survival and response Flashcards
why do plants react to changes?
plants respond to changes in their environment to increase their chances of survival
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
define tropism
the growth response of a plant to a directional stimulus
define phototropism
plant growth response to a light source
define gravitropism
plant growth response to gravity that directs roots downward
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 the cell wall
- disruption of H-bonds between cellulose molecules and action of expansins makes cell more permeable to water
- cells on shaded side elongate faster due to higher turgor pressure
- shoot bends towards the 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
contrast mammalian hormones and plant growth factors (CASTS)
- concentration
- in mammals response is not always dependent on concentration
- in plants response is proportional to the concentration - action
- in mammals growth factors bind to complementary proteins in/on target cells
- in plants growth factors can affect all cells - synthesis
- mammals have specialised glands
- plants have various tissues in growing regions - transport
- mammals have the circulatory system
- plants have diffusion or translocation - speed
- mammals are faster acting due to homeostasis
- plants are slower acting due to plant growth
define taxis and kinesis, state their advantage
- taxis: directional movement in response to an external stimulus
- kinesis: non-directional response to presence and intensity of external stimulus
- maintains a mobile organism in optimum environment
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 a sharp division between favourable and unfavourable environment: turning increases (the return to the original favourable environment)
- if an organism moves considerable distance into unfavourable environment: turning slowly decreases and begins to move in long straight lines, sharper turns (leads organism into new environment)
outline what happens in a simple reflex arc
- receptor detects stimulus
- passes stimulus to sensory neurone
- sensory neurone sends electrical impulses to the relay neurone in CNS coordinates response
- relay neurone connects to the motor neurone and passes the impulses on
- motor neurone carries impulse to the effector
- effector triggers response
give the advantages of a simple reflex
- rapid response to potentially dangerous stimuli since only 3 neurones are 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 the membrane causing stretch-mediated Na+ ion channels to open
- an 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 not in central fovea
cone - mainly central fovea no photoreceptors at blind spot
compare and contrast rod and cone cells (PACL)
- pigment in rod cells is rhodopsin, in cone cells its 3 types of iodopsin
- visual acuity: rod cells have low resolution, many rod cells synapse with 1 neuron, cone cells have high resolution because 1 cone cell synapses with 1 neurone so no retinal convergence
- colour sensitivity: rod cells are monochromatic so all wavelengths of light detected, cone cells are tricolour so only red blue and green wavelengths are absorbed
- light sensitivity: rod cells are very sensitive due to spatial summation of subthreshold impulses, cone cells are less sensitive and they are not involved in night vision
outline the pathway of light from a photoreceptor in the brain
photoreceptor -> neurone -> ganglion cell of optic nerve -> brain
define myogenic
contraction of the heart is initiated within the muscle itself rather than by nerve impulses
state and name the location of the 2 nodes involved in heart contraction
- sinoatrial note (SAN): within the wall of the right atrium
- atrioventricular node (AVN): near the lower end of the right atrium in the wall that separates the 2 atria
describe how heartbeats are initiated and coordinated
- sinoatrial node initiates a wave of depolarisation
- wave of depolarisation spreads across both atria causing atrial systole
- layer of fibrous, non-conducting tissue delays impulse while ventricles fill and valves close
- atrioventricular node conveys a wave of depolarisation down the septum via the Bundle of His, which branches into Purkinje fibres along ventricles
- causes ventricles to contract from the apex upwards
state the formula for cardiac output
cardiac output = stroke volume x heart rate
what is the autonomic nervous system?
- a system that controls involuntary actions of glands and muscles
- 2 subdivisions: sympathetic and parasympathetic
state the difference between the sympathetic and parasympathetic nervous system
- sympathetic involved in flight or fight responses that stimulate 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, in the carotid body
- chemoreceptors: detect changes in pH, carotid body and aortic body
how does the body respond to a decrease in blood pressure?
- baroreceptors detect low blood pressure
- Impulses are sent to the medulla oblongata
- which sends impulses along sympathetic neurones
- these secrete noradrenaline which binds to receptors on the sinoatrial node
- noradrenaline increases heart rate
- heart rate increases to increase blood pressure back to normal
how does the body respond to an increase in blood pressure?
- baroreceptors detect increase in blood pressure
- impulses are sent to the medulla
- which sends impulses along parasympathetic neurones
- these secrete acetylcholine, which binds to receptors on the sinoatrial node
- acetylcholine decreases heart rate which returns blood pressure back to normal
how does the body respond to a decrease in CO2 concentration and high ph levels?
- chemoreceptors detect an decrease in CO2 concentration and high pH levels
- Impulses are sent to the medulla which sends impulses along parasympathetic neurones
- These secrete acetylcholine, which binds to receptors on the sinoatrial node
- heart rate decreases to return carbon dioxide and pH back to normal
how does the body respond to an increase in CO2 and a decrease in pH
- chemoreceptors detect chemical changes in the blood
- impulses are sent to the medulla which sends impulses along sympathetic neurones
- these secrete noradrenaline which binds to receptors on the sinoatrial node
- heart rate increases to return CO2 and pH levels back to normal
