chapter 14💗 Flashcards
what is a stimulus💗
change in an organisms internal and external environment
why is it important organisms can respond to stimuli💗
organisms increase their chance of survival by responding to stimuli
what is a tropism💗
growth of a plant in response to a directional stimulus
positive tropism = towards a stimulus; negative tropism = away from stimulus
summarise the role of growth factors in flowering plants💗
specific growth factors eg auxins like IAA move via phloem or diffusion from growing regions eg roots where theyre produced to other tisshes where they regulate growth in response to directional stimuli💗
describe how indoleacetic acid affects cells in roots and shoots💗
in shoots, high conc of IAA stimulates cell elongation💗
in roots high conc of IAA inhibits cell elongation💗
explain gravitropism in flowering plants💗
- Cells in tip of shoot produce IAA
- IAA diffuses down shoot
- IAA moves to lower side of shoot so conc increases
- In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
- So shoots bend away from gravity whereas roots bend towards gravity💗
explain photropism in flowering plants💗
- Cells in tip of shoot produce IAA
- IAA diffuses down shoot
- IAA moves to shaded side of shoot - conc increases
- In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
- So shoots bend towards light whereas roots bend away from light💗
describe the simple responses that can maintain a mobile organism in a favourable environment💗
- Taxis - directional response - movement towards or away from a directional stimulus
- Kineses - non directional response - speed of movement or rate of direction change changes in response to a non directional stimulus depending on intensity of stimulus💗
explain the protective effect of a simple reflex💗
rapid as only 3 neurones and few synapses
autonomic so doesnt have to be learnt
protects from harmful stimuli eg escape predators💗
describe the basic structure of a pacinian corpuscle💗
lamellae, stretch mediated sodium ion channel, sensory neurone ending, gel, sensory nwurone axon, myelin sheath💗
describe how a generator potential is established in a pacinian corpuscle💗
- mechanical stimulus eg pressure deforms lamellae and stretch-mediated sodium ion channels
- so Na+ channels in membrane open and Na+ diffuse into sensory neurone - greater pressure causes more Na+ channels to open and more Na+ to enter
- causes depolarisation, leading to a generator potential - if reaches threshold it triggers an action potential💗
explain what a pacinian corpuscle illustrates💗
-receptors respond to specific stimuli - corpuscle only responds to mechanical pressure💗
-stimulation of a receptor leads to the establishment of a generator potential - when threshold is reached action potential sent💗
explain the differences in sensitivity to light in rods and cones in the retina💗
rods are more sensitive to light💗
*several rods connected to a single neurone
*spatial summation to reach threshold to generate action potential
cones are less sensitive to light💗
*each cone connected to a single neurone
*no spatial summation
explain the difference in visual acuity for rods and cones in the retina💗
rods give lower visual acuity💗
*several rods connected to a single neurone
*so several rods send a single set of impulses to brain
cones give a higher visual acuity💗
*each cone connected to a singls neurone
*cones send separate sets of impulses to brain
explain the differences in sensitivity to colour for rods and cones in the retina💗
rods allow monochromatic vision💗
*1 type of rod/ 1 pigment
cones allow colour vision💗
*3 types of cone - red, green and blue sensitive
*with different optical pigments - absorb different wavelengths
*stimulating different combinations of cones gives range of colour pereception
what does it mean by cardiac muscle is myogenic💗
it can contract and relax without receiving electrical impulses from nerves💗
describe the myogenic stimulation of the heart and transmission of a subsequent wave of electrical activity💗
- Sinoatrial node acts as a pacemaker - sends regular waves of electrical activity across atria - causing atria to contract simultaenously💗
- Non-conducting tissue between atria/ventricles prevents impulse passing directly to ventricles - preventing immediate contraction of ventricles💗
- Waves of electrical activity reach atriventricular node which delags impulss - allowing atria to fully contraxt and empty before ventricles contract💗
- AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where it branches into Purkyne tissue - causing ventriclss to contract simultaneously from the base up💗
where are chemoreceptors and pressure receptors located💗
aorta and carotid arteries💗
describe the role of chemoreceptors, pressure receptors, the autonomic nervous system and effectors in controlling heart rate💗
- Baroreceptors detect fall/rise in blood pressure and/or chemoreceptors detect blood rise/fall in blood CO2 conc or blood pH💗
- Send impulses to medulla/cardiac control centre💗
- Which send more frequent impulses to SAN along sympathetic/parasympathetic neurones💗
- So more/less frequent impulses sent from SAN and to or from AVN💗
- So cardiac muscle contracts more less frequently💗
- so heart rate increases/decreases💗
