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Biology yr 13 > Stimuli and response- BP > Flashcards

Stimuli and response- BP Flashcards

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1
Q

What is a Stimuli?

A

a change in the internal or external environment

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2
Q

Why do Organisms need to Respond to Stimuli?

A

for survival (predator/prey awareness, homeostasis)

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3
Q

How do Simple Organisms Respond to Stimuli?

A

Taxis and Kinesis

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4
Q

What is Taxis?

A

directional response to a stimuli (towards or away from)

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5
Q

What is Kinesis?

A

 non-directional movement from an unfavourable area to a favourable area
 organism moves rapidly and randomly in unfavourable area until they reach favourable area where they move slowly and less randomly
 so spends more time in favourable area, less time in unfavourable area

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6
Q

Example of Response to Stimuli in Plants?

A

Tropism

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7
Q

What is Tropism?

A

 directional growth in plants in response to a stimuli
 towards = positive, away = negative
 light = photo, water = hydro, gravity = geo
 shoot shows positive phototropism and negative geotropism
 root shows positive geotropism and positive hydrotropism
 controlled by a Plant Growth Factor = Indoleacetic Acid (IAA) - auxin

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8
Q

What is a Plant Growth Factor?

A

equivalent to animal hormones

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9
Q

What are the affects of IAA?

A
  • promotes growth in the shoot
  • inhibits growth in the root
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10
Q

How does positive phototropism in the shoot take place?

A

 normally: shoot tip produces IAA, sending it down both sides causing the shoot to grow forwards
 if light is present on one side, the IAA redistributes to the opposite side (shaded side)
 this causes the opposite side to grow faster
 so the shoot bends towards the light

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11
Q

How does negative geotropism in the shoot take place?

A

 if gravity is present on one side, the IAA redistributes to the same side
 this causes the same side to grow faster
 so the shoot bends away from gravity towards the light

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12
Q

How does positive geotropism/hydrotropism in the root take place?

A

 if gravity/water is present on one side, the IAA redistributes to the same side
 this causes the same side to grow slowly, so the opposite side grows faster
 so the root bends towards the gravity/water

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13
Q

Evidences for Tropism (positive phototropism in shoot)?

A
  • removing or covering shoot tip prevents tropism [tip causes tropism]
  • placing micin (prevents movement of chemicals e.g. IAA) across shoot inhibits tropism [tropism caused by movement of chemicals]
  • placing gelatine (prevents movement of electrical signals) across shoot does not affect tropism [tropism not caused by movement of electrical signals]
  • if shoot tip is moved to one side, that side grows faster and the shoot bends the other way [IAA promotes growth in shoot]
  • when in light or darkness the overall levels of IAA remain the same [light does not inhibit or breakdown IAA but rather redistributes it]
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14
Q

Response to Stimuli in Mammals?

A

uses Nervous System, Hormonal System (nervous and hormonal systems coordinate response to stimuli)

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15
Q

Job of Nervous System?

A
  • coordinate response to certain stimuli
  • response is fast, short acting, localised
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16
Q

Pathway of Nervous System?

A

stimuli to receptor to sensory neurone to spinal cord to brain to spinal cord to motor neurone to effector for response

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17
Q

What does a Receptor do?

A

 detects stimuli & converts stimuli energy into nerve impulse (acts as a transducer – converts one type of energy into another)
 each type of stimuli has a specific receptor
 uses stimuli energy to send Na+ ions into the start of the sensory neurone
 2 examples of receptors: Pacinian Corpuscle, Retina of Eye

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18
Q

What does a Pacinian Corpuscle do?

A

 touch receptor
 found in skin, fingers and toes
 responds to pressure/touch

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19
Q

How does the Retina of the Eye work?

A

 detects light so the brain can generate an image
 detected by retina (located at back of eye)
 made of Cone and Rod cells

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20
Q

Properties of Cone Cells in Retina?

A

 made of Iodopsin Pirgment which is only broken down at high light intensity
 one cone cell connects to one bipolar neurone which connects to one sensory neurone (therefore no summation of light can take place so only detects high light intensity)
 but because one cone cell connects to one bipolar neurone which connects to one sensory neurone, each stimuli can be distinguished = high visual acuity

21
Q

Properties of Rod Cells in Retina?

A

 made of Rhodopsin Pigment which can be broken down at low light intensity
 a few rod cells connect to one bipolar neurone which connects to one sensory neurone (therefore summation of light can take place so can detect low light intensity)
 but because a few rod cells connect to one bipolar neurone which connects to one sensory neurone, the stimuli will be merged together = low visual acuity

22
Q

What is the Central Nervous System (CNS)?

A

 made of brain and spinal cord
 brain = analyses and coordinates response to stimuli
 spinal cord = connects brain to sensory and motor neurones

23
Q

What is the Peripheral Nervous System (PNS)?

A

 made of the sensory and motor neurone
 a neurone transmits a nerve impulse
 sensory neurone takes nerve impulse from receptor to CNS
 motor neurone takes nerve impulse from CNS to effector
 sensory neurone has its cell body in the middle and has a dendron and axon
 motor neurone has its cell body at the start and only has a long axon

24
Q

What are the 2 different types of Motor Neurone?

A

 Voluntary (Somatic) and Involuntary (Autonomic) Motor Neurones
 Somatic supplies skeletal muscle = under conscious control
 Autonomic supplies cardiac muscle, smooth muscle, glands = under subconscious control
 Autonomic can be divided into Sympathetic and Parasympathetic (have opposite effects)

25
Q

What is a Nerve Impulse?

A

 movement of an action potential along a neurone
 action potential = change in membrane potential (charge’ in one section of the neurone
 changes from negative (polarised) to positive (depolarised) back to negative (repolarised/ hyperpolarised)

26
Q

What is Resting Potential?

A

 membrane potential of neurone at rest
 is -65mV
 polarised
 caused by having more positive ions outside neurone compared to inside
 involves Na+/K+ pump, pumping 3 Na+ ions out, 2 K+ ions in
 K+ channel allowing K+ ions to diffuse out
(K+ ions will eventually stop diffusing out due to a positive potential outside)

27
Q

What happens during an Action Potential?

A

 stimuli causes Na+ ions to enter the start of the neurone
 makes membrane potential less negative
 if it reaches threshold (-50mV), Na+ channels open
 therefore more Na+ ions diffuse into the neurone, therefore membrane potential becomes positive (depolarised)
 the membrane potential reaches +40mV
 then the Na+ channels close, the K+ channels open
 therefore K+ ions diffuse out, therefore membrane potential becomes negative (repolarised)
 too many K+ ions move out, so the membrane potential becomes more negative than normal (hyperpolarised)
 one action potential = depolarisation, repolarisation, hyperpolarisation

28
Q

How does an Action Potential move along a Neurone?

A
  • by local currents
  • if the stimuli energy is large enough and enough Na+ ions enter the start of the neurone, threshold will be reached and an AP will occur (the 1st AP is called a Generator Potential)
  • Na+ ions that move in during depolarisation of the generator potential diffuse along the neurone causing the next section to reach threshold and an AP to occur
  • this process continues along the neurone
  • an AP will always move along the neurone to the end
29
Q

why does AP not move back?

A
  • previous section has just finished an AP
  • therefore it is in refractory period
  • Na+ channels cannot be opened
  • it is hyperpolarised
  • therefore threshold cannot be reached
30
Q

How does the Size of Stimuli affect a Nerve Impulse?

A
  • does not affect size of AP (AP is all or nothing
  • reach threshold = get AP [all]
  • do not reach threshold = no AP [nothing])
  • larger stimuli increases the frequency (number) of APs
31
Q

What affects Speed of Nerve Impulse?

A
  • temperature = higher temp, higher kinetic energy, faster rate of diffusion of ions (faster nerve impulse)
  • axon diameter = wider diameter, neurone less leaky (faster nerve impulse)
  • myelination = schwann cells wrap around axon, insulates axon preventing AP, therefore AP only occurs in gaps – called node of ranvier, so AP jumps from node to node = saltatory conduction (faster nerve impulse)
32
Q

What is a Synapse?

A

 connection between 2 different neurones
 sends nerve impulse across the gap (synaptic cleft) using neurotransmitters (e.g. acetylcholine)

33
Q

What are the Properties of Synapses?

A
  • unidirectionality = AP/nerve impulse travels in one direction, from pre to post, pre has the neurotransmitter, post has the receptors
  • filters out low level stimuli = low level stimuli do not release enough neurotransmitter, therefore not enough Na+ ion channels open, therefore not enough Na+ ions enter postsynaptic neurone for threshold to be reached, therefore no AP produced
  • summation = low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, can be temporal or spatial
  • inhibitory = normal synapses are excitatory (cause AP), some can be inhibitory – prevent action potential from occurring by making postsynaptic neurone hyperpolarised
34
Q

what are the two types of summation?

A

temporal
spatial

35
Q

What is a Reflex?

A
  • a rapid involuntary response to a stimuli
  • does not use the brain
  • the sensory neurone connects directly to motor neurone
    (stimuli to receptor to sensory neurone to relay neurone to motor neurone to effector for response)
  • ensures less damage done and does not require learning
36
Q

How is Heart Rate controlled?

A

 the heart is myogenic, its heart beat is initiated by the SAN
 the Medulla Oblongata in the brain can increase or decrease heart rate
 receives nerve impulse from chemoreceptors (respond to blood pH) in the carotid arteries and pressure receptors (respond to blood pressure) in the carotid arteries and aorta
 sends impulse in sympathetic nerves to SAN to increase HR and sends impulse in parasympathetic nerves to SAN to decrease HR

37
Q

How does Exercise affect Heart Rate?

A

 exercise = muscle contraction, which requires respiration
 therefore, waste product CO2 is released into blood
 this lower pH of blood (acidic)
 this is detected by chemoreceptors in carotid arteries
 sends impulses to medulla oblongata
 then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase
 benefit = increase blood flow to lungs to remove CO2 and take in O2

38
Q

How does Low Blood Pressure affect Heart Rate?

A

 if a person moves from lying/sitting to standing, blood pressure falls (reducing blood flow to the brain)
 this is detected by pressure receptors in the carotid arteries and aorta
 sends impulses to medulla oblongata
 then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase
 benefit = increasing heart rate leads to an increase in blood pressure (so enough blood can reach the brain)

39
Q

how does a synapse transmit nerve impulses between 2 neurones?

A

 AP arrives in end of presynaptic neurone
 Ca2+ channels open
 Ca2+ ions enter presynaptic neurone
 causes vesicles containing neurotransmitter to move to presynaptic membrane
 vesicle binds to membrane releasing neurotransmitter into cleft
 neurotransmitter diffuses across cleft
 binds to complementary receptors on postsynaptic membrane
 Na+ channels open, Na+ ions enter
 if threshold is reached, AP occurs

40
Q

structure of pacinian corpuscule?

A

structure = corpuscle (several layers of tissue) wrapped around the start of a sensory neurone

41
Q

process of pacinian corpuscle?

A
  • pressure applied
  • corpuscle compressed
  • stretch-mediated Na+ channels opened
  • Na+ ions move into the start of the sensory neurone
42
Q

cone vs rod cells?

A

 Cone Cells detect high light intensity only, produces colour image, with high visual acuity
 Rod Cells can detect low light intensity, produces black and white image, with low visual acuity
 Cone Cells located in centre of retina (fovea) – site of high light intensity
 Rod Cells located in periphery of retina

43
Q

how does synapse return to rest?

A
  • enzyme used to breakdown neurotransmitter, e.g. acetylcholinesterase
  • breaks down acetylcholine into ethanoic acid and choline
  • diffuses back into presynaptic neurone
  • ATP used to reform neurotransmitter into vesicle and actively transport Ca2+ ions out
44
Q

difference between plant growth factor and human hormone?

A
  • made by cells throughout the plant
  • only affects cells locally
  • affects growth
45
Q

what is spatial summation?

A

a low level stimuli from a few presynaptic neurones add together

46
Q

what is temporal summation?

A

low level stimuli present for extended period of time

47
Q

what are the 3 main purposes of a refractory period?

A
  • AP propagated in one direction only
  • impulses produced are discrete
  • limits the number of action potentials
48
Q

saltatory conduction?

A

propagation of a nerve impulse along myelinated axon in which the AP jumps from one node of ranvier to another

Biology yr 13 (19 decks)

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