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AS and A level > Biology A2 Chapter 14 - Response To Stimuli > Flashcards

Biology A2 Chapter 14 - Response To Stimuli Flashcards

1
Q

Define the term stimulus

A

A detectable change in the internal or external environment of an organism that leads to a response in the organism

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2
Q

Define the term receptors

A

Receptors are cells adapted to detect changes in the environment

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3
Q

Define the term effector

A

An organ that responds to a stimulation by a nerve impulse resulting in a change or response

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4
Q

What is the order of the reflex arc?

A
  1. Stimulus
  2. Receptor
  3. Sensory neurone
  4. Coordinator (relay/intermediate neurone)
  5. Motor neurone
  6. Effector
  7. Response
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5
Q

What is a taxis?

A

A simple response whose direction is determined by the direction of the stimulus

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6
Q

What is the difference between positive and negative taxis?

A

Positive - movement is towards the stimulus
Negative - movement is away from the stimulus

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7
Q

What is a phototaxis?

A

A taxi that is determined by the direction of light, e.g. positive phototaxis would move towards the light

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8
Q

What is a chemotaxis?

A

A taxis in the direction of specific chemicals, e.g. some species of bacteria will move towards a region where glucose is more highly concentrated

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9
Q

What is a kinesis?

A

A form of response in which the organism does not move towards or away from a stimulus. Instead, it changes the speed at which is moves and the rate at which it changes direction. It will move slower if in a favorable environment and vise versa

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10
Q

What is a tropism?

A

The growth of a part of a plant in response to directional stimulus

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11
Q

What is a positive and negative phototropism?

A

Positive - shoots grow towards the light
Negative - roots grow away from the light

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12
Q

What is a positive and negative gravitropism?

A

Positive - roots grow towards gravity
Negative - shoots grow away from gravity

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13
Q

What is IAA?

A

Indoleacetic acid - belongs to a group of substances called auxins and, among other things, controls plant cell elongation

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14
Q

Describe the process of phototropism in flowering plants

A
  1. Cells in the tip of the shoot produce IAA which is then transported down the shoot
  2. The IAA is initially transported evenly throughout all regions as it begins to move down the shoot
  3. Light causes the movement of IAA from the light side to the shaded side of the shoot
  4. A greater concentration of IAA builds up in the shaded side of the shoot
  5. As IAA causes elongation of shoot cells and there is a greater concentration on the shaded side, the cells on this side elongate more
  6. The shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light
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15
Q

Describe the process of gravitropism in flowering plants

A
  1. Cells in the tip of the root produce IAA which is transported along the root
  2. The IAA is initially transported to all sides of the root
  3. Gravity influences the movement of IAA from the upper side to the lower side of the root
  4. A greater concentration of IAA builds up on the lower side of the root
  5. As IAA inhibits the elongation of root cells and thee is a greater concentration of IAA on the lower side, the cells on this side elongate less than those on the upper side
  6. The relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity
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16
Q

What is the acid growth hypothesis?

A

Proposes that IAA increases the plasticity (ability to stretch) of cells. It involves active transport of hydrogen ions from the cytoplasm into spaces in the cell wall causing the cell wall to become more plastic, allowing the cell to elongate by expansion

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17
Q

What is the central nervous system (CNS) made up of?

A

Brain and spinal chord

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18
Q

What is the peripheral nervous system (PNS) made up of?

A

Pairs of nerves that originate from either the brain or spinal chord

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19
Q

What is the PNS divided into, and what do these do?

A

Sensory neurones - carry nerve impulses from receptors towards the CNS
Motor neurones - carry nerve impulses away from the CNS to effectors

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20
Q

What can the motor nervous system be subdivided into?

A

Voluntary nervous system - carries nerve impulses to body muscles under voluntary (conscious) control
Autonomic nervous system - carries nerve impulses to glands, smooth muscle and cardiac muscle and is involuntary (subconscious)

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21
Q

Describe the reflex arc for touching a hot surface

A
  1. Stimulus - heat from the object
  2. Receptor - temperature receptors in the skin generate nerve impulses in the sensory neurone
  3. Sensory neurone - passes nerve impulses to the spinal chord
  4. Coordinator (intermediate neurone) - links the sensory neurone to the motor neurone in the spinal chord
  5. Motor neurone - carries nerve impulses from the spinal chord to the muscle in the upper arm
  6. Effector - the muscle in the upper arm which is stimulated to contract
  7. Response - pulling the hand away from the hot object
22
Q

What are the 4 reasons why reflex arcs are important?

A
  • They are involuntary and therefore do not require the decision making powers of the brain, thus leaving it free to carry out more complex responses.
  • They protect the body from harm
  • They are fast because the neurone pathway is short and with very few, typically one or two, synapses where neurones communicate with each other
  • The absence of any decision making process also means the action is rapid
23
Q

What is the Pacinian corpuscle and what does it do?

A

It is a type of receptor that responds to changes in mechanical pressure. They:
- are specific to a single type of stimulus. In this case, it responds to only mechanical pressure and will not respond to any other stimuli such as heat or sound
- produce a generator potential by acting as a transducer. All stimuli involve a change in some form of energy. It is the role of the transducer to convert the change in form of energy by the stimulus into a form, namely nerve impulses, that can be understood by the body. Receptors therefore convert, or transduce, one form of energy into another. Receptors in the nervous system convert the energy of the stimulus into a nervous impulse known as a generator potential. The Pacinian corpuscle transduces the mechanical energy of the stimulus into a generator potential

24
Q

How does the structure of a Pacinian corpuscle transduce the mechanical energy of the stimulus into a generator potential?

A
  1. In its normal (resting) state, the stretch-mediated sodium channels of the membrane around the neurone of a Pacinian corpuscle are too narrow to allow sodium ions to pass along them. In this state, the neurone has a resting potential
  2. When pressure is applied to the Pacinian corpuscle, it is deformed and the membrane around its neurone becomes stretched
  3. This widens the sodium channels in the membrane and sodium ions diffuse into the neurone
  4. The influx of sodium ions changes the potential of the membrane (it becomes depolarised), thereby producing a generator potential
  5. The generator potential in turn creates an action potential that passes along the neurone and then, via other neurones, to the CNS
25
Q

What are rod cells?

A

Cells found in the periphery of the retina. They cannot distinguish between different wavelengths of light and therefore lead to images being seen in only black and white. Used in low intensity light

26
Q

How many types of rod cells are there?

A

One

27
Q

How many rod cells are found in each eye?

A

120 million per eye

28
Q

What are rod cells connected to?

A

A single sensory neurone in the optic nerve

29
Q

What is retinal convergence?

A

When a number of rod cells are connected to a single bipolar cell

30
Q

Rod cells have retinal convergence, what does this cause?

A

A much greater chance that the threshold value to create a generator potential will be exceeded than if only a single rod cell were connected to each bipolar cell

31
Q

How many types of cone cells are there?

A

Three

32
Q

How many cone cells are found in each eye?

A

6 million per eye

33
Q

What is each cone cell connected to?

A

Their own separate bipolar cell connected to a sensory neurone in the optic nerve

34
Q

What are cone cells?

A

Cells mostly found at the fovea of the retina that respond to high light intensity - they help us see colour

35
Q

What is iodopsin and how is it broken down?

A

The pigment in cone cells. It is broken down by high light intensity as this has enough energy to break it down and create a generator potential

36
Q

Why do cone cells give good visual activity?

A

Each cell is connected to a single bipolar cell, meaning if two adjacent cone cells are stimulated, the brain receives two separate impulses. The brain can therefore distinguish between the two separate sources of light, meaning two dots close together can be resolved and appear as two dots

37
Q

What are the two divisions of the autonomic nervous system and what do they mean?

A
  • The sympathetic nervous system –> stimulates effectors and so speeds up any activity. It acts as an emergency controller, controlling effectors when we exercise strenuously or experience powerful emotions. Heightens out awareness and prepares us for activity in stressful situations
  • The parasympathetic nervous system –> inhibits effectors and so slows down any activity, controls activities under normal resting conditions and is concerned with conserving energy and replenishing the body’s reserves
38
Q

Why are the sympathetic and parasympathetic nervous systems described as antagonistic?

A

If one system contracts a muscle, the other relaxes it

39
Q

Why is the heart known as myogenic?

A

Its contraction is initiated from inside the muscle itself, rather than be nervous impulses from outside (neurogenic), as is the case with other muscles

40
Q

What group of cells determines the beat of the heart and where are they found?

A

The sinoatrial node (SAN) and it is found within the wall of the right atrium. It is from here the internal stimulus for contraction originates

41
Q

Why is the SAN referred to as a pacemaker?

A

It has a basic rhythm for stimulation that determines the beat of the heart

42
Q

What is the basic (3 bullet points) sequence of events that controls the heart rate?

A
  • Wave of electrical activity spreads out from the sinoatrial node
  • Wave spreads across both atria causing them to contract and reaches the atrioventricular node
  • Atrioventricular node conveys wave of electrical activity between ventricles along the bundle of His and releases it at the apex, causing ventricles to contract
43
Q

What is Purkyne tissue?

A

Specialised muscle fibres found between the ventricles

44
Q

What is the bundle of His?

A

A group of Purkyne tissues

45
Q

What is the detailed (6 bullet points) sequence of events that controls the heart rate?

A
  • 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 crossing to the ventricles
  • The wave of excitation enters a second group of cells called the atrioventricular node (AVN), which lies between the atria
  • The AVN, after a sort delay, conveys a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which collectively forms 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
46
Q

What controls changes to the heart rate?

A

A region of the brain called the medulla oblongata

47
Q

What are the two centres of the medulla oblongata concerned with heart rate?

A
  • A centre that increases heart rate, which is linked to the sinoatrial node by the sympathetic nervous system
  • A centre that decreases heart rate, which is linked to the sinoatrial node by the parasympathetic nervous system
48
Q

Where are chemoreceptors found?

A

In the wall of the carotid arteries (the arteries that serve the brain)

49
Q

What are chemoreceptors sensitive to?

A

Changes in the pH of the blood that result from changes in carbon dioxide concentration

50
Q

Describe the sequence of events that the effect of exercise has on cardiac output

A
  • increased muscular/metabolic activity
  • more carbon dioxide produced by tissues from increased respiration
  • blood pH is lowered
  • chemical receptors in the carotid arteries increase frequency of impulses to the medulla oblongata
  • centre in the medulla oblongata that increases heart rate increases frequency of impulses to SAN via the sympathetic nervous system
  • SAN increases heart rate
  • increased blood flow removes carbon dioxide faster
  • carbon dioxide returns to normal
51
Q

How do pressure receptors within the walls of the carotid arteries and aorta operate?

A
  • When blood pressure is higher than normal –> pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate. This sends impulses via the parasympathetic nervous system to the SAN of the heart, decreasing heart rate
  • When blood pressure is lower than normal –> pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate, this sends impulses via the sympathetic nervous system to the SAN which increases heart rate

AS and A level (30 decks)

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