Topic 6: Stimuli & Response Flashcards
What is a stimulus?
A detectable change in the environment
What are the cells that detect stimulus called?
Receptors
What increases when organisms can respond to stimulus?
Chance of survival
What is a tropism?
Term given when plants respond via growth to a stimulus
What are the 3 types of tropism?
Positive and Negative
Can grow towards or away from stimulus (light or gravity)
What are tropisms controlled by? And give an example
Growth factors
IAA (indoleacetic acid)
What is IAA?
Type of auxin that can control cell elongation in shoots and inhibit growth of cells in the roots
Where is IAA made?
In the tip or the roots and shoots but can diffuse to other cells
What is the term given to the tropism when the plant responds to light?
Phototropism
In shoots why does a phototropism help growth?
Light is needed in the LDR in photosynthesis so plants grow and bend towards the light
This is a positive phototropism
What happens in the shoots phototropism?
1) Shoot tip cells produced IAA, causing cell elongation
2) The IAA diffuses to other cells
3) If there is unilateral light (one sided) IAA will diffuse towards the shaded side of the shoot resulting in a higher conc of IAA there
4) The cells on the shaded side to elongate more and results in the plant bending towards the light source
Do roots photosynthesise? Why?
No, as they don’t require light they must anchor the plant deep in the soil
What does IAA do in the roots?
High conc inhibits cell elongation, causing root cells to elongate more on the lighter side and so the roots bend away from the light
(Negative phototropism)
What name is given to the responses to gravity in plants?
Gravitropism
What happen due to gravitropism’s in shoots?
IAA will diffuse to the lower side from the upper side
If the plant is vertical this causes the plant cells to elongate and plant grows upwards
If the plant is on it’s side, it will cause the shoot to bend upwards
(Negative gravitropism)
What happen due to gravitropism’s in roots?
IAA moves to the lower side of the roots so that the upper side elongates and the root bends down towards gravity and anchors the plant in
(Positive gravitropism)
What is a reflex?
Rapid, automatic response to protect you from danger
What is a reflex arc made from?
Motor, sensory and relay neuron
What is one reason why reflexes are so fast?
As there’s only 3 neurons that means that there’s only 2 synapses
Give 2 examples of a simple response?
Taxes and kinesis
What is meant by a taxes?
An organism will move its entire body towards (positive) a favourable stimulus or away (negative) from an unfavourable stimulus
What is meant by a kinesis?
An organism changes the speed of movement and the rate it changes direction
Non-directional (random) movement
Why are taxes and kinesis important?
They keep organisms within the favourable conditions of their environment (light, moisture and chemicals)
With kinesis what happens when an organism moves from with beneficial stimuli to harmful stimuli?
It’s kinesis response will be to increase the rate it changes direction to return to the favourable conditions quickly
(vise versa)
What does the stimulation of a receptor cause?
Leads to the establishment of generator potential which can cause a response e.g action potential
Name the 3 receptors we must know about
Pacinian corpuscle
Rods
Cones
What is the Pacinian corpuscle’s job?
Pressure receptor: detect changes in pressure located deep in skin, mainly in hands and feet
What does the sensory neuron in the Pacinian corpuscle have?
Special channel proteins in it’s plasma membrane
What type of neuron is the Pacinian corpuscle?
Sensory?
What are the special channel proteins in it’s plasma membrane called?
Stretch-mediated sodium channels
What does the Stretch-mediated sodium channels in the Pacinian corpuscle cause to happen?
Allow Na+ ions to enter the sensory neuron only when they are stretched and deformed
What causes the neuron plasma membrane on the Pacinian corpuscle to deform?
When pressure is applied it deforms
What happens due to the pacinian corpuscle being deformed?
When it deforms the neuron stretches and widens the Na+ channels so Na+ diffuses in which leads to the establishment of a generator potential
What 2 receptors are found in the human retina?
Rods and cones
What type of receptors are rods and cones?
Photoreceptors
How do rods process images?
Black and White
To create generator potential what must happen in a rod?
The pigment of rod cells (rhodopsin) must be broken down by light energy
They can detect light of very low intensity, as many rod cells connect to one sensory neuron (retinal convergence)
What is meant by retinal convergence?
When many rod cells connect to one sensory neuron
What is the pigment in rod cells?
Rhodopsin
What happens due to retinal convergence?
Meaning the brain cannot distinguish between the separate sources of light in low visual acuity
What is meant by low visual acuity?
Its difficult for the brain to distinguish between the different light sources
How do cones process images?
Colour
What are the 3 types if cone cells?
Red, blue and green
Why is there 3 different type of cone cells?
They contain different types of iodopsin pigment, which all absorb different wavelengths of light
In cone cells iodopsin is only broken down if… (why?)
If there is a high light intensity, so action potentials can only be generated with enough light
Do cone cells give a high or low visual acuity?
High
Why can cone cells give a high visual acuity?
As each cone is connected to one bipolar cell, the brain can distinguish between separate sources of light detected
What is the distribution of rods and cones like in the retina?
Uneven
Why is the distribution of rods and cones in the retina uneven?
As light ids focused by the lens on the fovea, which will receive the highest intensity of light
Where are most cone and rod cells located?
Cones near the fovea
But rods further away
What is cardiac muscle known as?
Myogenic
What is meant by the term myogenic?
It contracts on its own accord, but the rate of contraction is controlled by wave of electrical activity
Where is the SAN located?
in the right atrium
What is the SAN known as?
Pacemaker
What does the SAN stand for?
Sinoatrial node
What does the AVN stand for?
Atrioventricular node
Where is the AVN located?
Near the boarder of the right and left ventricle within the atria still
Where does the bindle of Hid run through?
Septum
Where is the purkyne fibres found?
In the walls of the ventricles
What is the process of controlling heart rate?
(STEPS 1+2)
1) SAN releases a wave of depolarisation across the atria
2) AVN releases another wave of depolarisation when the first reaches it. A non-conductive layer between the atria and ventricles prevents the wave of depolarisation travelling down to the ventricles
What is the process of controlling the heart?
(STEPS 3,4+5)
3) Instead the bundle of His, conducts the wave of depolarisation down the septum and purkyne fibres
4) As a result, the apex and walls of ventricles contract, there’s a short delay before this happens whilst the AVN transmits the 2nd wave of depolarisation
5) Allowing enough time for the atria to pump all the blood into the ventricles and then the cells can repolarise and cardia muscles relax
What part of the brain controls HR, via what?
Medulla oblongata via the autonomic NS
What are the 2 parts of controlling HR?
1) A centre linked to the SAN to increase HR via the sympathetic NS
2) Another that decreases the HR via the parasympathetic NS
What 2 stimulus lead to a change in HR and what detects them?
pH and blood pressure detected by chemoreceptors and pressure receptors in the aorta and carotid artery
When does pH of the blood decrease?
pH of the blood would decrease during times of high respiratory rate due to the production of lactic acid/co2.
Why do we have to remove excess acid/co2 from the blood?
To prevent denaturation of enzymes
How do we remove excess acid/co2 from the blood?
Increasing HR (more impulses via sympathetic NS to SAN)
So CO2 can diffuse out into the alveoli more rapidly
Why is it important to decrease pressure in the heart if it gets too high?
As if it is too high this can cause damage to the walls of the arteries and it is important to put mechanisms in place to reduce the blood pressure
What is done to decrease pressure in the heart?
More impulses via parasympathetic NS to decreases HR
Why is it important to increase pressure in the heart if it goes too low?
May be insufficient supply of oxygenated blood to respiring cells and removal of waste
What is done to increase pressure in the heart
More impulses via sympathetic NS to increases HR
