1. COMMUNICATIONS
Stimulus

2. ROLE OF STIMULUS
A receptor is a specialized structure that can detect a specific stimulus and initiate a response. The stimulus may come from the external environment (e.g. light intensity, sound) or may come from the internal environment (e.g. hormone levels, arrival of food).
There are many type of receptors:
Proprioreceptors in muscles, tendons and joints
Mechanoreceptors respond to stretching, movement, touch, pressure and gravity
Chemoreceptors respond to chemicals
Photoreceptors detect light
Thermoreceptors detect heat and cold
Electroreceptors detect electrical energy

3. RESPONSE TO A STIMULUS Response to a stimulus involves: Stimulus
Receptor
Messenger
Effector
Response

4. RESPONSE TO A STIMULUS
Any information that can provoke a response from us is called a stimulus. Our environment contains many stimuli and we have special receptors to detect them and send information about conditions to control centers of the body. This can initiate a response. Responses are brought about by effector organs, which are usually muscles or glands. The messenger that travels from the receptor to the effector may be nervous or hormonal.
In summary, the pathway from stimulus to response is as follows:
Stimulus  receptor  messenger  effector  response

5. Range of senses involved in communication
Communication is the ability to perform an act that will change the behavior of another organism. The methods of communication involve all the senses - sight, sound, touch, taste and smell. Each species has developed its own methods of communicating information, which relate to its lifestyle. Humans rely mostly on visual and auditory signals.
Chemical signals
Pheromones - chemicals released by an organism into the external environment that influence the behavior or development of other members of the same species.
Common among mammals and insects.
Examples: female insects produce pheromones to attract males of the same species, ants will follow a pheromone trail, in bees, queen bee secretes an ‘anti-queen pheromone’ which inhibits worker from raising a new queen.
Many species mark out territories with urine.
Blowflies fly towards chemical odour of decaying meat.

6. Range of senses involved in communication
Visual signals
Many species use different postures for communication and many use colourful displays to attract a mate (eg peacocks).
Honeybees have a sophisticated form of communication: a ‘dance’ to indicate the direction and distance of a source of nectar relative to the hive. Close food supplies are shown by a ‘round dance’ ‘Waggle dance’ gives the angle of the food source relative to the sun and the hive.
Male fireflies use flashing lights as a visual signal to attract female fireflies.
Sound signals
Birds sing either to attract a mate or establish their own territory.
The sound of beating wings of a female mosquito attracts the male mosquito.