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A-LEVEL-Biology-Edexcel A > Topic 8A - Responding to the Environment > Flashcards

Topic 8A - Responding to the Environment Flashcards

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1
Q

EQ. Explain the electrical changes in an axon that allow nerve impulses to be detected. (4 marks)

A
  • the potential difference of the axon changes
  • as sodium channel open
  • sodium ions enter the axon membrane
  • this is depolarisation
  • as sodium channels close and potassium channels open
  • potassium leaves the cell membrane during repolarisation
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2
Q

How does a sensory neurone structurally differ from motor and relay neurones

A

In a sensory neurone the cell body is in the middle of the axon

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3
Q

EQ. Explain why there is a difference in the conduction velocity of a myelinated neurone and a unmyelinated neurone. (5 marks)

A
  • schwann cells wrap around the axon to create a myelin sheath
  • this is an insulator as its impenetrable to Na+ and K+ ions
  • depolarisation occurs at the nodes of ranvier
  • electrical impulse jumps from node to node
  • this is called saltatory conduction
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4
Q

During depolarisation, are the K+ channels open or closed?

A

closed

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5
Q

During depolarisation, are the Na+ channels open or closed?

A

open

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6
Q

During repolarisation, are the Na+ channels open or closed?

A

closed

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7
Q

During repolarisation, are the K+ channels open or closed?

A

open

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8
Q

Describe the resting potential of the axon membrane

A

At rest, the inside of the axon membrane is more negatively charged than the outside

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9
Q

At what potential difference is an action potential produced

A

+30mV

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10
Q

At what potential difference is the threshold for depolarisation

A

-55mV

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11
Q

At what potential difference is the resting potential at?

A

-70mV

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12
Q

During hyperpolarisation, does the potential difference become more or less negative than the resting potential

A

more

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13
Q

State 3 factors that affect the speed of nerve transmission

A
  • myelination increases speed cuz of saltatory conduction
  • higher temperature increases speed
  • larger surface area
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14
Q

Describe saltatory conduction

A

When action potentials jump from node to node (node of Ranvier). This is because the axon is myelinated and wrapped in Schwann cells, making it impenetrable to Na+ and K+ ions.

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15
Q

What causes flowering in plants

A

phytochromes

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16
Q

Describe Pfr

A

Pfr is the active form and absorbs far red light

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17
Q

Describe Pr

A

Pr is the inactive form and absorbs red light

18
Q

What does a high proportion of Pfr represent

A

a longer day, shorter night

19
Q

What does a high proportion of Pr represent

A

a shorter day, longer night

20
Q

If Pr absorbs red lights what does it convert into

A

Pfr

21
Q

In short day plants, what effect will Pfr have on flowering

A

It will inhibit flowering

22
Q

In long day plants, what effect will Pr have on flowering

A

It will inhibit flowering

23
Q

In shoots, does IAA promote or inhibit growth?

A

promote

24
Q

In roots, does IAA promote or inhibit growth?

A

inhibit

25
Q

Describe the process of phototropism in shoots

A

Shoots are positively phototropic. So IAA is transported to the more shady parts, promoting growth and causing it to elongate towards the light.

26
Q

Describe the process of phototropism in roots

A

Roots are negatively phototropic. So IAA is transported to the more shady parts, inhibiting growth causing it to grow away from the light

27
Q

EQ. Explain how the structure of the cell surface membrane of a motor neurone is related to the conduction of a nerve impulse along its axon. (6 marks)

A
  • the membrane is made out of a phospholipid bilayer
  • with the hydrophobic tails facing inwards to inhibit the movement of charged particles across the membrane
  • there are protein channels like Na+ channels
  • to allow Na+ to diffuse during depolarisation
  • and K+ channels
  • to allow K+ to diffuse during repolarisation
  • theres a sodium-potassium pump
  • to export Na+ and take in K+
  • in saltatory conduction only the nodes of Ranvier will be used since the action potential jumps from node to node
28
Q

EQ. Suggest an explanation for how eugenol affects the movement of calcium ions and reduces pain. (6 marks)

A
  • because less Ca2+ channels will be open
  • less Ca2+ ions will diffuse into the pre-synaptic membrane
  • less vesicles carrying neurotransmitters will fuse with the pre-synaptic membrane
  • so less neurotransmitters will be released into the synaptic cleft
  • less neurotransmitter will bind to the receptors on the post-synaptic membrane
  • pain will not be sensed as the impulse will be stopped before leaving the senory neurone
29
Q

EQ. Explain how myelination increases the speed of transmission of nerve impulses in a sensory neurone. (5 marks)

A
  • when myelinated, sensory neurones are covered in schwann cells
  • this acts as an electrical insulator making it impenetrable to Na+ and K+ ions so no depolarisation can occur
  • however at the nodes of Ranvier theres no myelination -so depolarisation can occur at the nodes
  • the impulse jumps from node to node
  • this is called saltatory conduction
30
Q

Name one hormone and state its function.

A

Testosterone, stimulates sperm production

31
Q

EQ. Describe and explain the sequence of events that occurs at the synapse, after a neurotransmitter has been released. (5 marks)

A
  • neurotransmitters diffuse across the synaptic gap
  • they bind to receptors on the post-synaptic membrane
  • Na+ channels open, allowing Na+ ions to diffuse into the post-synaptic membrane
  • causing depolarisation
  • and therefore a action potential is produced
  • neurotransmitters are broken down by enzymes
  • and reabsorbed through the pre-synaptic membrane
32
Q

EQ. Explain why L-Dopa is used to treat people with Parkinson’s disease. (2 marks)

A
  • can convert to dopamine in the brain
  • and increase dopamine levels in the brain
  • can reduce symptoms of parkinson’s disease because they have low dopamine levels
33
Q

EQ. Explain how MDMA could affect levels of serotonin in the brain. (3 marks)

A
  • inhibits the reabsorbtion of seratonin into the pre-synaptic membrane from the synapse
  • increasing levels of seratonin
34
Q

EQ. In trials of this treatment, marmosets (small monkeys) were given a drug to reduce dopamine production. Suggest a reason why the marmosets were treated with a drug to reduce dopamine production. (1 mark)

A

to mimic parkinson’s disease

35
Q

EQ. Describe the steps that would need to be taken before a similar treatment could be used in humans. (3 marks)

A
  • test a small sample of healthy individuals for safety
  • test a large sample of patients for effectiveness
  • can use a double blind trial
  • where neither doctor or patient know whose been giving a drug or a placebo
36
Q

What is the non-protein part of the light-absorbing pigment in the rod cells of the retina called?

A

retinal

37
Q

What is the protein part of the light-absorbing pigment in the rod cells of the retina called?

A

opsin

38
Q

Name the part of the brain involved in interpreting the info processed in the visual cortex

A

cerebellum

39
Q

EQ. Describe the role of visual stimulation on the development of the visual cortex during the critical period. (3 marks)

A
  • ocular dominance columns develop in the visual cortex
  • neurones form synapses with these columns
  • stimuli is required to strengthen connections with the columns of ocular dominance in the visual cortex in the critical period
40
Q

EQ. What is the role of dendrites. (3 marks)

A
  • dendrites receive electrical impulses from other neurones
  • dendrites interconnect multiple neurones allowing them to send electrical impulses
  • it initiates an action potential to the axon
41
Q

What is tropical

A

The response of a plant to a directional stimulus

42
Q

Why do plants and animals need to responde to stimulus

A

To increase their chances of survival

A-LEVEL-Biology-Edexcel A (22 decks)

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