Response to stimuli Flashcards
1
Q
What is a stimulus?
A
A change in the internal or external environment of an organism that provokes a response.
2
Q
What are the hormone-like chemicals in plants called?
A
Growth factors.
3
Q
What is a tropism?
A
Growth response to a directional response.
4
Q
List 2 different types of tropism.
A
Gravitropism, phototropism.
5
Q
What is the difference between a negative and a positive response to a stimulus?
A
Positive is a move towards, negative is a movement away from the stimulus.
6
Q
What does IAA stand for?
A
Indoleacetic acid.
7
Q
Which piece of equipment can be used to test kinesis responses in woodlice?
A
A choice chamber.
8
Q
What is a reflex?
A
A protective, involuntary, rapid response to a stimulus.
9
Q
Is the brain involved in a reflex?
A
no.
10
Q
Which type of receptor is a Pacinian corpuscle?
A
A pressure or touch receptor.
11
Q
What is the first step in a Pacinian corpuscle generating a generator potential?
A
The cell membrane is deformed.
12
Q
Where do you find rods and cones in the human body?
A
In the retina of the eye.
13
Q
Explain why humans can only see in colour in natural light during the day.
A
Cones, which allows us to see in colour, only work in high light intensity.
14
Q
How many types of cones are there?
A
3, each detecting different wavelengths of visible light.
15
Q
Name the cells where iodopsin is found.
A
Cones.
16
Q
Name the three structures on the heart involved in propagating a heartbeat.
A
Sinoatrial node, atrioventricular node, Purkyne fibres on the bundle of His.
17
Q
What are the 2 parts of the autonomic nervous system called and how do they affect heart rate?
A
Sympathetic - increases heart rate
Parasympathetic - decreases heart rate
18
Q
List 2 key types of receptors involved in controlling heart rate and where they are located.
A
Chemoreceptors - in the aortic arch and wall of carotid artery.
Pressure receptors - in carotid artery wall and aorta.
19
Q
How is cardiac output calculated?
A
Heart rate x Stroke volume.
20
Q
List the pathway of a reflex action.
A
Stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response.
21
Q
What are the two main properties of receptors?
A
They respond to a specific stimulus once.
22
Q
Responding to their environment helps organisms survive.
A
Animals increase their chances of survival by responding to changes in their external environment.
They also respond to changes in their interval environment to make sure that the conditions are always optimal for their metabolism.
Plants also increase their chances of survival by responding to changes in their environment.
Any change in the internal or external environment is called a stimulus.
23
Q
Stimulus.
A
Any change in the internal or external environment.
24
Q
Receptor.
A
Detects stimulus, specific to one type of stimulus.
25
Coordinator.
Formulates a suitable response to a stimulus.
26
Effector.
Produces response to a stimulus.
27
Tropism.
Growth of a part of a plant in response to a directional stimulus.
28
Positive tropism.
Growth towards stimulus.
29
Negative tropism.
Growth away from stimulus.
30
Phototropism.
Growth response to light.
31
Gravitropism.
Growth response to gravity.
32
Plant growth factors.
They exert their influence by affecting growth and, they may be made by cells located throughout the plant rather than in particular organs.
Unlike animal hormones, some plant growth factors affect the tissues that release them rather than acting on a target distant organ.
33
In roots, indoleacetic acid (IAA) inhibits...
Cell elongation.
34
In shoots, IAA promotes...
Cell elongation.
35
How IAA results in phototropism in shoots?
Cells in the tip of the shoot produce IAA and it is transported down shoot.
IAA concentration increases on the shaded side.
Promotes cell elongation.
Shoot bends towards light.
36
How IAA results in phototropism in shoots?
Cells in the tip of the shoot produce IAA and it is transported down shoot.
IAA concentration increases on the shaded side.
Promotes cell elongation.
Shoot bends towards light.
37
How IAA results in gravitropism in roots?
Cells in the tip of the shoot produce IAA and are eventually transported down the shoot.
IAA concentration increases on the lower side of the root.
Inhibits cell elongation.
Root curves downwards towards gravity.
38
Phototropism in flowering plants.
Cells in the tip of the shoot produce IAA and it is transported down shoot.
IAA is transported evenly throughout all regions as it begins to move down the shoot.
Light causes the movement of IAA from light side to shaded side of shoot.
A greater concentration of IAA builds up on the shaded side of shoot than on the light side.
As IAA causes elongation of shoot cells and there's a greater concentration of IAA on shaded side of root, cells on side elongate more.
Shaded side of shoot elongates faster than light side, causing shoot tip to bend towards light.
39
Gravitropism in flowering plants.
Cells in tip of root produce IAA, which is then transported along the root.
IAA is initially transported to all sides of root.
Gravity influences movement of IAA from upper side to lower side of root.
A greater concentration of IAA builds up on the lower side of the root than on upper side.
As IAA inhibits elongation of root cells and there's a greater concentration of IAA on lower side, the cells on this side elongate less than those on upper side.
The relatively greater elongation of cells on upper side compared to lower side causes root to bend downwards towards the force of gravity.
40
When IAA moves into the elongating region,...
It binds to the protein receptors on the cell membranes.
It lowers the pH by releasing hydrogen bonds. This lowered pH breaks some of the bonds found between the microfibrils in cellulose cell walls.
This causes the cell wall to loosen and allows the cells to be more easily stretched when the turgor of the cell increases.
41
Controlling growth by elongation.
IAA molecules bind to a receptor protein on the cell surface membrane.
IAA stimulates ATPase proton pumps to pump hydrogen ions from the cytoplasm into the cell wall (across the cell surface membrane).
This acidifies the cell wall (lowers the pH of the cell wall).
This activates proteins known as expansins, which loosen the bonds between cellulose microfibrils.
At the same time, potassium ion channels are stimulated to open.
This leads to an increase in potassium ion concentration in the cytoplasm, which decreases the water potential of the cytoplasm.
This causes the cell to absorb water by osmosis (water enters the cell through aquaporins) which is then stored in the vacuole.
This increases the internal pressure of the cell, causing the cell wall to stretch (made possible by expansin proteins).
The cell elongates.
42
Phototropism affects shoots and the top of a stem.
The concentration of IAA determines the rate of cell elongation within the region of elongation.
If the concentration of IAA is not uniform on either side of a root or shoot then uneven growth can occur.
When the shoots grow towards the light it is known as positive phototropism.
In shoots higher concentrations of IAA results in a greater rate of cell elongation.
43
Gravitropism affects roots.
When the roots grow towards gravity it is known as positive gravitropism.
In roots, higher concentrations of IAA results in a lower rate of cell elongation.
IAA is actively transported to the region in the root tip where the amyloplasts have sunk. The larger concentration of IAA at the lower side of the root inhibits cell elongation. As a result, the lower side grows at a slower rate than the upper side of the root.
This causes the root to bend downwards.
44
Taxes and kineses are simple responses that...
enable mobile organisms to stay in a favourable environment.
45
Kinesis.
Non-directional response to a stimulus, change the speed of movement or the rate of direction change, in response to a non-directional stimulus
The rate of movement of an organism is affected by the intensity of the stimulus.
46
Taxis.
Directional response to a stimulus, moving towards a favourable stimulus (positive taxis) or away from an unfavourable one (negative taxis).
47
Reflex arc.
stimulus→receptor→sensory neurone→coordinator –CNS / relay neurone→motor neurone→effector →response
48
Importance of reflex arc.
Rapid (short pathway) because of only 3 neurons and few synapses (synaptic transmission is slow).
Autonomic because doesn’t involve passage to the brain – doesn’t have to be learnt.
Protects from harmful stimuli.
49
Sensory neuron.
Carry impulses from receptors to the Central Nervous System (CNS – the brain or spinal cord).
Tranmsit info from sensory receptors to other neurons.
Have an axon and a dendron, extending out from opposite sides of the cell body.
Signals travel from the dendron to the axon and on to the next neuron.
50
Relay neuron.
Found entirely within the CNS and connect sensory and motor neurons.
Carries electrical signals between neurons.
Highly branched dendrites and axons.
51
Motor neuron.
Carry impulses from the CNS to effectors (muscles or glands).
Receives signals from relay or sensory neurons.
Transmit info to effectors - cells that carry out response of nervous system.
Long axon and many short dendrites.
52
Central nervous system (CNS).
Made up of brain and spinal cord.
53
Peripheral nervous system (PNS).
Made up of pairs of nerves that originate from either the brain or the spinal cord.
54
Somatic nervous system (SNS).
Voluntary control.
| Carries nerve impulses to body muscles.
55
Autonomic nervous system (ANS).
Carries nerve impulses to glands, smooth muscle and cardiac muscle and is involuntary.
56
Spinal cord.
A column of nervous tissue that runs along the back and lies inside the vertebral column for protection.
57
Acceleratory centre.
Once the acceleratory centre has been activated impulses are sent along the sympathetic neurones to the SAN.
Noradrenaline is secreted at the synapse with the SAN.
Noradrenaline causes the SAN to increase the frequency of the electrical waves that it produces.
This results in an increased heart rate.
58
Inhibitory centre.
Once the inhibitory centre has been activated impulses are sent along the parasympathetic neurones to the SAN.
Acetylcholine is secreted at the synapse with the SAN.
This neurotransmitter causes the SAN to reduce the frequency of the electrical waves that it produces.
This reduces the elevated heart rate towards the resting rate.
59
Adrenaline.
A hormone produced by the adrenal glands.
Released during a fight-or-flight response.
Causes the heart rate to increase
The increase in heart rate is beneficial as it allows for a rapid increase in blood supply to respiring muscles; muscles will have more oxygen and glucose for respiration; enables high-intensity activities.
60
Cell body.
Contains the nucleus and other organelles. Carries out all the normal functions of the cell.
61
Dendron.
Cell body extension which further divides into smaller branched fibres (dendrites). Receive signals from other neurons and transmits nervous impulses towards the cell body.
62
Axon.
Transmits electrical signals away from the cell body towards the synapses.
63
Synapses.
Lie at the end (terminal) of the axon and pass the electrical signal on to the next cell.
64
Myelin sheath.
Covers the axon providing electrical insulation. Only present on some neurons which are known as myelinated neurons.
65
Sensory receptors are...
Specialised cells in the nervous system that detect physical stimuli. All stimuli involve a change in a form of energy.
66
Sensory receptors are energy transducers.
They convert the (change in) energy from the stimulus into another form of energy - an electrical signal called the generator potential.
67
Generator potential.
The depolarisation of the membrane of a receptor cell as a result of a stimulus.
68
Transducer cells.
Cells that convert non-electrical signals into an electrical signal and vice versa.
69
Pacinian corpuscles.
Receptor cells that lie deep under the skin and detect changes in pressure.
They transduce the mechanical energy of the stimulus into a generator potential.
End of the single sensory neuron of a Pacinian corpuscle contains stretch-mediated sodium channels in its plasma membrane.
Made up of concentric rings of connective tissue which surround a sensory neuron.
70
What changes the permeability to sodium ions?
Increases in pressure cause a deformation of the concentric rings of the Pacinian corpuscle.
71
The Function of the Pacinian Corpuscles.
1. When rings around the Pacinian corpuscle deform, the membrane of the sensory neuron is deformed, causing the stretch-mediated sodium channels in the membrane to open (widen).
2. Opening of these channels allows positively charged sodium ions to enter the cell in the resting state, the stretch-mediated sodium channels are too narrow to let sodium ions pass.
3. The influx of sodium ions causes the membrane potential to change producing a generator potential.
4. The generator potential leads to the formation of an action potential that passes along the sensory neuron, eventually reaching the CNS.
72
Electrical signals are sent during the deformation of the membrane. However, when the Pacinian corpuscle remains deformed for a period of time, the signals stop. This means that the...
Pacinian corpuscle only responds to changes in pressure.
73
The Retina.
Innermost layer of the eye, contains light receptors that can detect light
Part of retina opposite pupil is known as fovea. Lens focuses light to region, therefore, it is highly concentrated with light receptors.
No light receptors in blind spot, because it contains the optic nerve, where neurons carry signals out of the eye to the brain.
74
Light receptors.
Detects changes in light intensity, and this information is then sent to the brain for complex processing.
75
Rod cells.
```
Detects low-intensity light.
Uses pigment rhodopsin to detect light.
More abundant than cone cells.
Poor visual acuity.
Very sensitive to light.
More at periphery of retina; absent in fovea.
Rods connected in groups to one bipolar cell.
Black and white vision.
```
76
Cone cells.
```
Fewer numbers than rod cells.
Good visual acuity.
Uses pigment iodopsin to detect light.
Responds to high-intensity light.
Concentrated at fovea; fewer at periphery of retina.
Colour vision.
Less sensitive to light.
One cone joins one neuron.
3 types of cones containing different optical pigments.
```
77
A generator potential is created in light receptors only if their pigments are broken down.
Rods respond to low intensity light because there is enough energy in low-intensity light to breakdown the pigment rhodopsin. However, iodopsin requires higher intensity light for its breakdown, and therefore cone cells are less sensitive to low intensity light.
78
Bipolar cells - Light receptors in the eye pass their signal on to bipolar cells.
Cone cells mostly have their own separate bipolar cell.
Multiple rod cells connect to a single bipolar cell.
Bipolar cells pass the signal on to a sensory neuron, which takes the signal through the optic nerve to the brain where they are processed.
79
Rod Cells - Responding to low light intensity.
At peripheries of retina mostly rod cells are present.
As multiple rod cells are connected to a single bipolar cell (retinal convergence) there is a greater chance that the threshold potential of the bipolar cell is exceeded and a generator potential is produced.
Rod cells therefore, provide us with vision when light intensities are low.
80
Rod Cells - Visual Resolution.
If light hits one rod cell, it causes an action potential in the bipolar cell which is then sent to the brain.
If light hits a different rod cell connected to the same bipolar cell it will cause the same response.
The brain has no way of determining which rod cell the signal came from since the bipolar cell response is the same.
This lowers the resolution of the image since the exact location of the light cannot be determined. Thus, rod cells provide low visual acuity.
81
Visual resolution of cone cells.
Highest in fovea and contains most cone cells.
Each bipolar cells in fovea is connected to a single cone cell.
When a cone cell stimulates the bipolar cell, a signal is sent to the brain.
The brain can interpret this signal as coming from that exact cone cell.
This means cone cell signals give very accurate vision.
82
Describe and explain differences in sensitivity to colour.
Cones allow colour vision: 3 types of cones; with different optical pigments that absorb different wavelengths / red / green / blue and stimulation of different combinations / proportions of cones gives a range of colour perception.
Rods allow monochromatic vision: one type of cone / pigment.
83
Describe and explain differences in visual acuity.
Cones give higher visual acuity: One cone joins to one neurone; if 2 adjacent cone cells are stimulated, brain receives 2 separate impulses (information) → can distinguish between 2 separate sources of light.
Rods give lower visual acuity: rods connected in groups to one bipolar cell / ganglion cell / neurone (retinal convergence); spatial summation; many neurones only generate one impulse / action potential, regardless of how many neurones stimulated → can’t distinguish between separate sources of light.
84
Describe and explain differences in sensitivity to light.
Rods are more sensitive to light: rods connected in groups to one bipolar cell / ganglion cell / neurone (retinal convergence); spatial summation; stimulation of each individual-cell alone is sub-threshold / insufficient but cells connected in groups means threshold more likely met/ exceeded to generate action potential.
Cones are less sensitive to light / need higher intensity light: one cone joins to one neurone; no spatial summation.
85
Sympathetic nervous system.
Stimulates effectors and speeds up activity;
Helps us cope with stressful situations by heightening our awareness and preparing us for activity - fight or flight response.
86
Parasympathetic nervous system.
Inhibits effectors and slows down any activity.
Controls activities under normal resting conditions.
Conserves energy.
87
Control of heart rate - myogenic.
Can contract/relax without receiving electrical impulses from nerves;
heart will beat without w=any external influence.
88
Sinoatrial node (SAN).
Pacemaker.
Group of cells in wall of right atrium.
Initiates a wave of depolarisation that causes the atria to contract.
89
Waves of electrical activity reaches the atrioventricular node (AVN).
Delays impulse, allowing atria to fully contract and empty.
90
AVN passes wave of electrical activity to bundle of His.
Which conducts wave between ventricles to the apex of the heart, where the bundle branches into smaller fibres of Purkyne tissue.
Ventricles contract simultaneously, from the bottom up.
91
The bundle of His.
Collection of conducting tissue in the septum (middle) of the heart. The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them.
92
Purkyne fibres spread around the ventricles and..
Initiate the depolarisation of the ventricles from the apex (bottom) of the heart.
This makes the ventricles contract and blood is forced out of the pulmonary artery and aorta.
93
Where is the sinoatrial node located?
Right atrium's wall, where the initial contraction originates.
94
What does the sinoatrial node determine?
The heartbeat is due to SAN having a basic rhythm of stimulation.
95
The sequence of events controls the basic heart rate is:
A wave of electrical excitation spreads out from the SAN across both atria, causing them to contract.
A layer of non-conductive tissue (atrioventricular septum) prevents the wave from crossing to the ventricles.
The wave of excitation enters the second group of cells called the atrioventricular node (AVN), which lies between the atria.
The atrioventricular node, after a short delay, conveys a wave of electrical excitation between the ventricles along with a series of specialised muscle fibres called the Purknye tissue which collectively makes up a structure called the bundle of His.
The bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres of Purkyne tissue.
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.
96
Changes to the heart rate are controlled by a region of the brain called the...
Medulla oblongata.
97
The medulla oblongata has 2 centres concerned with heart rate:
A centre that increases heart rate and a centre that decreases heart rate.
98
The centre that increases the heart rate is linked to the...
Sinoatrial node by the sympathetic nervous system.
99
The centre that decreases the heart rate is linked to the...
Sinoatrial node by the parasympathetic nervous system.
100
Chemoreceptors.
Found in the wall of carotid arteries.
| Sensitive to changes in the pH of blood that changes in CO2 concentration.
101
What happens when the chemoreceptors detect high blood CO2 concentration/low pH?
More frequent impulses to medulla / cardiovascular control centre.
More frequent impulses are sent to SAN along sympathetic neurons.
More frequent impulses are sent from SAN, so cardiac muscle contracts more frequently hence heart rate increases.
102
What happens when the chemoreceptors detect low blood CO2 concentration/ high pH?
More frequent impulses to medulla / cardiovascular control centre.
More frequent impulses are sent to SAN along parasympathetic neurons.
Less frequent impulses are sent from SAN, so cardiac muscle contracts less frequently so heart rate decreases.
103
Pressure receptors.
Located in walls of carotid arteries and aorta.
| Stimulated by high/low blood pressure.
104
When blood pressure is higher than normal, pressure receptors...
Transmit more nerve impulses to the centre in the medulla oblongata that decreases heart rate.
The centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, which leads to a decrease in the rate at which the heartbeats.
105
When blood pressure is lower than normal, pressure receptors...
Transmit more nerve impulses to the centre in the medulla oblongata that increases heart rate. This centre sends impulses via the sympathetic nervous system to the sinoatrial node, which increases the rate at which the heartbeats.
106
Factors that influence heart rate:
Drugs, Caffeine, Alcohol, Sex, Weight, Height, Temperature, Diet, Dehydration.
