Stimuli and responses Flashcards
What is a taxis?
A taxis is a directional response where the direction of the stimulus determines the direction of movement.
Give an example of a taxis.
Negative phototaxis occurs when organisms move away from a light source.
What is kinesis?
Kinesis is a random (non-directional) response where the intensity of the stimulus affects the speed of movement.
Give an example of kinesis.
Woodlice move slower in a favourable environment (e.g., damp) and faster in an unfavourable one.
What is a stimulus?
A stimulus is a change in the internal or external environment of an organism.
What do the prefixes ‘photo-‘, ‘geo-‘, ‘chemo-‘, and ‘rheo-‘ mean?
Photo- means light, geo- means gravity, chemo- means chemical, and rheo- means movement.
What is a tropism?
A tropism is the growth movement of part of a plant in response to a directional stimulus.
What is phototropism?
Phototropism is the growth of a plant toward or away from light.
What is gravitropism (geotropism)?
Gravitropism is the growth of a plant upwards or downwards in response to gravity.
What are growth factors in plants?
Growth factors are hormone-like chemicals that regulate plant growth by speeding up or slowing down growth.
What is auxin?
Auxin is a plant hormone that stimulates growth by cell elongation.
How do high concentrations of auxin affect shoots and roots?
High concentrations of auxin stimulate growth in shoots but inhibit growth in roots.
What is IAA and where is it produced?
IAA (indoleacetic acid) is an auxin produced in the tips of shoots and roots in plants.
How does IAA cause phototropism in shoots?
IAA moves to the shaded side of shoots, causing cells to elongate and the shoot to bend toward light.
How does IAA cause gravitropism in roots?
IAA moves to the underside of roots, inhibiting growth and causing the root to bend downwards.
What are the structures of a neurone?
Neurones consist of dendrites, cell body, axon, myelin sheath, nodes of Ranvier, and axon terminal.
What is the function of dendrites?
Dendrites branch out from the cell body and carry impulses from neighbouring neurones.
What is the function of the cell body?
The cell body contains the nucleus and genetic material of the neurone.
What is the function of the axon?
The axon carries electrical impulses away from the cell body and down the length of the neurone.
What is the function of the myelin sheath?
The myelin sheath is a fatty layer that insulates the axon and speeds up electrical transmission.
What are nodes of Ranvier?
Nodes of Ranvier are gaps in the myelin sheath that speed up transmission by forcing impulses to jump across the gap.
What is the function of the axon terminal?
The axon terminal transmits impulses to neighbouring neurones across a synapse.
What are the three main types of neurones?
The three types are sensory neurones, motor neurones, and relay neurones.
What is the role of sensory neurones?
Sensory neurones transmit impulses from receptors to the central nervous system (CNS).
What is the role of motor neurones?
Motor neurones transmit impulses from the CNS to effectors such as muscles.
What is the role of relay neurones?
Relay neurones transmit impulses between sensory and motor neurones.
What is the central nervous system (CNS)?
The CNS consists of the brain and spinal cord.
What is the peripheral nervous system?
The peripheral nervous system connects the CNS to the rest of the body via neurones.
What is the role of the somatic nervous system?
The somatic nervous system controls conscious activities such as running.
What is the role of the autonomic nervous system?
The autonomic nervous system controls unconscious activities such as digestion.
What is the sympathetic nervous system?
The sympathetic nervous system prepares the body for action (‘fight or flight’).
What is the parasympathetic nervous system?
The parasympathetic nervous system calms the body down (‘rest and digest’).
What is a reflex arc?
A reflex arc is the pathway of information in a reflex, which allows for rapid responses without conscious thought.
What are the steps in a reflex arc?
- Receptors detect stimulus, 2. Sensory neurone transmits impulse, 3. Relay neurone connects to motor neurone, 4. Motor neurone sends impulse to effector.
What is an action potential?
An action potential is a reversal of charge across the axon membrane (+40mV).
What is the all-or-nothing principle?
An action potential is only generated if the stimulus reaches the threshold value; it is always the same size.
What is a generator potential?
A generator potential is the nervous impulse produced by a sensory receptor when a stimulus is detected.
What is the Pacinian corpuscle?
The Pacinian corpuscle is a sensory receptor that responds to mechanical stimuli (pressure).
How does a Pacinian corpuscle generate an action potential?
- Pressure deforms the lamellae, 2. Stretch-mediated sodium channels open, 3. Sodium ions enter the neurone, 4. If threshold is reached, an action potential is generated.
What happens to light entering the eye?
Light enters through the pupil, focused by the lens onto the retina, where photoreceptors detect light.
What is the fovea?
The fovea is a part of the retina where many photoreceptors are concentrated.
What is the difference between rods and cones?
Rods detect black and white light in low light intensity; cones detect colour and work in bright light.
What is visual sensitivity in rods?
Rods are very sensitive to light because many rods join one neurone, allowing generator potentials to combine.
What is visual acuity in cones?
Cones provide high visual acuity because each cone connects to one neurone, allowing close points to be seen as separate.
How do rods produce action potentials?
- Rhodopsin breaks down in low light, 2. Sodium ions enter rod cells, 3. Membrane depolarises, 4. Generator potential triggers an action potential.
What is the SAN and its role in heart rate control?
The sinoatrial node (SAN) sets the rhythm of the heart by sending out regular action potentials.
How does the medulla oblongata control heart rate?
The medulla sends impulses to the SAN via the sympathetic or parasympathetic nervous system.
How does the heart respond to high blood pressure?
Receptors send impulses to the medulla, which uses the parasympathetic nervous system to decrease heart rate.
How does the heart respond to low blood pressure?
Receptors send impulses to the medulla, which uses the sympathetic nervous system to increase heart rate.
