F214 unit 1
Communication, Homeostasis and Energy
Module 1 – Communication and Homeostasis
Name _________________________________
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F214 unit 1 – Communication, Homeostasis and Energy
Module 1 – Communication and Homeostasis
Communication
You MUST to be able to…..
Understood
Revised
Remembered
Understood
Revised
Remembered
Outline the need for communication systems within multicellular
organisms, with reference to the need to respond to changes in the
internal and external environment and to co-ordinate the activities of
different organs;
State that cells need to communicate with each other by a process
called cell signaling;
State that neuronal and hormonal systems are examples of cell
signaling;
Define the terms negative feedback, positive feedback and
homeostasis;
Explain the principles of homeostasis in terms of receptors, effectors
and negative feedback;
Describe the physiological and behavioral responses that maintain a
constant core body temperature in ectotherms and endotherms, with
reference to peripheral temperature receptors, the hypothalamus and
effectors in skin and muscles
Hormones
You MUST to be able to…..
Define the terms endocrine gland, exocrine gland, hormone and target
tissue
Explain the meaning of the terms first messenger and second
messenger, with reference to adrenaline and cyclic AMP (cAMP)
Describe the functions of the adrenal glands;
Describe, with the aid of diagrams and photographs, the histology of
the pancreas, and outline its role as and endocrine and exocrine gland
Explain how blood glucose concentration is regulated, with reference
to insulin, glucagon and the liver;
Outline how insulin secretion is controlled, with reference to potassium
channels and calcium channels and beta cells;
Compare and contrast the causes of Type I (insulin dependent) and
Type II (non-insulin-dependent) diabetes mellitus;
Discuss the use of insulin produced by genetically modified bacteria,
and the potential use of stem cells, to treat diabetes mellitus;
Outline the hormonal and nervous mechanisms involved in the control of
heart rate in humans.
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COMMUNICATION
Animals are an example of a multicellular organism. There is a division of labour between different
tissues and organs (and cells) which keeps the organism functioning.
Stimulus and response is required, to allow the different tissues to communicate with each other.
Multicellular organisms require communication as they are differentiated and have this division of
labour, in order to coordinate the functions of the different systems. It provides a link between the
receptor, detecting a stimulus, and the effector being triggered to carry out an appropriate
response.
Cell signalling
Use your text book page 5 to complete the following
1. Define cell signalling
2. What are the two major systems of cell signalling?
3. Give 5 requirements of a good communication system





Stimulus and response
The body must respond to external stimuli (such as changes in temperature, light, sound, taste, etc)
as well as internal stimuli (such as changes in body temperature, blood sugar levels and presence of
pathogens). The communication which takes place between the detection of a stimulus and the
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implementation of the response relies on two systems: the nervous system and the endocrine system
(hormonal system).
Nervous communication uses signals carried by nerves throughout the central nervous system (CNS),
in the form of an electrical impulse.
The endocrine system uses hormones, which travel around in the bloodstream and trigger a response
when they bind with target cells or target tissues.
Comparing the Nervous and Hormonal Systems
The nervous system is not the only means by which the activities of the body can be coordinated.
Chemicals called hormones act as a means of chemical communication with target cells. They are
secreted by endocrine glands into the bloodstream and transported throughout the body. Each
hormone affects only specific target cells, modifying their activity. Some hormones bind to receptors
on the cell surface, producing a second messenger that can activate enzymes within the cell; others
act on the cell by indirect or direct signaling to control transcription of enzymes. Many hormones are
produced steadily over long periods of time to control long-term changes in the body, such as growth
and sexual development.
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Complete the table below to contrast the hormonal and nervous systems
Aspect
Nervous Control
Communication in the form
of:
Electrical transmission by
nerve impulses and
chemicals at synapses
Hormonal Control
Speed of response
Associated with what
length of response
Usually associated with
sort-term changes e.g.
muscle contractions
Targets
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Can control long-term
changes such as growth and
puberty
Homeostasis
The term homeostasis describes the process of maintaining a constant internals environment despite
external changes which may be taking place.
Complete the table below:
Factor
Reason why it is important to maintain a constant level
Blood pH
Oxygen
Carbon
dioxide
Blood glucose
Temperature
Water balance
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Negative feedback
One mechanism, called negative feedback, operates by detecting the external change (stimulus), communicating
with other cells, and reversing the change (response)
Negative feedback is also known as end-product inhibition as it involves the product of a process
inhibiting the process that creates the product. In negative feedback, any change or deviation from
the normal range or set point is opposed or resisted. This opposition or resistance works to bring the
variable back into the range or set point.
Feedback mechanisms provide information about a factor in a system. This information is gathered
by receptors positioned around the body. The information will then be used to control the production
of the factor being monitored.
Many factors have a set level, in negative feedback any departure away from the set level will be
detected and will set in motion changes, which return it to the set level.
From page 6 draw a flow diagram to show how negative feedback works, define SENSORY RECEPTORS,
COMMUNICATION SYSTEM and EFFECTOR CELLS.
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Positive feedback
This type of feedback usually doesn’t lead to homeostasis, as the effector actually increases the change
detected by the receptor, and so it can be seen as a ‘vicious cycle’ approach. With positive feedback, the
change is amplified, which is usually harmful to the organism. One example of this is, again, using temperature.
However, this time, we must assume that the body is getting too cold due to a severely low temperature.
Normally, if the external temperature increases slightly, our bodies can react to the change, but when our
bodies get too hot heat stroke can occur.
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Another example might be childbirth: when contractions begin in labour, the cervix widens, which is detected
by receptors, which trigger the release of oxytocin which causes further contractions, so the cervix widens
further, which stimulates the release of yet more oxytocin, and so the cycle continues. This is an example of
where positive feedback is actually beneficial. When the cervix has widened enough, the baby can be born. Of
course, this cycle will eventually end at some point, but this cannot always be said for every type of positive
feedback, which is why (for example, with the temperature) it can be very dangerous.
From the notes above and your text book, define
1. Homeostasis
2. Negative feedback
3. Positive feedback
Outine the roles of the following in homeostasis
1. Receptors,
2. Effectors
3. Negative feedback
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Questions
1.
What is the difference between negative feedback and positive feedback?
EXTENSION – complete sheet on principals of homeostasis
Maintaining a constant core body temperature in Ectotherms and
Endotherms
Use pages 8- 11 in your text book to help you answer these questions
What is an ectotherm?
What is an endotherm?
Give 5 examples of each
Ectotherm
Endotherm
Ectotherms
The body temperature of an ectotherm will fluctuate with changes in external temperature.
Ectotherms used to be known as ‘cold-blooded’ animals, but again, this is not correct – many
ectotherms can maintain their body temperature at around 37oC, which is too high to be considered
cold. Ectotherms do not use internal energy sources to maintain their temperature when cold,
although once they are active the muscle contractions do generate some heat from the increased
respiration. When hot, an ectotherm will use cunning behavioural and physiological mechanisms to
decrease heat absorption from the sun and increase heat loss to the surroundings; and vice versa will
try to increase heat absorption and decrease heat loss when cold.
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To warm up, an ectotherm will normally bask in the sun, or lie on a warm surface, and when too hot will
find some shade to rest in, or alternatively hide in a burrow. These behavioural mechanisms help to
control heat absorption from the sun, but some ectotherms use physiological mechanisms too to
control heat loss to the environment. For example, locusts have been seen to increase abdominal
breathing when hot too increase evaporation of water and aid cooling.
Questions
1. Give 5 mechanisms in which ectotherms regulate their temperature and how it works

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


2. Use one BEHAVIOURAL adaptation that snakes and lizards use and EXPLAIN how it maintains
body temperature
Endotherms
As we have just stated, any change in temperature has an effect on an organism. A temperature
which rises too high or falls too low to fit within the acceptable range will cause enzyme action to
decrease, and may cause them to denature. With non-functioning proteins and enzymes, the level
of activity that organism can achieve is reduced.
Thermoregulation is a homeostatic process which aims to keep the body at a constant optimal internal
temperature. In order to do this the body must:


Detect changes in internal conditions using receptors
Coordinate the action of effectors to oppose the change and reset the normal conditions
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Receptors around the body detect changes in body temperature and will feedback information to the
hypothalamus in the brain. Once the hypothalamus receives information about a deviation of body
temperature away from set levels it will act to counteract the deviation and bring body temperature
back to normal.
An endotherm is an organism which can use physiological mechanisms to regulate internal body
temperature independently of the environment. Endotherms used to be classed as ‘warm-blooded’
animals, but this is not correct to say. Many chemical reactions within endothermic organisms are
exergonic – release heat. Endotherms have a variety of both physiological and behavioural
mechanisms of regulating their body temperature.
Vasodilation, vasoconstriction and radiation
The arterioles leading to capillaries in the skin have an important role in temperature regulation. When
an endotherm has a raise in body temperature, the areas of smooth muscle, called capillary sphincters,
dilate, allowing more blood to flow near to the surface of the skin so that more heat can be radiated
from the skin. This is called vasodilation. Alternatively, when the organism’s core body temperature
falls too low, the capillary sphincters can contract, to restrict blood flow into the capillaries – this is
called vasoconstriction reducing the amount of heat radiated from the skin
Sweat glands and hairs in the skin
When the body temperature gets too high, an endotherm will secrete more sweat onto the skin. The
water in the sweat evaporates, using the heat from the blood to supply the latent heat of the
vaporisation. Hairs on the skin also lay down flat in such conditions, so hardly insulate the skin, so
more heat is lost via convection and radiation.
However, when the body temperature gets too low, the opposite happens. Sweating is kept to a
minimum so that less heat is lost through evaporation of the water. Also, hairs will raise up to trap a
layer of insulating hair on the skin surface, which will reduce the amount of heat lost from the skin.
Spontaneous muscular contractions
When too hot, skeletal muscles make no spontaneous contractions – but when too cold, there are such
contractions within the muscles (commonly called shivering). These contractions generate more heat
are more respiration occurs.
Behavioural mechanisms
Some of the behavioural mechanisms endotherms have to control body temperature are:
 moving into the shade when too hot, and into the sunlight when too cold

orientating body to increase or decrease the surface area exposed to the sunlight
depending on the temperature

remaining inactive when too hot, and moving about when too cold in order to generate
heat from the muscles (unless it is extreme cold, where it is safer to stay still and roll
into a ball to reduce surface area)
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In each diagram label which one is vasodilation and which is vasoconstriction and annotate what is
happening at stages 1-3.
EXTENSION – complete the sheet control of body temperature and mechanisms of
thermoregulation
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Use the information below to complete the diagram on the following page:
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Temperature
falls.
Causes:
Temperature rises.
Causes:
Detected by
PERIPHERAL
receptors
Response:
Set Level of temperature in
body
Detected by
PERIPHERAL receptors
Response:
Control of Body Temperature in the Body
Temperature
returns to set level
Temperature
returns to set
level
Complete the diagram on this page making sure that the following are detailed:
 Set level for body core temperature
 The names and locations of the temperature receptors
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Advantages and disadvantages of endothermy and ectothermy
Being an endotherm and being an ectotherm have their own pros and cons. Endotherms have multiple
behavioural and physiological mechanisms to control body temperature. But it is not correct to say
that ectotherms do not regulate their body temperature, they do, using their own cunning
mechanisms.
Advantages and disadvantages and of endothermy are:
Advantages

generally speaking, endotherms have the ability to maintain a constant internal
body temperature regardless of external conditions (although extreme changes
may not be able to be regulated)

activity is possible when the external temperature is quite cool, such as at night,
early in the morning or during winter

the ability to inhabit colder parts of the planet due to their ability to maintain
that internal temperature
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Hormones
A hormone a molecule secreted by an endocrine gland directly into the blood, which acts as a
chemical messenger, carrying a signal to a target tissue or organ.
Use pages 22-23 to answer the following questions
Endocrine and exocrine glands
Hormonal communication is just another communication system, as is nervous communication. But
this system involves the use of hormones. The system, known as the endocrine system, relies on
blood circulation to transport its signals. Molecules called hormones are released into the blood
directly by endocrine glands (ductless glands). However, there are two types of gland in our
bodies – those with and without ducts. The duct glands, called exocrine glands do not release
hormones, but secrete materials along a duct directly to the target location, for example,
salivary glands secreting saliva which flows to the mouth.
There are two types of hormones:
1. protein and peptide hormones, and derivatives of amino acids (e.g. adrenaline, insulin and
glucagon)
2. steroid hormones (e.g. oestrogen, testosterone, androgens)
The two types work in different ways. Steroid hormones can pass through the cell surface
membrane and enter the cell directly to produce a direct effect on the DNA in the nucleus,
whereas the phospholipid bilayer is not permeable to proteins and so protein hormones do not
enter the cell.
Cells receiving a specific (protein) hormone must have a specific complementary receptor on the
surface membrane which allows the hormone to bind to the membrane. A hormone will bind to
the receptor site of any cell with the correct receptor. Such cells are called target cells,
grouped together to form a target tissue for the hormone.
What is the difference between exocrine and endocrine glands?
How do target organs know to respond to the hormone?
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Explain why target organs have to have specific receptors?
Explain the term endocrine gland.
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[Total 2 marks]
Adrenaline
As hormones will affect any tissue with receptors for that hormone, it is not unusual for a
hormone to trigger a number of responses in the body. For example, the hormone adrenaline
doesn’t only have one effect: it increases heart rate, increases breathing rate, causes arterial
contraction, causes pupil dilation, etc. Adrenaline is a protein hormone, and therefore cannot
enter the cell itself, but has to cause an effect somehow. The key is the adrenaline receptor on
target cells, which is shaped in a way which is complementary to the hormone molecule itself.
Every receptor for adrenaline has an enzyme associated with it on the inner surface membrane,
called adenyl cyclase. The adrenaline hormone is known as the primary messenger, which from
the blood binds to the receptor site on a target tissue, activating the adenyl cyclase enzyme.
The adenyl cyclase then converts ATP to cyclic AMP (cAMP), releasing two phosphates in the
process. The cyclic AMP is the secondary messenger which acts as an activator for various
enzymes within the cell, triggering certain effects, depending on which target tissue is being
activated.
The adrenal glands
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The adrenal glands are found just above the kidneys on both sides of the body, and can be
separated into a medulla region and a cortex region.
Adrenal medulla
The medulla is the central part of the gland. The cells there manufacture and release adrenaline
in response to stress such as pain or shock. The effects of the hormone are widespread as
there are receptors for the hormone on many tissues around the body. Some of the effects are
explained above.
Adrenal cortex
The adrenal cortex uses cholesterol to produce certain steroid hormones, which have a variety
of roles in the body. For example, aldosterone helps to maintain the concentrations of sodium
and potassium in the blood, and cortisol helps to control the metabolism of carbohydrates and
proteins in the liver.
Adrenal medulla
The medulla is the central part of the gland. The cells there manufacture and release adrenaline in
response to stress such as pain or shock. The effects of the hormone are widespread as there are
receptors for the hormone on many tissues around the body. Some of the effects are explained
above.
Adrenal cortex
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The adrenal cortex uses cholesterol to produce certain steroid hormones, which have a variety of
roles in the body. For example, aldosterone helps to maintain the concentrations of sodium and
potassium in the blood, and cortisol helps to control the metabolism of carbohydrates and proteins in
the liver.
Use page 23 to draw a diagram to show the action of adrenaline
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Give 8 functions of adrenaline








Explain how adrenaline can prepare the body for activity
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Regulation of blood glucose
The pancreas
The pancreas is an organ which is both an endocrine gland and an exocrine gland, as it has
functions of both types. The majority of cells in the pancreas have an exocrine function, in
secreting digestive enzymes. Such cells are found surrounding tiny tubules into which they
secrete pancreatic juice, a liquid containing a number of digestive enzymes, and the tubes
will join up at the pancreatic duct which carries the pancreatic juice into the first section of
the small intestine. The pancreatic juice includes the enzymes amylase, pancreatic lipase,
carboxypeptidase, elastase and trypsinogen.
22
Use the diagram on the right to identify the islets of Langerhans on the histology slide.
part of the pancreas secretes
What
Insulin
Glucagon
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Regulating blood glucose levels
It is the role of the cells in the islets of Langerhans to monitor the concentration of blood glucose. If they detect a concentration
which lies outside the acceptable range, the appropriate cells (either α-cells or β-cells) are activated to release hormones to
respond and return the blood glucose concentration to an acceptable level.
State why hepatocytes need to have receptors for both insulin and glucagon?
State if the following are first messengers or second messengers

cAMP

Insulin

Glucagon
A rise in blood glucose concentration When blood glucose levels increase, possibly just after
eating a meal, the change in concentration is detected by β-cells in the islets of Langerhans.
The cells then secrete the hormone insulin directly into the bloodstream. Insulin, like
adrenaline, has a number of effects on multiple cell types around the body. The target cells
for insulin are the hepatocytes (liver cells) as well as muscle cells. The diagram shows insulin
secretion:
Use the diagram below to write out the steps of how insulin is secreted
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Steps
1
2
3
4
25
5
6
7
8
In the resting β-cell, potassium ions (K+) are moving out of the cell down the concentration
gradient, via facilitated diffusion. When there is a concentration of glucose from outside the
cell to inside the cell, for example, after eating, glucose enters the cell through specialised
glucose channels in the membrane (again, by facilitated diffusion). The glucose inside the cell
is then respired, producing ATP.
The ATP moves to the potassium ion channels on the cell surface membrane, and binds to the
channels, causing them to close. This means that the potassium ions stay inside of the cell.
Quickly, the build up of the ions depolarises the membrane (it becomes less negative),
causing the voltage-gated calcium ion (Ca2+) channels to open, which results in an influx of
calcium ions into the cell. These ions then bind to vesicles within the cell which carry the
insulin hormones. The calcium causes the vesicles to move to the cell surface membrane, and
undergo exocytosis: the vesicle fuses with the membrane and the insulin is released out of
the cell, and into the bloodstream.
When insulin is released into the blood, it is transported all around the body, and when it
passes the target tissues (mainly the hepatocytes), the hormone binds to the receptor sites,
activating the adenyl cyclase enzyme on the inner cell membrane. This produces cyclic AMP
(cAMP) from a molecule of ATP, and the cyclic AMP activates a number of intracellular
reactions. The effects of the hormone insulin, or these end intracellular reactions, are:
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

more glucose channels are inserted into the cell surface membrane, so that more
glucose can enter the cell
glucose inside the cell is polymerised into glycogen by a process known as glycogenesis
more glucose is converted into fats, and more glucose is respired
Needless to say, as these events cause more and more glucose to enter the target cells, the
result is a decreased glucose concentration in the bloodstream. The concentration returns to
an acceptable level using this process.
A drop in blood glucose concentration
An example of an activity that would cause a fall in blood glucose level is after exercise. The
drop in glucose concentration in the bloodstream is detected by α-cells in the islets of
Langerhans. In response to this, the α-cells will secrete the hormone glucagon, which again
uses the hepatocytes as target cells.
When glucagon is released, it binds to the receptors on its target cells. This activates the
adenyl cyclase, stimulating the production of cAMP, which will be the eventual trigger for
the reactions. The effects of glucagon are:
 the polymer glycogen is broken down into the monomer glucose, this process is called
glycogenolysis
 more fatty acids are used in respiration
 amino acids and lipids are converted into glucose by a process known as
gluconeogenesis
The effects of glycogenolysis and gluconeogenesis (breakdown of glycogen and conversion of
non-sugars into glucose) results in the release of much glucose into the blood, restoring it to
an acceptable level.
Cells in the pancreas monitor blood glucose levels and compare it to the set point. If the level
of glucose falls above or below the set point the pancreas will send messages to target organs
to make them respond and bring blood glucose levels back to the set point. These messages
are carried by hormones.
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Use this information to complete the diagram on the next page:
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Glucose concentration
In blood falls.
Causes:
Glucose concentration
In blood rises.
Causes:
Detected by
Receptors
Response:
Set Level of Glucose in body
Detected by receptors
Response:
Control of Blood Glucose Levels in the Body
Blood
Glucose level
returns to set
level
Blood
glucose
level
returns to
set level
Complete the diagram on this page making sure that the following are detailed:
 Set level of blood glucose
 The names and locations of the receptors
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Diabetes
Diabetes mellitus is a disease where the body is no longer able to maintain an acceptable
blood glucose concentration, and is described as a lack of control over blood glucose
regulation. It can lead to hyperglycaemia (very high levels of blood glucose) after a meal rich
in sugars, and also hypoglycaemia (very low levels) after exercise.
Type I diabetes Also known as insulin dependent diabetes, type I diabetes is early-onset,
meaning it occurs from when the sufferer is very young. It is an auto-immune disease, where
the body’s own cells destroy the insulin-releasing β-cells, and so the effect is that little or
no insulin is released, which can lead to hyperglycaemia, for example after eating a meal.
The treatment for type I diabetes is using insulin injections. Precise dosages of insulin to
counteract food eaten is injected. The necessary dosage is calculated by measuring blood
glucose levels using a pin-prick. Originally, the insulin to be injected was obtained from the
pancreas of pigs. This was because it was fairly similar to humans’ insulin and easy to rear,
although there were some problems, including low extraction efficiency, a risk of the immune
system rejecting the pig insulin, and not to mention the moral and ethical issues.
Ergo the more modern treatment which uses injections of insulin produced by geneticallymodified bacteria. Larger quantities can be produced in batches more easily and quickly in
this method, and the chances of rejection by the immune system are far slimmer, as human
DNA coding is used in the genetic modification (restriction enzymes cut out the DNA coding
for insulin production, and other enzymes place that coding into the bacteria, which
reproduces over time). There are obviously fewer ethical issues concerning artificial insulin
production. This insulin is closer to human insulin, also, and so it is more likely to bind to the
receptor sites on hepatocytes than pig insulin is.
Type II diabetes Described as non-insulin dependent or late-onset diabetes, type II
diabetes is not due to problems with β-cells, but the problem lies with the not-functioning
receptors in the hepatocytes. People with type II diabetes can still manufacture and release
insulin, but certain factors will reduce the responsiveness to the hormone over time. The
most common factor is age: as people grow older, they become less reactive to the hormone,
and so insulin doesn’t bind to the target tissues as readily. But other factors can result in an
earlier onset of this type of diabetes, including obesity, diets high in sugars, race (Asian and
Afro-Caribbean people are less responsive to insulin) and family history.
The treatment of type II diabetes is simply monitoring lifestyle. Regular exercise and a
healthy diet are the best ways to reduce the chance of developing late-onset diabetes.
There are several diseases involving excessive excretion of urine, all of which are forms of
diabetes. The most common form of diabetes is diabetes mellitus. There are two ways in
which this form of diabetes can develop in humans:

Auto-immune destruction of insulin-secreting cells in the pancreas (Type I diabetes),
usually born with it or develops in early childhood, usually referred to as early onset
diabetes
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
Decreased sensitivity of cells to insulin, so they do not respond in the same manner
(Type II diabetes), often referred to as late onset diabetes as it usually develops as
an adult
1. Explain why a person with type I diabetes would be unable to regulate their glucose levels:
_____________________________________________________________________
_____________________________________________________________________
2. If cells are not as sensitive to insulin, can you predict what will / will not happen?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
The number of people developing type II diabetes is increasing. Studies of type II diabetes
have formed links between the development of Type II diabetes and the following:



Diets rich in fat and low in fibre
Obesity due to overeating and lack of exercise
Genetic factors which affect fat metabolism
Unless carefully managed, diabetes can lead to further health problems such as
hypertension, coronary heart disease and atherosclerosis.
3. Complete the table below to compare type I and type II diabetes:
Feature
Type I
Type II
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Past paper questions
1. The liver plays an important role in carbohydrate metabolism. The balance between
the processes of glycogenesis and glycogenolysis helps to regulate the
concentration of glucose in blood plasma. The figure below shows some of the
stages of these processes.
glucose 6-phosphate
glucose 1-phosphate
glucose
glycogen
glucose 6-phosphate
key:
(a)
(i)
glucose 1-phosphate
glycogenesis; promoted by insulin
glycogenesis; promoted by glucagon
Name one other hormone that promotes glycogenolysis.
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[1]
(ii)
Explain why glycogen is suitable for energy storage in cells.
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[3]
The last step in glycogenesis is catalysed by the enzyme glycogen synthetase. The
first step in glycogenolysis is catalysed by the enzyme glycogen phosphorylase.
Glucose molecules have direct effects on glycogen synthetase and on glycogen
phosphorylase. These effects do not require the presence of insulin and glucagon.
The table below shows the rate of activity of glycogen synthetase and glycogen
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phosphorylase inside liver cells, during exposure of the cells to a concentrated
solution of glucose.
time after addition of
glucose solution / s
rate of activity of
glycogen synthetase /
arbitrary units
rate of activity of
glycogen
phosphorylase /
arbitrary units
0
30
60
90
120
150
180
210
28
28
32
49
94
136
189
272
410
280
140
65
42
40
40
40
(b)
Explain how a high concentration of glucose causes the storage of glycogen in
liver cells. You will gain credit if you use the data in the table in your answer.
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[5]
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(c)
After a prolonged period of fasting, glycogen levels in the liver are depleted.
However, the liver can still produce glucose by the process of
gluconeogenesis.
Describe one way in which this is done.
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[3]
[Total 12 marks]
2. An investigation was carried out into the effect of consuming meals rich in
carbohydrate on two hormones in the blood.
The figure below shows the relationship between glucose concentration in the
blood and the concentrations in the blood of the two hormones, Q and R.
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10
blood
glucose
concentration
mmol dm –3
5
0
0600
1200
time of day
1800
2400
0600
1200
time of day
1800
2400
0600
1200
1800
2400
10
concentration
of Q in the
blood
arbitrary
units
5
0
10
concentration
of R in the
blood
arbitrary
units
5
0
time of day
key:
= carbohydrate
meal
Name hormones Q and R.
Q ..................................................................
R ..................................................................
[Total 2 marks]
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5.
The pancreas is a gland that has both endocrine and exocrine functions.
The figure below shows a section through part of the pancreas.
magnification × 400
(i)
Name A and B.
A ......................................................................................................................
B ......................................................................................................................
[2]
(ii)
Explain the difference between the terms endocrine and exocrine with
regard to the pancreas.
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[4]
[Total 6 marks]
36
6.
The pancreas contains endocrine tissue. The figure below shows an
electronmicrograph of a section of pancreatic endocrine tissue.
nucleus
rough endoplasmic reticulum
beta cell secretory vesicle
mitochondrian
alpha cell secretory vesicle
(a)
cell membrane
x 30000
Name the endocrine tissue shown in the figure.
.........................................................................................................................
[1]
(b)
Name the hormone present in the secretory vesicles of alpha cells.
.........................................................................................................................
[1]
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(c)
During vigorous exercise, the blood glucose concentration falls.
Describe the changes that take place to make sure that the blood glucose
concentration does not fall to a dangerous level.
In your answer, you should use appropriate technical terms, spelled correctly.
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[6]
[Total 8 marks]
38
7.
Over 2.3 million people in the UK are known to have diabetes. It is also estimated
that a further 0.5 million people have the condition but are unaware of it.
(i)
Explain how Type 1 diabetes is caused.
.........................................................................................................................
.........................................................................................................................
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.........................................................................................................................
[2]
(ii)
Describe three factors that increase a person’s risk of developing Type 2
diabetes.
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[3]
[Total 5 marks]
39
8.
Following a meal rich in carbohydrates, the plasma glucose concentration rises.
Describe the homeostatic mechanisms that would normally prevent glucose
appearing in the urine.
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[Total 5 marks]
9.
Untreated diabetes is a condition that can lead to blood glucose concentrations
often rising above 120 mg 100 cm–3 of blood. Genetic engineering has been used to
improve the treatment of diabetes.
Explain the advantages of using genetic engineering in the treatment of diabetics.
..................................................................................................................................
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[Total 3 marks]
40
Control of heart rate
Hormonal and nervous mechanisms involved in controlling human heart rate
Factors affecting heart rate
The heart pumps blood all around the body in the double-circulatory system. The blood
supplies tissues with oxygen, glucose, fatty acids, amino acids and other useful products, and
also removes waste products such as urea and carbon dioxide to prevent accumulation of
such products, which would lead to inhibition of cell metabolism.
These requirements of the cells vary according to level of activity, and there are a number
of factors which can affect this, so it is important that the heart can adapt to meet the
requirements of the body at any one given time. Factors affecting heart rate include
breathing rate, signals from the brain and hormones (e.g. adrenaline).
Regulation of heart rate Heart muscle is myogenic, so initiates its own contractions, and
involuntary. There is an area of tissue, called the sinoatrial node (SAN), which can initiate an
41
action potential to travel along the atrial walls as a wave of excitation, causing them to
contract. This is where one heartbeat originates. The signal then spreads through the
atrioventricular node (AVN) and down the Purkyne tissue to the ventricular apex, and finally
through the ventricles, causing them to contract.
The heart has an underlying frequency of 60-80bpm (beats per minute). Whilst heart rate
cannot be controlled wholly, the brain can send signals to tweak this frequency. These signals
are sent to the SAN through nerves from the brain to the heart. It is the medulla oblongata
in the brain which sends these signals to the SAN. There are two separate controls from the
medulla oblongata:
1 the accelerator nerve causes the rate of signals from the SAN to increase, resulting in an
increased heart rate
2 the vagus nerve reduces the rate of contractions, so resulting in a reduced heart rate
The medulla oblongata receives various signals itself, so that it can communicate with the
SAN how to respond appropriately to external changes. The types of signal it can receive
are:
 movement of limbs is detected by the stretch receptors (propioreceptors), which will
send signals to the cardiovascular centre in the medulla oblongata to inform it that
more oxygen may soon be needed, so heart rate is increased to provide that extra
oxygen
 chemoreceptors in the carotid arteries, aorta and brain detect the changes in pH
produced when excess carbon dioxide (due to, for example, exercise) reacts with
water in the blood plasma, lowering the pH, and so the chemoreceptors send signals to
the cardiovascular centre to increase heart rate
 when exercising stops, the concentration of carbon dioxide in the blood falls, which
reduces the activity of the accelerator nerve pathway, so the heart rate decreases,
preventing further carbon dioxide from being removed
If the SAN stops working, the heart cannot contract, and so death is inevitable. This is why
an artificial pacemaker would be fitted to a patient. The SAN is the natural pacemaker, but
an artificial pacemaker is capable of sending signals to the heart to keep it contracting and
to keep blood flowing around the body. They are around 4cm long and will be inserted under
the skin and fat on the chest, sometimes inserted in the chest cavity.
Similarly, if the AVN stops working, the signal from the SAN cannot be passed onto the
ventricular walls, and so those contractions stop. So some pacemakers are fitted to act upon
the AVN, in order to resume normal contractions, as in these cases, the SAN will be
functioning normally.
Cardiac muscle will continue to beat rhythmically even after it has been surgically removed
from the body provided that it is maintained in a favourable medium. This shows us that the
origin of the heartbeat is actually within the heart muscle itself rather than from an external
nerve impulse.
42
(Remember that nerve impulses can affect the rate of heartbeat –sympathetic and
parasympathetic nerves but not its intrinsic rate)
Because the origin actually arises in the heart itself it is referred to as being myogenic rather
than for example skeletal muscles, which are neurogenic and require an external nervous
impulse to contract.
Excitation of heart muscle originates in a small patch of tissue known as the sinoatrial node
(SAN) or pacemaker. Excitation spreads across the walls of the atrium from this node causing
contraction of the atria – atrial systole.
Excitation is prevented from spreading directly to the ventricles because of a wall of nonconducting tissue. This is important as it means there is a delay between contraction of the
atria and the ventricles, so preventing them contracting at the same time.
However, there is a second node located at the base of the atria called the atrio-ventricular
node (AVN), this picks up the excitation spreading from the atria and conducts a wave of
excitation down long muscle fibres called Purkinje (or Purkyne tissue) fibres collectively known
as the bundle of His located along the ventricular septum to the base of the heart. Contraction
of the ventricles starts from the bottom of the ventricles upwards.
43
Factors affecting heart rate
The heart pumps blood all around the body in the double-circulatory system. The blood
supplies tissues with oxygen, glucose, fatty acids, amino acids and other useful products, and
also removes waste products such as urea and carbon dioxide to prevent accumulation of
such products, which would lead to inhibition of cell metabolism.
These requirements of the cells vary according to level of activity, and there are a number
of factors which can affect this, so it is important that the heart can adapt to meet the
requirements of the body at any one given time. Factors affecting heart rate include
breathing rate, signals from the brain and hormones (e.g. adrenaline).
Regulation of heart rate
Heart muscle is myogenic, so initiates its own contractions, and involuntary. There is an area
of tissue, called the sinoatrial node (SAN), which can initiate an action potential to travel
along the atrial walls as a wave of excitation, causing them to contract. This is where one
heartbeat originates. The signal then spreads through the atrioventricular node (AVN) and
down the Purkyne tissue to the ventricular apex, and finally through the ventricles, causing
them to contract.
The heart has an underlying frequency of 60-80bpm (beats per minute). Whilst heart rate
cannot be controlled wholly, the brain can send signals to tweak this frequency. These signals
are sent to the SAN through nerves from the brain to the heart. It is the medulla oblongata
in the brain which sends these signals to the SAN. There are two separate controls from the
medulla oblongata:
1 the accelerator nerve causes the rate of signals from the SAN to increase, resulting in an
increased heart rate
2 the vagus nerve reduces the rate of contractions, so resulting in a reduced heart rate
The medulla oblongata receives various signals itself, so that it can communicate with the
SAN how to respond appropriately to external changes. The types of signal it can receive
are:
 movement of limbs is detected by the stretch receptors (propioreceptors), which will
send signals to the cardiovascular centre in the medulla oblongata to inform it that
more oxygen may soon be needed, so heart rate is increased to provide that extra
oxygen

chemoreceptors in the carotid arteries, aorta and brain detect the changes in pH
produced when excess carbon dioxide (due to, for example, exercise) reacts with
water in the blood plasma, lowering the pH, and so the chemoreceptors send signals to
the cardiovascular centre to increase heart rate
44

when exercising stops, the concentration of carbon dioxide in the blood falls, which
reduces the activity of the accelerator nerve pathway, so the heart rate decreases,
preventing further carbon dioxide from being removed
If the SAN stops working, the heart cannot contract, and so death is inevitable. This is why
an artificial pacemaker would be fitted to a patient. The SAN is the natural pacemaker, but
an artificial pacemaker is capable of sending signals to the heart to keep it contracting and
to keep blood flowing around the body. They are around 4cm long and will be inserted under
the skin and fat on the chest, sometimes inserted in the chest cavity.
Similarly, if the AVN stops working, the signal from the SAN cannot be passed onto the
ventricular walls, and so those contractions stop. So some pacemakers are fitted to act upon
the AVN, in order to resume normal contractions, as in these cases, the SAN will be
functioning normally.
QUESTION
In this question, one mark is available for the quality of spelling, punctuation and
grammar.
The autonomic nervous system contains neurones that carry impulses to the internal
organs. Describe the role of the autonomic nervous system in the control of the heart
beat.
[7]
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45
The diagram shows how electrical activity may spread over the surface of the heart during a
single heartbeat. The figures represent times, in seconds.
a. Give the name of the structure labelled A.
b. Describe the position of this structure in the heart.
c. Use the times on the diagram to describe the passage of electrical activity over the surface
of the heart.
46
Questions
1. What is meant by myogenic?
2. Why must the heart be able to respond to increased physical activity?
3.In this question, one mark is available for the quality of spelling, punctuation and
grammar.
The autonomic nervous system contains neurones that carry impulses to the
internal organs. Describe the role of the autonomic nervous system in the control
of the heartbeat.
[7]
Quality of Written Communication [1]
[Total 8 marks]
47