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(6) Organisms respond to changes in their internal and external environments > Detection of Stimuli > Flashcards

Detection of Stimuli Flashcards

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1
Q

What is a stimulus?

A

A detectable change in the external or internal environment of an organism.

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2
Q

What is an receptor?

A

A cell or organ that detects a stimulus.

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3
Q

what is a coordinator

A

a cell/ organ that gives the message to the effector to do something, decided what to do

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4
Q

what is the effector

A

organ which responds to the stimulus
eg. muscle contraction

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5
Q

what is the response

A

what happens when the organism reacts to the stimulus

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6
Q

What is a tropism?

A

A type of growth towards an external stimulus.
Gravitropism = gravity
Phototropism = light

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7
Q

Where is IAA synthesised?

A

The tips of roots and shoots.

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8
Q

What does IAA control?

A

Cell elongation.

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9
Q

Describe the mechanism of phototropism in shoots.

A
  • IAA will diffuse to the shaded side of the shoot resulting in high conc of IAA on shades side
  • this causes a faster rate of cell elongation
  • This causes the shoot to bend towards the light
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10
Q

Describe the mechanism of phototropism in roots.

A
  • roots don’t require light and are able to anchor the plant
  • in roots high conc of IAA inhibits cell elongation
  • causing root cells to elongate more on the lighter side and roots bend away from the light
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11
Q

Describe the mechanism of gravitropism in the shoots

A
  • IAA will diffuse from the upper side to the lower side of the shoot
  • IAA will diffuses towards the pull of gravity
  • if plant is vertical, it’ll cause plant to elongate upwards
  • if plant is on its side it will cause the shoot to bend upwards
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12
Q

Describe the mechanism of gravitropism in the roots

A
  • IAA moves towards the lower side of the roots
  • upper side elongates and the root bends downwards and anchors the plant in
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13
Q

What is taxis?

A

a directional response to a stimulus.

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14
Q

what are the differences between negative and positive taxis?

A

positive taxis: organisms move towards a stimulus
negative taxis: moves away from stimulus

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15
Q

What is kinesis?

A

Kinesis is a non-direction response to a stimulus.
- response when a organisms changes the speed of movement and the rate it changes direction

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16
Q

what are taxes and kinesis?

A

simple responses that keep organisms within the favourable conditions of their environment

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17
Q

what happens if an organism moves from an area of beneficial stimuli to area of harmful stimuli?

A

INCREASE the rate it changes direction to return to favourable conditions quickly

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18
Q

what happens if the organism is surrounded by negative stimuli?

A

rate of turning DECREASES to keep moving in a straight line to increase the chance of finding a new location with favourable conditions

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19
Q

Describe a reflex arc.

A

Stimulus → Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector → Response

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20
Q

what are sensory neruones

A

carry impulses from receptors to the central nervous system

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21
Q

what are relay neurones

A

found entirely w/in the central nervus system and connect the sensory and motor neurone

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22
Q

what are motor neurones

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A

carry impulses from the central nervous system to the effectors

23
Q

Importance of reflex arcs.

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A
  • doesn’t involve conscious decision making
  • doesn’t need to be learnt
  • immediate protection
  • extremely fast
  • controls everyday actions (i.e. digestion)
24
Q

describe the process of the reflex arc pathway

Study These Flashcards
A
  1. stimulus is detected by receptor
  2. sensory neurone sends electrical impulses to the spinal cord
  3. electrical impulses are passed onto relay neuron
    4.the relay neurone connects the motor neurone and passes the impulse on
  4. the motor neurone carries the impulses to the muscle in the leg
  5. the impulses cause the muscle to contract
25
Receptors will only respond to...
a **specific** stimulus.
26
What does the pancinian corpuscle respond to?
Changes in **pressure**.
27
Describe the structure of the pacinian corpuscle.
- layers of membrane separated by a gel containing Na+ - contains stretch-mediated sodium ion channels which open when sufficient pressure is applied
28
How is a generator potential established in the Pacinian corpuscle?
1. When **pressure is applied** to the Pacinian corpuscle, the membrane is stretched. 2. The **sodium channels open** and sodium ions diffuse in. 3. The influx of sodium ions will **depolarise the membrane**, leading to a generator potential
29
What are rod cells?
Cells that are sensitive to **light intensity** - cannot distinguish light and processes images in black and white
30
What are cone cells?
Cells that are sensitive to **different wavelengths of visible light**
31
What pigment is in rod cells?
**Rhodopsin**
32
What pigment is in cone cells?
**Iodopsin**
33
Sensitivity of rod cells
- Rods are **very sensitive to even low light intensities** _ They allow humans to distinguish between **light and dark objects when light is very dim** - They **do not allow** humans to see in **colour**
34
Sensitivity of cone cells
- Cones are **less sensitive to light** - They are sensitive to **different wavelengths of light** There are three cone types: **- Red** **- Blue** **- Green** - The **combined effect** of all three pigments allows humans to observe all the other colours that are on the visible spectrum
35
Visual acuity of rod cells?
**Lower** visual acuity - **Multiple rod cells** sare connected to a **single bipolar cell** - ensures there's a big enough stimulus to trigger action potential
36
Visual acuity of cone cells?
**Higher** visual acuity as **single cone cell** connected with a **single bipolar cell** (no spatial summation) - If two cones are stimulated to send an impulse the brain is able to interpret these as **two different spots of light**- so sharper clearer vision in colour able to distinguish better
37
Describe the importance of summation of rod cells.
- Group of rods are stimulated at the same time the **combined generator potentials are sufficient to reach the threshold** and stimulate the bipolar cell for the conduction of nerve impulses onwards towards the optic nerve - Summation produces a less sharp image but **enables organisms to see in much dimmer light** than cones allow
38
what is the sinoatrial node? SAN
located in the right atrium and initiates the wave of electricity
39
what is the atrioventricular node? AVN
located between atria and ventricles
40
what is the bundle of His
conductive tissue that runs through the septum and up the walls of the two ventricles
41
what is the purkyne fibres
conductive tissue that go through the walls of the ventricles
42
outline the control of the cardiac cycle
1 SAN releases a wave of depolarisation, across the atria causing them to **contract** 2. AVN will release another wave of depolarisation when the firs reaches it 3. Bundles of His conducts the wave of depolarisation and passes it through the septum to the **purkyne fibres** which branch into the walls of the ventricles 4. after short delay walls of ventricles **contract** 5. cells repolarise and cardiac muscle relaxes
43
what is the point of the short delay in contraction of ventricles
allows time for the atria to pump all the blood into the ventricles
44
what is the autonomic nervous system
- controls the heart rate through the medulla obloganta - controls how quickly the SAN releases the wav of depolarisation as there are nerves connecting the SAN to the heart
45
impulses sent down the sympathetic nerve will..
increase the heart rate, triggering SAN to release the wave of depolarisation more rapidly
46
impulses sent down the parasympathetic nervous system will..
DECEASE the heart rate - triggers the SAN to release wavelength of depolarisation more slowly
47
Where are pressure and chemoreceptors located?
- Aorta - Carotid Arteries
48
Describe the acceleratory centre.
1. Once acceleratory centre has been activated impulses are sent along the **sympathetic neurones** to the SAN 2. **Noradrenaline** is secreted at the synapse with the SAN 3. Noradrenaline causes the SAN to **increase the frequency of the electrical waves** that it produces 4. This results in an **increased heart rate**
49
Describe the inhibitory centre.
1. Once the inhibitory centre has been activated impulses are sent along the **parasympathetic neurones** to the SAN 2. **Acetylcholine** is secreted at the synapse with the SAN 3. This neurotransmitter causes the SAN to **reduce the frequency of the electrical waves** that it produces 4. This **reduces the elevated heart rate towards the resting rate**
50
How is an action potential reached
- stimulus has to be big enough that it causes an influx of sodium ions into the neuron large than -55mV - this leads to the action potential being generated
51
response in heart to increased pressure
- stimulus: increased pressure - receptor: pressure receptors in wall of aorta and carotoid artery are stretched - coordinator: more impulses are sent to medulla obloganta and more sent via parasympathetic pathway to decrease frequency of impulses - effector: cardiac muscles, SAN tissues, releasing fewer waves of depolarisation - response: reduced heart rate
52
response in the heart due to decreased pressure
- stimulus: decreased pressure - receptor: pressure receptors in wall of aorta and carotoid artery are NOT stretched - coordinator: more impulses are sent to medulla obloganta and more sent via sympathetic pathway to SAN to increase frequency of impulses - effector: cardiac muscles, SAN tissues, releasing fewer waves of depolarisation - response: increased heart rate
53
response in the heart due to decreased pH
- stimulus: decreased pH - receptor: chemoreceptor in wall of aorta and carotoid artery detect stimulus - coordinator: more impulses are sent to medulla obloganta and more sent via sympathetic pathway to SAN to increase frequency of electrical impulses - effector: cardiac muscles, SAN tissues - response: increased heart rate to deliver blood to lungs to remove CO2

(6) Organisms respond to changes in their internal and external environments (4 decks)

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