6.1- Internal and external stimuli are detected and lead to a response 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
- Indoleascetic 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 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 upper side of root elongate faster, so root bends downwards
Describe features of mammalian hormones (CASTS)
- Concentration: response not always dependent on concentration
- Action: bind to complementary proteins in/ on target cells
- Synthesis: specialised glands
- Transport: circulatory system
- Speed: faster acting (homeostasis)
Describe features of plant growth factors (CASTS)
- Concentration: response proportional to concentration
- Action: can affect all cells
- Synthesis: various tissues in growing regions
- Transport: diffusion or phloem translocation
- Speed: slower acting (plant growth)
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 and unfavourable environment: turning increases (return to 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 advantages of a simple reflex
- Rapid response
2.Automatic
Suggest a 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 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 2 types of photoreceptor cell located in retina
- Cone cells
- Rod cells
Where are rod and cone cells located in the retine?
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:
Rod- rhodopsin
Cone- 3 types of iodopsin
Visual Acuity:
Rod- low res; many rod cells synapse with 1 bipolar neuron
Cone- high res; 1 cone cell synapses with 1 bipolar neuron= no retinal convergence
Colour sensitivity:
Rod- monochromatic; all wavelengths of light detected
Cone- tricolour; red, blue, green wavelengths absorbed by different types of iodopsin
Light Sensitivity:
Rod- V.sensitive; spatial summation of subthreshold impulses
Cone- less sensitive= not involved in night vision
Outline 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 muscle itself rather than by nerve impulses
State name and location of the 2 nodes involved in heart contraction
- Sinoatrial node (SAN): within wall of right atrium
- Atrioventricular (AVN): near lower end of right atrium that separates the 2 atria
Describe how heartbeats are initiated and coordinated
- SAN initiates wave of depolarisation
- This spreads across both atria= atrial systole
- Layer of fibrous, non-conducting tissue delays impulse while ventricles fill & valves close
- AVN conveys the impulse down septum via Bundle of His, which branches into Purkynje fibres along ventricles
- Causes ventricles to contract from apex upwards
State formula for cardiac output
Stroke volume X heart rate
What is autonomic nervous system?
- System that controls involuntary action of glands and muscles
- 2 subdivisions: sympathetic & parasympathetic
State difference between sympathetic and parasympathetic nervous system
- Sympathetic involved in ‘fight or flight’ reponse: stimulates effectors to seed up activity
- Parasympathetic involved in normal resting conditions: inhibits effectors to slow down activity
Name receptors involved in changing HR and state location
Baroreceptors: (detect changes in blood pressure): carotid body
Chemoreceptors: (detect changes in pH): carotid & aortic body
How does body respond to an increase in blood pressure?
- Baroreceptors send more impulses to cardioinhibitory centre in meddula oblongata.
- More impulses to SAN down vagus nerve via parasympathetic nervous system
- Stimulates release of acetylchole, which decreases heart rate
How does body respond to a decrease in blood pressure?
- Baroreceptors send more impulses down accelerator nerve to medulla oblongata
- More impulses sent to SAN via sympathetic nervous system
- Stimulates release of noradrenaline, which increases heart rate and strength of contraction
How does body respond to an increase in CO2 concentration?
- Chemoreceptors detect pH decrease and send more impulses down accelerator nerve to 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 increase
