Topic 8A - Responding to the Environment

Question 1

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

Answer 1

• 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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

• 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

Question 4

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

Answer 4

closed

Question 5

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

Answer 5

open

Question 6

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

Answer 6

closed

Question 7

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

Answer 7

open

Question 8

Describe the resting potential of the axon membrane

Answer 8

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

Question 9

At what potential difference is an action potential produced

Answer 9

+30mV

Question 10

At what potential difference is the threshold for depolarisation

Answer 10

-55mV

Question 11

At what potential difference is the resting potential at?

Answer 11

-70mV

Question 12

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

Answer 12

more

Question 13

State 3 factors that affect the speed of nerve transmission

Answer 13

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

Question 14

Describe saltatory conduction

Answer 14

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.

Question 15

What causes flowering in plants

Answer 15

phytochromes

Question 16

Describe Pfr

Answer 16

Pfr is the active form and absorbs far red light

Question 17

Describe Pr

Answer 17

Pr is the inactive form and absorbs red light

Question 18

What does a high proportion of Pfr represent

Answer 18

a longer day, shorter night

Question 19

What does a high proportion of Pr represent

Answer 19

a shorter day, longer night

Question 20

If Pr absorbs red lights what does it convert into

Answer 20

Pfr

Question 21

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

Answer 21

It will inhibit flowering

Question 22

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

Answer 22

It will inhibit flowering

Question 23

In shoots, does IAA promote or inhibit growth?

Answer 23

promote

Question 24

In roots, does IAA promote or inhibit growth?

Answer 24

inhibit

Question 25

Describe the process of phototropism in shoots

Answer 25

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

Question 26

Describe the process of phototropism in roots

Answer 26

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

Question 27

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)

Answer 27

- 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

Question 28

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

Answer 28

- 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

Question 29

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

Answer 29

- 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

Question 30

Name one hormone and state its function.

Answer 30

Testosterone, stimulates sperm production

Question 31

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

Answer 31

- 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

Question 32

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

Answer 32

- 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

Question 33

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

Answer 33

- inhibits the reabsorbtion of seratonin into the pre-synaptic membrane from the synapse - increasing levels of seratonin

Question 34

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)

Answer 34

to mimic parkinson's disease

Question 35

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

Answer 35

- 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

Question 36

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

Answer 36

retinal

Question 37

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

Answer 37

opsin

Question 38

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

Answer 38

cerebellum

Question 39

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

Answer 39

- 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

Question 40

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

Answer 40

- 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

Question 41

What is tropical

Answer 41

The response of a plant to a directional stimulus

Question 42

Why do plants and animals need to responde to stimulus

Answer 42

To increase their chances of survival