paper 2: Stimuli and Receptors

Question 1

define tropism

Answer 1

a directional growth response to a stimulus

Question 2

what is positive phototrophism

Answer 2

plant grows towards the light

Question 3

what is negative phototrophism

Answer 3

plant grows away from the light

Question 4

what is positive gravitropism

Answer 4

plant grows with gravity

Question 5

what is negative gravitropism

Answer 5

plant grows against gravity

Question 6

where is IAA produced

Answer 6

cells in the tip of a root/shoot

Question 7

what does a high concentration of IAA do in a shoot.

Answer 7

IAA stimulates cell elongation in the shoot

Question 8

at does high concentrations of IAA do in a root

Answer 8

IAA inhibits cell elongation in the root

Question 9

describe steps by which IAA cases positive phototropism in shoots

Answer 9

• cells in tje tip of the shoot produce IAA
• IAA diffuses to the shaded side of the shoot, increases its concentration
• IAA stiumulation cell elongation on shaded side
• cells elongate more on the shaded side than the light side, bending the shoot towards the light

Question 10

describe the steps by which IAA causes positive gravitropism in roots

Answer 10

• cells in the tip of the eoot produce IAA
• IAA diffuses to th lower side of the root
• IAA inhibits cell elongation
• cells elongate less on the lower side than the upper side

Question 11

what is a taxis

Answer 11

a directional movement to a stimulus

Question 12

what is kinesis

Answer 12

a non-directional movement to a stimulus

Question 13

explain how a woodlice uses kinesis if it was an unfavourable environment suhc a slow humidity

Answer 13

negative taxis, allows woodlice to move away from area of low humidity towards a more favourab;e environment

Question 14

what is a reflex

Answer 14

reflex = rapid, involuntary response ti a stimulus

Question 15

xplain why organisms have reflexes

Answer 15

the prtoect against damage to body tissues and can help them escapre from predators

Question 16

state 3 neurons in a reflex arc in the correct order

Answer 16

sensory neurone, intermediate neurone, motor neurone

Question 17

describe the sequence of events in a reflex arc

Answer 17

• stimuli is detected by receptor
• sends information to the sensory neurone
• information sent to intermediate neurone in spinal cord
• information sent to motor neurone
• impulse sent to effector where response occurs

Question 18

define a receptor

Answer 18

detect stimuli and forms a generator potential

Question 19

what type of stimulus does the pacinin corpuscle detect

Answer 19

pressure

Question 20

draw and label a diagram of a pacinian corpuscle

Answer 20

Question 21

describe the steps by how pacinian corpuscle causes a generator potential

Answer 21

• the lamellae deform
• stretch mediated sodium ion channels in the neurone membrane open
• sodium ions diffuse into the neurone- depolarising it
• this produces a generator potential, which, if reaches threshold, causes an action potential
• the greater the pressure, the more Na+ channels open and the greater the generator potential

Question 22

list the difference between rods and cones in terms of position in retina, pigment, detecting colour, sensitivity, visual acuity and retinal convergence

Answer 22

Question 23

explain why cones have a higher visual acuity than rods

Answer 23

• each cone connects to a single neurone so a separate set of nerve impulses is sent to the brain from each cone cell

whereas

• several rod cells connect to a single neurone (retinal convergence) so one set of nerve impulses ar sent to the brain from multiple rods

Question 24

explain why cones see more colour and rods only see black and white

Answer 24

cones see colour as there are 3 different types of cone with different iodopsin so each one identifies a different wavelength of light.

rods contain rhodopsin which cannot distinguish between the different wavelengths of light

Question 25

explain why rods are more sensitive than cones to low light intensities

Answer 25

multiple rod cells connect to a single neurone (retinal convergence) so the generator potentials combine (spatial summation) to reach threshold in the neurone only one cone cell connects to a single neurone so a high light intensity is required for a generator potential to reach threshold in the neurone

Question 26

starting with the sinoatrial node, describe the steps of how heart rate is initiated and coordinated

Answer 26

- heart is myogenic - sino atrial node initiates the heartbeat by geerating electrical impulses - these electrical impulses are sent across the atria causing them to contact - a layer of non-conducting tissue prevents the impulses spreading to the ventricles so the ventricles dont contract - the atrioventricular node delays the impulses to give time for blood to leave the atria and fill the ventricles before the ventricles contract - the impulses then travel down the bundle of His and up the purkinje fibres - the ventricals contract from the bottom up

Question 27

where are the chemoreceptors found and what do they detect

Answer 27

found in the aorta and carotid arteries and they detect changes in concentration of CO2 and pH

Question 28

where are the pressure recpetors found and what do they detect

Answer 28

found in walls of aorta and carotid arteries and detect chnages in blood pressure

Question 29

what does the sypathetic nerve do in terms of heart rate

Answer 29

increases heart rate

Question 30

what does the parasympathtic nerve do in terms of heart rate

Answer 30

decreases heart rate

Question 31

during exercise, explain how an increase in heart rate occurs

Answer 31

- during exercise, muscles aerobically respire more to produce more ATP for muscle contraction. This prouces more carbon dioxide - since carbon diocide is an acidic gas, blood pH becomes lower - this is detected by chemoreceptors in the aorta and carotid arteries. the chemorecptors send more nerve impulses to the medulla in the brain - the medulla sends more nerve impulses down the sympathetic nerve and less impulses down the parasympathetic nerve to the sionatria node. - the sinoatrial node produces more frequent electrical impulses resulting in an increased heart rate

Question 32

after exrcise, explain how a decrease in heart rate occurs

Answer 32

- chemoreceptors detcect a decrease in blood carbon dioxide and an increase in blood pH - less nerve impulses sent to the medulla - more nerve implses sent down the parasympathetic nerve and less impulses are sent down the sympathetic nerve to the sinoatrial node - less frequent electricla impulses sent from the sinoatrial node

Question 33

explain how a decrease in heart rate occurs when blood pressure is too high

Answer 33

- pressure receptors (baroreceptors) in the walls of the aorta and carotid arteries detect a rise in blood pressure - less nerve impulses are sent to the medulla from the pressure receptors - more nerve impulses are sent down the parasympathetic nerve and less impulses are sent down the sympathetic nerve to the sioatrial node - less frequent electrical impulses from the sinoatrial node, which decreases heart rate

Question 34

explain how an increase in heart rate occurs when blood pressure is too low

Answer 34

- pressure receptors detect a fall in blood pressure - more nerve impulses are sent from the pressure receptor to the medulla - more nerve umpulses are sent down the sympathetic nerve and less impulses are sent down the parasympathetic nerve to the sinoatrial node - more frequent electrical impulses are sent from the sioatrial node, increasing heart rate