Internal And Extermal 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
- 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 pressure
- Shoots bend 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 the upper side of the root elongate faster so the root tip bends downwards
Contrast mammalian hormones and plant growth factors. (CASTS)
Conc — MH: response not always dependent on conc, PGF: response proportional to conc
Action — MH: bind to complementary proteins in/on target cells, PGF: can affect all cells
Synthesis — MH: specialised glands, PGF: various tissues in growing regions
Transport — MH: circulatory system, PGF diffusion or phloem translocation
Speed — MH: faster-acting (homeostasis), PGF: 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
- If organism moves considerable distance into unfavourable environment
Outline what happens in a simple reflex arc.
Receptor detects stimulus —> sensory neuron —> relay neuron in CNS coordinates response—> motor neuron —> response to effector
Give the advantages of a simple reflex.
- Rapid response to potentially dangerous stimuli 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 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 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 but NOT in central fovea
Cone: mainly central fovea no photoreceptors at blind spot
Compare and contrast rod and cone cells. (PACL)
Pigment — R: rhodopsin, C: 3 types of iodopsin
Visual Acuity — R: low res only one bipolar neuron, C: high res no retinal convergence
Colour sensitivity — R: monochromatic all wavelengths detected, C: tricolour
Light sensitivity— R: v. Sensitivity spatial summation, C: 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 and name the location of the 2 nodes involved in heart contraction.
- sinoatrial node (SAN): within wall of 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 = atria systole
- Layer of fibrous, non-conducting tissue delays impulse while bentricles fill & valves close
- AVN convery 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 (CO)
Stroke volume x heart rate
What is the autonomic nervous system?
- system that controls involuntary actions of glands and muscles
- 2 subdivisions: sympathetic & parasympathetic
State the difference between the sympathetic and parasympathetic nervous system.
Sympathetic involved in ‘fight or flight’ response: stimulates 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): carotid body
Chemoreceptors (detect changes in pH e.g. due to increase in CO2 conc): carotid body & aortic body
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
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 body 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 p, so rate of blood flow to lungs increases = rate of gas exchanges and ventilation rate increases
