3.6.1 Internal and external stimuli are detected and lead to a response

Question 1

What are plant growth factors and where are they produced

Answer 1

Chemicals that regulate plant growth response directional to stimuli
Produced in plant growing regions (meristems)
Diffuse from cell to cell/phloem mass transport

Question 2

Explain why shoots show positive photoropism
maybe rewrite from notes

Answer 2

1. IAA diffuses to shaded side of shoot tip
2. As IAA diffuses down shaded side, it causes active transport of H+ ions into cell wall
3. Disruption to H-bonds between cellulose molecules and action of expansins make cell more permeable to water
4. Cells on shaded side elongate faster due to higher turgor pressure
5. Shoot bends towards light

Question 3

Explain why roots show positive gravitropism

Answer 3

1. Gravity causes IAA to accumulate on lower side of the root
2. IAA inhibits elongation of root cells
3. Cells on the upper side of the root elongate faster, so the root tip bends downwards

Question 4

Contrast mammalian hormones and plant growth factors (CASTS)

Answer 4

Conc - M(response not always dependent on conc) P(response proportional to conc)
Action - M(bind to comp proteins in/on target cells) P(can affect all cells)
Synthesis - M(specialised glands) P(various tissues in growing regions)
Transport - M(circulatory system) P(diffusion or phloem translocation)
Speed - M(faster acting - homeostasis) P(slower acting - plant growth)

Question 5

Define taxis and kinesis state their advantage

Answer 5

Taxis - directional movement in response to external stimulus
Kinesis - non directional response to presence and intensity of external stimulus
Maintain mobile organism in optimum environment

Question 6

Many organisms respond to temperature and humidity via kinesis rather than taxis, why

Answer 6

Less directional stimuli; often no clear gradient from one extreme to the other

Question 7

How could a student recognise kinesis in an organisms movement

Answer 7

1. Organism crosses sharp division between favourable and unfavourable environment: turning increases
2. If organism moves considerable distance into unfavourable environment: turning slowly decreases, beings to move in long straight lines, sharper turns

Question 8

Outline what happens in a reflex arc

Answer 8

receptor detects stimulus –> sensory neuron –> relay neuron in CNS coordinates response –> motor neuron –> response by effector

Question 9

Give the advantages of a simple reflex arc

Answer 9

1. Rapid response to potentially dangerous stimuli since only 3 neurons involved
2. Instinctive

Question 10

Suggest a suitable statistical test to determine whether a factor has a significant effect on the movement of an animal in a choice chamber

Answer 10

Chi squared

Question 11

What features are common to all sensory receptors

Answer 11

Act as energy transducers which establish a generator potential
Respond to specific stimuli

Question 12

Describe the basic structure of a pacinian corpuscle

Answer 12

Single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
Stretch mediated Na+ channels on plasma membrane
Capillary runs along base layer of tissue

Question 13

What stimulus does a pacinian corpuscle respond to? how?

Answer 13

1. Pressure deforms membrane, causing stretch mediated Na+ ion channels to open
2. If influx of Na+ raises membrane to threshold potential, a generator potential is produced
3. Action potential moves along sensory neuron
4. FIND IF INSIDE OUR OUT MORE NEGATIVE

Question 14

Name the 2 types of photoreceptor cell located in the retina

Answer 14

1. Cone cells
2. Rod cells

Question 15

Where are rod and cone cells located in the retina

Answer 15

Rod - evenly distributed around periphery but not in central fovea
Cone - mainly central fovea no photoreceptors at blind spot

Question 16

Compare and contrast rod and cone cells
PACL

Answer 16

Pigment - R(rhodopsin) C(3 types of iodopsin)
Visual Acuity - R(low res - many rod cells synapse with one bipolar neuron) C(high res - 1 cone cell synapses with 1 bipolar neuron - no retinal convergence)
Colour sensitivity - R(monochromatic - all wavelengths of light detected) C(tricolour - RGB wavelengths absorbed by different types of iodopsin
Light sensitivity - R(V sensitive, spatial summation of subthreshold impulses) C(less sensitive - not involved in night vision)

Question 17

Outline the pathway of light from a photoreceptor to the brain

Answer 17

Photoreceptor –> bipolar neuron –> ganglion cell of optic nerve –> brain

Question 18

Define myogenic

Answer 18

Contraction of heart is initiated within the muscle itself rather than by nerve impulses

Question 19

State the name and location of the 2 nodes involved in heart contraction

Answer 19

Sinoatrial node (SAN); within the wall of the right atrium
Atrioventricular node (AVN); near lower end of right atrium in the wall that separates the 2 atria

Question 20

Describe how heartbeats are initiated and coordinated
maybe rewrite from notes

Answer 20

1. SAN initiates wave of depolarisation (WOD)
2. WOD spreads across both atria = atrial systole
3. Layer of fibrous, non-conducting tissue delays impulse while ventricles fill and valves close
4. AVN conveys WOD down septum via bundle of his, which branches into purkinjie fibres along ventricles
5. Causes ventricles to contract from apex upwards

Question 20

What is the autonomic nervous system

Answer 20

System that controls involuntary actions of glands and muscles
2 subdivisions: sympathetic and parasympathetic

Question 20

Formula for cardiac output

Answer 20

stroke volume x heart rate

Question 21

State the difference between the sympathetic and parasympathetic nervous system

Answer 21

Sympathetic involved in fight or flight response; stimulates effectors to speed up activity
Parasympathetic involved in normal resting conditions; inhibits effectors to slow down activity

Question 21

Name the receptors involved in changing heart rate and state their location

Answer 21

Baroreceptors(detect changes in blood pressure): carotid body
Chemoreceptors(detect changes in pH due to increase in CO2): carotid body and aortic body

Question 21

How does the body respond to an increase in blood pressure
maybe rewrite from notes

Answer 21

1. Baroreceptors send more impulses to CNS along medulla
2. More impulses to SAN via parasympathetic nerve
3. Stimulates release of AChE, decreases heart rate

Question 22

How does the body respond to a decrease in blood pressure

Answer 22

1. Baroreceptors send more impulses to CNS along medulla
2. More impulses to SAN via sympathetic neuron
3. Stimulates release of noradrenaline which increases heart rate and strength of contraction

Question 23

How does the body respond to increase in CO2 conc

Answer 23

1. Chemoreceptors detect pH decrease and send more impulses to CNS along medulla
2. More impulses to SAN via sympathetic nervous system
3. Heart rate increases, blood flow to lungs increases, rate of gas exchange and ventilation rate increase