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1.1.1 The Need for Communication
Stimulus and Response
· All living things need to maintain the conditions in their cells because enzymes need to work well. They need a suitable
temperature, pH and an aqueous environment to keep substrates and products in solution as well as freedom from toxins
and excess inhibitors.
· External environments change and place stress on the organism. The environmental changes (stimulus) must be monitored
and the organism must change its behaviour (response) to reduce the stress.
· The accumulation of toxins or excess waste in the internal environment must act as a stimulus to cause removal of these
wastes so the cells can survive. The concentrations of all substances in the blood must be monitored closely to ensure that
the body does not excrete too much of any useful substance but removes enough of the wastes to maintain good health.
Coordination
· A good communication system is needed to ensure that different parts of the body work together effectively.
· A good communication system will:
­ Cover the whole body
­ Enable cells to communicate with each other
­ Enable specific communication
­ Enable rapid communication
­ Enable both short-term and long-term responses
Cell Signalling
· Cells communicate with each other by cell signalling. This is where one cells releases a chemical that is detected by another
cell. The second cell will respond to the signal released by the first cell.
· The Neuronal System and the Hormonal System works by cell signalling.…read more

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1.1.2 Homeostasis and Negative Feedback
Homeostasis
· Homeostasis is the maintenance of the internal environment in a constant state despite external changes. A number of
conditions need to be kept constant inside the body:
­ Body temperature
­ Blood glucose concentration
­ Blood salt concentration
­ Water potential of the blood
­ Blood pressure
­ Carbon dioxide concentration
Negative & Positive Feedback
· Negative Feedback is a process that brings about a reversal of any change in conditions. It ensures that an optimum steady
state can be maintained as the internal environment is returned to its original set of conditions after any change.
Optimum Change away
Condition from Optimum
Return to Receptor
Optimum detects Change
Conditions
Effector reacts Communication
to Reverse systems informs
Change Effector
· Positive Feedback is a process that increases any change detected by the receptors. It tends to be harmful but is less
common than negative feedback.
· Positive feedback can be beneficial! At the end of pregnancy it is used to dilate the cervix by causing the secretion of
oxytocin to stretch the cervix even more.…read more

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1.1.3 Ectotherms
· The body temperature of an ectotherm tends to fluctuate with the external temperature, they rely on external sources of
heat to keep warm.
· ADVANTAGES: They use less of their food in respiration so they need to find less food and survive longer without eating. A
greater amount of the energy from food can be used for growth.
· DISADVANTAGES: They are less active in cooler temperatures and may need to `warm up' in the morning before they can be
active ­ greater risk of predation. They may not be capable of activity during the winter as they never warm up sufficiently.
Temperature Regulation
· Temperature regulation relies upon increasing the exchange of heat with their environment.
· When an ectotherm is cold it will change its behaviour to increase heat absorption and VV.
Adaptation How it helps to regulate temperature Example
Expose body to sun Enables more heat to be absorbed Snakes
Orientate body to sun Exposes larger surface area for more heat Locusts
absorption
Orientate body away from sun Exposes lower surface area so that less heat is Locusts
absorbed
Hide in burrow Reduces heat absorption by keeping out of the sun Lizards
Alter body shape Exposes more/less surface area to sun Horned lizards
Increase breathing movements Evaporates more money Locusts…read more

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1.1.4 Endotherms
· Endotherms use internal sources of heat to help maintain their body temperature. Many chemical reactions in the body
release heat energy. They can also use behavioural mechanisms as well to help maintain body temperature .
· ADVANTAGES: They have a fairly constant body temperature despite external temperatures. Activity is also possible when it
is cold and they can live in the colder parts of the planet.
· DISADVANTAGES: A lot of the energy intake is used to maintain body temperature which means more food is required. Less
energy from food is used for growth.
Temperature Regulation
· Behavioural and Physiological responses are used by endotherms to maintain their constant body temperature.
Component of body involved Response if core body temperature is Response if core body temperature
too high is too low
Sweat glands in skin Secrete more sweat , evaporates = heat Secrete less sweat, less evaporation
loss = less heat loss
Lungs, mouth and nose Panting increases, evaporation of water No panting, no evaporation = less
= heat loss heat loss
Hairs on skin Hairs lie flat, less insulation = more heat Hairs are raised to trap a layer of
lost insulating air = less heat loss
Arterioles leading to capillaries in Vasodilation = more blood into Vasoconstriction = less blood into
skin capillaries near skin surface = more capillaries near skin surface = less
heat radiated heat radiated
Liver cells Metabolism rate reduced = less heat Metabolism rate increased = more
generated heat generated
Skeletal muscles No spontaneous reactions Spontaneous contractions
(shivering) = heat generated…read more

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Behaviour if too hot Behaviour if too cold
Move into shade or hide in burrow Move into sunlight
Orientate body to decrease surface area exposed to Orientate body to increase surface area exposed to
sun sun
Remain inactive and spread out limbs to increase Move about to generate heat in muscles or reduce
surface area surface area in very cold conditions
Control of Temperature Regulation
· Endotherms monitor the temperature of their blood in the hypothalamus of the brain. If the core temperature drops below
optimum the hypothalamus sends signals to reverse the change. The will involve several changes:
­ Increased rate of metabolism to release more heat from exergonic reactions
­ Release of heat through extra muscle contractions
­ Decreased loss of heat to the environment
· If core temperature rises above the optimum the hypothalamus sends signals that bring about the opposite changes. This is
Negative Feedback.
Peripheral Temperature Receptors
· The Thermoregulatory Centre in the Hypothalamus monitors blood temperature and detects any changes in the core body
temperature.
· Peripheral temperature receptors in the skin monitor the temperature of the extremities ­ this information is sent to the
thermoregulatory centre. The brain can then initiate behavioural mechanism for maintaining body temperature if needed.…read more

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Comments

Harri.P

Good content and gives some material that is above and beyond the syllabus (good for essays)

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