14.Response To Stimuli

Question 1

What is phototropism

Answer 1

Directional movement to unilateral light, shoot tip bends towards light due to IAA moving moving to the shaded side of the shoot top, cells on shaded side elongate faster than those on light side, so top bends towards light

Question 2

What is gravitrophism

Answer 2

Directional to gravity, root tip bends downwards due to IAA moving to lower side, IAA inhibits the cells elongation so those on top side elongate faster and so tip bends downwards

Question 3

What is IAA

Answer 3

Auxin - hormone produced by frowning shoot and root tips

Question 4

What were Darwin’s experiments

Answer 4

Normal plant shoot
Shoot tip removed
Lightproof cover on tip

Question 5

What was boysens-jensons experiments

Answer 5

Thin impermeable mica inserted in sunny side of tip - tip bends same away and hormone can pass down to shaded side

Mica inserted on shaded side-tip doesn’t bend as movement of IAA prevented down shaded side

Tip removed and gelatin block placed between-gelatin allowed movement of chemicals to pass through it, bending must be due to chemical passing from tip

Question 6

What was Paals experiment

Answer 6

Removed tip and placed to one side of shoot-shoots bend towards the side where no tip is present

Question 7

What was Briggs experiment

Answer 7

Put shoot in darkness

Thin glass plate between two sides of shoot-amount or IAA is same on either side of plate as chemical can’t move across

Glass plate half way up shoot, not through tip-shoot bends towards light as chemical can move to shaded side

Question 8

What is a stimulus

Answer 8

Detectable change in the internal or external environment of an organism that leads to a response in the organism

Question 9

What are receptors

Answer 9

Specific to one type of stimulus

Question 10

What’s an effector

Answer 10

What produced the response

Question 11

What’s the sequence of nervous system

Answer 11

Stimulus 
Receptor
Sensory
Coordinator
Motor
Effector
Response

Question 12

What’s a taxis

Answer 12

Simple response whose direction is determined by the direction of stimulus as result motile organism response directly to environs changes by moving whole body either towards favourable stimulus or away from unfavourable one.

Question 13

What’s a kineses

Answer 13

Form of response in which organism doesn’t move towards or away from stimulus, changes speed at which it moves and rate at which it changes direction
If organism crosses from favourable to unfavourable area it’s turning rate increases

Question 14

What’s a tropism

Answer 14

Growth part of a plant in response to directional stimulus.
Shoot tips positive phototropism
Root tips positive gravitropism

Question 15

What are the external stimulus plants respond to

Answer 15

Light - need for photosynthesis

Gravity - need to be firmly anchored

Water - to absorb for support, metabolic processes and photosynthesis

Question 16

What’s an example of a plant growth factor

Answer 16

IAA - indolescetic acid

Type of auxin

Question 17

What does IAA do to shoot tips

Answer 17

IAA moves to shaded side of shoot

Greater conc of IAA builds up on shaded side than light side

IAA causes elongation of shoot cells and as there’s greater concern on shaded side, shaded side cells elongate more

Shaded side of shoot elongates faster than light side causing it to bend towards light

Question 18

What does IAA do to root tips

Answer 18

Gravity influences IAA to build up on lower side of tip

Greater conc on lower side

IAA inhibits elongation of root cells

Greater conc on lower side, cells elongate less than those on top side of root

Causing root to bend downwards towards force of gravity

Question 19

What are the major divisions of the nervous system

Answer 19

Central nervous system - brain spinal chord

Peripheral nervous system - pairs of nerves originate from brain or spinal chord

Question 20

What is the peripheral nervous system split into

Answer 20

Sensory neurones-impulse from receptor to cns

Motor neurones-impulse away from cns to effectors

Question 21

What’s the further split of the motor neurone nervous systems

Answer 21

Voluntary- nerve impulse to body muscles and under conscious control

Autonomic-nerve impulses to glands,smooth muscle and cardiac muscle under unconscious control

Question 22

What’s the spinal chord made of

Answer 22

Column of nervous tissue run alongside back and lies inside vertebral column for protection

Emerging at intervals along spinal chord are pairs of nerves

Question 23

What’s the steps of a reflex arc

Answer 23

Stimulus 
Receptor
Sensory neurone 
Coordinate/intermediate 
Motor 
Effector
Response

Question 24

What is a reflex arc

Answer 24

Rapid short lived response that’s localised and involuntary

Question 25

Whata the importance of reflex arcs

Answer 25

- involuntary, don’t require decision making powers of brain-leaving it free to carry out more complex responses-brain not overloaded-some go to brain to be overridden if needed - protect body from harm- not learnt - fast- neurone pathway short and don’t have lots of synapses which slow transmission - absence of decisions means action rapid

Question 26

What does a pacinian corpuscle detect

Answer 26

Changes in mechanical pressure

Question 27

What does a pacinian corpuscle do

Answer 27

Response to mechanical pressure and produces a generator potential by acting’s as a transducer

Question 28

What is a generator potential

Answer 28

Receptors convert energy of stimulus into nervous impulse

Question 29

What’s the structure of pacinian corpuscle

Answer 29

Sensory Neurone that ends in layers of connective tissue that has viscous gel between Sensory neurone ending has special type of sodium channels in its plasma membrane-stretch mediated sodium channels.

Question 30

How does the Pacinian corpuscle function

Answer 30

- in resting state stretch mediated challenge too narrow to allow sodium ions to diffuse through, has resting potential - when pressure applied to pacinian corpuscle, it’s deformed and membrane and neurone becomes stretched - widens sodium channels and na+ diffuse into neurone - influx of sodium ions changes membrane potential and it becomes depolarised producing generator potential - generator potential creates action potential and that propagates along neurone

Question 31

What are the two types of receptors in a mammalian eye

Answer 31

Rod and cones

Question 32

Difference between cone cells and rod cells

Answer 32

Rod shaped / cone shaped More / less More at periphery / concentrated at fovea Poor visual acuity / give visual acuity Sensitive to low intensity / not sensitive to low intensity One type / three types for different wavelength

Question 33

How does a rod cell act as a transducer

Answer 33

Conserve light energy into the electrical energy of a nerve impulse Pigments in rod cell must be broken by light in order for this to happe

Question 34

What’s a cone cells job in the eye

Answer 34

- Contain different pigment which requires higher intensity light to break it down and create generator potential - each cone cell specific range of wavelengths - each has own connection to bipolar cells so if two adjacent cone cells stimulated brain receives two impulses, two dots can be resolved

Question 35

What’s the distribution of rod n cone cells

Answer 35

Uneven - Light focused by lens on part part of retina opposite pupil-fovea - fovea receives highest internist, cone cells found at fovea - conc of cone cells diminish further away from fovea - at peripheries of retina only rod cells found

Question 36

What’s the importance of having different light receptors

Answer 36

Both respond to different stimuli | Mammals benefit form good all round vision day n night

Question 37

Why are the types of autonomic nervous systems

Answer 37

Sympathetic-stimulates effectors, speed up activity (heightens awareness - fight or flight) Parasympathetic-inhibits effectors and slow down activity, controls under normal resting conditions, conserve energy

Question 38

How in heart rate controlled

Answer 38

- wave of electrical excitation spread out from sinoatrial node across both atria-contract - layer of non/conductive tissue prevents wave crossing to ventricles - wave of excitation enters atrioventricular node - atrioventricular node after short delay conveys wave of excitation along bundle of his to purkyne tissue fibres - bundle of his conducts wave through atrioventricular septum to base of ventricles - wave of electrical excitation released and moved up from base, ventricles contract from bottom upwards simultaneously

Question 39

How is heart rate modified

Answer 39

- Medulla oblongata - sympathetic nervous system which increases HR which is linked to sinoatrial node - parasympathetic nervous system which decreased heart rate which linked to sinoatrial node

Question 40

How do chemoreceptors control heart rate

Answer 40

- found in wall or carotid arteries - when blood has higher conc of carbon dioxide, pH lowers - chemoreceptors detect this and increase frequency of impulse to medulla oblongata - increases frequency of impulses via sympathetic system to sinoatrial node, increasing procession of electrical waves and therefore increase HR - increases blood flow leads to more carbon dioxide being removed by lungs - pH roses to normal and chemoreceptors reduce their frequency of nerve impulses to medulla oblongata - therefore medulla oblongata reduces frequency of impulses to sinoatrial node and leads to recursion in HR

Question 41

How is heart rate controlled by pressure receptors

Answer 41

-when blood pressure higher, pressure receptions transmit more nervous impulses to centre in medulla oblongata that decreased HR, centre sends impulses via parasympathetic system to sinoatrial node which leads to decrease in rate of heart beat

Question 42

Why is the pigment in cone cells

Answer 42

iodopsin