Unit 5.9 Response To Stimuli

Starter: What are the stimuli here and what would be the response? Learning Outcomes - define terms stimulus and response - Identify the advantages of being able to respond to stimuli - describe the mechanisms of taxes, kineses and tropisms - Explain how the nervous system is organised in animals - Outline the mechanism of a reflex arc

Stimulus and Response Learning Outcomes - define terms stimulus and response - Identify the advantages of being able to respond to stimuli - describe the mechanisms of taxes, kineses and tropisms - Explain how the nervous system is organised in animals - Outline the mechanism of a reflex arc Stimulus: Detectable change in the internal or external environments of an organism that provokes a response. Response: A reaction to a stimulus Why is it important organisms can respond to stimuli? Increases the chances of survival for an organism. (avoid predators or harmful stimuli, detect and movement towards resources) Means that those that produce more appropriate responses can pass on their alleles. There is always a selection pressure facing those that can produce the most appropriate responses.

Stimulus and Response Learning Outcomes - define terms stimulus and response - Identify the advantages of being able to respond to stimuli - describe the mechanisms of taxes, kineses and tropisms - Explain how the nervous system is organised in animals - Outline the mechanism of a reflex arc How do organisms produce a response against stimuli? StimulusResponse

Taxis, Kineses, Tropisms Learning Outcomes - define terms stimulus and response - Identify the advantages of being able to respond to stimuli - describe the mechanisms of taxes, kineses and tropisms - Explain how the nervous system is organised in animals - Outline the mechanism of a reflex arc Around the room is information about these 3 mechanisms of responding to stimuli. For each: 1) describe how the mechanism works. 2) give examples in nature of how each mechanism is used.

The Nervous Systems Learning Outcomes - define terms stimulus and response - Identify the advantages of being able to respond to stimuli - describe the mechanisms of taxes, kineses and tropisms - Explain how the nervous system is organised in animals - Outline the mechanism of a reflex arc In animals the fastest mechanism for responding to stimuli is by use of the nervous systems. - CNS – brain and spinal - PNS – all other nerves

Plenary Write an exam question based on the learning today. Write it on the table in whiteboard pens. 5 minutes to write You have 10 mins to answer each others questions 5 to go through after Learning Outcomes - define terms stimulus and response - Identify the advantages of being able to respond to stimuli - describe the mechanisms of taxes, kineses and tropisms - Explain how the nervous system is organised in animals - Outline the mechanism of a reflex arc

Taxis A simple response in which when a stimulus is detected, the effect is movement towards or away from the direction of stimulus. - Movement away from the stimulus is called negative taxis. - Movement towards the stimulus is called positive taxis. Examples: Phagocytes detect toxins released by pathogens and move towards the pathogen along a concentration gradient. (positive chemotaxis) Algae cells move towards light as they are photosynthetic (Positive phototaxis) Earthworms move away from light where they can better conserve water and avoid predators (negative phototaxis, positive hydrotaxis) Bacteria will move towards an area of high concentration of glucose (positive chemotaxis) They will also move away from areas when they detect high amounts of waste excreted (negative chemotaxis)

Kineses A simple response in which when an unpleasant stimulus is detected, the effect is increased rapid random movement. The more unpleasant the stimulus, the more rapid the movement and its change in direction. (The idea being that it will move enough to bring it into favourable conditions) Examples: Woodlice lose water rapidly in dry conditions, they respond by kinesis. They begin to move rapidly and uncontrollably, changing directions. This increases the chance of moving into favourable conditions. Once this happens, the unpleasant stimulus is no longer detected and kinesis stops. (NEGATIVE FEEDBACK)

Tropisms A growth response to a stimulus or away from a stimulus by a plant. Plant growth and elongation is controlled by the hormone Auxin. Examples: Plant stems tend to grow towards the light source as the hormone auxin collects on the shaded side of the plant, only one side grows and this causes the plant stem to ‘bend’. (Positive phototropism) Plant roots grow towards water (positive hydrotropism), away from light (negative phototropism), towards gravity (positive gravitotropism)