wallace theory of evolution by

natural selection 412
Species and speciation 413
Molecular comparisons between species 416
Extinctions 417
End-of-chapter questions 420

18 Biodiversity, classification and
conservation 423
Ecosystems 425
Biodiversity 426
Simpson’s Index of Diversity 430
Systematic sampling 431
Correlation 433
Classification 435
Viruses 440
Threats to biodiversity 441
Why does biodiversity matter? 444
Protecting endangered species 445
Controlling alien species 451
International conservation organisations 452
Restoring degraded habitats 453
End-of-chapter questions 455

19 Genetic technology 462
Genetic engineering 463
Tools for the gene technologist 464
Genetic technology and medicine 475
Gene therapy 477
Genetic technology and agriculture 480
End-of-chapter questions 487

P2 Planning, analysis and evaluation 490
Planning an investigation 491
Constructing a hypothesis 491
Using the right apparatus 491
Identifying variables 492
Describing the sequence of steps 495
Risk assessment 495
Recording and displaying results 495
Analysis, conclusions and evaluation 495
Pearson’s linear correlation 501
Spearman’s rank correlation 503
Evaluating evidence 504
Conclusions and discussion 506
End-of-chapter questions 507

Appendix 1: Amino acid R groups 512

Appendix 2: DNA and RNA triplet codes 513

Glossary 514

Index 526

Acknowledgements 534

CD-ROM CD1

Advice on how to revise for and approach
examinations
Introduction to the examination and changes
to the syllabus
Answers to self-assessment questions
Answers to end-of-chapter questions
Recommended resources

CD1

CD16
CD21
CD64
CD128

Cambridge International AS Level Biology

vi

How to use this book
Each chapter begins with a short
list of the facts and concepts that
are explained in it.

There is a short
context at the
beginning of each
chapter, containing
an example of how
the material covered
in the chapter relates
to the ʻreal world .̓

This book does not contain detailed
instructions for doing particular
experiments, but you will find
background information about
the practical work you need to do
in these boxes. There are also two
chapters, P1 and P2, which provide
detailed information about the
practical skills you need to develop
during your course.

The text and illustrations describe and
explain all of the facts and concepts
that you need to know. The chapters,
and oft en the content within them
as well, are arranged in the same
sequence as in your syllabus.

Important equations and
other facts are shown in
highlight boxes.

Questions throughout the text give you a chance to check that you have understood
the topic you have just read about. You can find the answers to these questions on
the CD-ROM.

are explained in it.

to the ʻreal world .̓

the topic you have just read about. You can find the answers to these questions on

This book does not contain detailed

that you need to know. The chapters,

highlight boxes.

vii

How to use this book

Wherever you need to know how to use a formula to carry out a calculation,
there are worked example boxes to show you how to do this.

Key words are highlighted in the text
when they are first introduced.

You will also find definitions of
these words in the Glossary.

Definitions that are required by the
syllabus are shown in highlight boxes.

There is a summary of key
points at the end of each
chapter. You might find
this helpful when you are
revising.

Questions at the end of each chapter begin with a few multiple choice questions, then move on
to questions that will help you to organise and practise what you have learnt in that chapter.
Finally, there are several more demanding exam-style questions, some of which may require use of
knowledge from previous chapters. Answers to these questions can be found on the CD–ROM.

there are worked example boxes to show you how to do this.

syllabus are shown in highlight boxes.

when they are first introduced.

these words in the Glossary.

There is a summary of key
points at the end of each

knowledge from previous chapters. Answers to these questions can be found on the CD–ROM.

Cambridge International AS Level Biology

viii

Introduction

This fourth edition of Cambridge International AS and
A Level Biology provides everything that you need to
do well in your Cambridge International Examinations
AS and A level Biology (9700) courses. It provides full
coverage of the syllabus for examinations from 2016
onwards.

The chapters are arranged in the same sequence as the
material in your syllabus. Chapters 1 to P1 cover the AS
material, and Chapters 12 to P2 cover the extra material
you need for the full A level examinations. The various
features that you will find in these chapters are explained
on the next two pages.

In your examinations, you will be asked many
questions that test deep understanding of the facts and
concepts that you will learn during your course. It’s
therefore not enough just to learn words and diagrams that
you can repeat in the examination; you need to ensure that
you really understand each concept fully. Trying to answer
the questions that you will find within each chapter, and
at the end, should help you to do this. There are answers
to all of these questions on the CD-ROM that comes with
this book.

Although you will study your biology as a series of
different topics, it’s very important to appreciate that all of
these topics link up with each other. Some of the questions
in your examination will test your ability to make links
between different areas of the syllabus. For example, in

the AS examination you might be asked a question that
involves bringing together knowledge about protein
synthesis, infectious disease and transport in mammals.
In particular, you will find that certain key concepts come
up again and again. These include:

■■ cells as units of life
■■ biochemical processes
■■ DNA, the molecule of heredity
■■ natural selection
■■ organisms in their environment
■■ observation and experiment

As you work through your course, make sure that you
keep on thinking about the work that you did earlier, and
how it relates to the current topic that you are studying.
On the CD-ROM, you will also find some suggestions
for other sources of particularly interesting or useful
information about the material covered in each chapter.
Do try to track down and read some of these.

Practical skills are an important part of your biology
course. You will develop these skills as you do experiments
and other practical work related to the topic you are
studying. Chapters P1 (for AS) and P2 (for A level) explain
what these skills are, and what you need to be able to do to
succeed in the examination papers that test these skills.

1

Chapter 1: Cell structure

Chapter 1:
Cell structure

1

Learning outcomes
You should be able to:
■■ describe and compare the structure of animal,

plant and bacterial cells, and discuss the non-
cellular nature of viruses

■■ describe the use of light microscopes and
electron microscopes to study cells

■■ draw and measure cell structures

■■ discuss the variety of cell structures and their
functions

■■ describe the organisation of cells into tissues
and organs

■■ outline the role of ATP in cells

2

Cambridge International AS Level BiologyCambridge International AS Level Biology

Progress in science often depends on people thinking
‘outside the box’ – original thinkers who are often
ignored or even ridiculed when they first put forward
their radical new ideas. One such individual, who
battled constantly throughout her career to get her
ideas accepted, was the American biologist Lynn
Margulis (born 1938, died 2011: Figure 1.1). Her
greatest achievement was to use evidence from
microbiology to help firmly establish an idea that had
been around since the mid-19th century – that new
organisms can be created from combinations
of existing organisms which are not necessarily
closely related. The organisms form a symbiotic
partnership, typically by one engulfing the other
– a process known as endosymbiosis. Dramatic
evolutionary changes result.

The classic examples, now confirmed by later
work, were the suggestions that mitochondria and
chloroplasts were originally free-living bacteria
(prokaryotes) which invaded the ancestors of modern
eukaryotic cells (cells with nuclei). Margulis saw
such symbiotic unions as a major driving cause of

evolutionary change. She continued to challenge the
Darwinian view that evolution occurs mainly as a
result of competition between species.

In the early days of microscopy an English scientist,
Robert Hooke, decided to examine thin slices of plant
material. He chose cork as one of his examples. Looking
down the microscope, he was struck by the regular
appearance of the structure, and in 1665 he wrote a book
containing the diagram shown in Figure 1.2.

If you examine the diagram you will see the ‘pore-
like’ regular structures that Hooke called ‘cells’. Each cell
appeared to be an empty box surrounded by a wall. Hooke
had discovered and described, without realising it, the
fundamental unit of all living things.

Although we now know that the cells of cork are dead,
further observations of cells in living materials were
made by Hooke and other scientists. However, it was
not until almost 200 years later that a general cell theory
emerged from the work of two German scientists. In 1838
Schleiden, a botanist, suggested that all plants are made
of cells, and a year later Schwann, a zoologist, suggested
the same for animals. The cell theory states that the basic
unit of structure and function of all living organisms is the
cell. Now, over 170 years later, this idea is one of the most
familiar and important theories in biology. To it has been
added Virchow’s theory of 1855 that all cells arise from
pre-existing cells by cell division.

Figure 1.2 Drawing of cork cells published by Robert Hooke
in 1665.

Figure 1.1 Lynn Margulis: ‘My work more than didn’t fit in.
It crossed the boundaries that people had spent their lives
building up. It hits some 30 sub-fields of biology,
even geology.’

Thinking outside the box

2

3

Chapter 1: Cell structure

Why cells?
A cell can be thought of as a bag in which the chemistry
of life is allowed to occur, partially separated from the
environment outside the cell. Th e thin membrane which
surrounds all cells is essential in controlling exchange
between the cell and its environment. It is a very eff ective
barrier, but also allows a controlled traffi c of materials
across it in both directions. Th e membrane is therefore
described as partially permeable. If it were freely
permeable, life could not exist, because the chemicals of
the cell would simply mix with the surrounding chemicals
by diff usion.

Cell biology and microscopy
Th e study of cells has given rise to an important branch of
biology known as cell biology. Cells can now be studied
by many diff erent methods, but scientists began simply
by looking at them, using various types of microscope.

Th ere are two fundamentally diff erent types of
microscope now in use: the light microscope and the
electron microscope. Both use a form of radiation in order
to create an image of the specimen being examined. Th e
light microscope uses light as a source of radiation, while
the electron microscope uses electrons, for reasons which
are discussed later.

Light microscopy
Th e ‘golden age’ of light microscopy could be said to be
the 19th century. Microscopes had been available since
the beginning of the 17th century but, when dramatic
improvements were made in the quality of glass lenses in
the early 19th century, interest among scientists became
widespread. Th e fascination of the microscopic world
that opened up in biology inspired rapid progress both in
microscope design and, equally importantly, in preparing
material for examination with microscopes. Th is branch
of biology is known as cytology. Figure 1.3 shows how the
light microscope works.

By 1900, all the structures shown in Figures 1.4 and
1.5 had been discovered. Figure 1.4 shows the structure of
a generalised animal cell and Figure 1.5 the structure of a
generalised plant cell as seen with a light microscope.
(A generalised cell shows all the structures that are
typically found in a cell.) Figure 1.6 shows some actual
human cells and Figure 1.7 shows an actual plant cell
taken from a leaf. Figure 1.4 Structure of a generalised animal cell (diameter

about 20 μm) as seen with a very high quality light microscope.

Golgi body

cytoplasm

mitochondria

small structures that
are di�cult to identify

nuclear envelope

chromatin –
deeply staining
and thread-like nucleus

nucleolus –
deeply staining

cell surface
membrane

centriole – always
found near nucleus,
has a role in nuclear
division

Figure 1.3 How the light microscope works.

eyepiece

light beam

objective

glass slide

condenser

iris diaphragm

light source Condenser iris
diaphragm is closed
slightly to produce a
narrow beam of light.

Condenser lens focuses
the light onto the
specimen held between
the cover slip and slide.

Objective lens collects
light passing through the
specimen and produces a
magni�ed image.

Eyepiece lens magni�es
and focuses the image
from the objective onto
the eye.

pathway of light

cover slip

4

Cambridge International AS Level Biology

QUESTION

1.1 Using Figures 1.4 and 1.5, name the structures
that animal and plant cells have in common, those
found in only plant cells, and those found only in
animal cells.

Figure 1.6 Cells from the lining of the human cheek (× 400),
each showing a centrally placed nucleus, which is a typical
animal cell characteristic. The cells are part of a tissue known
as squamous (flattened) epithelium.

Figure 1.5 Structure of a generalised plant cell (diameter about 40 μm) as seen with a very high quality light microscope.

Golgi apparatus

cytoplasm

chromatin –
deeply staining
and thread-like

nucleus
small structures that
are di�cult to identify

nucleolus –
deeply staining

nuclear envelope

mitochondria
chloroplast

grana just visible

tonoplast – membrane
surrounding vacuole

vacuole – large
with central position

plasmodesma –
connects cytoplasm
of neighbouring cells

cell wall

cell wall of
neighbouring
cell

cell surface membrane
(pressed against cell wall)

middle lamella – thin layer
holding cells together,
contains calcium pectate

Figure 1.7 Photomicrograph of a cells in a moss leaf (×400).

5

Chapter 1: Cell structure

Animal and plant cells
have features in common
In animals and plants each cell is surrounded by a very
thin cell surface membrane. This is also sometimes
referred to as the plasma membrane.

Many of the cell contents are colourless and
transparent so they need to be stained to be seen. Each
cell has a nucleus, which is a relatively large structure
that stains intensely and is therefore very conspicuous.
The deeply staining material in the nucleus is called
chromatin and is a mass of loosely coiled threads.
This material collects together to form visible separate
chromosomes during nuclear division (page 98). It
contains DNA (deoxyribonucleic acid), a molecule which
contains the instructions that control the activities of the
cell (see Chapter 6). Within the nucleus an even more
deeply staining area is visible, the nucleolus, which is
made of loops of DNA from several chromosomes. The
number of nucleoli is variable, one to five being common
in mammals.

The material between the nucleus and the cell surface
membrane is known as cytoplasm. Cytoplasm is an
aqueous (watery) material, varying from a fluid to a
jelly-like consistency. Many small structures can be seen
within it. These have been likened to small organs and
hence are known as organelles. An organelle can be
defined as a functionally and structurally distinct part
of a cell. Organelles themselves are often surrounded
by membranes so that their activities can be separated
from the surrounding cytoplasm. This is described as
compartmentalisation. Having separate compartments
is essential for a structure as complex as an animal or
plant cell to work efficiently. Since each type of organelle
has its own function, the cell is said to show division of
labour, a sharing of the work between different
specialised organelles.

The most numerous organelles seen with the light
microscope are usually mitochondria (singular:
mitochondrion). Mitochondria are only just visible,
but films of living cells, taken with the aid of a light
microscope, have shown that they can move about,
change shape and divide. They are specialised to carry
out aerobic respiration.

The use of special stains containing silver enabled the
Golgi apparatus to be detected for the first time in 1898 by
Camillo Golgi. The Golgi apparatus is part of a complex
internal sorting and distribution system within the cell
(page 15). It is also sometimes called the Golgi body or
Golgi complex.

Differences between animal
and plant cells
The only structure commonly found in animal cells which
is absent from plant cells is the centriole. Plant cells also
differ from animal cells in possessing cell walls, large
permanent vacuoles and chloroplasts.

Centrioles
Under the light microscope the centriole appears as a small
structure close to the nucleus (Figure 1.4, page 3). Centrioles
are discussed on page 18.

Cell walls and plasmodesmata
With a light microscope, individual plant cells are more
easily seen than animal cells, because they are usually
larger and, unlike animal cells, surrounded by a cell wall
outside the cell surface membrane. This is relatively rigid
because it contains fibres of cellulose, a polysaccharide
which strengthens the wall. The cell wall gives the cell a
definite shape. It prevents the cell from bursting when
water enters by osmosis, allowing large pressures to
develop inside the cell (page 84). Cell walls may also be
reinforced with extra cellulose or with a hard material
called lignin for extra strength (page 141). Cell walls are
freely permeable, allowing free movement of molecules
and ions through to the cell surface membrane.

Plant cells are linked to neighbouring cells by means of
fine strands of cytoplasm called plasmodesmata (singular:
plasmodesma), which pass through pore-like structures in
their walls. Movement through the pores is thought to be
controlled by the structure of the pores.

Vacuoles
Although animal cells may possess small vacuoles such
as phagocytic vacuoles (page 87), which are temporary
structures, mature plant cells often possess a large,
permanent, central vacuole. The plant vacuole is
surrounded by a membrane, the tonoplast, which controls
exchange between the vacuole and the cytoplasm. The
fluid in the vacuole is a solution of pigments, enzymes,
sugars and other organic compounds (including some
waste products), mineral salts, oxygen and carbon dioxide.

Vacuoles help to regulate the osmotic properties of cells
(the flow of water inwards and outwards) as well as having
a wide range of other functions. For example, the pigments
which colour the petals of certain flowers and parts of
some vegetables, such as the red pigment of beetroots, may
be located in vacuoles.

6

Cambridge International AS Level Biology

Chloroplasts
Chloroplasts are found in the green parts of the plant,
mainly in the leaves. They are relatively large organelles
and so are easily seen with a light microscope. It is even
possible to see tiny ‘grains’ or grana (singular: granum)
inside the chloroplasts using a light microscope. These
are the parts of the chloroplast that contain chlorophyll,
the green pigment which absorbs light during the process
of photosynthesis, the main function of chloroplasts.
Chloroplasts are discussed further on page 19.

Points to note
■■ You can think of a plant cell as being very similar to an

animal cell, but with extra structures.
■■ Plant cells are often larger than animal cells, although

cell size varies enormously.
■■ Do not confuse the cell wall with the cell surface

membrane. Cell walls are relatively thick and
physically strong, whereas cell surface membranes are
very thin. Cell walls are freely permeable, whereas cell
surface membranes are partially permeable. All cells
have a cell surface membrane.

■■ Vacuoles are not confined to plant cells; animal cells
may have small vacuoles, such as phagocytic
vacuoles, although these are not usually
permanent structures.

We return to the differences between animal and plant
cells as seen using the electron microscope on page 13.

Units of measurement
In order to measure objects in the microscopic world, we
need to use very small units of measurement, which are
unfamiliar to most people. According to international
agreement, the International System of Units (SI units)
should be used. In this system, the basic unit of length is
the metre (symbol, m). Additional units can be created
in multiples of a thousand times larger or smaller, using
standard prefixes. For example, the prefix kilo means
1000 times. Thus 1 kilometre = 1000 metres. The units
of length relevant to cell studies are …

Basic introduction to chemistry
This section is not assessed directly but is important background knowledge for the following subject.

LO basic chemistry
State the parts of an atom and know their charge
Predict whether a substance is reactive based on it’s out electron shell
Discuss the difference between an atom, molecule and compound
Describe three types of bonding:
Ionic
Covalent
Hydrogen
Explain the polar nature of water
Discuss the effect of temperature on bonds

Atoms and elements

Protons are positively charged
Neutrons are neutral
Electrons are negatively charged
Atoms have an equal number of protons and electrons so are neutral

Electrons
1-5 shells
Electrons move within the shells
Stable when the shell is full
Reactive when the outer shell is not full
Reactions cause bonding

Molecules and compounds
A molecule is where two or more atoms are bonded together

A compound is where two different types of atoms are joined together

Bonding – ionic
Example is table salt or NaCl
Sodium has one electron in its outer shell – very reactive
Chlorine has seven electron in it’s outer shell, also unstable
Sodium atoms lose an electron to chlorine
Both now ions

Question after the exchange how many protons and electrons does sodium have? What is the net charge?

Bonding – covalent
In covalent bonding the electrons are shared between both outer shells
This stabilises both atoms in the molecule
So covalent bonds are strong
O2 or oxygen gas is an example of covalent bonding

Water molecules are polar
Polar means different at either end
For water molecules the charge is slightly different at either end
Because the oxygen is larger it has more weight and more protons
So the electrons are pulled towards the oxygen end making it slightly more negative.
The hydrogen ends become slightly positive

Hydrogen bonding
Hydrogen bonding occurs between polar molecules
These bonds are less strong than covalent bonds
They are responsible for water being liquid over such a big range of temperatures as the molecules are attracted to each other.
Heat can break hydrogen bonds

Water as a solvent
It is the polar nature of water that makes it such a good solvent
Any molecule with a charge will attract the polar water molecules
This allows them to be dissolved in the water
Water is the universal solvent

Kinetic theory
Kinetic energy is movement energy
theory states that molecules can move. In solid state not very much but in liquid they do move and as a gas they move fastest.
Heating a substance cause the molecules to move more, they have more kinetic energy.
So solid becomes liquid and liquid becomes gas.

LO basic chemistry
State the parts of an atom and know their charge
Predict whether a substance is reactive based on it’s out electron shell
Discuss the difference between an atom, molecule and compound
Describe three types of bonding:
Ionic
Covalent
Hydrogen
Explain the polar nature of water
Discuss the effect of temperature on bonds

Starter – prefixes
Saccharide means sugar unit. Complete the table of prefixes for the word saccharide and guess what they mean

prefix meaning

Example: Oligo 3-9 units

Mono

Di

Poly

Organic Molecules
Carbohydrates

Objectives
Review key carbohydrates based on your research over half term.

Produce monosaccharides, disaccharides and polysaccharides using simple practical models

Explain how complex carbohydrates are formed

Relate the structure of a polysaccharide to its function.

Grab a miniwhite, pen, duster EACH!!

Carbohydrates

Write on your board what this means and some examples

Types of Carbohydrates

3 sucrose or table sugar:
4. Sugar to make cakes – sucrose, fructose, glucose
5.
Polysaccharide, starch: mention GI
6: disacch milk: lactose intolerance; genetic predisposition to tolerance in europe lack of sunlight?
7 chitin: house dust mite. exoskeletons of insects. Thought to induce some forms of asthma. We have enyzme that breaks down chitin to reduce our allergic response but some people are oversensitive and perhaps have issues with producing this enzyme so develop an allergic reaction, e.g. people that work in shellfish factories;
http://www.hhmi.org/research/induction-allergic-immunity

5

Carbohydrates

Composed of:
Carbon (carbo)
Hydrogen
Oxygen

Carbs are characterised by either number of rings or number of carbons

(hydrate hint: water)

6

Monosaccharides

Monosaccharides – Glucose
Glucose is a key monosaccharide in biology
Main transport of sugar in blood
Used in cellular respiration in both plants and animals to provide energy
Plants produce glucose as part of photosynthesis
It is a six carbon sugar
With a ring structure
molecular formula is: C6H12O6
Structure of monosaccharide: see handout.

Add on C numbers e.g. C1
1
2
3
4
5
6
What is the chemical formula for glucose?
HANDOUT

What is the difference between this and your handout?

This is
 – glucose

Isomers

Isomers have the same chemical formula when written but the atoms are arranged differently so they are structurally different

Use of molecular models
In pairs put together a 3D model of  glucose

When you finish that, show another pair how you would produce  glucose

Disaccharides

Disaccharides

These are formed when two monosaccharides are joined together.

The bond is called a glycosidic bond

Glycocidic Bond

Glycocidic Bonds

The reaction involves the removal of water so is called a condensation reaction.

Condenser

Disaccharides

Draw an  glucose molecule on your mini white board

Now in pairs produce a glycosidic bond by removing H-O from C1 and H from C4. Draw an oxygen bond.

3D Model of Disaccharide

Use of molecular models
In groups of 4 now put together two monosaccharides to form maltose.

What did you have to remove?

What is the chemical formula of maltose?

C12H22O11

Disaccharides Mix and Match

polysaccharides

Polysaccharides
Long chains of monosaccharides joined together by glycosidic bonds.

Three main examples
Starch
Glycogen
Cellulose

22

Starch

Complex carbohydrates

Insoluble storage carbohydrate in plants.
Mixture of amylose and amylopectin.

Starch
Amylose molecule: coils up into helix so can be stored easily (formed by 1,4 glycosidic bonds)
Amylopectin: very few side chains so cannot be broken down easily (formed by 1,6 glycosidic bonds)
Since it is insoluble it does not add to the osmotic load

Use of molecular models

On each bench put your models together to form a polysaccharide with at least one branch

Hint: branching glycosidic bond are 1-6 bonds

Glycogen
Insoluble storage carbohydrate in animals.

Found in muscle and liver

Highly branched so can be broken down easily.

Why do you think it is more important that the storage polysaccharide in animals can be broken down more easily than starch in plants?

Glycogen storage disease

Rare diseases caused by abnormal or missing function of enzymes involved in the conversion of glycogen.
They cause hypoglycemia.

Glycogen storage diseases examples

1 in 40 000 births have some form of glycogen storage disease (Dutch study); higher in US (20-25,000). Thought to be 11 distinct types
30

The last polysaccharide?

Cellulose
Most abundant organic compound in nature.
Makes up 30 % of plants and is major component of cell walls.
Made up of β glucose units which means that cellulose is made up of straight chains.
The chains cross-link with each other by hydrogen bonding
These chains form microfibrils which are very strong and rigid.

Cellulose

Carbohydrates Summary

34

Objectives
Review key carbohydrates based on your research over half term.

Produce monosaccharides, disaccharides and polysaccharides using simple practical models

Explain how complex carbohydrates are formed

Relate the structure of a polysaccharide to its function.

Reducing and non-reducing sugars

E.g.
Glucose
Fructose
Galactose
Monosaccharides
E.g.
Maltose
Sucrose
Lactose
Disaccharides
E.g.
Starch
Glycogen
Cellulose
Polysaccharides
Sugars
Carbohydrates

Types of carbohydrate

Monosaccharides
1 sugar unit
Disaccharides
2 sugar unit
Polysaccharides
multiple sugar unit

Isomers and Glycocidic bonds

Starch, Glycogen and Cellulose

Fatty acids, triglycerides and cholesterol

What we will cover in this session

Simple Diffusion
Facilitated Diffusion
Active Transport

Osmosis

Exocytosis and Endocytosis

Exocytosis
Endocytosis

Amino acids and peptide bonds

Protein folding Summary

Enzymes – lock and key, induced fit

Factors that affect enzyme function

Enzymes and health

Assignment
Write an essay on the structures, functions and movement of biological molecules. In your assignment you should start by comparing the structures of carbohydrates including glucose, starch and cellulose (1.1)
Then go on to describe the plasma membrane. Discuss ways molecules move through the membrane including: diffusion; osmosis; facilitated diffusion; and active transport (2.1). Relate how the phospholipid bilayer and membrane proteins affect the movement of molecules through the membrane (2.2).
Next use the lock and key and induced fit hypotheses to explain how enzymes work (3.1). Explain how all the following factors affect the rate of enzyme-catalysed reactions: enzyme concentration, substrate concentration, temperature, pH and enzyme inhibitors (3.2). Finally, describe how disruption of an enzyme’s function can lead to health problems e.g. lactose intolerance (3.3)
The essay should be approximately 1500 words (+/– 10%)

Quality
Your essay should be concise and written in a suitable scientific style.
Make good use of appropriate scientific terms
Have an extensive reference list used selectively and appropriately within the text.
Have an introduction that sets the scene.
Have a conclusion that summarises the main points covered.
Each section or paragraph covering each point should be clearly referenced (i.e. in text citation).
All figures and tables used in your essay should be in the scientific format
The essay should demonstrate the ability to use the mechanics and conventions of written English including proper use of paragraphs.
As this is an essay, there should be no bullet points or subheadings.

Indicative Content for Merit Indicative content for Distinction

1 Understanding of the subject

The student, student’s work or performance:
demonstrates a very good grasp of the relevant knowledge base The student, student’s work or performance:
demonstrates an excellent grasp of the relevant knowledge base

2 Application of knowledge

The student, student’s work or performance:
a makes use of relevant: The student, student’s work or performance:
a makes use of relevant:

ideas
facts
theories
models
 
with either
b breadth or depth that goes beyond the minimum required to Pass
 
and/or
 
c very good levels of:
accuracy
insight
analysis ideas
facts
theories
models
 
with both
b breadth and depth
 
 
and / or
 
c excellent levels of:
accuracy
insight
analysis

7 Quality

The student, student’s work or performance:
a is structured in a way that is generally logical and fluent
 
c taken as a whole, demonstrates a very good response to the demands of the brief/assignment The student, student’s work or performance:
a is structured in a way that is consistently logical and fluent
 
c taken as a whole, demonstrates an excellent response to the demands of the brief/assignment

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