Unit 1
Communication, Homeostasis and Energy
What effect does temperature change
have on enzyme action?
 What other environmental factors inhibit the
action of enzymes?
 List three changes to the external
environment to which we might need to
respond.
 What is the main role of the

 Heart
 The lungs
 The kidneys



What is meant by cell signalling?
In what other process in the body is
cell signalling particularly important?
Explain the role of cell surface
receptors in cell signalling.

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 coordinate the
activities of different organs.



Sensitivity
Stimulus
Internal communication
 Plants
 Animals


Receptor
Effector


All living things need to maintain a
certain limited set of conditions inside
their cells.
Why?


Cellular activities rely on the action of
enzymes
Specific limited set of conditions
 Suitable temperature
 Suitable pH
 Aqueous environment
 No toxins / inhibitors


As the external environment changes
it places stress on the living organism.
The environmental change is a
stimulus and the way in which the
organism changes its behaviour or
physiology is its response to the stress.

Stimulus
 Any change in environment that causes a
response

Response
 A change in behaviour or physiology as a
result of a change in the environment.


State that cells need to communicate
with each other, which they do by a
process called cell signalling.
State that neuronal and hormonal
systems are examples of cell signalling
The internal environment of the cells in
animals is tissue fluid.
 Activity of the cell alters its environment

 Use up substrates
 Produce products, some of which may be toxic

Accumulation of excess waste acts as a
stimulus to cause the removal of these
wastes

Summary
 Composition of the tissue fluid is
maintained by the blood
 Wastes accumulating in tissue fluid enter
the blood
 Excretion prevents the accumulation of
wastes in the blood
 Concentrations of all substances in the
blood are monitored


In a multicellular organism cells
become differentiated (specialised)
forming tissues and organs.
A good communication system is
required
 List the features of a good communication
system





Whole body
Cell communication
Specific
Rapid
Short term and long term


How cells communicate with each
other
The neuronal system and the
hormonal system work by cell
signalling.


define the terms negative feedback,
positive feedback and homeostasis;
explain the principles of homeostasis in
terms of receptors, effectors and
negative feedback;
Maintaining a constant internal
environment despite external changes
 Examples

 Body temperature
 Blood glucose concentrations
 Blood salt concentration
 Water potential of blood
 Blood pressure
 Carbon dioxide concentration

Reversal of any change in internal
environment to return to an optimum
steady state.
Optimum
condition
Return to
optimum
conditions
Effector reacts
to reverse
change
Change away
from optimum
Receptor
detects
change
Communication
system informs
effector

Structures required for pathway to
work
 Sensory receptors
 Communication system
 Effector cells




Control of room temperature
Control of body temperature
Control of blood glucose levels
Control of body water concentration


Increases any change that is
detected by receptors
Does not lead to homeostasis
Optimum
condition
Change away
from optimum
Receptor
detects
change
Effector reacts
to increase
change
Communication
system informs
effector


If core temperature drops too low
Dilation of the cervix at the end of
pregnancy

Enzyme action and temperature
regulation
 As core body temperature rises the
increase will affect the activity of
enzymes. This can lead to heat
exhaustion and even death.
▪ Describe the effect of increasing body
temperature on enzyme action.
▪ Suggest what actually causes death as body
temperature rises.

Temperature increase – rate of
enzyme action increases
 10oC increase will double the rate of
reaction
 Above 50oC enzymes denature – rate of
reaction falls quickly

Death

The stress response
 The usual response to stress is to release
the hormone adrenaline. This hormone
has a wide range of target cells and
prepares the body for activity. The activity
may be to stay and fight or it may be to
run away. The hormone is known as the
“fight or flight” hormone.

The stress response
 When under stress women also release the
hormone oxytocin. This results in a
tendency to pacify or protect. It has
been called the “tend and befriend”
hormone. Oxytocin prompts a mother to
protect her children.

Suggest how these responses to
adrenaline and oxytocin may have
evolved.

describe the physiological and
behavioural responses that maintain a
constant core body temperature in
ectotherms
Changes in body temperature affects the
structure of proteins
 Endotherms

 Maintain body temperature within strict limits
 Independent of external temperature

Ectotherms
 Body temperature fluctuates with external
temperature

Advantages
 Use less food in
respiration
 Need less food
 Greater proportion
energy used for
growth

Disadvantage
 less active in cooler
temperatures
 May not be capable
of activity in winter
months

Increasing the heat exchange with
their environment






Expose body to sun
Orientate body to sun
Orientate body away from sun
Hide in burrow
Alter body shape
Increase breathing movements

Design an A4 poster to summarise
behavioural and physiological
adaptions of ectotherms for
temperature regulation.

Temperature regulation in bee swarms
 Bees are ectothermic.
 However, it has been shown that the
temperature of a bee swarm can be
maintained accurately to within one
degree of 35oC.
 This is achieved by bees moving to
different parts of the swarm and by
allowing passages for air flow through the
swarm.

Suggest how movement of bees within
a swarm and air movement through
the swarm can help to maintain the
temperature of the swarm.



Bees in the centre of the swarm will be
warmer than those on the outside.
Warmer bees move towards the outer
parts of the swarm while colder bees
move toward the centre.
This transfers heat from the centre to
the outer parts of the swarm.



In hot weather the bees create more
passages for air flow; the passages are
also wider
Thus more air can pass through the
swarm and carry heat away.
In cooler weather there are fewer air
passages and they are narrower.



Why is it important to maintain body
temperature?
Make a list of 5 ectotherms
Explain how basking on a hot rock in
the sun can help an ectotherm to
regulate its body temperature.

describe the physiological and
behavioural 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



Use internal sources of heat to
maintain body temperature
Many chemical reactions in the body
are exergonic
Endotherms also show behavioural
and physiological adaptations
ADVANTAGES



Constant body temp.
Activity possible even
when cool
Inhabit colder parts of
planet
DISADVANTAGES



Energy used up to
maintain constant
temp.
More food required
Less energy used in
growth
Too hot
Too cold
Sweat glands in
skin
Secrete more
sweat
Less sweat secreted
Lungs, mouth and
nose
panting
No panting
Hairs on skin
Lie flat
Raised
arterioles
Vasodilation
vasoconstriction
Liver cells
Reduce rate of
metabolism
Increase rate of
metabolism
Skeletal muscles
Spontaneous
contractions (shivering)
TOO HOT



Move into shade
Decrease exposed
surface area
Remain inactive /
increase surface area
TOO COLD




Move into sunlight
Increase exposed
surface area
Move about to
generate heat in
muscles
Extreme cold – roll into
a ball to decrease
surface area

Change in core temperature
 Thermoregulatory centre in hypothalamus
detects change.
 Nervous and hormonal systems carry
signals to skin, liver and muscles
▪ Fall in core temperature
▪
▪
▪
▪
Rise in metabolic reactions
Release more heat from exergonic reactions
Release heat through muscle contractions
Decrease loss of heat, temperature rises
Skin temperature
External
HYPOTHALAMUS
Core Temperature
Thermoregulatory
centre
TOO COLD
TOO HOT
-Shivering
-Reduce metabolism
-Increased metabolism
-Vasodilation
-Vasoconstriction
- increased sweating
-Reduced sweating
-Skin hairs erected

Thermoregulatory centre in the
Hypothalamus
 Monitors blood temperature
 Detects changes in core temperature

Peripheral temperature receptors
 “early warning” system
 Detect changes in temperature of the extremities
 Sends signals to the brain to initiate behavioural
mechanisms to maintain core temperature.

Should mountain rescue dogs carry
brandy?
 In early part of the twentieth century St
Bernard dogs were used for mountain
rescues.
 Traditionally they carried a small container
of brandy for the lost or injured climber to
drink.
 Alcohol causes vasodilation.

Explain why drinking brandy is not a
good idea for someone who is lost or
injured and exposed to cold weather.
If the climber is unable to find shelter, the
low temperature could reduce the body
temperature to the point where enzyme
activity is severely reduced.
 Vasodilation caused by the alcohol in
the brandy will increase the rate of heat
loss from the body, because more blood
carries heat from the body’s core to the
surface where it can be lost.
 Hypothermia and death will happen
sooner in a person who has drunk
alcohol.



Explain why a shrew has to eat almost
its own body mass each day, but an
elephant eats less than one percent of
its body mass each day.
Suggest why the fairy penguin of
Australia grows to about 25cm in
height while the emperor penguin of
Antarctica grows to a metre in height.





Shrew is very small with a large surface
area to volume ratio.
It loses heat through it’s skin
A lot of food must be used to replace
the heat lost
Elephant is large with a small surface
area to volume ratio
Loses a smaller proportion of body
heat.



Australia is warm – penguins do not
need to be large to maintain their
body temperature
Antarctica is very cold – larger
penguins have a smaller surface area
to volume ratio – so can maintain
body temperature more easily.
a huddle of penguins has a smaller
surface area to volume ratio than a
solitary penguin.


Outline the roles of sensory receptors
in mammals in converting different
forms of energy into nerve impulses.
Describe, with the aid of diagrams, the
structure and functions of sensory and
motor neurones.


Specialised cells that detect changes
in surroundings
Energy transducers
 Convert one form of energy to electrical
energy of a nerve impulse

Stimulus
 Change in energy levels in environment

Receptors

Energy changes detected

Light sensitive cells

Light intensity and wavelength

Olfactory cells

Presence of volatile chemicals

Taste buds

Presence of soluble chemicals

Pressure receptors (pacinian
corpuscles)

Pressure on skin

Sound receptors

Vibrations in air

Muscle spindles
(proprioceptors)

Length of muscle fibres

Function
 To transmit the action potential

Structure
 Very long
 Maintain potential difference across cell
membrane
▪ Gated ion channels in cell membrane
▪ Sodium/potassium pumps
 Myelin sheath / schwann cells / node of ranvier
 Cell body contains nucleus, mitochondria and
ribosomes.


Describe and explain how the resting
potential is established and
maintained.
Describe and explain how an action
potential is generated.

Gated channel proteins specific to either
sodium or potassium ions
 Increase permeability when open
 reduces permeability when closed

Carrier proteins
 Active transport
 Sodium-potassium pump
▪ Transports more Na2+ out of cell than K+ into cell.

Result is that inside cell is more negatively
charged than outside the cell
 Cell membrane is polarised.



3 Na+ leave the cell
2 K+ enter the cell
Potential difference is created across
the membrane
1
3

Summary of
the sodium
potassium
pump!


Describe and explain how an action
potential is generated.
Interpret graphs of the voltage changes
taking place during the generation and
transmission of an action potential.



Potential difference across the
neurone cell membrane while the
neurone is at rest
Inside the cell is -60mv compared with
outside the cell.
Cell membrane is polarised





The permeability of the cell
membrane to sodium ions is increased
Sodium ions move down a
concentration gradient into the cell
Creating a change in the potential
difference across the membrane
Inside the cell becomes less negative
This is depolarisation

Generator potential
 Small depolarisation caused by sodium
ions entering the cell

Action potential
 Depolarisation of the cell membrane
 Inside is more positive than the outside
 Potential difference +40mv

Threshold potential
 Potential difference across membrane of -
50mv
1.
2.
3.
4.
5.
Membrane is polarised at rest (-60mv)
Sodium ion channels open
Membrane depolarises (threshold
value -50mv)
Voltage-gated sodium ion channels
open and many sodium ions flood in
Potential difference across plasma
membrane reaches +40mv
6.
7.
8.
9.
Sodium ion channels close and
potassium channels open
Potassium ions diffuse out of the cell,
this is repolarisation
Hyperpolarisation = the potential
difference overshoots slightly
Resting potential restored
Resting potential –
K+ voltage-gated
channels open,
Na+ voltage-gated
channels closed
 Hyperpolarisation
and repolarisation:
sodium-potassium
pumps restablish
the resting
potential

Action potential
established
 Repolarisation
 Sodium ions enter
causing a greater
influx of sodium ions
(positive feedback)
 Na+ voltage-gated
channels open


Look at the animation

For a narrated animation look at
http://bcs.whfreeman.com/thelifewire
/content/chp44/4402002.html


Allows the cell to recover after an
action potential
Ensures action potentials are only
transmitted in one direction

Sensory receptors
 Are specific to a single type of stimulus
 Act as transducers
 Produce a generator potential
 Give and “all or nothing” response
 Become adapted

Describe and explain how an action
potential is transmitted in a myelinated
neurone, with reference to the roles of
voltage-gated sodium ion and potassium
ion channels.

Key ideas
 Local currents
 Voltage-gated sodium ion channels
 The myelin sheath
 Saltatory conduction

This is the movement of ions along the
neurone
 During an action potential
▪ Sodium ion channels open
▪ Sodium ions diffuse across membrane
▪ Upsets balance of ionic concentrations
▪ Concentration sodium ions inside neurone rises
▪ Sodium ions diffuse sideways
▪ Movement of charged particles is a local
current.





These gates are operated by changes
in the voltage across the membrane
Movement of sodium ions alters the
potential difference
Depolarisation causes gates to open
Sodium ions enter neurone at a point
further along the membrane
Action potential moves along the
membrane

Is this an example of positive or
negative feedback
 Give reasons for your answer


This speeds up the transmission of the
action potential (up to 120ms-1)
In a myelinated neurone
 Ionic exchanges can only occur at the
nodes of Ranvier
 Local currents are elongated, sodium ions
diffuse along neurone from one node of
Ranvier to the next, a distance of 1 – 3 mm
 Action potential appears to jump from
one node to the next
Transmission of an action potential


Outline the significance of the
frequency of impulse transmission.
Compare and contrast the structure
and function of myelinated and nonmyelinated neurones.


Action potentials are always the same
size
Strength of stimulus
 Frequency of action potentials
▪ Strong stimulus will generate more frequent
action potentials
▪ Brain interprets a stream of closely spaced
action potentials as a “strong stimulus”
 A strong stimulus is likely to stimulate more
neurones than a weak stimulus

Nature of stimulus
 Deduced by the position of the sensory
neurone bringing the information


The wider the axon the faster the
speed of transmission
Myelin insulates axons, speeding up
transmission of an action potential
along them
 Myelinated neurones
 Unmyelinated neurones
100 – 120 ms-1
2 – 20 ms-1



Read through the handout on Multiple
Sclerosis
Complete the table
Answer the question.



Describe, with the aid of diagrams, the
structure of a cholinergic synapse.
Outline the role of neurotransmitters in
the transmission of action potentials.
Outline the roles of synapses in the
nervous system.
The Cholinergic
Synapse
A synapse is a
junction between
two or more
neurones.
A synapse which uses
acetylcholine as a
neurotransmitter is
called a cholinergic
synapse.

The synaptic knob (bulb) is a swelling
at the end of the presynaptic
membrane. It contains:
 Many mitochondria
 Smooth endoplasmic reticulum
 Vesicles containing acetylcholine
 Voltage-gated calcium ion channels in
the membrane
1.
2.
3.
4.
An action potential arrives
Calcium ion channels open
Vesicles containing acetylcholine
move to the presynaptic membrane.
Vesicles fuse with the presynaptic
membrane and release
acetylcholine into the synaptic cleft.
5.
6.
7.
Acetylcholine diffuse across the
synaptic cleft to the postsynaptic
membrane
Acetylcholine binds to receptors in
postsynaptic membrane
Sodium ion channels open – the
membrane is depolarised and an
action potential is produced.

On the worksheet
 Label the diagram of the synapse
 Sort out the sentences into the correct
order



Acetylcholinesterase is an enzyme
found in the synaptic cleft
It hydrolyses acetylcholine into
ethanoic acid and choline
Choline is taken back to the
presynaptic membrane to reform
Acetylcholine





Transmit information between
neurones
Are unidirectional
Act as junctions
Filter out low level stimuli
Summation
 Amplification of low level signals

Acclimatisation
 Prevent overstimulation and fatigue

Memory and learning

The cytoplasm in the synaptic knob has a
high proportion of certain organelles.
These include smooth endoplasmic
reticulum, mitochondria and vesicles.
Each organelle has a specific role to play
in the functioning of the cell.
 Describe the role of each of these organelles
and explain why they are found in relatively
large numbers in the synaptic knob.

Describe the roles of:
 Sodium ion channels
 Potassium ion channels
 Calcium ion channels
In the transmission of information along
and between neurones

20 marks = 20 minutes

You should be able to complete this
prep in 20 minutes

Papers taken from OCR June 05 & 06

Compare the structure of a motor
neurone to that of the “typical”
animal cell. How does the specialised
structure of a neurone relate to its
function?



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.

Endocrine Gland
 Secretes it’s product directly into the
blood or lymph.

Exocrine gland
 Secretes its product into a duct to take
the secretions to the site of action.

A hormone
 Is a protein or steroid molecule which acts
as a chemical messenger
 Causes a specific response in target cells

Target cells
 Possess a specific receptor on cell surface
membrane complementary to the
hormone
First Messenger
1.
Protein hormone secreted from a
cell in an endocrine organ
2.
Hormone circulates in body fluids
3.
Hormone binds to receptor on
the plasma membrane of a
target cell
Endocrine
cell
target cell
Second Messenger
4.
Activation of a second
messenger inside the cell
target of
second
messenger
inside the
cell





Adrenaline is released by the adrenal
glands
Binds to glycoprotein receptors on the
plasma membrane of target cells
The enzyme adenyl cyclase becomes
active
Concentration of cAMP in the cell
increases
cAMP activates the first of a
“cascade” of enzymes



The last enzyme in the cascade is
kinase
Kinase binds to glycogen
phosphorylase
This catalyses the breakdown of
Glycogen into glucose in the liver cells

Adrenal Cortex
 Uses cholesterol to produce steroids
▪ Glucocorticoids stimulate the synthesis of
glycogen in the liver
▪ Mineralocorticoids increase the uptake of Na+
in the gut and raise blood pressure

Adrenal Medulla
 Secretes Adrenaline in response to stress
 Preparing the body to fight or take flight

The role of adrenaline is to prepare the
body for action, list as many of the effects
of adrenaline as you can, and explain how
the effect prepares the body for action.








Relax smooth muscle in bronchioles
Increase stroke volume of the heart
Increase heart rate
Cause general vasoconstriction
Stimulates breakdown of glycogen
Dilates the pupils
Increase mental awareness
Inhibit the action of the gut


Describe, with the aid of diagrams
and photographs, the histology of the
pancreas, and outline its role as an
endocrine and exocrine gland.
Explain how blood glucose
concentration is regulated, with
reference to insulin, glucagon and the
liver.


The islets of langerhans are patches of
endocrine tissue scattered throughout
the exocrine tissue of the pancreas
Islets make up 15% of the pancreas
 A-cells secrete glucagon
 B-cells secrete insulin

These hormones help to regulate
blood glucose concentrations

Islets of Langerhans
 Groups of cells which carry out the endocrine
functions
 Alpha cells (α cells)
▪ Secrete glucagon which stimulates glycogen  glucose
 Beta cells (β cells)
▪ Secrete insulin which stimulates glucose  glycogen
 These two types of cells work antagonistically
Blood glucose concentration in a healthy
human 80 – 120mg/100cm3
 A decrease in blood glucose

 Cells may run out of blood glucose for respiration

An increase in blood glucose
 May upset the normal behaviour of cells

Blood glucose levels never remain constant
they oscillate above and below a required
level due to the time delay between the
change and the onset of corrective actions.

Glucagon leads of activation of enzymes to:
 Convert glycogen to glucose
 Increase the rate of gluconeogenesis

Insulin
 Rate of respiration increases
 Rate of conversion glucose to glycogen
increases
 Rate at which glucose is converted to fat and
stored in adipose tissue increases


Compare and contrast the causes of
Type 1 (insulin-dependent) and Type 2
(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.

Type I diabetes
 Insulin-dependent diabetes or juvenile
onset diabetes
 Beta cells do not make insulin

Type II diabetes
 Non-insulin dependent diabetes
 Insulin is produced, but target cells do not
respond to it adequately

Hyperglycaemia
 High blood glucose levels
 Associated with ketoacidosis

Hypoglycaemia
 Low blood glucose levels

Type 1 Insulin dependent diabetes
 Viral infection
 Autoimmune response
 ? Genetic?

Type 2 non-insulin dependent diabetes






Obesity
Genetic link – family history
A diet high in sugars
Asian or afro-Caribbean origin
Apple –shaped
BMI > 27


There is no cure
Type 1
 Patients monitor blood glucose levels,
take insulin injections
 Most common form of insulin is now GM
insulin

Type II
 Well-controlled diet / weight loss diet

Stem Cell
 An undifferentiated cell capable of cell
division and forming specialised cells

Transplant stem cells into a pancreas
that has no functioning beta cells
 Persuade these cells to form new beta
cells that can secrete insulin.

Use stem cells to produce white blood
cells that do not attack the beta cells
in the pancreas

Outline the hormonal and nervous
mechanisms involved in the control of
heart rate in humans.



Beating of the heart is myogenic
Each contraction is initiate by the sinoatrial node
Information can be transferred
through the body and to the SAN by
nerves and hormones to increase the
pace set by the SAN.

SAN receives nerve impulses along
two nerves
 Vagus nerve (parasympathetic nerve)
▪ Slows down the rate of the SAN
 Sympathetic nerve
▪ Speeds up heart rate

Both these nerves arise from the
cardiac centre in the brain

Adrenaline speeds up the rate of the
SAN, increasing heart rate.