6a (stimuli/ response) Flashcards
how do organisms increase their chances of survival?
they respond to changes in their external and internal environment
eg for external animals- move away from harmful environments
plants- cant move but can change the way the grow
what is a stimulus?
any change in the external or internal environment
what is a simple response?
simple mobile organisms have simple responses the keep them in favourable conditions
can be tactic or kinetic
what is a tactic response (taxis)
eg
directional movement in response to a stimulus
direction of stimulus affects the response
eg woodlice move away from light
what is a kinetic response (kinesis)
non-directional (random) movement in response to a stimulus
intensity of the stimulus affects the response
eg woodlice move slower and turn less often in high humidity
practical?
investigating simple animal response
what are receptors?
cells/ proteins on cell surface membrane that detect stimuli
receptors are specific to one type of stimulus
what are effectors?
cells that bring about a response to a stimulus to produce an effect
eg muscle cells, cells found in glands
how to receptors and effectors communicate?
via the nervous system or hormonal system or both
sensory neurones
transmit electrical impulses from receptors to CNS
motor neurones
transmit electrical impulses from CNS to effectors
relay neurons
transmit electrical impulses between sensory and motor neurones
how does nervous communication occur?
stimulus is detected by receptor and electrical impulse sent along sensory neurone
when electrical impulse reaches end of neurone, neurotransmitters take info across synapse to next neurone where another electrical impulse is generated
the CNS processes the information and send impulses along motor neurones to an effector
what is a simple reflex?
a rapid, involuntary response to a stimulus
pathway of communication goes through spinal cord but not through conscious parts of the brain so the response happens automatically
they are protective as they help the organism to avoid damage
what is a tropism?
positive?
negative?
the response of a plant to a directional stimulus
growth towards the stimulus
growth away from the stimulus
what is a phototropism?
growth in response to light
shoots are positively phototropic
roots are negatively phototropic
what is a gravitropism?
growth of a plant in response to gravity
shoots are negatively gravitropic
roots are positively gravitropic
what are auxins?
specific growth factors that speed up/slow down plant growth
produced in growing regions and move to where they’re needed
how does auxin cause tips to elongate?
cell walls become stretchy and cells get longer
what happens if the tip of a shoot is removed?
no auxin will be available and the shoot will stop growing
what does auxin do in roots and shoots?
stimulates growth in shoots
(high concentration) inhibit growth in roots
what is indoleacetic acid (IAA)?
a type of auxin that is produced in tips of shoots and roots in flowering plants
moved around to control tropisms- moves by diffusion and active transport over short distances and via phloem over long distances
results in diff parts of plant having diff conc of IAA- causes uneven growth
experiments
what are receptors?
cells/ proteins on cell surface membranes that detect one particular stimuli and pass this info along the nervous pathway
what is resting potential?
when a nervous system receptor is in its resting state, there is a diff in charge between inside and outside of cell (inside - compared to outside)
means theres a potential difference across the membrane
resting pot is the difference when a cell is at rest
it is generated by ion pumps and ion channels
what is the generator potential?
when a stimulus is detected, cell membrane is excited and becomes more permeable allowing more ions to move in and out altering the pd
change in pd due to stimulus is the generator potential
bigger stimulus excites membrane more causing bigger movement of ions and bigger change in pot diff so bigger generator pot
what is action potential?
if generator pot is big enough, it’ll trigger an action pot (electrical impulse along neurone)
action pot is only triggered if generator pot reaches threshold level
all one size so strength of stimulus is measured by freq of action pot
what are Pacinian corpuscles?
mechanoreceptors- detect mechanical stimuli eg pressure
found in skin
contain the sensory nerve ending which is wrapped in lots of layers of connective tissue called lamellae
what happens when a Pacinian corpuscle is stimulated?
lamellae are deformed and press on sensory nerve ending
causes sensory neurone’s cell membrane to stretch, deforming stretch-mediated sodium ion channels
channels open and sodium ions diffuse into the cell, creating a generator potential which triggers action potential if reaches threshold
what are photoreceptors?
receptors in eye that detect light
structure of eye?
light enters through pupil- amount controlled by muscles of iris
light rays focused on retina by lens
retina contains photoreceptors
fovea is area of retina where there are lots of photoreceptors
nerve impulses from photoreceptor cells are carried from retina to brain by optic nerve (bundle of neurones)
blind spot is where optic nerve leaves as there are no photoreceptors
how do photoreceptors work?
light enters eye, hits photoreceptors and is absorbed by light-sensitive optical pigments
light bleaches pigments, causing chemical change and altering membrane permeability to sodium ions
generator potential is created and nerve impulse sent along bipolar neurone if threshold reached
bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain
rods
found mainly in periphery of retina
only give info in black and white (monochromatic vision)
cones
found mainly at fovea
give info in colour (trichromatic vision)
3 types, each contain diff optical pigment:
red-sensitive, green-sensitive, blue-sensitive
when stimulated in diff proportions, you see diff colours
why are rods and cones sensitive to diff wavelengths of light?
they contain diff optical pigments
sensitivity of rods
very sensitive to light because many rods join one bipolar neurone, so many weak generator pots combine to reach threshold and trigger action pot
sensitivity of cones
less sensitive than rods because one cone joins one bipolar neurone, so it takes more light to reach threshold and trigger action potential
visual acuity of rods
low as many rods join same bipolar neurone so light from 2 points close together cant be told apart
visual acuity of cones
high as cones are close together and one cone joins one bipolar neurone
when light from 2 points hits 2 cones, 2 action potentials go to brain so you can distinguish 2 points that are close together and 2 separate points
compare rods and cones
rods:
peripheral parts of retina
black and white
many rods join 1 bipolar neurone
high sensitivity to light
low visual acuity
cones:
fovea
colour
one cone joins one bipolar neurone
low sensitivity to light
high visual acuity
structure of nervous system
CNS- brain and spinal cord
PNS- neurones that connect CNS to rest of body
PNS split into:
somatic- conscious activities
autonomic- unconscious activities eg heart rate
autonomic split into:
sympathetic- flight/ flight- gets body ready for action
parasympathetic- rest and digest- calms body down
(they have opposite effects)
what does myogenic mean?
cardiac muscle can contract and relax without receiving signals from nerves
this pattern of contractions controls regular heartbeat
what is the sinoatrial node?
small mass of tissue in wall of right atrium
has basic rhythm of stimulation that determines beat of heart- acts as pacemaker
describe control of basic heart rate
- wave of electrical excitation spreads out from sinoatrial node across both atria causing them to contract
- layer of non-conductive tissue (atrioventricular septum) prevents wave crossing the ventricles
- wave of excitation enters atrioventricular node which lies between the atria
- after short delay, AVN conveys wave of electrical excitation between ventricles along Purkinje tissue which makes up bundle of His
- bundle of His conducts wave through atrioventricular septum to base of ventricles where bundle branches into smaller fibres of Purkinje tissue
- wave of excitation is released from Purkinje tissue causing ventricles to contract quickly at same time- from bottom upwards
what is the medulla?
part of the brain that unconsciously controls the rate at which the SAN fires
what are baroreceptors?
pressure receptors in the aorta and carotid arteries
stimulated by high and low blood pressure
what are chemoreceptors?
chemical receptors in the aorta, carotid arteries and medulla
monitor O2 level in blood and CO2 and pH (which are indicators of O2 level)
how does the heart communicate with the brain?
electrical impulses from receptors are sent to medulla along sensory neurones
medulla processes info and sends impulses to SAN along sympathetic/ parasympathetic neurones
how is heart rate controlled in response to high blood pressure?
baroreceptors detect high bp and send impulses along neurones to medulla which sends impulses along parasympathetic neurones
these secrete acetylcholine which binds to receptors on SAN
causes hr to slow and reduce bp
how is heart rate controlled in response to low blood pressure?
baroreceptors detect low bp and send impulses along neurones to medulla which sends impulses along sympathetic neurones
these secrete noradrenaline which binds to receptors on SAN
causes hr to increase and raise bp
how is heart rate controlled in response to high blood O2/ low CO2/ high blood pH?
chemoreceptors detect chemical changes in blood and send impulses along sensory neurones to medulla which sends impulses along parasympathetic neurones
these secrete acetylcholine, which binds to receptors on SAN
causes hr to decrease and return O2, CO2 and pH levels back to normal
how is heart rate controlled in response to low blood O2/ high CO2/ low blood pH?
chemoreceptors detect chemical changes in blood and send impulses along sensory neurones to medulla which sends impulses along sympathetic neurones
these secrete noradrenaline, which binds to receptors on SAN
causes hr to increase and return O2, CO2 and pH levels back to normal
