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included
Student Book
Philip Bradfield, Steve Potter
BIOLOGY
EDEXCEL INTERNATIONAL GCSE (9 –1)
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Steve Potter
Philip Bradfield
Student Book
BIOLOGY
EDEXCEL INTERNATIONAL GCSE (9 –1)
 CONTENTS iii
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COURSE STRUCTURE IV
ABOUT THIS BOOK VI
ASSESSMENT OVERVIEW VII
UNIT 1: ORGANISMS AND LIFE PROCESSES 02
UNIT 2: ANIMAL PHYSIOLOGY 38
UNIT 3: PLANT PHYSIOLOGY 134
UNIT 4: ECOLOGY AND THE ENVIRONMENT 186
UNIT 5: VARIATION AND SELECTION 226
UNIT 6: MICROORGANISMS AND GENETIC MODIFICATION 280
APPENDIX 303
GLOSSARY 306
INDEX 311
 98 ANIMAL PHYSIOLOGY CHEMICAL COORDINATION
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7  CHEMICAL COORDINATION

The nervous system (Chapter 6) is a coordination system forming a link between stimulus and response. The body
has a second coordination system, which does not involve nerves. This is the endocrine system. It consists of organs
called endocrine glands, which make chemical messenger substances called hormones. Hormones are carried in the
bloodstream.

LEARNING OBJECTIVES

By the end of this chapter you should be able to: ◼ progesterone*

◼ describe how responses can be controlled by hormonal ◼ oestrogen*
communication
BIOLOGY ONLY
◼ understand the differences between nervous and ◼ antidiuretic hormone (ADH)*
hormonal control
◼ follicle stimulating hormone (FSH)*
◼ understand the sources, roles and effects of the
following hormones: ◼ luteinising hormone (LH)*
◼ adrenaline
◼ insulin
*These hormones will be dealt with in more detail in later
chapters.
◼ testosterone*

GLANDS AND HORMONES

A gland is an organ that releases or secretes a substance. This means that
cells in the gland make a chemical which leaves the cells through the cell
membrane. The chemical then travels somewhere else in the body, where it
carries out its function. There are two types of glands – exocrine and endocrine
glands. Exocrine glands secrete their products through a tube called a duct.
For example, salivary glands in your mouth secrete saliva down salivary ducts,
and tear glands secrete tears through ducts that lead to the surface of the eye.
Endocrine glands have no duct, and so are called ductless glands. Instead,
their products, the hormones, are secreted into the blood vessels that pass
through the gland (Figure 7.1).
exocrine gland endocrine gland

blood supply
duct

(outside of
gland, e.g. lumen
of gut)
▲ Figure 7.1 Exocrine glands secrete their products though a duct, while endocrine glands secrete
hormones into the blood.

This chapter looks at some of the main endocrine glands and the functions of
the hormones they produce. Because hormones are carried in the blood, they
can travel to all areas of the body. They usually only affect certain tissues or
 ANIMAL PHYSIOLOGY CHEMICAL COORDINATION 99
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KEY POINT organs, called ‘target organs’, which can be a long distance from the gland
that made the hormone. Hormones only affect particular tissues or organs
The receptors for some hormones
if the cells of that tissue or organ have special chemical receptors for the
are located in the cell membrane
of the target cell. Other hormones particular hormone. For example, the hormone insulin affects the cells of the
have receptors in the cytoplasm, and liver, which have insulin receptors.
some in the nucleus. Without specific
receptors, a cell will not respond to a
hormone at all. THE DIFFERENCES BETWEEN NERVOUS AND ENDOCRINE
CONTROL
Although the nervous and endocrine systems both act to coordinate body
functions, there are differences in the way that they do this. These are
summarised in Table 7.1.
Table 7.1: The nervous and endocrine systems compared.

NERVOUS SYSTEM ENDOCRINE SYSTEM

works by nerve impulses transmitted through nerve cells (although
works by hormones transmitted through the bloodstream
chemicals are used at synapses)
nerve impulses travel fast and usually have an ‘instant’ effect hormones travel more slowly and generally take longer to act

response is usually short-lived response is usually longer-lasting

impulses act on individual cells such as muscle fibres, so have a very hormones can have widespread effects on different organs (although they
localised effect only act on particular tissues or organs if the cells have the correct receptors)

THE ENDOCRINE GLANDS The positions of the main endocrine glands are shown in Figure 7.2. A summary
of some of the hormones that they make and their functions is given in Table 7.2.
pituitary
The pituitary gland (often just called ‘the pituitary’) is found at the base of
the brain. It produces a number of hormones, including antidiuretic hormone
(ADH), which acts on the kidneys, controlling the amount of water in the
blood (see Chapter 8). The pituitary also releases hormones that regulate
thyroid reproduction (see Chapter 9).
Just above the pituitary is a part of the brain called the hypothalamus. The
pituitary contains neurones linking it to the hypothalamus, and some of its
hormones are produced under the control of the brain.
Table 7.2: Some of the main endocrine glands, the hormones they produce and their functions.
adrenal
GLAND HORMONE SOME FUNCTIONS OF THE HORMONES
pituitary follicle stimulating hormone stimulates egg development and oestrogen
(FSH) secretion in females and sperm production in males
pancreas luteinising hormone (LH) stimulates egg release (ovulation) in females and
testosterone production in males
antidiuretic hormone (ADH) controls the water content of the blood
ovary
thyroid thyroxine controls the body’s metabolic rate (how fast
(in women)
chemical reactions take place in cells)
pancreas insulin lowers blood glucose
testis (in men)
glucagon raises blood glucose
▲ Figure 7.2 The main endocrine glands of the adrenals adrenaline prepares the body for physical activity
body.
testes testosterone controls the development of male secondary sexual
KEY POINT characteristics
The pituitary is a link between the ovaries oestrogen controls the development of female secondary
nervous and endocrine coordination sexual characteristics
systems. progesterone regulates the menstrual cycle
 100 ANIMAL PHYSIOLOGY CHEMICAL COORDINATION
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The pancreas is both an endocrine and an exocrine gland. It secretes two

hormones involved in the regulation of blood glucose, and is also a gland of
the digestive system, secreting enzymes through the pancreatic duct into the
small intestine (see Chapter 4). The sex organs of males (testes) and females
(ovaries) are also endocrine organs. In addition to their role in producing sex
cells, the testes and ovaries make hormones that are involved in controlling
reproduction. This topic is covered more fully in Chapter 9. We will now look at
the functions of two hormones in more detail.

ADRENALINE – THE ‘FIGHT OR FLIGHT’ HORMONE

DID YOU KNOW?
When you are frightened, excited or angry, your adrenal glands secrete the
‘Adrenal’ means ‘next to the hormone adrenaline.
kidneys’, which describes where
Adrenaline acts at a number of target organs and tissues, preparing the body
the adrenal glands are located for action. In animals other than humans this action usually means dealing
– on top of these organs (see with an attack by an enemy, where the animal can stay and fight or run away
Figure 7.2). – hence ‘fight or flight’. This is not often a problem with humans, but there are
plenty of other times when adrenaline is released (Figure 7.3).

hair stands on end,

glucose is released making the animal
from the liver look larger

blood is directed
away from the gut pupils dilate
and towards the
muscles

heart beats faster

breathing becomes
faster and deeper

▲ Figure 7.3 Many human activities cause adrenaline to be produced, not ▲ Figure 7.4 Adrenaline affects the body of an animal in many ways.
just a ‘fight or flight’ situation!

If an animal’s body is going to be prepared for action, the muscles need a

good supply of oxygen and glucose for respiration. Adrenaline produces
several changes in the body that make this happen (Figure 7.4) as well as other
changes to prepare for fight or flight.
◾◾ The breathing rate increases and breaths become deeper, taking more
oxygen into the body.
◾◾ The heart beats faster, sending more blood to the muscles, so that they
receive more glucose and oxygen for respiration.
◾◾ Blood is diverted away from the intestine and into the muscles.
◾◾ In the liver, stored carbohydrate (glycogen) is changed into glucose and
released into the blood. The muscle cells absorb more glucose and use it
for respiration.
◾◾ The pupils dilate, increasing visual sensitivity to movement.
◾◾ Body hair stands upright, making the animal look larger to an enemy.
◾◾ Mental awareness is increased, so reactions are faster.
 ANIMAL PHYSIOLOGY CHEMICAL COORDINATION 101
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In humans, adrenaline is not just released in a ‘fight or flight’ situation, but in

many other stressful activities too, such as preparing for a race, going for a job
interview or taking an exam.

INSULIN – CONTROL OF BLOOD GLUCOSE

You saw earlier that adrenaline can raise blood glucose from stores in the
liver. The liver cells contain carbohydrate in the form of glycogen. Glycogen
is made from long chains of glucose sub-units joined together, forming a large
insoluble molecule (see Chapter 4). Being insoluble makes glycogen a good
storage product. When the body is short of glucose, the glycogen can be
broken down into glucose, which then passes into the bloodstream.
Adrenaline raises blood glucose concentration in an emergency, but other
hormones act all the time to control the level, keeping it fairly constant at a
little less than 1 g of glucose in every dm3 (cubic decimetre) of blood. The main
hormone controlling glucose is insulin. Insulin is made by special cells in the
pancreas. It stimulates the liver cells to take up glucose and convert it into
glycogen, lowering the level of glucose in the blood.
The concentration of glucose in your blood will start to rise after you have had
DID YOU KNOW? a meal. Sugars from digested carbohydrate pass into the blood and are carried
The pancreas also makes a to the liver in the hepatic portal vein (Chapter 5). In the liver the glucose is
hormone called glucagon, which converted to glycogen, so the blood leaving the liver in the hepatic vein has a
lower concentration of glucose than when it enters the liver.
has the opposite effect to insulin
– it raises blood glucose. DIABETES
Some people have a disease where their pancreas cannot make enough
insulin to keep their blood glucose level constant – it rises to very high
concentrations. The disease is called diabetes. One symptom of diabetes can
be detected by a chemical test on urine. Normally, people have no glucose
at all in their urine. Someone suffering from diabetes may have such a high
concentration of glucose in the blood that it is excreted in their urine. This can
be shown up by using coloured test strips (Figure 7.5).

KEY POINT
We should really refer to this disease by its full name, which is 'type 1' diabetes. There
is also a ‘type 2’ diabetes, where the pancreas produces insulin but the body shows
insulin resistance, where insulin
has less effect than it should do. At first the pancreas makes extra insulin, but
eventually it can’t continue to make enough to maintain blood glucose at a normal
level. Type 2 diabetes is common in people who are overweight and eat a poor diet
that is high in sugar and other carbohydrates. It can be prevented and controlled by
▲ Figure 7.5 Coloured test strips are used to eating a good diet and taking regular exercise. Type 2 diabetes also tends to happen in
detect glucose in urine. middle-aged or older people, whereas type 1 can happen at any age, and is common
in childhood.

Another symptom of diabetes is a constant thirst. This is because the high

blood glucose concentration stimulates receptors in the hypothalamus of the
brain. These ‘thirst centres’ are stimulated, so that by drinking, the person will
dilute their blood.
Severe diabetes is very serious. If it is untreated, the sufferer loses weight and
becomes weak and eventually falls into a coma and dies.
Carbohydrates in the diet, such as starch and sugars, are the source of
glucose in the blood, so a person with diabetes can help to control their blood
 102 ANIMAL PHYSIOLOGY CHEMICAL COORDINATION
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KEY POINT sugar if they limit the amount of carbohydrate that they eat. However a person
with diabetes (type 1) also needs to receive daily injections of insulin to keep
Insulin is a protein, and if it were to be
the glucose in their blood at the right level.
taken by mouth in tablet form, it would
be broken down by protease enzymes People with diabetes can check their blood glucose using a special sensor.
in the gut. Instead it is injected into They prick their finger and place a drop of blood on a test strip. The strip is
muscle tissue, where it is slowly then put into the sensor, which gives them an accurate reading of how much
absorbed into the bloodstream.
glucose is in their blood (Figure 7.6). They can then tell when to inject insulin
and how much to inject.

DID YOU KNOW?

Insulin for the treatment of
diabetes has been available
since 1921, and has kept millions
of people alive. It was originally
extracted from the pancreases of
animals such as pigs and cows,
and much insulin is still obtained
in this way. However, since
the 1970s, human insulin has
been produced commercially,
from genetically modified (GM)
bacteria. The bacteria have their
DNA ‘engineered’ to contain
the gene for human insulin (see
Chapter 22).
▲ Figure 7.6 Sensor for measuring blood glucose.

CHAPTER QUESTIONS
More questions on chemical coordination can be found at the end of Unit 2 on
page 136

SKILLS CRITICAL
1 2 THINKING
3 4 5 6 7 1 Which
8 9 of the
10 following
11 12 statement(s) is/are true?

1 Insulin converts glucose to glycogen

2 Insulin causes blood glucose levels to fall
3 Glucose is stored as glucagon in the liver
4 Glycogen can be broken down to release glucose into the blood

A 2 only
B 2 and 4
C 3 and 4
D 1 and 2

1 2 3 4 5 6 7 2 Which
8 9 hormone
10 11controls
12 the development of the male secondary sexual
characteristics?
A testosterone
B oestrogen
C progesterone
D follicle stimulating hormone (FSH)
 ANIMAL PHYSIOLOGY CHEMICAL COORDINATION 103
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1 2 3 4 5 6 3
7 Which
8 of
9 the10 following
11 12will not happen when the hormone adrenaline is

released?
A an increase in heart rate
B an increase in blood flow to the gut
C dilation of the pupils
D an increase in breathing rate
1 2 3 4 5 6 4
7 Which
8 of
9 the 10 following
11 12is a symptom of type 1 diabetes?

A high insulin level in the blood

B low glucose level in the blood
C glucose present in the urine
D insulin present in the urine

1 2 3 4 5 6 7 85 a 9Hormones
10 11 are 12
secreted by endocrine glands. Explain the meaning of the
four words in italics
SKILLS ANALYSIS
1 2 3 4 5 6 7 b 8Identify
9 the
10 hormones
11 12 A to D in the table.

HORMONE ONE FUNCTION OF THIS HORMONE

A stimulates the liver to convert glucose to glycogen

B controls the ‘fight or flight’ responses

C controls the breaking of the voice at puberty in boys

D completes the development of the uterus lining during the menstrual cycle

6 The graph shows the changes in blood glucose in a healthy woman over a
12-hour period.

130
/mg per 100cm3 of blood

120
blood glucose

110
100 X Y
90
80
70

0800 1200 1600 2000

time of day

1 2 3 4 5 6 7 8 9 a 10Explain
11 why
12 there was a rise in blood glucose at X.

1 2 3 4 5 6 7 8 9 b 10How11does12the body bring about a decrease in blood glucose at Y? Your

answer should include the words insulin, liver and pancreas.
c Diabetes is a disease where the body cannot control the concentration of
glucose in the blood.
1 2 3 4 5 6 7 8 9 10 i Why
11 is
12 this dangerous?

SKILLS1 CRITICAL
2 3THINKING
4 5 6 7 8 9
ii 10
Describe
11
two
12
ways a person with diabetes can monitor their blood
glucose level.
1 2 3 4 5 6 7 8 9 iii Explain
10 11 12 two ways that a person with diabetes can help to control their
blood glucose level.
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EDEXCEL INTERNATIONAL GCSE (9 –1)

BIOLOGY
Student Book
Philip Bradfield, Steve Potter

Edexcel International GCSE (9–1) Biology prepares students for the new
2017 International GCSE (9–1) Biology specification. This resource provides
comprehensive coverage of the new specification. This book, which includes
access to the eBook, is designed to provide students with the best preparation
possible for the examination:

• Written by highly experienced International GCSE Biology teachers and

authors Philip Bradfield and Steve Potter
• Content is mapped closely to the specification to provide
comprehensive coverage
• Exam practice throughout, with differentiated revision exercises and exam-
style practice
• Signposted transferable skills
• Integrated Pearson Progression Scale
• Reviewed by a language specialist to ensure the book is written in a clear
and accessible style for students whose first language may not be English
• Glossary of key Biology terminology, along with full answers included on
the eBook
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