responses Flashcards
What are plant growth factors and where are they produced?
● Chemicals that regulate plant growth response to directional stimuli.
● Produced in plant growing regions (apical meristems).
● Diffuse from cell to cell/ phloem mass transport.
Explain why shoots show positive phototropism.
- Indoleacetic acid (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. (acid growth
hypothesis). - 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.
Define taxis and kinesis. State their advantage.
● Taxis: directional movement in response to external stimulus.
● Kinesis: non-directional response to presence and intensity of external stimulus.
● Maintain mobile organism in optimum environment e.g. to prevent dessication.
Many organisms respond to temperature and humidity via kinesis rather than taxis. Why?
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
Give 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? 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.
Name 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
Compare and contrast rod and cone cells. (PACL)
Pigment in rods is rhodopsin whereas in cone it’s iodopsin
visual Acuity - rods have a low resolution and cone cells have a high resolution cone cells have no retinal convergence
Colour sensitivity - rods detect all wavelengths of light whereas cone cells only red blue and green wavelengths are absorbed by different types of iodopsin
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.
State the formula for cardiac output.
cardiac output (CO)
stroke volume (V) x heart rate (R)
What is the autonomic nervous system?
● System that controls involuntary actions of glands and muscles.
● 2 subdivisions: sympathetic & parasympathetic.
State the difference between the sympathetic and parasympathetic nervous system.
Sympathetic involved in ‘fight or flight’ response: stimulates effectors to speed up activity.
Parasympathetic involved in normal resting conditions: inhibits effectors to slow down activity.
Name the receptors involved in changing heart rate and state their location.
Baroreceptors (detect changes in blood pressure): carotid body.
Chemoreceptors (detect changes in pH e.g. due to increase in CO2 concentration): carotid body & aortic body.
How does the body respond to an increase in blood pressure?
- Baroreceptors send more impulses to cardioinhibitory centre in the medulla oblongata.
- More impulses to SAN down vagus nerve via parasympathetic nervous system.
- Stimulates release of acetylcholine, which decreases heart rate.
