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A Level > Biology: Organisms respond to changes in their environments > Flashcards

Biology: Organisms respond to changes in their environments Flashcards

1
Q

state the order of the reflex arc

A

stimulus, receptor, coordinator, effector.

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2
Q

what is a kinetic response?

A
  • movement of whole organisms
  • alteration in the rate of movement
  • rate changes in response to the intensity of a stimulus
  • non-directional
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3
Q

what is a tactic response?

A
  • movement of entire organism/cell.
  • in respose to and directed by stimulus.
  • positive taxis (moving towards) or negative taxis (moving away)
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4
Q

what is a tropic response?

A
  • movement of a part of a plant
  • directed by stimulus
  • growth response
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5
Q

where is IAA made in a plant?

A

the tip

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6
Q

what does IAA cause?

A

cell elongation

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7
Q

what happens when one side of a plant faces light?

A
  • tip of the plant produces more IAA
  • IAA travels to the shaded side
  • stimulates growth, cells elongate and this causes the shoot to bend towards the light
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8
Q

what does the central nervous system consist of?

A

brain and spinal cord

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9
Q

what is the PNS (periphery nervous system)?

A

pairs of nerves travelling from the CNS to nerves and organs

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10
Q

what is the order in which electrical impulses travel through neurones?

A

sensory, relay, motor

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11
Q

what is the sympathetic nervous system responsible for?

A

it stimulates effectors to speed up any activity`

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12
Q

what is the parasympathetic nervous system responsible for?

A

inhibits effectors to slow down activity

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13
Q

which part of the brain is responsible for subconscious activities such as heart rate?

A

medulla oblongata

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14
Q

what are the 2 centres of the medulla oblongata?

A
  • centre that increases heart rate

- centre that decreases heart rate

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15
Q

how is co2 level in the blood regulated?

A
  • more co2 makes the blood acidic
  • chemoreceptors in the carotid arteries detect the change and increase the frequency of nervous impulses to the medulla oblongata.
  • this centre increases the frequency of impulses via the symphatetic nervous system to the SAN.
  • this increases the frequency of electrical impulses sent by the SAN, increasing heart rate.
  • this leads to more co2 being removed by the lungs.
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16
Q

how is blood pressure regulated?

A
  • HIGHER THAN NORMAL: pressure receptors transmit impulses to the centre of the medulla oblongata which reduces heart rate. this sends impulses via the parasympathetic nervous system to the SAN, decreasing heart rate.
  • LOWER THAN NORMAL: pressure rceptors transmit nervous impulses to the centre of the medulla oblongata which increases heart rate. this sends impulses via the sympathetic nervous system to the SAN, increasing heart rate.
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17
Q

which receptors can be found in the eye?

A

rod cells, cone cells

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18
Q

what are the characteristics of rod cells and what are they responsible for?

A
  • it only requires low intensity light to break down the pigments within these cells, this allows animals with many rod cells to see in the dark.
  • it cannot distinguish between different wavelengths of light so the image produced is in black and white.
  • low visual acuity
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19
Q

what are the characteristics of cone cells and what are they responsible for?

A
  • 3 different types, each responding to different wavelengths of light.
  • only respond to high light intensity, this is because the stimulation of a number of cone cells cannot exceed the threshold value and create a generator potential. it requires high-intensity light to break down iodopsin.
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20
Q

What are neurons?

A
  • highly specialised cells
  • adapted to rapidly carry electrochemical charges
  • amongst the largest cells in the body.
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21
Q

name the 3 types of neurone and their function.

A
  • Sensory neurone: transmit impulses from a receptor to an intermediate/motor neurone.
  • motor neurone: transmit nervous impulses from a relay neurone to an effector, such as a gland or muscle.
  • relay neurons: transmit impulses between neurons.
22
Q

list the components of a motor neurone and their functions.

A
  • cell body: contains all usual cell organelles.
  • dendrons: contains dendrites which carry impulses towards the cell’s body.
  • axon: a single long fibre, carried impulses away from cell body.
  • schwann cells: protect the axon and provide insulation.
  • myelin sheath: forms a covering around the axon.
  • nodes of ranvier: connect adjacent schwann cells
23
Q

What is a resting potential in an axon?

A
  • 65 mV

- outside positive, inside negative

24
Q

What is an action potential in an axon?

A

40mV

-outside negative, inside positive.

25
Q

How is an action potential formed?

A
  • a stimulus causes sodium channels in the axon to open.
  • this causes an influx of sodium into the axon, this happens by diffusion.
  • the positive sodium ions increase the voltage inside the axon, acting as a stimulus and causing more voltage-gated sodium channels to open.
  • membrane potential is increased to 40mV.
  • this is called depolarisation.
26
Q

how is a resting potential formed from an action potential?

A
  • potassium channels open so potassium diffuses out of the cell.
  • this decreases the voltage inside the axon.
  • potassium leaving the axon acts as a stimulus, causing more to open.
  • instead of stopping at -65mV, it overshoots and goes to -70mV. This is called hyperpolarization.
  • the sodium potassium pump starts again to return it to resting potential
27
Q

Explain the process of salutatory conduction.

A
  • sodium channels in the axon open, causing sodium to diffuse in.
  • this causes an action potential.
  • sodium ions diffuse along their chemical gradient.
  • voltage gated channels open and more sodium diffuses in.
  • the action potential continues to move along the axon. this action potential jumps from node to node.
28
Q

how does myelination effect the speed of conduction?

A
  • myelination provides insulation.
  • insulation means no ATP has to be produced for active transport.
  • ATP production takes time, insulation means that this doesn’t happen, increasing the speed of conduction.
29
Q

how does axon diameter effect the speed of conduction?

A

the greater the diameter, the faster the action potential.

30
Q

how does temperature effect the speed of conduction?

A

has an effect on the rate of diffusion of sodium ions. high temperature increases speed of conduction due to more kinetic energy in sodium ions.

31
Q

what is the all-or-nothing principle?

A
  • there’s a certain level of stimulus (threshold value) which must be met in order for an action potential to be triggered.
  • the threshold value must be met for depolarization to happen, forming an action potential
32
Q

how can the threshold value be met more easily?

A
  • larger number of impulses generated in a given time.

- by having different neurones with different threshold values.

33
Q

what is the purpose of the refractory period?

A
  • ensures that action potentials travel in one direction only.
  • ensures that action potentials can’t be formed directly after the one before, keeps them separate.
  • limits the number of action potentials.
34
Q

what are the components of a synapse?

A

synaptic cleft: separates pre and post synaptic cells.
synaptic vesicles: store neurotransmitters
synaptic knob: contains lots of mitochondria and endoplasmic reticulum, manufactures the neurotransmitter.

35
Q

what is spatial summation

A

when a number of presynaptic neurones together release enough neurotransmitter to reach the threshold value.

36
Q

what is temporal summation?

A

when a single presynaptic neurone releases neurotransmitter many times over a short period, reaching the threshold value.

37
Q

how do inhibitory synapses work?

A
  • releases a type of neurotransmitter than binds to the chloride ion protein channels on the postsynaptic neurone.
  • causes chloride ion protein channels to open.,
  • chloride ions move into postsynaptic neurone.
  • binding of the neurotransmitter causes potassium protein channels to open.
  • potassium ions move out of postsynaptic neurone into synapse
  • this makes the inside of the postsynaptic membrane more positive and the outside more positive.
  • the membrane potential increases to as much as -80mV
  • hyperpolarization, less likely for threshold value to be met as it requires more sodium ions to produce one.
38
Q

what is a chorigenic synapse?

A

a synapse where acetylcholine is the neurotransmitter.

39
Q

describe transmission across a chlorigenic synapse.

A
  • action potential arrives at presynaptic neurone, causes calcium ion channels to open, calcium ions enter the presynaptic knob.
  • influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft.
  • acetylcholine binds to receptor sites on sodium channels, causing them to open. sodium diffuses in.
  • influx of sodium ions causes new action potential.
  • acetylcholinesterase hydrolyses acetylcholine into acetyl and choline. this diffuses back into the presynaptic knob.
  • ATP released by mitochondria is used to bind acetyl and choline to make mitochondria.
40
Q

what are the 3 types of muscle and where are they found?

A

cardiac: found exclusively in the heart
smooth: found in the walls of blood vessels and the gut.
skeletal muscle: attached to bone, acts under voluntary control.

41
Q

what are muscle fibres made up of?

A

myofibrils

42
Q

what is the sarcoplasm?

A

a shared ‘cytoplasm’ between muscle fibres that have bound together.

43
Q

what are the 2 types of protein filament found in muscles?

A

actin: thin, consisted of 2 strands twisted around eachother
myosin: thick, rod shaped fibres with bulbous heads

44
Q

what are the 4 bands/zones found in sarcomere? describe each

A

I bands: appear lighter due to non-overlapping actin.
A bands: appear dark as actin and myosin overlap.
H zone: lighter than A band, consists of only myosin
Z line: found in the centre of each I band.

45
Q

where is tropomyosin found?

A

it’s a fibrous strand around the actin filament.

46
Q

what are the 2 types of muscle fibre, describe each.

A

slow twitch: responsible for slow, weak contractions. have lots of blood vessels, myoglobin and mitochondria.

fast twitch: responsible for fast, powerful contractions over shorter periods of time. contains lots of myosin filaments, glycogen, enzymes involved in anaerobic respiration, phosphocreatine to make ATP.

47
Q

what are neuromuscular junctions, describe their structure.

A
  • a point where a motor neurone meets skeletal muscle fibre. there are many junctions across the muscle so it can respond to a number of stimuli and it’s more powerful.
  • when a nerve impulse is sent to a junction, acetylcholine is the neurotransmitter.
48
Q

what is the sliding filament mechanism?

A

actin and myosin filaments sliding past eachother, causing muscle contractions.

49
Q

describe the process of muscle stimulation in terms of the sliding filament mechanism

A
  • an action potential reaches many neuromuscular junctions, calcium channels open and enter the presynaptic knob
  • calcium ions cause vesicles to fuse to the presynaptic membrane, acetylcholine released into synaptic cleft.
  • binds to receptors on muscle cell-surface membrane, causing it to depolarize.
50
Q

describe the process of muscle contraction in terms of the sliding filament mechanism.

A
  • action potential travels deep into muscle fibre through T tubules.
  • T tubules are in contact with the endoplasmic reticulum of the muscle, it’s actively transported calcium from the cytoplasm, low calcium concentration in the cytoplasm.
  • action potential causes calcium channels to open, causes calcium to enter the cytoplasm.
  • calcium ions cause tropomyosin blocking the binding sites on actin to pull away.
  • ADP molecules attached to the myosin heads change angle, pulling the actin filament along and releasing ADP.
  • an ATP molecule attaches to each myosin head, it detaches from the actin filament.
  • calcium ions activate the enzymes ATPase, hydrolyses ATP into ADP and provides energy for the myosin head to return to its normal position.
  • the myosin head reattaches itself further along the actin filament, the process repeats.
51
Q

describe the process of muscle relaxation in terms of the sliding filament mechanism.

A
  • calcium ions return to endoplasmic reticulum

- tropomyosin blocks binding sites

A Level (36 decks)

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