Pheromones: Definition and Characteristics

Pheromones are specific chemical substances that are released by an organism into the environment. These emitted chemicals act as signals, influencing the social behavior and physiological responses of other individuals, typically of the same species. They are crucial for communication in many species, playing roles in mating, alarm signals, territory marking, and aggregation.

Analysis of Options

Let's evaluate each option based on the definition of pheromones:

• Option 1: Biochemicals found within the brain which effect a person’s behaviour. This describes substances like neurotransmitters or hormones acting internally within the brain, not pheromones which are typically external signals.
• Option 2: Biochemials which play an important role in transmitting information from neuron to neuron. This describes neurotransmitters, the chemical messengers used in synaptic transmission within the nervous system.
• Option 3: Chemical messengers found in the Central Nervous System. This is too general and also focuses internally within the CNS, unlike pheromones which act externally.
• Option 4: Chemical substances emitted by the person into the environment affecting the behaviour of others. This accurately describes pheromones as external signals that modify the behavior of recipients.

Therefore, the correct definition aligns with Option 4.