6.1 - Internal and external; stimuli are detected and lead to a response Flashcards
What are the plant growth factors and where are they produced?
- Chemicals that regulate plant growth response to directional stimuli
- Produced in plant growing regions
- 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.
- Cells on shaded side elongate faster due to higher turgor.
- Shoots bend towards light.
Explain why roots show positive gravitropism
- Gravity causes IAA to accumulate on lower side of the root
- IAA in hibits 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
Advantage: maintains mobile organism in optimum environment.
Many organisms respond to temperature and humidity via kinesis than taxis. Why?
Less directiona 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.
- If organism moves considerable distance into unfavourable environment: turning slowly decreases; begins to move in long straight lines; sharper turns lead to 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
Advantages of a simple reflex.
- rapid response to potentially dangerous 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 capsule.
- Stretch-mediated Na+ channels on plasma membrane
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 cells 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 + contrast rod and cone cells.
Pigment
Visual acuity
Colour sensitivity
Light sensitivity
ROD:
- Pigment: rhodopsin
- Visual acuity: low res - many rod cells synapse with 1 bipolar neuron
- Colour sensitivity: Monochromatic - all wavelengths of light detected
- Light sensitivity: Very good - spatial summation of subthreshold impulses
CONE:
- Pigment: 3 types of iodopsin
- Visual acuity: high res- 1 cone cell synapses with 1 bipolar neuron = no retinal convergence
- Colour sensitivity: tricolour - red, blue and green wavelengths absorbed by different types of iodopsin
- Light sensitivity: less sensitive - 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
State 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 subdivisions: sympathetic & parasympathetic
Sate the difference between the sympathetic and parasympathetic nervous system
- Sympathetic is involved in ‘fight or flight’ response: stimulates effectors to speed up activity.
- Parasympathetic involved in normal resting conditions: inhibits effectors to slow down activity.
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.
Name the receptors involved in changing heart rate and state their location.
- Baroreceptors (detect changes in blood pressure): carotid body
- Chemereceptors (detect changes in pH e.g. due to increase in CO2 concentration): carotid body & aortic body.
How does the body respond to a decrease in blood pressure?
- Baroreceptors send more impulses to cardioacceleratory centre in the medulla oblongata
- More impulses to SAN via sympathetic nervous system
- Stimulates release of noradrenaline, which increases heart rate and strength of contraction
How does the bdy respond to an increase in CO2 concentration?
- Chemoreceptors detect pH decrease and send more impulses to cardioacceleratory centre of medulla oblongata.
- More impulses to SAN via sympathetic nervous system.
- Heart rate increases, so rate of blood flow to lungs increases = rate of gas exchange and ventilation rate increase.
Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process.
- Sympathetic nervous system increases heart rate.
- Due to chemoreceptors detecting a rise in Co2 levels in the blood.
- It then sends impulses to the cardiac centre / medulla oblongata.
- More impulses are sent to SAN.
