Stimuli Are Detected + Lead To A Response Flashcards
What are plant growth factor and where are they produced?
- chemicals that regulate plant growth response to directional stimuli
- produce in apical meristems
- diffuse from cell to cell/phloem mass transport
Explain why shoots show positive phototropism
- IAA diffuses to shaded side of shoot tip
- As IAA diffuses down shaded side it causes active transport of H+ ions into cell wall
- Disruption to H-bonds between cellulose molecules & action of expansins make cell more permeable to water
- Cells on shaded side elongate faster due to higher turgor pressure
- Shoot bends towards light
Explain why roots show positive gravitropism
- Gravity causes IAA to accumulate on lower side of the root
- IAA inhibits elongation of root cells
- Cells on the upper side of the root elongate faster so the root tip bends downwards
What is taxis?
Directional movement in response to external stimulus
What is kinesis?
Non-directional response to presence and intensity of external stimulus
What is the advantage of taxis and kinesis?
Maintain mobile organism in optimum environment
Why do many organisms respond to temperature and humidity via kinesis rather than taxis?
Less directional stimuli; often no clear gradient from one extreme to the other
How could a student recognise kinesis in an organism’s movement?
- Organism crosses sharp division between favourable & unfavourable environment: turning increases
(Return to the original favourable environment) - If organism moves considerable distance into unfavourable environment: turning slowly decreases; begins to move in long, straight lines; sharper turns
(Lead organism to new environment)
Outline what happens in a simple reflex arc
Receptor detects stimulus—>sensory neuron—>relay neuron in CNS coordinates response —> motor neuron —> response by effector
What are the advantages of a simple reflex?
- Rapid response to potentially dangerous stimuli since only 3 neurons involved
- Instinctive
Suggest a suitable statistical test to determine whether a factor has a significant effect on the movement of an animal in a choice chamber
Chi squared
What features are common to all sensory receptors?
- act as energy transducers which establish a generator potential
- respond to specific stimuli
Describe the basic structure of a pacinian corpuscle
- single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
- stretch-mediated Na+ channels on plasma membrane
- capillary runs along base layer of tissue
What stimulus does a pacinian corpuscle respond to and how?
- Pressure deforms membrane causing stretch-mediated Na+ ion channels to open
- If influx of Na+ raises membrane to threshold potential a generator potential is produced
- Action potential moves along sensory neuron
What are the 2 types of photoreceptor cell located in the retina?
- cone cells
- rod cells
Where are rod and cone cells located in the retina?
Rod: evenly distributed around periphery but NOT in central fovea
Cone: mainly central fovea no photoreceptors at blind spot
What are some properties of rod cells?
- rhodopsin pigment
- low visual acuity since many rod cells synapse with 1 bipolar neuron
- monochromatic: all wavelengths of light detected
- very sensitive to light: spatial summation of subthreshold impulses
What are some properties of cone cells?
- 3 types of iodopsin pigment
- high visual acuity: 1 cone cell synapses with 1 bipolar neuron so no retinal convergence
- tricolour: red, blue, green wavelengths absorbed by different types of iodopsin
- less sensitive to light so not involved in night vision
Outline the pathway of light from a photoreceptor to the brain
Photoreceptor—>bipolar neuron—>ganglion cell of optic nerve—>brain
Define myogenic
Contraction of heart is initiated within the muscle itself rather than by nerve impulses
State the name and location of the 2 nodes involved in heart contraction
- sinoatrial node (SAN): within the wall of the right atrium
- atrioventricular node (AVN): near lower end of right atrium in the wall that separates the 2 atria
Describe how heartbeats are initiated and coordinated
- SAN initiates wave of depolarisation (WOD)
- WOD spreads across both atria = atrial systole
- Layer of fibrous, non-conducting tissue delays impulse while ventricles fill & valves close
- AVN conveys WOD down septum via bundle of His which branches into Purkinje fibres along ventricles
- Causes ventricles to contract from apex upwards
What is the formula for cardiac output?
Cardiac output = stroke volume (v) x heart rate (r)
What is the autonomic nervous system?
- system that controls involuntary actions of glands and muscles
- 2 subdivison: sympathetic & parasympathetic
