AQA A Level Biology: Survival and response Flashcards
What is a stimulus?
A detectable change in the internal or external environment that triggers a response.
What is the role of receptors?
Detect stimuli and convert energy from the stimulus into a nerve impulse.
What is the role of effectors?
Carry out the response, usually muscles or glands.
What is the definition of a response?
A reaction produced by an effector after a stimulus is detected.
What is a reflex?
A rapid, involuntary response to a stimulus that protects the body.
What is the reflex arc?
The pathway taken by nerve impulses during a reflex action:
Stimulus → Receptor → Sensory neuron → CNS → Motor neuron → Effector → Response
What is taxis?
A directional movement in response to a stimulus.
What are the types of taxis?
- Positive taxis: Movement towards the stimulus.
- Negative taxis: Movement away from the stimulus.
Give examples of taxis.
- Phototaxis: Movement towards/away from light.
- Chemotaxis: Movement towards/away from chemicals.
What is kinesis?
A non-directional movement in response to a stimulus where the speed and rate of turning change.
What is the difference between taxis and kinesis?
- Taxis: Directional movement towards/away from a stimulus.
- Kinesis: Random movement where the organism moves faster and changes direction more in unfavourable conditions.
Why is kinesis beneficial to organisms?
It increases the chance of finding a more favourable environment.
What is tropism?
A growth response in plants where the direction is determined by the stimulus.
What are the types of tropism?
- Phototropism: Growth in response to light.
- Gravitropism (geotropism): Growth in response to gravity.
- Hydrotropism: Growth in response to water.
What is positive and negative phototropism?
- Positive phototropism: Growth towards light (shoots).
- Negative phototropism: Growth away from light (roots).
What is IAA?
Indoleacetic acid, a type of auxin that controls plant growth by affecting cell elongation.
How does IAA cause phototropism in shoots?
- IAA accumulates on the shaded side of the shoot.
- This causes cell elongation, resulting in bending towards the light.
How does IAA cause gravitropism in roots?
- IAA accumulates on the lower side of the root.
- It inhibits cell elongation in roots, causing them to grow downwards.
What is the role of the nervous system in response?
It detects stimuli, processes information, and coordinates a response.
What are the divisions of the nervous system?
- Central nervous system (CNS): Brain and spinal cord.
- Peripheral nervous system (PNS): Sensory and motor neurons.
What are the divisions of the motor nervous system?
- Somatic nervous system: Controls voluntary movements.
- Autonomic nervous system: Controls involuntary responses.
What are the divisions of the autonomic nervous system?
- Sympathetic nervous system: Stimulates “fight or flight.”
- Parasympathetic nervous system: Promotes “rest and digest.”
What is the difference between the sympathetic and parasympathetic nervous system?
- Sympathetic: Increases heart rate, dilates pupils, inhibits digestion.
- Parasympathetic: Decreases heart rate, constricts pupils, stimulates digestion.
What is the role of sensory neurons?
Carry nerve impulses from receptors to the CNS.
What is the role of motor neurons?
Carry nerve impulses from the CNS to effectors.
What is the role of relay neurons?
Connect sensory and motor neurons within the CNS.
What is the role of the spinal cord in reflex actions?
It acts as a relay centre, quickly transmitting impulses to and from the brain.
What is a pacinian corpuscle?
A mechanoreceptor that detects pressure and vibration in the skin.
How does a pacinian corpuscle work?
- Pressure deforms the corpuscle.
- Stretch-mediated sodium channels open.
- Sodium ions diffuse in, depolarising the membrane and creating a generator potential.
What is a generator potential?
A small depolarisation of the membrane caused by a stimulus.
How is an action potential generated?
If the generator potential reaches the threshold, an action potential is triggered.
What is the importance of survival and response in organisms?
It increases the chance of survival by allowing organisms to avoid danger, locate food, and find favourable conditions.
What is habituation?
A decrease in response to a repeated stimulus over time.
What is learned behaviour?
Behaviour that is modified by experience and environmental conditions.
How do plants respond to stimuli?
Through tropisms controlled by plant growth factors such as auxins.
Why is the control of heart rate essential?
It maintains homeostasis by matching the heart rate to the body’s needs.
What is the role of chemoreceptors in heart rate control?
Detect changes in blood pH due to CO₂ levels and send signals to the medulla to adjust heart rate.
What is the role of baroreceptors in heart rate control?
Detect changes in blood pressure and send signals to the medulla to adjust heart rate.
What is the role of the sinoatrial node (SAN)?
Acts as the pacemaker by generating impulses that control heart contractions.
What is the sequence of events in the control of heart rate?
- SAN generates impulses.
- Impulses spread across the atria, causing contraction.
- Impulses reach the atrioventricular node (AVN).
- Impulses travel down the bundle of His and through Purkyne fibres.
- Ventricles contract from the base upwards.
