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Bio Aqa > Organisms Respond To Internal And External Environments > Flashcards

Organisms Respond To Internal And External Environments Flashcards

1
Q

What is a stimulus?

A

change in an organisms internal or external environment.

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2
Q

Why is it important that organisms can respond to stimuli?

A

Organisms increase their chance of survival by responding to stimuli

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3
Q

What is a tropism (+ve and -ve)

A

Growth of a plant in response to a directional stimulus
Positive tropism = towards a stimulus;
negative tropism = away from stimulus

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4
Q

Summarise the role of growth factors in flowering plants

A

● Specific growth factors (hormone-like growth substances) eg. Auxins (such as IAA) move
(via phloem or diffusion) from growing regions eg. shoot / root tips where they’re produced
● To other tissues where they regulate growth in response to directional stimuli (tropisms)

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5
Q

Describe how indoleacetic acid (IAA) affects cells in roots and shoots

A

● In shoots, high concentrations of IAA stimulates cell elongation
● In roots, high concentrations of IAA inhibits cell elongation

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6
Q

Explain gravitropism in flowering plants
*hint - are 5 steps

A
  1. Cells in tip of shoot / root produce IAA
  2. IAA diffuses down shoot / root (evenly initially)
  3. IAA moves to lower side of shoot / root (so concentration increases)
  4. In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
  5. So shoots bend away from gravity whereas roots bend towards gravity
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7
Q

Explain phototropism in flowering plants

A
  1. Cells in tip of shoot / root produce IAA
  2. IAA diffuses down shoot / root (evenly initially)
  3. IAA moves to shaded side of shoot / root (so conc. ↑)
  4. In shoots this stimulates cell elongation whereas in
    roots this inhibits cell elongation
  5. So shoots bend towards light
    whereas roots bend away from ligh
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8
Q

Explain gravitropism in flowering plants

A

Cells in tip of shoot / root produce IAA
IAA diffuses down shoot / root (evenly initially)
IAA moves to lower side of shoot / root (so concentration increases)
In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
So shoots bend away from gravity whereas roots bend towards gravity

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9
Q

List the 2 simple responses that can maintain a mobile organism in a
favourable environment

A

Taxes
Kinesis

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10
Q

List the 2 simple responses that can maintain a mobile organism in a
favourable environment

A

Taxes
Kinesis

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11
Q

Describe taxes

A

Taxes (tactic response)
○ Directional response
○ Movement towards or away from a directional stimulus

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12
Q

Describe kinesis

A

Kinesis (kinetic responses)
○ Non-directional response
○ Speed of movement or rate of direction change
changes in response to a non-directional stimulus
○ Depending on intensity of stimulus

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13
Q

Example of taxis and kinesis in woodlice in response to light

A

Examples: taxis- woodlice moving away from light to avoid predators; kinesis- woodlice moving faster in drier
environments to increase their chance of moving to an area with higher humidity to prevent drying out.

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14
Q

Explain the protective effect of a simple (eg. 3 neurone) reflex

A

● Rapid as only 3 neurones and few synapses (synaptic transmission is slow)
● Autonomic (doesn’t involve conscious regions of brain) so doesn’t have to be learnt
● Protects from harmful stimuli eg. escape predators / prevents damage to body tissues

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15
Q

Describe the basic structure of a Pacinian corpuscle

A

Lamellae (layers of connective tissue)
Stretch mediated sodium ion channel (closed)
Sensory neurone ending
Sensory neurone axon
Myelin sheath (Schwann cells)

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16
Q

Describe how a generator potential is established in a Pacinian corpuscle

A
  1. Mechanical stimulus eg. pressure deforms
    lamellae and stretch- mediated sodium ion
    (Na+) channels
  2. So Na+ channels in membrane open and Na+
    diffuse into sensory neurone
    ○ Greater pressure causes more Na
    channels to open and more Na+ to enter
  3. This causes depolarisation, leading to a
    generator potential
    ○ If generator potential reaches threshold
    it triggers an action potential
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17
Q

Explain what the Pacinian corpuscle illustrates

A

● Receptors respond only to specific stimuli
○ Pacinian corpuscle only responds to mechanical pressure
● Stimulation of a receptor leads to the establishment of a generator potential
○ When threshold is reached, action potential sent (all-or-nothing principle)

18
Q

Explain the differences in sensitivity to light for rods & cones in the retina

A

Rods are more sensitive to light
● Several rods connected to a single neurone
● Spatial summation to reach / overcome threshold (as enough
neurotransmitter released) to generate an action potential

Cones are less sensitive to light
● Each cone connected to a
single neurone
● No spatial summation
Explain

19
Q

Explain the differences in visual acuity for rods & cones in the retina

A

Rods give lower visual acuity
● Several rods connected to a single neurone
● So several rods send a single set of impulses
to brain (so can’t distinguish between
separate sources of light)

Cones give higher visual acuity
● Each cone connected to a single neurone
● Cones send separate (sets of) impulses to brain
(so can distinguish between 2 separate sources
of light)

20
Q

Explain the differences in sensitivity to colour for rods & cones in the retina

A

Rods allow
monochromatic vision
● 1 type of rod / 1
pigment

Cones allow colour vision
● 3 types of cones - red-
, green- and blue-sensitive
● With different optical pigments → absorb different wavelengths
● Stimulating different combinations of cones gives range of colour perception

21
Q

Cardiac muscle is myogenic. What does this mean?
It

A

It can contract and relax without receiving electrical impulses from nerves.

22
Q

Structures in the heart

A

Sinoatrial node (SAN)
Atrioventricular node (AVN)
Bundle of his
Purkyne tissue

23
Q

Describe the myogenic stimulation of the heart and transmission of a
subsequent wave of electrical activity

A
  1. Sinoatrial node (SAN) acts as pacemaker → sends regular waves of electrical activity across atria
    ○ Causing atria to contract simultaneously
    2 . Non-conducting tissue between atria / ventricles prevents impulse passing directly to ventricles
    ○ Preventing immediate contraction of ventricles
  2. Waves of electrical activity reach atrioventricular node (AVN) which delays impulse
    ○ Allowing atria to fully contract and empty before ventricles contract
  3. AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where it branches into Purkyne tissue
    ○ Causing ventricles to contract simultaneously from the base up
24
Q

Where are chemoreceptors and pressure receptors located?

A

Chemoreceptors and pressure receptors are located in the aorta and carotid arteries.

25
Q

Describe the roles of chemoreceptors, pressure receptors, the autonomic
nervous system and effectors in controlling heart rate

A
  1. Baroreceptors detect [fall / rise] in blood
    pressure and / or chemoreceptors detect
    blood [rise / fall] in blood CO2 conc. or [fall
    / rise] in blood pH
  2. Send impulses to medulla / cardiac
    control centre
  3. Which send more frequent impulses to
    SAN along [sympathetic /
    parasympathetic] neurones
  4. So [more / less] frequent impulses sent
    from SAN and to / from AVN
  5. So cardiac muscle contracts [more / less]
    frequently
  6. So heart rate [increases / decreases]
26
Q

List the structures in a myelinated motor neurone

A

Dendrite
Cell body/soma
Axon
Myelin sheath made of Schwann cells
Node of ranvier
Axon terminal

27
Q

Describe resting potential

A

Inside of axon has a negative charge relative to outside (as more positive ions outside compared to inside).

28
Q

Explain how a resting potential is established across the axon membrane in
a neurone

A

● Na +/K+ pump actively transports:
○ (3) Na+ out of axon AND (2) K+ into axon
● Creating an electrochemical gradient:
○ Higher K+ conc. inside AND higher Na+
conc. outside
● Differential membrane permeability:
○ More permeable to K+ → move out by facilitated diffusion
○ Less permeable to Na+ (closed channels)

29
Q

Explain how changes in membrane permeability lead to depolarisation and
the generation of an action potential

A
  1. Stimulus
    ● Na+ channels open; membrane permeability to Na+ increases
    ● Na+ diffuse into axon down electrochemical gradient (causing depolarisation)
  2. Depolarisation ● If threshold potential reached, an action potential is generated
    ● As more voltage-gated Na+ channels open (positive feedback effect)
    ● So more Na
    + diffuse in rapidly
  3. Repolarisation ● Voltage-gated Na
    +
    channels close
    ● Voltage-gated K+ channels open; K+ diffuse out of axon
  4. Hyperpolarisation ● K+
    channels slow to close so there’s a slight overshoot – too many K+ diffuse
    out
  5. Resting potential ● Restored by Na
    +/K+
    pump
30
Q

Describe the all-or-nothing principle

A

● For an action potential to be produced, depolarisation must exceed threshold potential
● Action potentials produced are always same magnitude / size / peak at same potential
○ Bigger stimuli instead increase frequency of action potentials

31
Q

Explain how the passage of an action potential along non-myelinated axons results in nerve impulses

A

● Action potential passes as a wave of
depolarisation
● Influx of Na
+ in one region increases
permeability of adjoining region to Na+ by
causing voltage-gated Na+ channels to open
so adjoining region depolarises

32
Q

Explain how the passage of an action potential along non-myelinated and
myelinated axons results in nerve impulses

A

● Myelination provides electrical insulation
● Depolarisation of axon at nodes of Ranvier only
● Resulting in saltatory conduction (local
currents circuits)
● So there is no need for depolarisation along
whole length of axon

33
Q

Suggest how damage to the myelin sheath can lead to slow responses and /
or jerky movement

A

● Less / no saltatory conduction; depolarisation occurs along whole length of axon
○ So nerve impulses take longer to reach neuromuscular junction; delay in muscle contraction
● Ions / depolarisation may pass / leak to other neurones
○ Causing wrong muscle fibres to contract

34
Q

Describe the nature of the refractory period

A

● Time taken to restore axon to resting potential when no further action potential can be generated
● As Na+ channels are closed / inactive / will not open

35
Q

Explain the importance of the refractory period
●

A

● Ensures discrete impulses are produced (action potentials don’t overlap)
● Limits frequency of impulse transmission at a certain intensity (prevents over reaction to stimulus)
○ Higher intensity stimulus causes higher frequency of action potentials
○ But only up to certain intensity
● Also ensures action potentials travel in one direction– can’t be propagated in a refractory region

In the second half of the refractory period an action potential can be produced but requires greater stimulation
to reach threshold.

36
Q

List the factors that affect speed of conductance

A

Myelination
Axon diameter
Temperature

37
Q

Describe how myelination affects

A

● Depolarisation at Nodes of Ranvier only → saltatory conduction

● Impulse doesn’t travel / depolarise whole length of axon

38
Q

Describe how axon diameter affects the speed of conductance

A

● Bigger diameter means less resistance to flow of ions in cytoplasm

39
Q

Describe how temperature affects the speed of conductance

A

● Increases rate of diffusion of Na+ and K+ as more kinetic energy
● But proteins / enzymes could denature at a certain temperature

40
Q

Describe the structure of a synapse

A

Pre synaptic neurone
Axon
Vesicle containing neurotransmitter
Voltage gated calcium ion Channel
Axon terminal
Synaptic cleft
Receptor and sodium ion Channel

41
Q

What are cholinergic synapses

A

Synapses that use the neurotransmitter acetylcholine (ACh).

Bio Aqa (12 decks)

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