3.6 Organisms respond to changes in their internal and external environments (A-level only) Flashcards
1
Q
Stimulus
A
- Detectable change in the environment
- detected by cells called receptors
2
Q
Nervous system structure
A
- Central nervous system = brain and spinal cord
- Peripheral nervous system = receptors, sensory and motor neurones
3
Q
Simple reflex arc
A
Stimulus (e.g. touching hot object) → receptor → sensory neurone → coordinator (CNS/relay neurone) → motor neurone → effector (muscle) → response (contraction).
4
Q
Importance of simple reflexes
A
-
Rapid – short pathway
◦ only three neurones & few synapses -
autonomic
◦ conscious thought not involved – spinal cord coordination - protect from harmful stimuli e.g. burning
5
Q
Tropism
A
- Response of plants to stimuli via growth
- can be positive (growing towards stimulus) or negative (growing away from stimulus)
- controlled by specific growth factors (IAA)
6
Q
Specific tropisms
A
- Response to light
◦ phototropism - response to gravity
◦ gravitropism - response to water
◦ hydrotropism
7
Q
Indoleacetic acid
A
- Type of auxin (plant hormone)
- controls cell elongation in shoots
- inhibits growth of cells in roots
- made in tips of roots/shoots
- can diffuse to other cells
INSERT IMAGE HERE
8
Q
Phototropism in shoots
A
- Shoot tip produces IAA
- diffuses to other cells
- IAA accumulates on shaded side of shoot
- IAA stimulates cell elongation so plant bends towards light
- positive phototropism
INSERT IMAGE HERE
9
Q
Phototropism in roots
A
- Root tip produces IAA
- IAA concentration increases on lower (darker) side
- IAA inhibits cell elongation
- root cells grow on lighter side
- root bends away from light
- negative phototropism
10
Q
Gravitropism in shoots
A
- Shoot tip produces IAA
- IAA diffuses from upper side to lower side of shoot in response to gravity
- IAA stimulates cell elongation so plant grows upwards
- negative gravitropism
11
Q
Gravitropism in roots
A
- Root tip produces IAA
- IAA accumulates on lower side of root in response to gravity
- IAA inhibits cell elongation
- root bends down towards gravity and anchors plant
- positive gravitropism
12
Q
Taxis
A
- Directional response by simple mobile organisms
- move towards favourable stimuli (positive taxis) or away from unfavourable stimuli (negative taxis)
13
Q
Kinesis
A
- When an organism changes its speed of movement and rate of change of direction in response to a stimulus
- if an organism moves to a region of unfavourable stimuli it will increase rate of turning to return to origin
- if surrounded by negative stimuli, rate of turning decreases – move in straight line
14
Q
Receptors
A
- Responds to specific stimuli
- stimulation of receptor leads to establishment of a generator potential – causing a response
◦ pacinian corpuscle
◦ rods
◦ cones
15
Q
Pacinian corpuscle
A
- Receptor responds to pressure changes
- occur deep in skin mainly in fingers and feet
- sensory neurone wrapped with layers of tissue
16
Q
Pacinian corpuscle structure
A
INSERT IMAGE HERE
17
Q
How pacinian corpuscle detects pressure?
A
- When pressure is applied,
stretch-mediated sodium ion channels are deformed - sodium ions diffuse into sensory neurone
- influx increases membrane potential – establishment of generator potential
18
Q
Rod cells
A
- Concentrated at periphery of retina
- contains rhodopsin pigment
- connected in groups to one bipolar cell (retinal convergence)
- do not detect colour
19
Q
Cone cells
A
- Concentrated on the fovea
- fewer at periphery of retina
- 3 types of cones containing different iodopsin pigments
- one cone connects to one neurone
- detect coloured light
20
Q
Rods and cones: Describe differences in sensitivity to light
A
- Rods are more sensitive to light
- cones are less sensitive to light
21
Q
Rods and cones: Describe
differences in visual acuity
A
- Cones give higher visual acuity
- rods have a lower visual acuity
22
Q
Visual acuity
A
- Ability to distinguish between separate sources of light
- a higher visual acuity means more detailed, focused vision
23
Q
Rods and cones: Describe differences in colour vision
A
- Rods allow monochromatic vision (black and white)
- cones allow colour vision
24
Q
Why rods have high sensitivity to light?
A
- Rods are connected in groups to one bipolar cell
◦ retinal convergence
◦ spatial summation - stimulation of each individual-cell alone is sub-threshold but because rods are connected in groups more likely threshold potential is reached
25
Q
Why cones have low sensitivity to light?
A
- One cone joins to one neurone
- no retinal convergence/spatial summation
- higher light intensity required to reach threshold potential
26
Q
Why rods have low visual acuity?
A
- Rods connected in groups to one bipolar cell
- retinal convergence
- spatial summation
- many neurones only generate one impulse/action potential → cannot distinguish between separate sources of light
27
Q
Why cones have high visual acuity?
A
- One cone joins to one neurone
- 2 adjacent cones are stimulated, brain receives 2 impulses
- can distinguish between separate sources of light
28
Q
Why rods have monochromatic vision?
A
- One type of rod cell
- one pigment (rhodopsin)
29
Q
Why cones give colour vision?
A
- 3 types of cone cells with
different optical pigments
which absorb different wavelengths of light - red-sensitive, green-sensitive and blue-sensitive cones
- stimulation of different proportions of cones gives greater range of colour perception
30
Q
Myogenic
A
- When a muscle (cardiac muscle) can contract and relax without receiving signals from nerves
31
Q
Sinoatrial node
A
- Located in right atrium and is known as the pacemaker
- releases wave of depolarisation across the atria, causing muscles to contract
32
Q
Atrioventricular node
A
- Located near the border of the right/left ventricle within atria
- releases another wave of depolarisation after a short delay when it detects the first wave from the SAN
33
Q
Bundle of His
A
- Runs through septum
- can conduct and pass the wave of depolarisation down the septum and Purkyne fibres in walls of ventricles
34
Q
Purkyne fibres
A
- In walls of ventricles
- spread wave of depolarisation from AVN across bottom of the heart
- the muscular walls of ventricles contract from the bottom up
35
Q
Role of non-conductive tissue
A
- Located between atria and ventricles
- prevents wave of depolarisation travelling down to ventricles
- causes slight delay in ventricles contracting so that ventricles fill before contraction
36
Q
Importance of short delay between SAN and AVN waves of depolarisation
A
- Ensures enough time for atria to pump all blood into ventricles
◦ ventricle becomes full
37
Q
Role of the medulla oblongata
A
- Controls heart rate via the
autonomic nervous system - uses sympathetic and parasympathetic nervous system to control SAN rhythm
38
Q
Chemoreceptors
A
- Located in carotid artery and aorta
- responds to pH/CO2 conc. changes
39
Q
Baroreceptors
A
- Located in carotid artery and aorta
- responds to pressure changes
40
Q
Response to high blood pressure
A
- Baroreceptor detects high blood pressure
- impulse sent to the medulla
- more impulses sent to SAN via parasympathetic neurones (releasing acetylcholine)
- fewer impulses from SAN
- heart rate slowed
41
Q
Response to low blood pressure
A
- Baroreceptor detects low blood pressure
- impulse sent to the medulla
- more impulses sent to SAN along sympathetic neurones (releasing noradrenaline)
- heart rate increases
42
Q
Response to high blood pH
A
- Chemoreceptor detects low CO2 conc./high pH
- impulse sent to medulla
- more impulses sent to SAN along parasympathetic neurones (releasing acetylcholine)
- heart rate slowed so less CO2 was removed and pH lowers
43
Q
Response to low blood pH
A
- Chemoreceptor detects high CO2 conc./low pH
- impulse sent to medulla
- more impulses sent to SAN along sympathetic neurones (releasing acetylcholine)
- heart rate increases to deliver blood to heart to remove CO2
44
Q
Structure of myelinated
motor neurone
A
INSERT IMAGE HERE
45
Q
Resting potential
A
- The difference between electrical charge inside and outside the axon when a neuron is not conducting an impulse
- more positive ions (Na+/K+) outside axon compared to inside
- inside the axon -70mV
46
Q
How is resting potential established?
A
- Sodium potassium pump actively transports 3 Na+ out of the axon, 2 K+ into the axon
- membrane more permeable to K+ (more channels and always open)
- K+ diffuses out down conc. gradient – facilitated diffusion
- membrane less permeable to Na+ (closed Na+ channels)
- higher conc. Na+ outside
47
Q
Action potential
A
- When the neurone’s voltage increases beyond the -55mV threshold
- nervous impulse generated
- generated due to membrane becoming more permeable to Na+
48
Q
Action potential: Stimulus
A
- Voltage-gated Na+ channels open – membrane more permeable to Na+
- Na+ diffuse (facilitated) into neurone down conc. gradient
- voltage across membrane increases
49
Q
A
