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Year 2 Biology > Organisms respond to changes in their environment- chapter 14: Response to stimuli > Flashcards

Organisms respond to changes in their environment- chapter 14: Response to stimuli Flashcards

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1
Q

What is a stimulus?

A

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

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2
Q

The ability to respond to stimuli is a characteristic of life and increases the chances of

A

Survival for an organism- e.g. To be able to detect and move away from harmful stimuli such as predators and extremes of temperatures, or to detect and move towards a source of food clearly aids survival

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3
Q

Those organisms that survive have a greater chance of raising offspring and passing their allele to the next generation. There is always therefore a ______ _______ favouring organisms with more appropriate responses

A

Selection pressure

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4
Q

Stimuli are detected by

A

Receptors

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5
Q

Receptors are specific to _ type of stimulus

A

1

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6
Q

A coordinator formulates a suitable response to a stimulus-coordination may be at the molecular lever or involve a large organ such as the

A

Brain

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7
Q

Response is produced by an effector and this may be at the molecular level or involve the behaviour of a whole

A

Organism

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8
Q

What are the 2 means of communication in large multicellular organisms

A

Via hormones (relatively slow process found in both animals and plans) and more rapid means of communication, the nervous system

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9
Q

Sequence of events for a reflex arc (involve either chemical control or nerve cells) and can be summarised as:

A

Stimulus - receptor- coordinator- effector- response

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10
Q

What is a taxis?

A

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

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11
Q

As a result of taxis,

A

A motile organism responds directly to environmental changes by moving its whole body either towards a favourable stimulus or away from an unfavourable one

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12
Q

Taxes are classified according to whether the movement is towards the stimulus (positive taxis) or

A

Away from the taxis (negative taxis)

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13
Q

Single-celled algae will move towards light (positive phototaxis). Why is this useful?

A

This increases their chance of survival being photosynthetic, they require light to manufacture their food

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14
Q

Earthworms will move away from light (negative phototaxis) why is this useful?

A

This increases their chance of survival because it takes them into the soil, where they are better able to conserve water, find food and avoid some predators

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15
Q

Some species of bacteria will move towards a region where glucose is more highly concentrated (positive chemotaxis). Why is this useful?

A

This increases their chance of survival because they use glucose as a source of food

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16
Q

What is kinesis?

A

A kinesis is a form of response in which the organism does not move towards or away from a stimulus- instead it changes the speed at which it moves and the rate at which it changes direction

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17
Q

If an organism crosses a sharp dividing line between a favourable and an unfavourable environment

A

it’s rate of turning increases

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18
Q

When is kinesis important?

A

When stimulus is less directional e.g. humidity and temp do not always produce a clear gradient from one extreme to another

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19
Q

Give an example of an organism that relies on kinesis

A

Woodlice

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20
Q

Explain why woodlice rely on kinesis

A
  • woodlice lose water from their bodies in dry conditions
  • when they move from a damp area into a dry one, they move more rapidly and change direction more often- this will increase their chance of moving back into a damp area
  • once back in damp area, they slow down and change direction less often- this means they are more likely to stay within the damp area
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21
Q

What happens if after some time the woodlice spent changing direction rapidly they are in the damp area?

A
  • they move rapidly in straight lines, which increases their chance of moving through the dry area into a new damp on; in this way, they spend more time in favourable damp conditions than in less favoured drier conditions
  • this prevents them drying out, and so increases their chance of survival
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22
Q

What is tropism?

A

A tropism is the growth of part of a plant in response to a directional stimulus

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23
Q

Plants shoots grow towards light ( _____ _______) and away from gravity ( ______ _______), so their leaves are in the most favourable position to capture light and photosynthesis

A

1- positive phototropism

2- negative gravitropism

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24
Q

Plant roots grow away from light (______ ________) and towards gravity (______ _______)

A

1- negative phototropism

2- positive gravitropism

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25
Q

In both cases of plant roots and plant shoots, the response

A

Increases the probability that the roots will grow into the soil, where they are better able to absorb water and mineral ions

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26
Q

Some species of bacteria move away from the waste products that they produce- what kind of response is this?

A

Negative chemo-taxis- wastes are often removed from an organism because they are harmful. Moving away prevents the waste harming the organism and so increases its chance of survival

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27
Q

The sperm cell of a moss plant are attracted towards a chemical produced by the female reproductive organs of another moss plant- what type of response is this?

A

Positive chemo-taxis = increases the chances of the sperm cells fertilising the egg cells of other mosses and so helps to produce more moss plants —-> cross-fertilisation increases genetic variability, making species better able to adapt to future environmental changes

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28
Q

The young stems of seedlings grow away from gravity- what type of response is this?

A

Negative gravitropism- takes the seedlings above ground and into the light where they can photosynthesis = more photosynthesis= means more carbohydrates and so better chance of survival

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29
Q

Unlike animals, plants have no nervous system. Nevertheless, in order to survive, plants respond to changes in both their external and internal environments. For example plants respond to:

A
  • light (shoots grow towards light (positively phototropic) as light is needed for photosynthesis)
  • gravity (plants need to be firmly anchored in the soil and roots are positively gravitropic)
  • water ( almost all plant roots grow towards water- positively hydrotropic- in order to absorb it for use in photosynthesis and other metabolic processes as well as support
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30
Q

Plants responses to external stimuli involve hormone-like substances, or, more correctly

A

Plant growth factors

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31
Q

Why is plant growth factors more descriptive than plant responses to external stimuli involve hormone-like substances?

A

Hormones exert their influences by affecting growth and they be made by cells located throughout the plant rather than in particular organs

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32
Q

Unlike animal hormones, some plant growth factors affect the tissues that release them rather than acting on a

A

distant target organ

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33
Q

Plant growth factors are released in ____ quantities

A

Small

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34
Q

What’s an example of a plant growth factor?

A

IAA which belongs to a group of substances called auxins; among other things, IAA controls plant cell elongation

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35
Q

Control of tropism by IAA:
Phototropism in flowering plants:
The response of the shoots of flowering plants to unilateral light is due to the following sequences of events:

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 on the shaded side of the shoot rather than on the light side
5- as IAA causes elongation of shoot cells and there is a greater concentration of IAA on the shaded side of the root, 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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36
Q

IAA also controls the bending of roots in response to light. However, whereas a high concentration of IAA increases cell elongation it ______ cell elongation in roots

A

Inhibits

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37
Q

An IAA concentration of 10 parts per million increases shoot cell elongation by 200% but decreases root cell elongation by 100% as a result

A

In roots, the elongation of cells is greater on the light side than in the shaded side and so roots bend away from light, that is, they are negatively phototropic

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38
Q

Gravitropism in flowering plants:

The response of a horizontally- growing root to gravity is as followed

A

1- cells in the top of the root produce IAA, which is then 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 rather than the upper side
5- as IAA inhibits the elongation of root cells and there 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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39
Q

Role of IAA in elongation growth: the transport of IAA is in one direction, namely away from

A

the tip of the shoots and roots where it is produced

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40
Q

IAA has a number of effects on plant cells including increasing plasticity (ability to stretch of their cell walls). This only occurs

A

On young cell walls where cells are able to elongate. As the cells mature they develop greater rigidity; therefore older parts of the root/shoot will not be able to respond

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41
Q

The proposed explanation of how IAA increases the plasticity of cells is called the

A

Acid growth hypothesis

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42
Q

What is the acid growth hypothesis?

A

It involves the 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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43
Q

The elongation of cells on one side only of a stem or root can lead to bending. This is the means by which plants respond relatively quickly to environmental stimuli like light and gravity; these responses can be explained in terms of the stimuli causing

A

Uneven distribution of IAA as it moves away from the tip of the stem or the root

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44
Q

Explain how the movement of IAA in shoots helps a plant to survive

A

More IAA moves towards the shaded side of shoots than the light side when the light is unidirectional. In response to this uneven distribution of IAA, the cells on the shaded side elongate faster than those on the light side and the shoot bends towards the light. This ensures that the shoot and leaves attached to it have a greater chance of being well illuminated as light is essential for photosynthesis, so the plant has a greater chance of survival

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45
Q

Suggest 2 advantages to a plant of having roots that respond to gravity by growing in the direction of its force

A

Response ensures that roots grow down into the soil, anchoring the plant firmly and bringing them closer to water, which is needed for photosynthesis

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46
Q

The fact that IAA is readily absorbed, easily synthesised and is lethal to plants in low concentrations makes it useful as a

A

Herbicide

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47
Q

The fact that IAA more readily kills broad-leaves plants than narrow-leaved plants is an advantage because

A

Many agricultural crops are narrow-leaves while the weeds that compete with them are broad-leaved. As a result, application of IAA at appropriate concentrations will kill only the weeds with little to no harm to the crop

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48
Q

What is an advantage of IAA not being easily broken down?

A

It will persist in the soils and continue to act as a selective weed killer for some time

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49
Q

What is a disadvantage of IAA not being easily broken down?

A

As it will persist in the soil for a long time and continue to act as a selective weed killer for some time and this may prevent a broad-leaved crop being grown on the land- also danger that IAA might accumulate along food chains with possible harm to animals in those chains

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50
Q

The nervous system has two major divisions:

A
  • central nervous system- made up of brain and spinal cord

- the peripheral nervous system- made up of pairs of nerves that originate from either the spinal cord or the brain

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51
Q

The peripheral nervous system can be divided into:

A
  • sensory neurones= carry nerve impulses (electrical signals) from receptors towards CNS
  • motor neurones which carry nerve impulses away from the CNS to the effectors
52
Q

Motor nervous system can be further subdivided as followed:

A
  • voluntary nervous system= which carries nerve impulses to the body muscles and is voluntary (conscious control)
  • autonomic nervous system= carries nerve impulses to glands, smooth muscles and cardiac muscles and is involuntary (subconscious)
53
Q

What is the spinal cord?

A

Column of the nervous tissue that runs along the back and lies inside the vertebral column (for protection)

54
Q

Emerging at intervals along the spinal cord are pairs of

A

Nerves

55
Q

What is a reflex?

A

An involuntary response to a sensory stimulus

56
Q

State the stages of reflex arc

A 
1- stimulus 
2- receptor
3- sensory neurone
4- synapse
5- relay neurone
6- coordinator
7- motor neurone 
8- effector
9- response
57
Q

What is a stimulus? (Arc reflex)

A

Change in environment that can be detected and may provoke a response

58
Q

What is a sensory neurone?

A

Nerve cell that carries an electrical impulse from a receptor to the CNS

59
Q

What is a synapse?

A

Gap between 2 neurones

60
Q

What is a relay neurone?

A

A nerve cell that acts as a coordinator between sensory and motor neurone

61
Q

What is a coordinator?

A

Formulates a suitable response to stimulus

62
Q

What is a motor neurone?

A

Nerve cell that carries electrical impulses from the CNS to the effector

63
Q

What is an effector?

A

An organ or cell that carries out a response to an electrical impulse

64
Q

Response examples

A

Hormone releases by a gland or a muscle contracts as a result of an electrical impulse

65
Q

Why are reflex arcs important?

A
  • involuntary = do not receive the decision-making powers of the brain, thus leaving it free to carry out more complex responses; in this way, the brain is not overloaded with situations in which the response is always the same (NOTE: some impulses are sent to the brain so that it is informed of what is happening and can sometimes override the reflex if necessary)
  • protect body from harm- they are effective from birth and do not have to be learnt
  • they are fast as neurone pathway is short with very few, typically 1-2, synapses
  • absence of any decision-making process also means action is rapid
66
Q

What is the role of a receptor?

A

Receptors change the energy in the stimulus into an action potential

67
Q

Receptors are _____ as they convert energy from stimulus into an action potential or impulse

A

Transducers

68
Q

Thermoreceptors detect

A

Heat

69
Q

Chemoreceptors detect

A

Chemicals

70
Q

Mechanoreceptor detect

A

Pressure

71
Q

Receptors are specific as a thermoreceptor will not ______ the energy in light

A

Transduce

72
Q

What are the 2 receptors we need to know?

A

Pacinian corpuscle and rod/cone cells

73
Q

Where is the pacinian corpuscle found and what does it do?

A

Found in the skin along with the other receptors and is responsible for detecting changes in pressure exerted on the skin (mechanoreceptor). PC also occur in joints, ligaments and tendons where they enable the organism to know which joints are changing direction

74
Q

Draw the pacinian corpuscle

A

(Check kerboodle)

75
Q

Describe the structure of the pacinian corpuscle

A
  • consists of a series of membranes containing a gel
  • in the centre is a naked axon I.e. does not have a myelin sheath
  • naked axon is attached to a sensory neurone (myelinated)
  • sensory neurone at the centre of the PC has a special type of sodium channel in its plasma membrane called a stretch-mediated sodium channel (so called because their permeability to sodium changes when they are deformed)
76
Q

What causes an impulse to travel along the sensory neurone from the pacinian corpuscle?

A

Pressure is applied to the pacinian corpuscle and the pressure distorts the axon and causes an impulse to travel along the sensory neurone

77
Q

Describe the sequence of events by which pressure on a PC results in the production of a generator potential

A
  • sodium channels of the membrane around the neurone of a PC are too narrow to allow sodium ions to pass along them
  • pressure on PC
  • corpuscle changes shape
  • stretches membrane of the neurone
  • widens stretch mediated sodium ion channels
  • allows sodium ions into neurone
  • depolarises membrane
  • generator potential in turn creates action potential
78
Q

Describe a stretch-mediated sodium channel

A

a special type of sodium channel that changes its permeability to sodium ions when it changes shape

79
Q

The light receptor cells of mammalian eye are found on its inner most layer, the _____

A

Retina

80
Q

The millions of light receptor cells found in the retina are of 2 main types:

A

Rod cells and cone cells

81
Q

Both rod cells and cone cells act as transducers by

A

Converting light energy into the electrical energy of a nerve impulse

82
Q

Rod cells cannot distinguish different wavelengths of light and therefore lead to images being in only

A

B&W

83
Q

Rod cells are more numerous than cone cells with around ___ million in each eye

A

120

84
Q

Rod cells are used to detect light of ___ ______ . A certain threshold value has to be exceeded before a generator potential is created in the bipolar cells to which they are connected

A

Low intensity

85
Q

As a number of rod cells are connected to a single bipolar cell (retinal convergence) there is a much greater chance that the threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell- this is due to

A

Summation

86
Q

Why do rod cells respond to low light intensity?

A

In order to create the GP, the pigment in rod cells (rhodopsin) must be broken down. There is enough energy from low-intensity light to cause this breakdown; this explains why rod cells respond to low-intensity light

87
Q

Why do rod cells give a low visual acuity (clarity of vision?)

A

As a consequence of many rod cells linking to a single bipolar cell is that light received by rod cells sharing the same neurone will only generate a single impulse travelling to the brain regardless of how many neurones are stimulated; this means that, in perception, the brain cannot distinguish between the separate sources of light that stimulated them. Two dots close together cannot be resolved and so will appear as a single blob. Rod cells therefore give a low visual acuity

88
Q

Cone cells are of 3 different types, each responding to a different range of wavelength of light. Depending upon the proportion of each type that is stimulated, we can perceive

A

Images in full colour

89
Q

In each human eye there are around _ million cone cells

A

6

90
Q

Why do cone cells only respond to high light intensity?

A

In each human eye there are around 6 million cone cells often with their separate bipolar cell connected to a sensory neurone in the optic nerve. This means that the stimulation of a number of cone cells cannot be combined to increase threshold value and so create a generator potential. As a result, cone cells only respond to high intensity

91
Q

Cone cells contain different types of pigment from that found in rod cells- the pigment in cone cells, iodopsin requires a higher light intensity for its breakdown and so

A

Only light of high intensity will therefore provide enough energy to break it down and create a generator potential

92
Q

There are 3 different types of cone cell, each containing a specific type of iodopsin. As a result,

A

Each cone cell is sensitive to different wavelengths

93
Q

Why do cone cells have good visual acuity?

A

Each cone cell has its own connection to a single bipolar cell, which means that if 2 adjacent cone cells are stimulated, the brain receives 2 separate impulses. The brain can therefore distinguish between 2 separate sources of light that stimulated the 2 cone cells. This means that 2 dots close together can be resolved and so will appear as 2 dots- cone cells therefore give very accurate vision (a good visual acuity)

94
Q

The distribution of rod and cone cells on the retina is

A

Uneven

95
Q

Light is focused by the lens on the part of the retina opposite the pupil, the

A

Fovea

96
Q

Fovea receives the highest intensity of light. What kind of cells are found at the fovea?

A

Cone cells, not rod cells- the concentration of cone cells diminishes further away from the fovea

97
Q

At the peripheries of the retina, where light intensity is at its lowest, what cells are found?

A

Only rod cells

98
Q

Explain why brightly coloured objects often appear grey in dim light

A

Only rod cells are stimulated by low-intensity (dim) light. Rod cells cannot distinguish between different wavelengths, therefore the object is perceived only in a mixture of black and white I.e. grey

99
Q

Explain why at night it is often easier to see a star in the sky by looking slightly to the side of it rather than looking directly at it

A

Light reaching Earth from a star is of low intensity. Looking directly at a star, light is focused on the fovea, where there are only cone cells. Cone cells respond only to high intensity light so they are not stimulated by the low light intensity from the star and it cannot be seen. Looking to one side of the star means that light from the star is focused towards the outer regions of the retina, where there are mostly rod cells- these are stimulated by low light intensities and therefore the star is seen

100
Q

Summarise the key differences between cone cells and rod cells

A

Rod cells:

  • rod-shaped
  • greater number than cone cells
  • distribution more at the periphery of the retina and absent at the fovea
  • poor visual acuity (visual clarity)
  • sensitive to low-intensity light
  • one type only

Cone cells:

  • cone-shaped
  • fewer numbers than rod cells
  • fewer at periphery of the retina, concentrated at the fovea
  • give good visual acuity
  • not sensitive to low-intensity light
  • 3 types responding to different wavelengths of light
101
Q

What does the autonomic nervous system control?

A

The involuntary activities of internal muscles and glands

102
Q

What are the 2 divisions of the autonomic nervous system?

A

1- sympathetic nervous system

2- parasympathetic nervous system

103
Q

Briefly describe the sympathetic nervous system

A

In general, this stimulates effectors and so speeds up any activity- acts rather like an emergency controller. It helps us to cope with stressful situations by heightening our awareness and preparing us for activity (fight or flight response)

104
Q

Briefly describe the parasympathetic nervous system

A

In general, this inhibits effectors and so slows down any activity. It controls activities under normal resting conditions. It is concerned with conserving energy and replenishing the body’s reserves

105
Q

What word describes the actions of the sympathetic and parasympathetic nervous systems normally opposing one another?

A

Antagonistic e.g. if one system contracts a muscle, the other relaxes

106
Q

The activities of internal glands and muscles are regulated by a balance of

A

the two systems

107
Q

Muscle of the heart is known as

A

Cardiac muscle

108
Q

Cardiac muscle is myogenic. What does this mean?

A

Its contraction is initiated from within the muscle itself, rather than by the nervous impulse from outside (neurogenic), as is the case with other muscles

109
Q

Within the right atrium is a distinct group of cells known as the

A

Sinoatrial node (SAN)- it is from here that the initial stimulus for contraction originates

110
Q

Why is the SAN referred to as the pacemaker of the heart?

A

The SAN has a basic rhythm of stimulation that determines the beat of the heart

111
Q

Describe the sequence of events that control the basic heart rate:

A

1- SAN initiates heartbeat
2- SAN sends wave of electrical activity across atria causing atrial contraction
3- AVN delays electrical activity
4- allowing atria to empty before ventricles contract
5- AVN sends wave of electrical activity down Bundle of His
6- causing ventricles to contract (from bottom up)

112
Q

The resting heart rate of a typical adult human is around 70bpm. However, it is essential that this rate can be altered to meet varying demands for oxygen such as

A

During exercise, this may need to more than double

113
Q

Changes to the heart rate are controlled by a region of the brain called the

A

Medulla oblongata

114
Q

What are the 2 centres the medulla oblongata has that are concerned with heart rate?

A

1- a centre that increases heart rate, which is linked to the SAN by the sympathetic nervous system

2- a centre that decreases heart rate, which is linked to the SAN by the parasympathetic nervous system

115
Q

Which of the centres is stimulated depends upon the nerve impulses they receive from 2 types of receptor which respond to stimulus of either

A

Chemical or pressure change I.e. control by chemoreceptors and pressure receptors

116
Q

Where are chemoreceptors found?

A

In the wall of the carotid arteries that serve the brain

117
Q

Chemoreceptors are sensitive to

A

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

118
Q

In solution, carbon dioxide forms an acid and therefore

A

Lowers PH of the blood

119
Q

Describe the process of control by chemoreceptors

A

1- increased metabolic activity means more carbon dioxide is produced by tissues due to increased respiration
2- chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the frequency of nerve impulses to the centre in the medulla oblongata that increases heart rate
3- this centre increases the frequency of impulses via the sympathetic nervous system to the SAN. This in turn increases the rate of production of electrical waves by the SAN and therefore increases heart rate
4- the increased blood flow leads to more carbon dioxide being removed by the lungs and so the carbon dioxide concentration of the blood returns to normal
5- the PH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata
6- the medulla oblongata reduces the frequency of impulses to the SAN which therefore leads to a reduction in heart rate

120
Q

Where are pressure receptors found?

A

Within the walls of the carotid arteries and the aorta

121
Q

Describe the process of control by pressure receptors when blood pressure is higher than normal

A
  • pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decrease heart rate
  • this centre sends impulses via the parasympathetic nervous system to the SAN of the heart, which leads to a decrease in the rate at which the heart beats
122
Q

Describe the process of control by pressure receptors when blood pressure is lower than normal

A
  • pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate
  • this centre sends impulses via the sympathetic nervous system to the SAN which increases the rate at which the heart beats
123
Q

Suppose the parasympathetic nervous system nerve connections from the medulla oblongata to the SAN were cut. Suggest what might happen if a person’s blood pressure increases above normal

A

Blood pressure remains high because the parasympathetic nervous system is unable to transmit nerve impulses to the SA node, which decreases heart rate and so lowers blood pressure

124
Q

What is the equation to work out cardiac output? ( volume per minute)

A

CO= stroke volume (1 heart contraction) X heart rate

125
Q

What are the features of a reflex arc?

A
  • immediate- very quick response, only 3 neurones involved- the fewer the number of synapses, the quicker the response
  • specific- one stimulus leads to one response
  • involuntary- happens without conscious thought
  • innate- present from birth

Year 2 Biology (4 decks)

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