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A-level Biology (Year 2) > 3.6.1 Stimuli > Flashcards

3.6.1 Stimuli Flashcards

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1
Q

What’s a stimulus

A

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

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2
Q

Why do organisms respond to stimuli

A

Increases chance of survival

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3
Q

What’s a receptor

A

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

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4
Q

What’s a coordinator

A

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

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5
Q

What’s an effector

A

Produces a response

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6
Q

What’s are two types of response

A

Hormonal
Nervous system

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7
Q

What’s the sequence of a response to stimuli

A

Stimulus, receptor, coordinator, effector, response

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8
Q

Three types of simple responses to stimuli

A

Taxis
Kinesis
Tropism (plants)

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9
Q

What’s taxis

A

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

eg earthworks move away from light

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10
Q

What’s kinesis

A

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

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11
Q

What’s the central nervous system (CNS)

A

Brain and spinal cord

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12
Q

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

A

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

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13
Q

Two types of motor nervous system

A

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

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14
Q

What’s a reflex arc

A

The pathway of neurones involved in a reflex

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15
Q

What’s a reflex

A

A rapid and automatic response to a stimulus

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16
Q

Stages of a reflex arc

A

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

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17
Q

Why is a reflex arc important

A

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

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18
Q

What’s phototropism

A

Response of shoots to light

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19
Q

What’s gravitropism

A

The response of roots to gravity

20
Q

What are specific growth factors

A

Regulate growth of shoots/roots in response to directional stimuli

21
Q

Explain phototropism in plants

A

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

22
Q

Explain gravitropism in plants

A

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

23
Q

What types of tropisms effect shoots and roots

A

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

24
Q

How does IAA elongate cells

A

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

25
Q

Two types of light receptors in the eye

A

Cone cells
Rod cells

26
Q

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

A

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

27
Q

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

A

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

28
Q

What pigment do rod cells contain

A

Rhodopsin

29
Q

What pigment do come cells contain

A

Iodopsin

30
Q

How do the photoreceptors work

A

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,

31
Q

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

A

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

32
Q

What’s a pacinian corpuscle

A

A receptor

33
Q

How does a pacinian corpuscle work

A

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)

34
Q

Structure and function of a pacinian corpuscle

A

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

35
Q

How is a generator potential established in a pacinian corpuscle

A

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

36
Q

What’s a property of a the heart

A

Myogenic, contraction is initiated from within the muscle itself

37
Q

What cells are found in the right atrium of the heart

A

SAN, known as pacemaker, sets the Rhythm of stimulation

38
Q

How is basic heart rate controlled

A

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 after a short delay conveys a wave of electrical excitation between ventricles along muscle fibres called the purkyne tissue, these tissues collectively form 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

39
Q

Location of chemoreceptors

A

Found in wall of carotid arteries,

40
Q

Role of chemoreceptors

A

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

41
Q

What’s the location of pressure receptors

A

Found in walls of carotid artery and aorta

42
Q

Role of pressure receptors

A

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

43
Q

Why’s the autonomic nervous system

A

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

44
Q

What’s the sympathetic nervous system

A

Stimulates effectors, speeds up activity, flight or fight response

45
Q

What’s the parasympathetic nervous system

A

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

46
Q

Equation to calculate cardiac output

A

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

A-level Biology (Year 2) (8 decks)

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