Response to Stimuli Flashcards
1
Q
What is a stimulus?
A
- a detectable change in the in the internal or external environment that leads to a response in the organism
2
Q
What are the advantages to organisms for being able to respond to stimuli?
A
- increases chance of survival e.g. move away from harmful stimuli such as predators and extreme temperature or move towards a source of food
- have a greater chance of raising offspring and passing alleles to the next generation
- selection pressure favouring organisms with more appropriate responses
3
Q
What are taxes?
A
- simple response determined by the direction of the stimulus
- towards stimulus positive taxis
- or away from stimulus negative taxis
- moves whole body directly towards favourable stimulus or away from an unfavourable stimulus
4
Q
What is kinesis?
A
- organism doesn’t move towards or away from a stimulus but changes the speed at which it moves and the rate at which it changes direction
- this response tends to bring the organism into a new region with favourable conditions
5
Q
What is a tropism?
A
- the growth of the part of a plant in response to a directional stimulus
- grows towards (positive response) or away from (negative response) the stimulus
6
Q
How does tropism increase plant survival?
A
- plant shoots grow towards light (positively phototropic) and away from gravity (negatively gravitropic) so that their leaves are in the most favourable position to capture light for photosynthesis
- plant roots grow away from light and towards gravity , the roots grow into the soil where they can absorb mineral ions and water
7
Q
What stimuli do plants respond to?
A
- light - shoots grow towards it, needed in photosynthesis
- gravity - roots grow towards it, plants are firmly anchored in the soil
- water - grow towards water to absorb it for use in photosynthesis and other metabolic processes
8
Q
What are plant growth factors?
A
- affect growth and can be made by cells (rather than in organs like hormones)
- affect tissues that they are released in
- e.g. indoleacetic acid IAA which is an auxin
9
Q
How is phototropism controlled by IAA?
A
- cells in shoot produce IAA, which is transported down the shoot
- light causes the movement of IAA from the light side of the shoot to the shaded side of the shoot
- there is a greater concentration of IAA on the shaded side than the light and IAA causes the elongation of shoot cells
- the shaded side of the shoot elongates more and the shoot bends towards the light
10
Q
How is gravitropism controlled by IAA?
A
- cells in the top of the root produce IAA which is transported along the root
- gravity causes IAA to move to the lower side of the root and there is a greater concentration of IAA on the lower side of the root
- IAA inhibits the elongation of root cells, and so cells on the lower side of the root elongate less than cells on the upper side and so the root bends downwards towards gravity
11
Q
What is the nervous system divided into?
A
- central nervous system- made up of brain and spinal cord
- peripheral nervous system - pairs of nerves originating from the brain or spinal cord
12
Q
What is the peripheral nervous system divided into?
A
- sensory neurones
- motor neurones
13
Q
What is the motor nervous system divided into?
A
- the voluntary nervous system - carries nerve impulses to body muscles and is under voluntary control
- the automatic nervous system - carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under voluntary control
14
Q
What is a simple reflex arc (for touching a hot object)?
A
- stimulus - heat from object
- receptor - temperature receptors in hand generates nerve impulses in sensory neurone
- sensory neurone - passes nerve impulses to spinal cord
- relay neurone - links sensory neurone to motor neurone in spinal cord
- motor neurone - carries nerve impulses from spinal cord to muscle in the arm
- effector - muscle in upper arm is stimulated to contract
- response - hand pulls away
15
Q
Why are reflex arcs important?
A
- involuntary and don’t require the brain to make a decision so that the brain can continue more complex responses
- protective from harm and are effective from birth
- fast because the neurone pathway is short with few synapses
- absence of decision-making process means the action is rapid
16
Q
What are the features of sensory reception?
A
- specific to a single type of stimulus such as mechanical pressure
- produces a generator potential by acting as a transducer - transducer converts the change in form of energy in receptor into nerve impulses that can travel round the body
17
Q
What is the structure and function of the Pacinian copruscule?
A
- a single sensory neurone is at the centre of layers of tissue, each separated by a gel
- acts as a transducer to produce a generator potential
18
Q
How does the Pacinian copruscule work?
A
- sensory neurone in the PC contains stretch-mediated sodium channels in its plasma membrane (permeability to sodium changes when stretched)
- in resting state, the stretch-mediated sodium channels are too narrow for sodium ions to diffuse and in this state, has a resting potential
- when pressure is applied, the membrane becomes stretched which widens the sodium channels and sodium ions diffuse into the neurone
- the influx of sodium ions depolarises the membrane, producing a generator potential
- the generator potential creates an action potential that passes along the neurone
19
Q
What are rod cells?
A
- cannot distinguish between different wave lengths of light (image in black and white), detect light of low intensity
- many rod cells are connects to a single sensory neurone in the optic nerve
20
Q
Why do rod cells have high sensitivity?
A
- threshold value must be exceeded for a generator potential to be created in bipolar cells to which rods are connected
- many rod cells are connected to a single bipolar cell (retinal convergence) and so there is a greater chance that the threshold value will be exceeded
- this is due to summation
21
Q
Why do rod cells have low visual acuity?
A
- many rods are connected to one neurone and will only generate a single impulse regardless of how many rods are stimulated
22
Q
What are cone cells?
A
- see colour
- less than rod cells
- most found at centre of retina at fovea
23
Q
Why do cones have a high visual acuity?
A
- each cone is connected to a single bipolar cell
- if 2 adjacent cone cells are stimulate the brain receives 2 separate impulses and can distinguish between the 2 sources of light that stimulated the cone cells
24
Q
What are the difference between rod and cone cells?
A
- rod shaped vs cone shaped
- greater numbers vs smaller numbers
- more at periphery of retina vs fewer at periphery and concentrated at fovea
- poor visual acuity vs good visual acuity
- sensitive to low level light vs not
- one type vs 3 types for different wavelengths of light
25
Q
What is the automatic nervous system?
A
- made up of:
- sympathetic nervous system - stimulates the effectors and helps to cope with stressful situations by heightening awareness and preparing for activity (fight or flight)
- parasympathetic nervous system - inhibits effectors and controls activities under normal resting conditions
- the actions of the 2 divisions are antagonistic
26
Q
How does the automatic nervous system control heart rate?
A
- a wave of excitation spreads from the sinoatrial node (SAN) across both atria, causing them to contract
- the atrioventricular septum prevents the wave from crossing to the ventricles
- the wave of excitation enters a second group of cells called the atrioventricular node (AVN) (which lies between the atria)
- the AVN conveys a wave of excitation between the ventricles along the Purkyne tissue which makes up the bundle of His
- the wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time from the bottom of the heart upwards
27
Q
What is the sinoatrial node?
A
- the SAN is a group of cells in the wall of the right atrium
- initial stimulus for contraction
- basic rhythm of stimulation determines the beat of the heart (referred to as the pacemaker)
28
Q
How is the resting heart rate controlled in the brain?
A
- controlled by the medulla oblongata in the brain
- it has a centre that increases heart rate linked to the SAN by the sympathetic nervous system
- and a centre that decrease heart rate linked to the SAN by the parasympathetic nervous system
29
Q
How is heart rate controlled by chemoreceptors?
A
- found in the wall of the carotid arteries, they are sensitive to changes in pH
- carbon dioxide conc increases and pH decreases
- chemoreceptors detect this and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate
- centre increases frequency of impulses via sympathetic nervous system to the SAN, increasing production of waves of excitation and increases heart rate
- increased blood flow increases carbon dioxide removed by lungs and carbon dioxide conc decreases
30
Q
How is heart rate controlled by pressure receptors?
A
- pressure receptors occur within the walls of the carotid arteries and the aorta
- when blood pressure is higher than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate, impulses sent via the parasympathetic nervous system to the SAN, decrease in heart rate
- when blood pressure is lower than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increase heart rate, impulses sent via the sympathetic nervous system to the SAN, increase in heart rate
