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Communication
Changes in the environment place stress on a living
organism. If the organism is to remain active, the changes
in the environment must be monitored and the organism
must change its behaviour to reduce the stress.
Internal Environment must be maintained. Internal cells are
bathed in tissue fluid. The composition of the tissue fluid must
be kept constant. Metabolic activities in the cell itself alter its
environment – the CO2 produced in respiration for example
makes tissue fluid acidic, and the change in pH can damage
enzymes.
Cell Signalling is the process by which cells
communicate. One cell releases a chemical
that is detected by a second cell; the second
cell will respond to the signal sent by the
first.
 The Neuronal System is an interconnected
network of neurones that signal to each
other across synapses
 The Hormonal System uses the blood to
transport hormones all over the body, to
be recognised only by specific target cells.
A good
communication
system must:





Extend over the whole body
Enable communication between cells
Enable specific communication
Enable rapid communication
Enable short term and long term
responses
Homeostasis is the maintenance of a constant
internal environment despite external changes.
Temperature, Carbon Dioxide levels, blood water potential, blood
glucose concentration, blood pressure and blood salt concentration
must all be controlled by homeostasis.
In order for homeostasis to work:
 Any change must be detected
 Change must be signalled to other cells
 Must be a response that reverses the
change
Optimum
condition
Return to
optimum
conditions
Change away
from
optimum
Effector
reverses
change
Receptor
detects
change
Negative feedback is when a change is
reversed to return to a steady,
optimum position.  The communication


The stimulus is the
change in the internal
environment
The receptor monitors
any changes and sends
out a signal if a change
is detected: this could
be a chemoreceptor or
a thermoreceptor.

system is the nervous
or hormonal system –
it acts by signalling
between cells. A
message is transmitted
form receptor to
effector.
Effector cells, like liver
or muscle cells, bring
about a response that
reverses the change.
Communication
system informs
effector
Positive
Feedback
The response in positive feedback is to increase the
original change. This destabilises the system.
Usually
Harmful…
When the body gets too cold,
below a certain core
temperature, enzymes
become less active. If they
are less active, exothermic
reactions tat release heat are
slower and release less heat.
This allows the body to cool
further and stops the enzyme
controlled reactions even
more, so temperature spirals
downwards.
Positive feedback can be
beneficial however…
At the end of pregnancy, the cervix must dilate. As the
cervix begins to stretch, the anterior pituitary gland is
stimulated to secrete oxytocin. Oxytocin increases
uterine contractions which stretch the cervix more,
which causes the secretion of more oxytocin.
Ectotherms are organisms that rely on external
sources of heat to regulate their body
temperature.
Fish, reptiles,
amphibians and
invertebrates are
Ectotherms.
When an ectotherm
is too cold, it will
change its
behaviour or
physiology to
increase absorption
of heat form its
environment. If too
hot, it will increase
loss of heat and
decrease
absorption of heat.
Advantages
Disadvantages
 Use less food in respiration
 Need to find less food; may be
able to survive for ling periods
without eating
 Greater proportion of energy
obtained from food can be
used for growth
 Less active on cooler
temperatures; need to warm up
in morning before they can be
active so greater risk of
predation
 May not be capable of activity
on the winter as they don’t
warm up sufficiently.
Physiological or Anatomical Adaptations to regulate
temperature…
1. Expose body to sun: more heat absorbed
2. Orientate body towards or away from sun: larger surface area exposed
for more heat absorption or less area exposed to absorb less heat
3. Hide in burrow: keeping out of sun reduced heat absorption
4. Alter body shape to expose more or less area to sun: horned lizards
expand their ribcage and frilled lizards use their frill to absorb heat.
5. Increase abdominal breathing movements to evaporate more water
Endotherms are organisms that can use
internal sources of heat, such as heat
generated from metabolism in the liver, to
maintain body temperature.
Dolphins,
lions,
elephants
and humans
are
endotherms.
Advantages
Disadvantages




Fairly constant body temperature
whatever external temperature
Activity possible when temperatures are
cool
Ability to inhabit colder parts of the planet


Large part of energy intake used to
maintain body temperature in cold
More food required
Less of the energy obtained from food
is used for growth
The thermoregulatory centre in the hypothalamus monitors blood temperature and monitors any changes
on core temperature. Early warnings that body temperature may change come from peripheral
temperature receptors on the skin in the extremities. If they signal to the brain that the external
environment is very cold or very hot, the brain can initiate behavioural mechanisms for maintaining body
temperature, like moving into the shade.
Thermoregulatory
centre in
hypothalamus
detects change
Nervous and
hormonal systems
carry signals to
liver, skin and
muscles
Too hot: Less heat
generated, more
heat lost
Too Cold: More
heat generated,
less heat lost
Temperature
falls or rises,
towards optimum
Arteriole of
capillary beds
dilate, arteriole
sphincters open –
vasodilation. More
blood reaches the
skin so more heat
can be radiated
away from body.
Reduction of
sweat so less
loss of latent
heat.
Pili erector
muscles contract
so hairs stand on
end, trapping an
insulating layer of
air.
Hairs lie flat, so
more heat lost
through
convection and
radiation.
More sweat excreted: more
heat energy from the body is
needed to evaporate the swat
– heat from the blood
supplies the latent heat of
vaporisation.
If
temperature
increases…
If
temperature
decreases…
Shivering:
Increased
muscular
contraction
releases heat.
Panting
increases
evaporation
of water
form lungs
and tongue,
to remove
heat energy.
Vasoconstriction:
arteriole sphincters
constrict, reducing
blood flow to skin
surface.
Increased metabolic rate: thyroid
stimulated to produce thyroxine which
increases respiration in tissues.