3.6.1 Stimuli

Question 1

What’s a stimulus

Answer 1

Change in internal or external environment of an organism, leads to a response

Question 2

Why do organisms respond to stimuli

Answer 2

Increases chance of survival

Question 3

What’s a receptor

Answer 3

Detects stimuli, each receptor is specific to a type of stimulus

Question 4

What’s a coordinator

Answer 4

Links receptors and effectors, formulates a suitable response to a stimulus

Question 5

What’s an effector

Answer 5

Produces a response

Question 6

What’s are two types of response

Answer 6

Hormonal
Nervous system

Question 7

What’s the sequence of a response to stimuli

Answer 7

Stimulus, receptor, coordinator, effector, response

Question 8

Three types of simple responses to stimuli

Answer 8

Taxis
Kinesis
Tropism (plants)

Question 9

What’s taxis

Answer 9

Organism responds directly to stimulus by moving towards (a favourable) or away from (an unfavourable) stimulus

eg earthworks move away from light

Question 10

What’s kinesis

Answer 10

Organism changes the rate at which it moves/ rate it changes direction

In favourable conditions organisms turn lots to stay In that environment
In unfavourable conditions organisms turn less to help them move into a new favourable environment

Question 11

What’s the central nervous system (CNS)

Answer 11

Brain and spinal cord

Question 12

What’s the peripheral nervous system (PNS) and which nerves do they contain

Answer 12

Pairs of nerves that originate from the brain or spinal cord

Sensory neurones, carry nerve impulses from receptors towards the central nervous system

Motor neurones, carry nerve impulses from CNS to effectors

Question 13

Two types of motor nervous system

Answer 13

Voluntary nervous system, nerve impulses are carried to body muscle, under conscious control

Autonomic nervous system, nerve impulses carried to glands/smooth muscle/Cardiac muscle, subconscious

Question 14

What’s a reflex arc

Answer 14

The pathway of neurones involved in a reflex

Question 15

What’s a reflex

Answer 15

A rapid and automatic response to a stimulus

Question 16

Stages of a reflex arc

Answer 16

Stimulus eg heat from an object
Receptor eg Receptors on skin generates a nerve impulse in the sensory neurone
Sensory neurone, passes nerve impulse to spinal cord
Coordinator (relay neurone), connects sensory neurone to motor neurone in spinal cord
Motor neurone, carries nerve impulses from spinal cord to an effector eg muscle
Effector eg muscle in upper arm contracts
Response eg hand pulled away from hot object

Question 17

Why is a reflex arc important

Answer 17

Involuntary, response is always the same
Protect body from harm, effective from birth
Fast, neurone pathway has one or two synapses, response is also automatic

Question 18

What’s phototropism

Answer 18

Response of shoots to light

Question 19

What’s gravitropism

Answer 19

The response of roots to gravity

Question 20

What are specific growth factors

Answer 20

Regulate growth of shoots/roots in response to directional stimuli

Question 21

Explain phototropism in plants

Answer 21

IAA evenly distributed through plant, Light causes movement of IAA to shaded side of plant, higher conc of IAA on dark side of shoot, cells on this side elongate more than the other side, shoot too bends towards light

Question 22

Explain gravitropism in plants

Answer 22

IAA evenly distributed through roots, greater conc of IAA on lower side of root, IAA in roots inhibits elongation of cells on lower side, roots bend downwards towards gravity

Question 23

What types of tropisms effect shoots and roots

Answer 23

Both tropisms effect both shoots and roots, IAA always inhibits cell elongation in roots

Question 24

How does IAA elongate cells

Answer 24

H+ ions are actively transported from the cytoplasm into the cell wall, cells become more plastic allowing it to elongate

Question 25

Two types of light receptors in the eye

Answer 25

Cone cells Rod cells

Question 26

How are rod cells connected to a sensory neurone and it’s impact on light sensitivity colour sensitivity and visual acuity

Answer 26

Many rod cells are connected to a single sensory neurone this is called retinal convergence, this allows for spatial summation, threshold value is reached, more sensitivity to light Due to many rod cells sharing a single impulse the brain can’t differentiate between the separate sources of light, low visual acuity Cannot distinguish differences in the wavelength of light

Question 27

How are cone cells connected to a sensory neurone and it’s impact on visual acuity colour sensitivity and light sensitivity

Answer 27

Each cone cells connects to its own sensory neurone, no summation, not very sensitive to light Each cell makes its own connection, where each sends its own SEPERATE impulse to the brain, brain can distinguish between two different light sources, high visual acuity Each cell contains one of three different iodopsin pigments, each cell absorbs a different wavelength of light, colours depend on the proportion of each type that is stimulated

Question 28

What pigment do rod cells contain

Answer 28

Rhodopsin

Question 29

What pigment do come cells contain

Answer 29

Iodopsin

Question 30

How do the photoreceptors work

Answer 30

Rhodopsin in rod cells or iodopsin in cone cells absorb light, the pigment breaks down, if threshold value is reached (depends on light intensity) a generator potential is created,

Question 31

Structure of the retina and its effect on visual acuity, sensitivity to light

Answer 31

Lens, focuses light onto retina Retina, back of eye opposite pupil Fovea- light focused by lens, highest light intensity, cone cells found here, NO rod cells, low sensitivity to light but high visual acuity Rest of retina, low light intensity, only rod cells found, very sensitive to light, low visual acuity Blind spot, no cells

Question 32

What’s a pacinian corpuscle

Answer 32

A receptor

Question 33

How does a pacinian corpuscle work

Answer 33

Specific to stimulus of mechanical pressure Acts as a transducer to produce a generator potential, transducers mechanical energy into a generator potential (one for of energy converted into another)

Question 34

Structure and function of a pacinian corpuscle

Answer 34

Single sensory neurone at centre of tissue layers, contain stretch mediated sodium channels Capsule surrounds layers of tissue and gel Tissue layers separated by gel

Question 35

How is a generator potential established in a pacinian corpuscle

Answer 35

Resting state, stretch mediated Na+ channels are too narrow for Na+ to pass through Pressure applied to corpuscle, deformed, membrane around neurone becomes stretched, widens Na+ channel, Na+ diffuses in Membrane becomes depolarised, produces generator potential, which produces an action potential

Question 36

What’s a property of a the heart

Answer 36

Myogenic, contraction is initiated from within the muscle itself

Question 37

What cells are found in the right atrium of the heart

Answer 37

SAN, known as pacemaker, sets the Rhythm of stimulation

Question 38

How is basic heart rate controlled

Answer 38

Wave of electrical excoriation spreads out from SAN across north atria, they both contract A layer of non conductive tissue prevent this wave from crossing to the ventricles The wave of excitation enters the AVN which lies between the atria The AVN detects and after a short delay conveys a wave of electrical excitation between ventricles along muscle fibres called the purkyne tissue, in the bundle of his The bundle of his conducts the wave through atrioventricular septum to base of ventricles, bundle branches into smaller fibres of purkyne tissue Wave of excitation is released from purkyne tissue, causing ventricles to contract quickly, from the bottom of the heart upwards

Question 39

Location of chemoreceptors

Answer 39

Found in wall of carotid arteries,

Question 40

Role of chemoreceptors

Answer 40

Sensitive to changes in pH of the blood, result in changes to CO2 concentration, in a solution CO2 is acidic lowering pH Blood has a higher than normal conc of CO2, pH is lowered Chemoreceptors in wall of carotid artery and aorta detects this, increases frequency of nervous impulses to centre in medulla oblongata, increases heart rate Centre increases frequency of impulses via sympathetic nervous system to SAN, increases rate of production of electrical waves by SAN, increases heart rate Increases blood flow, more CO2 removed, CO2 conc returns to normal pH in blood rises, chemoreceptors in wall of carotid artery and aorta reduce frequency of nerve impulses to medulla oblongata Medulla oblongata reduces the frequency of impulses to SAN, reduced heart rate

Question 41

What’s the location of pressure receptors

Answer 41

Found in walls of carotid artery and aorta

Question 42

Role of pressure receptors

Answer 42

Higher than normal blood pressure Pressure receptors transmit more nervous impulses to centre in medulla oblongata, decreases heart rate, centre sends impulses via parasympathetic nervous system to SAN, decreased heart rate Lower blood pressure than normal Pressure receptors transmit more nervous impulses to centre in medulla oblongata to increase heart rate, centre sends impulses via sympathetic nervous system to SAN increases heart rate

Question 43

Why’s the autonomic nervous system

Answer 43

Controls involuntary activities of internal muscles or glands Consists of sympathetic nervous system and parasympathetic nervous system

Question 44

What’s the sympathetic nervous system

Answer 44

Stimulates effectors, speeds up activity, flight or fight response

Question 45

What’s the parasympathetic nervous system

Answer 45

Inhibits effectors, slows down activity, conserves energy and replenished body’s reserves

Question 46

Equation to calculate cardiac output

Answer 46

CO= R x V CO- cardiac output R-heart rate V-stroke volume