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.