topic 6 Flashcards
(69 cards)
What is a stimulus?
something that causes a change in an organism’s internal or external environment.
Why is it important that organisms can respond to stimuli?
Organisms increase their chance of survival by responding to stimuli.
What is a tropism?
A growth response of a plant towards (positive) or away from (negative) a directional stimulus.
Summarise the role of growth factors in flowering plants.
Hormone-like substances (e.g., auxins like IAA) produced in growing regions, transported via phloem or diffusion, regulating growth in response to directional stimuli.
Describe how indoleacetic acid (IAA) affects cells in roots and shoots.
In shoots: high IAA stimulates cell elongation; in roots: high IAA inhibits cell elongation.
Explain gravitropism in flowering plants.
IAA moves to the lower side of the root/shoot, stimulating cell elongation in shoots but inhibiting in roots, causing shoots to bend away from gravity and roots towards gravity.
Explain phototropism in flowering plants.
IAA moves to the shaded side, stimulating cell elongation in shoots and inhibiting in roots, causing shoots to bend towards light and roots away.
Describe taxes.
A directional response towards or away from a stimulus.
Describe kinesis.
A non-directional response involving changes in speed or rate of turning in response to stimulus intensity.
Explain the protective effect of a simple reflex.
Rapid, automatic, involves few neurones and synapses, protecting from harm.
Describe the structure of a Pacinian corpuscle.
Concentric layers of connective tissue around a sensory neurone ending.
How does a generator potential form in a Pacinian corpuscle?
Pressure deforms lamellae, opens stretch-mediated Na+ channels, Na+ enters, depolarises, triggers action potential if threshold reached.
What does the Pacinian corpuscle illustrate about receptors?
They respond only to specific stimuli and produce a generator potential leading to an action potential.
Compare light sensitivity of rods and cones.
Rods more sensitive (summation of many rods to one neurone); cones less sensitive (one cone to one neurone).
Compare visual acuity of rods and cones.
Rods: low acuity (signals merged); cones: high acuity (separate signals).
Compare colour sensitivity of rods and cones.
Rods: monochromatic; cones: trichromatic (red, green, blue).
Define myogenic cardiac muscle.
It contracts without external nervous stimulation.
Describe the conduction system of the heart.
SAN generates impulse → atria contract → non-conducting tissue → AVN delays → Bundle of His → Purkyne tissue → ventricles contract from apex.
Where are chemoreceptors and baroreceptors located?
Aorta and carotid arteries.
Explain how chemoreceptors and pressure receptors affect heart rate.
Detect pH/CO2 or blood pressure changes → medulla → sympathetic/parasympathetic nerves to SAN → adjust heart rate.
Describe resting potential in a neurone.
Inside negative relative to outside due to Na+/K+ pump and differential membrane permeability.
Explain how resting potential is established.
3 Na+ out, 2 K+ in by active transport; K+ leaks out, few Na+ leak in.
Describe depolarisation.
Stimulus opens Na+ channels; Na+ influx; if threshold reached, action potential fired.
Explain all-or-nothing principle.
Action potential occurs only if threshold reached; same size each time; stronger stimulus increases frequency, not amplitude.
