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Biology Revision > Responding to Changes In Environment (Topic 6) > Flashcards

Responding to Changes In Environment (Topic 6) Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are plant growth factors and where
are they produced?

A

• Chemicals that regulate plant growth response
to directional stimuli.
• Produced in plant growing regions (apical
meristems).
• Diffuse from cell to cell/ phloem mass transport.

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2
Q

Explain why shoots show positive
phototropism.

A
  1. Indoleacetic acid (IAA) diffuses to shaded side of shoot tip.
  2. As IAA diffuses down shaded side, it causes active transport of
    H
    +
    ions into cell wall.
  3. Disruption to H-bonds between cellulose molecules & action of
    expansins make cell more permeable to water. (acid growth
    hypothesis).
  4. Cells on shaded side elongate faster due to higher turgor
    pressure.
  5. Shoot bends towards light.
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3
Q

Explain why roots show positive
gravitropism.

A
  1. Gravity causes IAA to accumulate on lower
    side of the root.
  2. IAA inhibits elongation of root cells.
  3. Cells on the upper side of the root
    elongate faster, so the root tip bends
    downwards.
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4
Q

Contrast mammalian hormones and
plant growth factors. (CASTS)

A

CASTS- Concentration, Action, Synthesis, Transport, Speed
Mammalian hormones:
C- response not always based on concentration
A- bind to complimentary proteins in/on target cells
S- specialised glands
T- circulatory system
S- faster-acting (homeostasis)
Plant growth factors:
C- response proportional to concentration
A- can affect all cells
S- various tissues in growing regions
T- diffusion of phloem translocation
S- slower-acting (plant growth)

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5
Q

Define taxis and kinesis. State their
advantage.

A

•** Taxis: directional movement in response to
external stimulus.
• Kinesis**: non-directional response to presence
and intensity of external stimulus.
• Maintain mobile organism in optimum
environment e.g. to prevent dessication.

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6
Q

Many organisms respond to temperature
and humidity via kinesis rather than
taxis. Why?

A

Less directional stimuli; often no clear
gradient from one extreme to the other.

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7
Q

How could a student recognise kinesis in
an organism’s movement?

A
  1. Organism crosses sharp division between favourable &
    unfavourable environment: turning increases
    (return to the original favourable environment).
  2. If organism moves considerable distance into
    unfavourable environment: turning slowly decreases;
    begins to move in long, straight lines; sharper turns
    (lead organism to new environment).
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8
Q

Outline what happens in a simple reflex
arc.

A

receptor detects stimulus → sensory
neuron → relay neuron in CNS
coordinates response → motor neuron
→ response by effector

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9
Q

Give the advantages of a simple reflex

A
  1. Rapid response to potentially
    dangerous stimuli since only 3
    neurons involved
  2. Instinctive
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10
Q

Suggest a suitable statistical test to
determine whether a factor has a
significant effect on the movement of an
animal in a choice chamber.

A

Chi squared

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11
Q

What features are common to all sensory
receptors?

A

• Act as energy transducers which
establish a generator potential.
• Respond to specific stimuli.

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12
Q

Describe the basic structure of a
Pacinian corpuscle.

A

• Single nerve fibre surrounded by layers of
connective tissue which are separated by
viscous gel and contained by a capsule.
• Stretch-mediated Na+
channels on plasma
membrane.
• Capillary runs along base layer of tissue.

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13
Q

What stimulus does a Pacinian corpuscle
respond to? How?

A
  1. Pressure deforms membrane, causing
    stretch-mediated Na+
    ion channels     to open.
  2. If influx of Na+
    raises membrane to threshold
    potential, a generator potential is produced.
  3. Action potential moves along sensory neuron.
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14
Q

Name the 2 types of photoreceptor cell
located in the retina.

A
  1. Cone cells
  2. Rod cells
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15
Q

Where are rod and cone cells located in
the retina?

A

Rod: evenly distributed around periphery
but NOT in central fovea
Cone: mainly central fovea no
photoreceptors at blind spot

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16
Q

Compare and contrast rod and cone
cells. (PACL)

A

PACL = Pigment, Visual Activity, Colour sensitivity, Light sensitivity
Rod cells:
P- rhodopsin
A- low res: many rod cells synapse with one bipolar neuron
C- monochromatic: all wavelength of light detected
L- very sensitive: spacial summation of subthreshold impulses
Cone:
P- 3 types of iodopsin
A- high res: 1 cone cell synapses with 1 bipolar neuron = no retinal convergence
C- tricolour: red, green, blue wavelengths absorbed by different types of iodopsin
L- less sensitive: not involved in night vision

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17
Q

Outline the pathway of light from a
photoreceptor to the brain.

A

photoreceptor → bipolar neuron →
ganglion cell of optic nerve → brain

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18
Q

Define myogenic.

A

Contraction of heart is initiated within the
muscle itself rather than by nerve
impulses.

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19
Q

State the name and location of the 2
nodes involved in heart contraction.

A

• Sinoatrial node (SAN): within the wall of the
right atrium.
• Atrioventricular node (AVN): near lower end
of right atrium in the wall that separates the
2 atria.

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20
Q

Describe how heartbeats are initiated
and coordinated.

A
  1. SAN initiates wave of depolarisation (WOD).
  2. WOD spreads across both atria= atrial systole.
  3. Layer of fibrous, non-conducting tissue delays impulse
    while ventricles fill & valves close.
  4. AVN conveys WOD down septum via Bundle of His, which
    branches into Purkinje fibres along ventricles.
  5. Causes ventricles to contract from apex upwards.
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21
Q

State the formula for cardiac output

A

cardiac output (CO)

stroke volume (V) x heart rate (R)

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22
Q

What is the autonomic nervous system?

A

• System that controls involuntary
actions of glands and muscles.
• 2 subdivisions: sympathetic &
parasympathetic.

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23
Q

State the difference between the
sympathetic and parasympathetic
nervous system.

A

Sympathetic involved in ‘fight or flight’ response:
stimulates effectors to speed up activity.
Parasympathetic involved in normal resting
conditions: inhibits effectors to slow down
activity.

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24
Q

Name the receptors involved in changing
heart rate and state their location.

A

Baroreceptors (detect changes in blood
pressure): carotid body.
Chemoreceptors (detect changes in pH e.g.
due to increase in CO2
concentration): carotid
body & aortic body.

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25
Q

How does the body respond to an
increase in blood pressure?

A
  1. Baroreceptors send more impulses to
    cardioinhibitory centre     in the medulla oblongata.
  2. More impulses to SAN down vagus nerve via
    parasympathetic nervous system.
  3. Stimulates release of acetylcholine, which
    decreases heart rate.
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26
Q

How does the body respond to a
decrease in blood pressure?

A
  1. Baroreceptors send more impulses to
    cardioacceleratory centre     in the medulla oblongata.
  2. More impulses to SAN via sympathetic nervous
    system    .
  3. Stimulates release of noradrenaline, which increases
    heart rate and strength of contraction.
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27
Q

How does the body respond to an
increase in CO2
concentration?

A
  1. Chemoreceptors detect pH decrease and send more
    impulses to cardioacceleratory centre     of medulla
    oblongata    .
  2. More impulses to SAN via sympathetic nervous system.
  3. Heart rate increases, so rate of blood flow to lungs
    increases = rate of gas exchange and ventilation rate
    increase.
28
Q

Describe the general structure of a motor
neuron.

A

Cell body: contains organelles & high proportion of
RER.
Dendrons: branch into dendrites which carry
impulses towards cell body.
Axon: long, unbranched fibre carries nerve impulses
away from cell body.

29
Q

Describe the additional features of a
myelinated motor neuron.

A

• Schwann cells: wrap around axon many times.
•** Myelin sheath: made from myelin-rich membranes of
Schwann cells.
• Nodes of Ranvier**: very short gaps between
neighbouring Schwann cells where there is no myelin
sheath.

30
Q

Name 3 processes Schwann cells are
involved in.

A

• electrical insulation
• phagocytosis
• nerve regeneration

31
Q

How does an action potential pass along
an unmyelinated neuron?

A
  1. Stimulus leads to influx of Na+ ions. First section of
    membrane depolarises.
  2. Local electrical currents cause sodium voltage-gated
    channels further along membrane to open.
    Meanwhile, the section behind begins to repolarise.
  3. Sequential wave of depolarisation.
32
Q

Explain why myelinated axons conduct
impulses faster than unmyelinated
axons.

A

Saltatory conduction: Impulse ‘jumps’ from one
node of Ranvier to another. Depolarisation cannot
occur where myelin sheath acts as electrical
insulator.
So impulse does not travel along whole axon length.

33
Q

What is resting potential?

A

Potential difference (voltage) across
neuron membrane when not stimulated
(-50 to -90 mV, usually about -70 mV in
humans).

34
Q

How is resting potential established?

A
  1. Membrane is more permeable to K+
    than Na+
    .
  2. Sodium-potassium pump actively transports
    3Na+
    out of cell & 2K+
    into cell.
    Establishes electrochemical gradient: cell contents
    more negative than extracellular environment.
35
Q

Name the stages in generating an action
potential.

A
  1. Depolarisation
  2. Repolarisation
  3. Hyperpolarisation
  4. Return to resting potential
36
Q

What happens during depolarisation?

A
  1. Stimulus→facilitated diffusion of Na+
    ions into cell
    down electrochemical gradient.
  2. p.d. across membrane becomes more positive.
  3. If membrane reaches threshold potential (-50mV),
    voltage-gated Na+
    channels open.
  4. Significant influx of Na+
    ions reverses p.d. to
    +40mV.
37
Q

What happens during repolarisation?

A
  1. Voltage-gated Na+
    channels close and
    voltage-gated K+
    channels open.
  2. Facilitated diffusion of K+
    ions out of cell
    down their electrochemical gradient.
  3. p.d. across membrane becomes more
    negative.
38
Q

What happens during hyperpolarisation?

A
  1. ‘Overshoot’ when K+
    ions diffuse out = p.d.
    becomes more negative than resting potential.
  2. Refractory period: no stimulus is large enough to
    raise membrane potential to threshold.
  3. Voltage-gated K+
    channels close &
    sodium-potassium pump re-establishes resting
    potential.
39
Q

Explain the importance of the refractory
period.

A

No action potential can be generated in
hyperpolarised sections of membrane:
• Ensures unidirectional impulse
• Ensures discrete impulses
• Limits frequency of impulse transmission

40
Q

What is the ‘all or nothing’ principle?

A

Any stimulus that causes the membrane
to reach threshold potential will generate
an action potential.
All action potentials have same
magnitude.

41
Q

Name the factors that affect the speed of
conductance.

A

• Myelin sheath
• Axon diameter
• Temperature

42
Q

How does axon diameter affect the
speed of conductance?

A

greater diameter = faster
• Less resistance to flow of ions
(depolarisation & repolarisation).
• Less ‘leakage’ of ions (easier to maintain
membrane potential).

43
Q

How does temperature affect speed of
conductance?

A

Higher temperature = faster
• Faster rate of diffusion (depolarisation & repolarisation).
• Faster rate of respiration (enzyme-controlled) = more ATP
for active transport to re-establish resting potential.
Temperature too high = membrane proteins denature.

44
Q

Suggest an appropriate statistical test to
determine whether a factor has a
significant effect on the speed of
conductance.

A

Student’s t-test (comparing means of
continuous data)

45
Q

Suggest appropriate units for the
maximum frequency of impulse
conduction.

A

Hz

46
Q

How can an organism detect the strength
of a stimulus?

A

Larger stimulus raises membrane to
threshold potential more quickly after
hyperpolarisation = greater frequency of
impulses.

47
Q

What is the function of synapses?

A

• Electrical impulse cannot travel over junction
between neurons.
• Neurotransmitters send impulses between
neurons/ from neurons to effectors.
• New impulses can be initiated in several
different neurons for multiple simultaneous
responses.

48
Q

Describe the structure of a synapse.

A

Presynaptic neuron ends in synaptic knob: contains
lots of mitochondria, endoplasmic reticulum &
vesicles of neurotransmitter.
synaptic cleft: 20-30 nm gap between neurons.
Postsynaptic neuron: has complementary receptors
to neurotransmitter (ligand-gated Na+
channels).

49
Q

Outline what happens in the presynaptic
neuron when an action potential is
transmitted from one neuron to another.

A
  1. Wave of depolarisation travels down presynaptic neuron,
    causing voltage-gated Ca2+ channels to open.
  2. Vesicles move towards & fuse with presynaptic
    membrane.
  3. Exocytosis of neurotransmitter into synaptic cleft.
50
Q

How do neurotransmitters cross the
synaptic cleft?

A

Via simple diffusion

51
Q

Outline what happens in the postsynaptic
neuron when an action potential is
transmitted from one neuron to another.

A
  1. Neurotransmitter binds to specific receptor on
    postsynaptic membrane.
  2. Ligand-gated Na+
    channels open .
  3. If influx of Na+
    ions raises membrane to
    threshold potential, action potential is generated.
52
Q

Explain why synaptic transmission is
unidirectional.

A

Only presynaptic neuron contains vesicles
of neurotransmitter & only postsynaptic
membrane has complementary receptors.
So impulse always travels presynaptic →
postsynaptic.

53
Q

Define summation and name the 2 types

A

Neurotransmitter from several sub-threshold
impulses accumulates to generate action potential:
• temporal summation
• spatial summation
NB no summation at neuromuscular junctions.

54
Q

What is the difference between temporal
and spatial summation?

A

**Temporal: one **presynaptic neuron releases
neurotransmitter several times in quick
succession.
Spatial: multiple presynaptic neurons release
neurotransmitter.

55
Q

What are cholinergic synapses?

A

Use acetylcholine as primary neurotransmitter.
Excitatory or inhibitory. Located at:
• Motor end plate (muscle contraction).
• Preganglionic neurons (excitation).
• Parasympathetic postganglionic neurons
(inhibition e.g. of heart or breathing rate).

56
Q

What happens to acetylcholine from the
synaptic cleft?

A
  1. Hydrolysis into acetyl and choline by
    acetylcholinesterase (AChE).
  2. Acetyl & choline diffuse back into presynaptic
    membrane.
  3. ATP is used to reform acetylcholine for storage
    in vesicles.
57
Q

Explain the importance of AChE.

A

• Prevents overstimulation of skeletal
muscle cells.
• Enables acetyl and choline to be
recycled.

58
Q

What happens in an inhibitory synapse?

A
  1. Neurotransmitter binds to and opens Cl-
    channels on postsynaptic membrane & triggers
    K
    + channels to open.
  2. Cl- moves in & K+
    moves out via facilitated
    diffusion.
  3. p.d. becomes more negative: hyperpolarisation.
59
Q

Describe the structure of a
neuromuscular junction.

A

Synaptic cleft between a presynaptic
neuron and a skeletal muscle cell.

60
Q

Contrast a cholinergic synapse and a
neuromuscular junction.

A

Topics: 1- postsynaptic cell 2- AChE location 3- action potential 4- response 5- neurons involved
Cholinergic:
1- another neuron
2- synaptic cleft
3- new action potential produced
4- excitatory or inhibitory
5- motor, sensory or relay
Neuromuscular:
1- skeletal muscle cell
2- postsynaptic membrane
3- end of neural pathway
4- always excitatory
5- only motor

61
Q

How might drugs increase synaptic
transmission?

A

• Inhibit AChE
• Mimic shape of neurotransmitter

62
Q

How might drugs decrease synaptic
transmission?

A

• Inhibit release of neurotransmitter.
• Decrease permeability of postsynaptic
membrane to ions.
• Hyperpolarise postsynaptic
membrane.

63
Q

Name the 3 types of muscle in the body
and where they are located.

A

• Cardiac: exclusively found in heart.
• Smooth: walls of blood vessels and
intestines.
•** Skeletal**: attached to incompressible
skeleton by tendons.

64
Q

What does the phrase ‘antagonistic pair
of muscles’ mean?

A

Muscles can only pull, so they work in
pairs to move bones around joints.
Pairs pull in opposite directions: agonist
contracts while antagonist is relaxed.

65
Q

Describe the gross structure of skeletal
muscle.

A

Muscle cells are fused together to form bundles of
parallel muscle fibres (myofibrils).
Arrangement ensures there is no point of weakness
between cells.
Each bundle is surrounded by endomycium: loose
connective tissue with many capillaries.

66
Q

Describe the microscopic structure of
skeletal muscle.

A

Myofibrils: site of contraction.
Sarcoplasm: shared nuclei and cytoplasm with lots
of mitochondria & endoplasmic reticulum.
Sarcolemma: folds inwards towards sarcoplasm to
form transverse (T) tubules.

Biology Revision (9 decks)

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