Survival and response

• Stimulus = a detectable change in the internal or external environment of an organism that leads to a response in the organism
• Receptors = detect stimuli
• Effectors = a muscle or gland that produces responses
• Stimulus -> receptor -> co-ordinator -> effector -> response
• Taxis = a simple response who’s direction is determined by the direction of the stimulus
• Positive or negative phototaxis = moving toward or away from light
• Positive or negative chemotaxis - moving towards or away from chemicals
• Kinesis - the organism moves more or less but in random directions so increases its chances of finding favourable conditions
• Tropism - the growth of a plant part towards a stimulus
• Positive or negative phototropism = movement toward or away from light stimulus
• Positive or negative gravitropism = plant grows towards or away from gravity
• Plant shoots experience positive phototropism and negative gravitropism
• Plant roots experience positive gravitropism and negative phototropism