Chapter 15: Control and co-ordination

Question 1

what are the nervous and endocrine systems two examples of?

Answer 1

communication systems. They respond to changes in internal and external environments

Question 2

what is the node of Ranvier?

Answer 2

the gap between two Schwann cells.

Question 3

in which direction does the conduction of a nerve impulse travel?

Answer 3

from the cell body to the terminal branches

Question 4

describe the function of sensory receptor cells

Answer 4

• detect changes in their surroundings

- energy transducers: they convert energy into different forms

Question 5

give an example of a sensory receptor cell

Answer 5

Pacinian corpuscles- they detect pressure changes in the skin

Question 6

describe the action of Na/K pumps

Answer 6

• 3x Na moved OUT
• 2x K moved IN
• the inside of the axon is more negative than the outside so the cell membrane is polarised

Question 7

define ‘polarised membrane’

Answer 7

a membrane with a potential difference across it

Question 8

define ‘depolarisation’

Answer 8

the loss of polarisation across a membrane

Question 9

define ‘generator potential’

Answer 9

a small depolarisation caused by Na+ entering the cell

Question 10

what is the ‘refractory period’?

Answer 10

the period after each action potential where it is impossible to stimulate the cell membrane to reach another action potential

Question 11

what is the purpose of the refractory period?

Answer 11

it ensures that action potentials are only transmitted in one direction

Question 12

how are action potentials transmitted?

Answer 12

• the temporary depolarisation causes a ‘local circuit’ between the depolarised and resting regions
• these local circuits depolarise and create APs in adjoining regions

Question 13

what are the consequences of the refractory periods?

Answer 13

• action potentials do not merge
• there is a minimum time between action potentials
• the length of the refractory period determines the frequency of impulses

Question 14

compare the speed of impulses in myelinated vs non-myelinated cells

Answer 14

myelinated = 100-120 ms-1
non-myelinated = 2-20 ms-1

Question 15

how does myelin speed up the rate?

Answer 15

• insulates the axon
• Na+/K+ cannot flow through the sheath
• action potentials can only occur in the nodes of Ranvier
• local circuits exist between nodes, so APs ‘jump’ to nodes

Question 16

define ‘saltatory conduction’

Answer 16

• the propagation of action potentials along myelinated axons from one node to the next

Question 17

what is contained within the pre-synaptic knob?

Answer 17

• mitochondria
• smooth ER
• vesicles containing acetylcholine
• voltage-gated Ca2+ ion channels

Question 18

describe the Na+ channels in the post-synaptic knob

Answer 18

• 5x polypeptide molecules
• 2x molecules have a receptor specific to acetylcholine
• it fits in the receptor
• this stimulates the Na+ channels to open

Question 19

how is the signal transmitted across the synapse?

Answer 19

• AP arrives at knob and Ca2+ channels open
• Ca2+ diffuses into knob, causing vesicles to move to and fuse with the presynaptic membrane
• acetylcholine is released by exocytosis
• acetylcholine molecules diffuse across cleft and bind to Na+ channels
• Na+ channels open and Na+ diffuses into neurone
• generator potential is created. A threshold potential is reached, so a new action potential is generated in the post-synaptic neurone

Question 20

describe acetylcholinesterase

Answer 20

• found in synaptic cleft
• hydrolyses acetylcholine –> ethanoic acid + choline
• stops the transmission of APs
• the products are recycled and recombined using ATP

Question 21

how do muscles contract?

Answer 21

• tropomyosin and troponin on the actin prevents myosin from binding
• upon muscle contraction, they change shape and the myosin heads can bind to actin
• the myosin heads tilt and pull the actin. The muscle contracts
• ATP hydrolysis causes the release of myosin heads

Question 22

describe the roles of the synapses

Answer 22

• ensure one-way transmission
• allow integration of impulses (the brain is not overloaded)
• allow the interconnection of pathways

Question 23

what are the T-tubules?

Answer 23

deep infoldings into the interior of the muscle

Question 24

describe the structure of a microfibril

Answer 24

made of two filaments:

• thick = myosin
• thin = actin

Question 25

describe the structure of myosin

Answer 25

• fibrous protein
• globular head
• the molecules line up with their globular heads all pointing away from the M line

Question 26

describe the structure of actin

Answer 26

• globular protein
• link together to form a chain
• tropomyosin is twisted around the actin
• troponin is attached to the actin at regular intervals

Question 27

describe the adaptations of a venus flytrap

Answer 27

• stimulation of a single hair does not result in closure

- the gaps between the hairs allow small, unwanted insects to crawl out

Question 28

describe how auxins control growth

Answer 28

• stimulates cells to pump H+ into the cell wall
• the cell walls are acidified
• bonds between cellulose fibres and the matrix weaken
• the cells can absorb water, so stretch

Question 29

describe how the height of plants is partially controlled by genes

Answer 29

• Le (dominant allele) = tall
• le (recessive allele) = short
• Le codes for a functioning enzyme in the gibberellin synthesis pathway

Question 30

describe how seeds germinate

Answer 30

• water uptake into the seed
• embryo synthesises gibberellin in response to water uptake
• aleurone layer synthesises amylase in response to gibberellin