Internal and External Stimuli Detected and Response

Question 1

what are plant growth factors and where are they produced

Answer 1

• chemicals that regulate plant growth response to directional stimuli
• produced in plant growing regions (apical meristems)
• diffuse from cell to cell/phloem mass transport

Question 2

explain why shoots show positive phototropism

Answer 2

1. Indoleacetic acid (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 (acid growth hypothesis)
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 on concentration

Answer 4

mammalian: response not always dependent on concentration
plant growth factor: response proportional to concentration

Question 5

contrast mammalian hormones and plant growth factors on action

Answer 5

mammalian: bind to complementary proteins in/on target cells
plant growth factor: can affect all cells

Question 6

contrast mammalian hormones and plant growth factors on synthesis

Answer 6

mammalian: specialised glands
plant growth factor: various tissues in growing regions

Question 7

contrast mammalian hormones and plant growth factors on transport

Answer 7

mammalian: circulatory system
plant growth factor: diffusion or phloem translocation

Question 8

contrast mammalian hormones and plant growth factors on speed

Answer 8

mammalian: faster-acting (homeostasis)
plant growth hormones: slower-acting (plant growth)

Question 9

define taxis

Answer 9

directional movement in response to external stimuli

Question 10

define kinesis

Answer 10

non-directional response to presence and intensity of external stimuli

Question 11

advantage of taxis and kinesis

Answer 11

maintain mobile organism in optimum environment e.g. to prevent dessication

Question 12

many organisms respond to temperature and humidity via kinesis rather than taxis. why?

Answer 12

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

Question 13

how could a student recognise kinesis in an organisms movement

Answer 13

1. organism crosses sharp division between favourable and unfavourable environment: turning increases (return to the original favourable environment)
2. if organism moves considerable distance into unfavourable environment: turning slowly decreases; begins to move in long, straight lines; sharper turns (lead organisms to new environment)

Question 14

outline what happens in a simple reflex arc

Answer 14

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

Question 15

give advantages of a simple reflex

Answer 15

1. rapid response to potentially dangerous stimuli since only 3 neurons involved
2. instinctive

Question 16

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 16

chi squared

Question 17

what features are common to all sensory receptors

Answer 17

• act as energy transducers which establish a generator potential
• respond to specific stimuli

Question 18

describe the basic structure of a Pacinian corpuscle

Answer 18

• 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 19

what stimulus does a Pacinian corpuscle respond to? how?

Answer 19

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

Question 20

name the 2 types of photoreceptor cell located in the retina

Answer 20

1. cone cells
2. rod cells

Question 21

where are rod cells located in the retina

Answer 21

evenly distributed around periphery but NOT central fovea

Question 22

where are cone cells located in retina

Answer 22

mainly central fovea no photoreceptors at blind spot

Question 23

compare and contrast rod and cone cells: pigment

Answer 23

rod: rhodopsin
cone: 3 types of iodopsin

Question 24

compare and contrast rod and cone cells: visual acuity

Answer 24

rod: low res - many rod cells synapse with 1 bipolar neuron
cone: high res - 1 cone cell synapse with 1 bipolar neuron = no retinal convergence

Question 25

compare and contrast rod and cone cells: colour sensitivity

Answer 25

rod: monochromatic - all wavelengths of light detected cone: tricolour - red/blue/green wavelengths absorbed by different types of iodopsin

Question 26

compare and contrast rod and cone cells: light sensitivity

Answer 26

rod: V sensitive - spatial summation of subthreshold impulses cone: less sensitive - not involved in night vision

Question 27

outline the pathway of light from a photoreceptor to the brain

Answer 27

photoreceptor bipolar neuron ganglion cell of optic nerve brain

Question 28

define myogenic

Answer 28

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

Question 29

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

Answer 29

- 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 30

describe how heartbeats are initiated and coordinated

Answer 30

1. SAN initiated 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 Purkinje fibres along ventricles 5. causes ventricles to contract from apex upwards

Question 31

state the formula for cardiac output

Answer 31

cardiac output (CO) = stroke volume (V) x heart rate (R)

Question 32

state the formula for cardiac output

Answer 32

cardiac output (CO) = stroke volume (V) x heart rate (R)

Question 33

what is the autonomic nervous system

Answer 33

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

Question 34

what is the difference between the sympathetic and parasympathetic nervous system

Answer 34

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 35

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

Answer 35

- baroreceptors (detect changes in blood pressure): carotid body - chemoreceptors (detect changes in pH e.g. due to increase in CO2 concentration): carotid body and aortic body

Question 36

how does the body respond to an increase in blood pressure

Answer 36

1. baroreceptors send more impulse to cardioinhibitory centre in the medulla oblongata 2. more impulses to SAN down vagus nerve via parasympathetic nervous system 3. stimulates release of acetylcholine, which decreases heart rate and strength of contraction

Question 37

how does the body respond to an increase in CO2 concentration

Answer 37

1. chemoreceptors detect pH decrease and send more impulses to cardioacceleratory centre of medulla oblongata 2. more impulses to SAN via sympathetic nervous system 3. heart rate increases, so rate of blood flow to lungs increases = rate of gas exchange and ventilation rate increases