1. A good communication system must:
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.
Communication
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

2. 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.
Optimum condition
Change away from optimum
Receptor detects change
Communication system informs effector
Effector reverses change
Return to optimum conditions
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
Negative feedback
Negative feedback is when a change is reversed to return to a steady, optimum position.
The communication 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.
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.

3. Positive feedback can be beneficial however…
The response in positive feedback is to increase the original change. This destabilises the system.
Usually Harmful…
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.
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.

4. Physiological or Anatomical Adaptations to regulate temperature…
Ectotherms
Ectotherms are organisms that rely on external sources of heat to regulate their body temperature.
Fish, reptiles, amphibians and invertebrates are Ectotherms.
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.
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.
Physiological or Anatomical Adaptations to regulate temperature…
Expose body to sun: more heat absorbed
Orientate body towards or away from sun: larger surface area exposed for more heat absorption or less area exposed to absorb less heat
Hide in burrow: keeping out of sun reduced heat absorption
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.
Increase abdominal breathing movements to evaporate more water

5. Endotherms Dolphins, lions, elephants and humans are endotherms.
Endotherms are organisms that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain body temperature.
Endotherms
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.
Temperature
falls or rises, towards optimum
Too hot: Less heat generated, more heat lost
Too Cold: More heat generated, less heat lost
Nervous and hormonal systems carry signals to liver, skin and muscles
Thermoregulatory centre in hypothalamus detects change

6. If temperature decreases… If temperature increases…
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.
Arteriole of capillary beds dilate, arteriole sphincters open – vasodilation. More blood reaches the skin so more heat can be radiated away from body.
Panting increases evaporation of water form lungs and tongue, to remove heat energy.
If temperature decreases…
If temperature increases…
Physiological Mechanisms
Reduction of sweat so less loss of latent heat.
Vasoconstriction: arteriole sphincters constrict, reducing blood flow to skin surface.
Pili erector muscles contract so hairs stand on end, trapping an insulating layer of air.
Shivering: Increased muscular contraction releases heat.
Increased metabolic rate: thyroid stimulated to produce thyroxine which increases respiration in tissues.