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Biology Y2 > 6.1 Stimulus & Response > Flashcards

6.1 Stimulus & Response Flashcards

(59 cards)

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1
Q

Define stimulus

A

change in the internal or external environment

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2
Q

What is kinesis

A

When the organism changes speed and the rate it changes direction in order to find a more favourable environment

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3
Q

What do taxes and kinesis involve

A

both involve the movement of the whole animal in response to a stimulus and improve the animal’s chance of survival

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4
Q

What are taxes and what is the difference between positive and negative taxis

A

directional response to a stimulus
positive taxis - movement TOWARDS stimulus
negative taxis - movement AWAY stimulus

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5
Q

What is a tropism

A

directional growth response to a stimulus

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6
Q

What two different stimuli are there that affect tropisms and name them

A

light - phototropism
gravity - gravitropism

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7
Q

Describe where IAA is produced

A

tips of roots and shoots

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8
Q

Do shoots show a positive or negative phototropism and name the group of chemicals involved in this

A

Shoots show a positive phototropism and this is controlled by IAA

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9
Q

Where in the shoot is IAA is produced, where does it go and what does it do

A

IAA is produced in the shoot tip - meristem, where mitosis occurs - and it diffuses down the shoot and stimulates elongation of cells

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10
Q

name and describe the 3 zones in the shoot tip

A

End of tip of shoot is the zone of growth where mitosis occurs
Middle of shoot tip is the zone of elongation where cells get longer but don’t divide
Bottom of shoot tip is the zone of differentiation which contains the xylem/phloem

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11
Q

Describe and explain the way IAA works

A

IAA breaks the hydrogen bonds within the cellulose microfibrils, weakening the plant cell wall, and so due to turgor pressure, the cell walls can stretch -> cell elongation

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12
Q

Describe the response that shoot tips have to unidirectional light

A

IAA diffuses down the shaded side of the shoot, stimulating elongation on that side, and so shoot tip grows towards the light

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13
Q

What are two theories for the way shoot tips grow, and which one has been disproved

A

1- Sunlight destroys IAA - evidence disproves this theory
2- IAA diffuses to the shaded side of the shoot

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14
Q

What type of gravitropism do shoots and roots show

A

shoots- negative gravitropism
roots- positive gravitropism

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15
Q

How is gravity involved in the growth of the shoot and the root

A

Gravity will pull the IAA to the lower surface of the shoot and root. In the shoot, IAA stimulates cell elongation and so shoot grows upwards. In the root, IAA inhibits cell elongation and so root grows downwards

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16
Q

Describe the effect of different IAA concentrations on root/shoot growth

A

IAA in the shoot causes cell elongation and promotes growth
IAA in the root inhibits growth

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17
Q

What causes the movement of IAA in shoots

A

Light

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18
Q

How do shoot and root gravitropisms affect the chance of survival of the plant, describe and explain

A

Increases chance of survival
1- Roots grow further into the soil: anchorage, gain inorganic ions, gain water
2- Shoot grows up out of the soil: light for photosynthesis

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19
Q

What are receptors

A

Cells/structures that detect stimuli.

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20
Q

What do receptors do

A

Receptors are transducers - they convert one form of energy (stimulus) into another (generator potential), and receptors are specific to a single type of stimulus

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21
Q

Give an example of a receptor

A

Pacinian corpuscles

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22
Q

Where are pacinian corpuscles found and what are they sensitive to

A

Found beneath the skin and around joints and tendons
sensitive to mechanical pressure

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23
Q

Describe the structure of a Pacinian corpuscle

A

Single sensory neurone is at the centre of layers of tissue called lamellae each separated by a gel. A capsule surrounds the layers. The sensory neurone at the centre has stretch mediated sodium channels in its membrane

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24
Q

What do pacinian corpuscles consist of that make them a basic type of receptor

Study These Flashcards
A

unmyelinated end of a myelinated sensory neurone
surrounded by concentric rings of connective tissue

25
How do pacinian corpuscles work
The neurone membrane contains stretch mediated Na+ channels, when stimulated they change their shape and alter the membrane permeability to Na+ ions
26
Explain how pacinian corpuscles detect pressure
When no pressure is applied, pacinian corpuscle is round, Na+ channels are closed and a resting potential is established across the membrane. When pressure is applied, the pacinian corpuscle is distorted and the Na+ channels open, Na+ diffuse into the neurone. Membrane becomes depolarised and inside of neurone becomes positively charged, creating a generator potential. This generator potential results in an action potential in the sensory neurone, which is then transmitted along the neurone to the CNS
27
What are the 2 types of photoreceptor cells in the retina
Rods and Cones
28
What do the photoreceptor cells in the retina do
convert light energy to electrical energy (a generator potential / nerve impulse)
29
What is visual acuity
Refers to how clearly an image can be resolved by the brain
30
What is visual sensitivity
refers to wavelengths of light detected and intensity of light needed for an impulse to be sent to the brain
31
Describe the arrangement of rod cells in the retina, what this is called and what is is an example of
Several rod cells synapses with a single bipolar cells/ganglion cell This is called retinal convergence and is an example of spatial summation
32
Explain what the arrangement of rod cells in the retina ensures
good visual sensitivity, as the threshold is more likely to be exceeded in the bipolar neurone (as there are multiple rod cells per bipolar neurone), and so effective in low light intensities poor visual acuity as there are a small number of nerve impulses reaching the brain from a large area of the retina
33
Describe the arrangement of cone cells in the retina
Individual cone cells synapses with an individual bipolar cell/ganglion cell
34
Explain what the arrangement of cone cells in the retina ensures
Poor visual sensitivity, as the threshold is less likely to be exceeded in the bipolar neurone (as there is only one cone cell per bipolar neurone), and so only effective in high light intensity. Good visual acuity as a large number of nerve impulses reach the brain from a small area of the retina
35
Describe and explain the roles of rod and cone cells in the retina, to allow colour vision
Rod cells contain rhodopsin and provide monochromatic vision Cone cells contain 3 types of iodopsin sensitive to: red, blue & green wavelengths of light Different colours are seen due to the relative absorption by the different cone cells
36
Which parts of the heart are involved in controlling the heart rate/cardiac cycle
Sino-atrial node (SAN) Atrio-ventricular node (AVN) Right + left bundles of His Purkinje fibres
37
Cardiac muscle is myogenic, what does this mean
Cardiac muscle generates its own contraction, and so doesn't require neural input.
38
What is cardiac muscle which means it doesn't require neural input to generate contractions
Cardiac muscle is myogenic
39
Where is the Sino-atrial node (SAN) located and how does it act
SAN is located in the upper wall of the right atrium and acts as a pacemaker
40
How does the cardiac muscle cause atrial systole
The Sino-atrial node (SAN) initiates a wave of excitation that spreads out into the walls of the atria causing atrial systole
41
What prevents the wave of excitation passing into the walls of the ventricles during atrial systole
A layer of non-conductive tissue prevents the wave passing into the walls of the ventricles from the atria
42
How does the cardiac muscle cause ventricular systole
Atrio-ventricular node is stimulated by the wave of excitation, Bundles of His conduct an impulse to the apex of the ventricles, where the purkinje fibres allow the impulse to travel upwards through the walls of the ventricles, the ventricles contract from the bottom upwards, forcing blood into the arteries, this is the ventricular systoles
43
Where is the Atrio-ventricular node (AVN) located
The AVN is located in the lower part of the right atrium
44
There is a time delay between the arrival and departure of the wave of excitation at the AVN, why is this significant?
Allows time for ventricles to fill with blood
45
What receptors are there in the aorta
Chemoreceptors and pressure receptors
46
Where are chemoreceptors and pressure receptors located
in the aorta close to the heart and the carotid arteries that pass through the neck to the brain
47
What is the name of the 'co-ordinator' in the brain, that controls the heart rate
Medulla oblongata
48
Explain the role of the medulla oblongata in increasing the heart rate
Cardio-acceleratory centre in the medulla oblongata sends nerve impulses along the sympathetic neurone which releases noradrenalin at the SAN and AVN. SAN discharges at a higher frequency, increasing the heart rate
49
Explain the role of the medulla oblongata in decreasing the heart rate
Cardio-inhibitory centre in the medulla oblongata sends nerve impulses along the parasympathetic neurone which releases acetylcholine at the SAN and AVN. SAN discharges at a lower frequency, decreasing the heart rate
50
Fully explain the process of the roles of chemoreceptors in the aortic and carotid bodies, the medulla and the SAN during exercise
Exercise increases muscle contraction ∴ more ATP required and increase in rate of respiration ∴ increase in pCO2 and decrease in pH. This stimulates chemoreceptors in the aortic and carotid bodies, sending impulses to the cardio-acceleratory centre in the medulla -> more impulses sent down sympathetic nerve ∴ SAN discharges at higher frequency and so increase in heart rate. This increases blood flow and so more CO2 is removed from muscles and body via lungs, and more O2 and glucose supplied to muscles for respiration
51
Explain the process that occurs when there is high blood pressure
Stimulates pressure receptors, sending impulses to the cardio-inhibitory centre in the medulla -> more impulses sent down parasympathetic nerve, SAN discharges at a lower frequency, decreasing heart rate and in turn decreasing blood pressure
52
Explain the process that occurs when there is low blood pressure
Stimulates pressure receptors, sending impulses to the cardio-acceleratory centre in the medulla -> more impulses sent down sympathetic nerve, SAN discharges at a higher frequency, increasing heart rate and in turn increasing blood pressure
53
What hormone is involved in our 'flight or fight' mechanism, how does it work and what are its advantages
Adrenalin which has a similar structure to noradrenalin, causes SAN to discharge at a higher frequency increasing the heart rate. Adrenalin is fast acting and so increases animal chances of survival
54
What are reflexes
Rapid involuntary responses
55
Explain the role of reflexes and why they are important
They protect against damage to body tissues, effective from birth and do not have to be learnt, enable homeostatic control and escape from predators
56
What is it that makes reflexes rapid and involuntary/automatic
rapid - only 3 neurones involved involuntary/automatic - don't involve the cerebral cortex (decision making)
57
What are the 3 neurones involved in a reflex
sensory, relay and motor neurones
58
Explain the role of the 3 neurones in a reflex arc
sensory neurones carry electrical nerve impulses from the receptor (which receives a stimulus) to the CNS. Relay neurones synapse with the sensory neurone and then with a motor neurone which carries the impulse to the effector (muscles/glands) resulting in a response
59
Explain the sequence of events which brings about a reflex action
stimulus -> receptor -> sensory neurone -> CNS / relay neurone -> motor neurone -> effector -> response

Biology Y2 (16 decks)

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