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biology paper 2 > organisms response to changes in internal and external environment > Flashcards

organisms response to changes in internal and external environment Flashcards

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1
Q

what is a stimulus

A

a detectable change in the environment tha leads to a response in an organism

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2
Q

why is response to stimuli advantageous

A

there is a selection pressure that favours organisms with the most appropriate responses

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3
Q

what are the 3 types of simple responses

A
  1. taxis
  2. kinesis
  3. tropisms
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4
Q

what is taxis (by motile whole organisms)

A

an organism moving towards or away from a directional stimulus

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5
Q

what is positive taxis

A

an organism moving towards a stimulus

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6
Q

what is negative taxis

A

an organism moving away from a stimulus

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7
Q

types of taxis

A
  1. phototaxis (light)
  2. chemotaxis (chemicals)
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8
Q

what is kinesis (by motile whole organisms)

A

randomly changing speed and rate of turning in response to a non-directional stimulus (usually temperature or humidity)

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9
Q

what are tropisms

A

plant cell growth in response to a stimulus

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10
Q

what are phototropisms

A

plant cell growth in response to light

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11
Q

what do roots and shoots exhibit (phototropism)

A

shoots exhibit positive phototropism, roots exhibit negative phototropism

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12
Q

what is geo/gravitropism

A

plant cell growth in response to gravity

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13
Q

what do roots and shoots exhibit (gravitropism)

A

shoots exhibit negative gravitropism, roots exhibit positive gravitropism

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14
Q

what is hydrotropism

A

plant cell growth in response to water

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15
Q

what do roots exhibit (hydrotropism)

A

roots exhibit positive hydrotropism

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16
Q

what is the plant growth hormone

A

IAA (a type of auxin)

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17
Q

where is iaa produced in a plant

A

the tip

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18
Q

how does iaa cause plants to grow

A

iaa causes growth/elongation of plant cells. it diffuses down the plant shoot so it elongates those plant cells too.

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19
Q

features of iaa

A
  • controls growth in response to light, gravity, and water
  • produced in the tips of roots and shoots
  • causes cell elongation in shoots and inhibits cell elongation in roots
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20
Q

describe the acid growth hypothesis

A
  • iaa increases the plasticity (stretchability) of cell walls, allowing them to elongate
  • iaa travels to proton pumps in the membrane of plant cells and causes them to work more
  • protons are actively transported
  • this disrupts the celluloses hydrogen bond cross links (cellulose loosens, cells can elongate)
  • protons are positive, disrupt hydrogen bonds between positive and negative regions in the cellulose
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21
Q

describe the process of positive phototropism in shoots

A
  1. light causes iaa to diffuse to the shaded side of the shoot
  2. iaa stimulates shoot growth
  3. shaded side elongates
  4. unequal growth
  5. shoot bends towards the light (positive phototropism)
  6. more light = more photosynthesis
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22
Q

describe the process of negative gravitropism in shoots

A
  1. iaa builds up on the lower side of the shoot
  2. iaa stimulates shoot growth
  3. cell elongation of lower side
  4. unequal growth
  5. shoot bends upwards (negative gravitropism)
  6. more light = more photosynthesis
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23
Q

describe the process of positive gravitropism in roots

A
  1. iaa builds up on the lower side of the root
  2. iaa inhibits root growth
  3. unequal growth
  4. root bends downwards (positive gravitropism)
  5. more water = more photosynthesis
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24
Q

describe the process of positive hydrotropism in roots

A
  1. iaa builds up on the lower side of the root
  2. iaa inhibits root growth
  3. unequal growth
  4. root bends downwards (positive hydrotropism)
  5. more water = more photosynthesis
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25
Q

describe the method of weed removal

A
  1. pull each weed out
  2. use a selective weed killer e.g 2 4-d (dichlorophenoxyacetic acids - a selective weed killer, very similar to iaa, only works on plants with large leaves and makes them grow so fast they die)
26
Q

what makes up the nervous system

A
  1. central nervous system (brain, spinal cord - electrical impulses travel both up and down the spinal cord)
  2. peripheral nervous system (sensory neurones, motor neurones)
27
Q

reflex arc

A
  • reflexes are rapid, short lived, localised, and involuntary responses
  • theyre sometimes called simple reflexes because there are only 3 neurones involved
28
Q

advantages of reflex actions

A
  1. theyre rapid
  2. they protect body tissues
  3. theyre innate (dont have to be learnt)
  4. allow escape from predators (adrenaline release)
  5. enable homeostatic control (e/g heart rate, breathing rate)
  6. maintain posture/balance
  7. allow us to find suitable conditions
  8. involuntary so the brain isnt overloaded with conditions
29
Q

process of stimulus –> response

A
  1. stimulus
  2. pain receptors stimulated
  3. electrical impulses are sent along the sensory neurone
  4. the signal is passed along the relay neurone (message sent to brain)
  5. signal sent along motor neuron
  6. impulse sent to effector
  7. response
30
Q

name the process of a reflex arc

A
  • stimulus
  • receptor
  • sensory neurone
  • relay neurone
  • motor neurone
  • effector
    -response
31
Q

nervous system organisation

A
  • nervous system = peripheral nervous system and central nervous system
  • central nervous system = brain and spinal cord
  • peripheral nervous system = sensory nervous system and motor nervous system
  • motor nervous system = voluntary nervous system and autonomic nervous system
32
Q

what does the voluntary nervous system

A

carries electrical impulses to skeletal muscle under ‘conscious’ control

33
Q

autonomic nervous system

A

carries electrical impulses to smooth and cardiac muscle under ‘unconscious’ control

34
Q

features of pacinian corpuscles

A
  • pressure receptors
  • convert mechanical energy into electrical impulses
  • all receptors are transducers (something that converts energy into different forms)
  • found at the end of nerve endings (dendrite endings)
35
Q

potential difference in a pacinian corpuscle

A
  1. if there are more ions in one area relative to another we call it a potential difference (pd)n
  2. at rest, the pd inside of the cell relative to the outside of the cell is negative (typically -65mV). this is the resting potential of the neurone
  3. this is maintained by an Na+/K+ pump (carrier protein) which actively transports 3 Na+ out of the neurone and 2 K+ in i/e the membrane is more permeable to K+ than Na+ (when going in - K+ moves in, Na+ is thrown out)
36
Q

how do pacinian corpuscles detect pressure

A
  1. apply pressure to PC
  2. layers of connective tissue deform and pass deformation to nerve ending (deformed to get stimulus to stretch mediated Na+ channel)
  3. stretch mediated na+ channel opens
  4. na+ diffuse into neurone
  5. this regions begins to depolarise
  6. nearby voltage gated na+ channels open, more na+ diffuse (facilitated diffusion) into the cell
  7. complete depolarisation (flipping potential differences) occurs in this region. this is called a generator potential as it causes VG channels further down the neurone to open

*the SM na+ channel needs to be opened enough to let enough na+into the neurone to trigger the vg channel - this is the threshold and is usually -45mV

37
Q

what is a failed initiation

A

when a stimulus doesnt apply enough pressure to the PC to reach threshold so VG channels dont open so the region doesnt become fully depolarised so the message doesnt make it to your brain

38
Q

features of rod and cone cells

A
  • photoreceptors
  • transducers - convert light energy into electrical energy
  • found at the back of the eye (retina)
  • the outer segment of rod cells contains photosensitive chemicals
  • rods contain chemicals that, when broken down, the products bind to SM Na+ channels and cause them to open
  • the outer segment of cone cells contains photosensitive chemicals
  • rods register low levels of light (cant see colour)
  • cones register colour
39
Q

structure of the eye

A
40
Q

structure of rod cells

A
41
Q

structure of cone cells

A
42
Q

overview of rod cells

A
  • contain a pigment called rhodopsin that breaks down in low intensity light
  • when rhodopsin breaks down, a generator potential (initial depolarisation) is initiated
  • electrical activity then moves onto the bipolar neurone
  • rod cells cant differentiate between wavelengths of light which leads to black and white images
  • many rods are connected to a single sensory neurone (retinal convergence) - this increases the sensitivity (via spatial summation - combining the neurotransmitters from many rods) but the brain cant distinguish which rod cell was stimulated - poor acuity
43
Q

overview of cone cells

A
  • 3 types - each is connected to their own bipolar sensory neurone (no spatial summation = less sensitivity)
  • the brain can distinguish between which cell is stimulated (higher acuity - resolving power)
  • each type contains a variation of the pigment iodopsin which is broken down by different wavelengths of high intensity light
  • when iodopsin breaks down a generator potential ia initiated in the cone
  • electrical activity then moves onto the bipolar neurone
44
Q

rods vs cones: rods

A
  • rod-shaped
  • many (120 million per eye)
  • more located at periphery of retina, absent at fovea
  • poor visual acuity
  • sensitive to low intensity light
  • one type only, cant differentiate wavelengths of light
45
Q

rods vs cones: cones

A
  • cone-shaped
  • fewer (6 million per eye)
  • fewer at periphery of retina, many at fovea
  • good visual acuity
  • not sensitive to low intensity light
  • 3 types (red, green, blue) responping to different wavelengths of light
46
Q

control of heart rate - basic facts

A
  • resting heart rate = 70bpm
  • heart is made from cardiac tissue/muscle
  • cardiac tissue is myogenic (self contracting)
  • blood pH is 7.35-7.45 (exercise decreases blood pH due to increased co2 dissolving in the blood)
47
Q

the process of the control of heart rate: an increase in blood pressure

A
  1. an increase in blood pressure is registered by baroreceptors in the aorta/carotid arteries
  2. they send impulses along a sensory neurone to the cardioinhibitory centre in the medulla oblongata in the brain
  3. impulses travel from the cardioinhibitory centre along the parasympathetic neurone to the sinoatrial node (natural pacemaker)
  4. this inhibits the SAN
  5. this reduces the amount of impulses the SAN sends to the atrioventricular node (AVN) (reduces the number of waves excitation sent across the atria by the SAN)
  6. this reduces the amount of impulses sent from the AVN down the bundle of His so less impulses are then sent to the purkinje/purkyne fibres, causing HR to decrease
48
Q

the process of the control of heart rate: a decrease in blood pressure

A
  1. a decrease in blood pressure is registered by baroreceptors in the aorta/carotid arteries
  2. they send impulses along a sensory neurone to the cardioacceleratory centre in the medulla oblongata in the brain
  3. impulses from the cardoacceleratory centre travel along the sympathetic neurone to the SAN
  4. this stimulates the SAN to release more waves of excitation across the atria which then reach the AVN
  5. this increases the amount of impulses sent from the AVN down the bundle of His so also the amount of impulses sent to the purkinje fibres, causing HR to increase
49
Q

the process of the control of heart rate: an increase in blood pH

A
  1. an increase in blood pH is registered by chemoreceptors in the aorta/carotid arteries
  2. they send impulses along a sensory neurone to the cardioinhibitory centre in the medulla oblongata in the brain
  3. impulses travel from the cardioinhibitory centre along the parasympathetic neurone to the sinoatrial node (natural pacemaker)
  4. this inhibits the SAN
  5. this reduces the amount of impulses the SAN sends to the atrioventricular node (AVN) (reduces the number of waves excitation sent across the atria by the SAN)
  6. this reduces the amount of impulses sent from the AVN down the bundle of His so less impulses are then sent to the purkinje/purkyne fibres, causing HR to decrease
49
Q

the process of the control of heart rate: a decrease in blood pH

A
  1. a decrease in blood pH is registered by chemoreceptors in the aorta/carotid arteries
  2. they send impulses along a sensory neurone to the cardioacceleratory centre in the medulla oblongata in the brain
  3. impulses from the cardoacceleratory centre travel along the sympathetic neurone to the SAN
  4. this stimulates the SAN to release more waves of excitation across the atria which then reach the AVN
  5. this increases the amount of impulses sent from the AVN down the bundle of His so also the amount of impulses sent to the purkinje fibres, causing HR to increase
50
Q

cell body

A

contains all usual cell organelles including a nucleus and a lot of rough endoplasmic reticulum. this is associated with production of proteins and neurotransmitters

51
Q

dendrons/dendrites

A

dendrons: extensions of the cell body which subdivide into smaller branched fibres (dendrites) that carry nerve impulses towards the cell body

52
Q

axon

A

a single long fibre that carries nerve impulses away from the cell body

53
Q

schwann cells

A

surround the axon, protecting it and providing electrical insulation. they also carry out phagocytosis and play a part in nerve regulation. they wrap themselves around the axon so many layers of their membrane build up

54
Q

myelin sheath

A

forms a covering to the axon and is made of the membranes of schwann cells. they are rich in a lipid called myelin. neurones with a myelin sheath are called myelinated neurones

55
Q

nodes of ranvier

A

constrictions between adjacent schwann cells where there is no myelin sheath. the constrictions are 2-3µm long and occur every 1-3mm in humans

56
Q

axon terminal

A

the end of an axon

57
Q

what do motor neurones do

A

transmit nerve impulses from an inermediate/relay neurone to an effector (a gland or muscle). motor neurones have a long axon and many short dendrites

58
Q

what do relay neurones do

A

transmit impulses between neurones, e/g from sensory to motor neurones. they have numerous short processes

59
Q

what do sensory neurones do

A

transmit nerve impulses from a receptor to a relay or motor neurone. they have one dendron that is often very long. it carries the impulse towards the cell body and one axon that carries it away from the cell body (unipolar)

60
Q

nervous vs hormonal systems: nervous

A
  • communication via nerve impulses
  • transmission by neurones
  • rapid transmission
  • impulses are sent only to specific body parts
  • response is localised
  • rapid response
  • response is short-lived
  • effect is temporary and reversible
61
Q

nervous vs hormonal systems: hormonal

A
  • communication is via hormones
  • transmission by blood
  • slow transmission
  • hormones travel around the whole body - target cells respond only
  • response is widespread
  • response is slow
  • response is long - lasting
  • effects may be permanent and irreversible

biology paper 2 (4 decks)

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