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AQA A Level Biology > 6-14 Response to stimuli > Flashcards

6-14 Response to stimuli Flashcards

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1
Q

What is a stimulus?

A

A detectable change in the internal or external environment of an organism that leads to a response in the organism

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2
Q

What is a receptor?

A

Detects stimuli

Specific to one type of stimulus

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3
Q

What is a coordinator?

A

It formulates a response to a stimulus

This may be at the molecular level or involve a large organ such as the brain

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4
Q

What does an effector do?

A

It produces a response

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5
Q

What is the general sequence of events for the reaction to a stimulus?

A

Stimulus
Receptor

Coordinator
Effector
Response

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6
Q

What is a taxis?

A

A simple response whose direction is determined by the direction of the stimulus
Towards stimulus = positive taxis

Away from the stimulus = negative taxis

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7
Q

What is kinesis?

A

A form of response where the organism does not move towards or away from a stimulus
Instead it changes the speed at which it moves and the rate at which it changes direction

Important when the stimulus is less directional e.g. humidity and temperature

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8
Q

What is a tropism?

A

The growth of a plant in response to a directional stimulus
Towards stimulus = positive

Away from stimulus = negative

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9
Q

What is the name for the response of plants to a light stimulus?

A

Phototropic

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10
Q

What is the name for the response of plants to a gravity stimulus?

A

Gravitropic

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11
Q

What is the name for the response of plants to a water stimulus?

A

Hydrotropic

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12
Q

What are plant growth factors?

A

Hormone-like substances which are involved in the response to external stimuli
They affect growth

They affect tissues which release them rather than a target organ

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13
Q

What is the process of phototropism?

A

Cells in the tip of the shoot produce IAA which is transported down the shoot
IAA is initially transported evenly as it moves through the shoot

Light causes the movement of IAA from the light to the dark side of the shoot
This creates a greater concentration on the shaded site
IAA causes the cells on the shaded side to elongate more
The shaded side elongates which causes the root tip to bend towards the light

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14
Q

What does IAA do?

A

It causes elongation of the shoot cells
It controls the bending of the shoots and roots in response to light

High concentrations inhibit cell growth in the roots and increase elongation in the shoots

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15
Q

What is the process of gravitropism?

A

Cells in the root tip produce IAA which are transported along the root
IAA is initially transported to all sides

Gravity influences IAA to move from the upper to lower side of the roots
IAA inhibits elongation of root cells so it inhibits the cells on the lower side
This causes the root to bend downwards towards gravity

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16
Q

Why does IAA only affect young cells?

A

IAA increases plasticity of the cell walls
The response only occurs in young cell walls where cells are able to elongate

Older cells develop greater rigidity

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17
Q

What is the acid growth hypothesis?

A

Hydrogen ions are actively transported by active transport from the cytoplasm into spaces in the cell wall, causing the cell wall to become more plastic
This allows the cells to elongate by expansion

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18
Q

What is a behaviour?

A

The response of an organism to the environment which increases the chance of survival

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19
Q

What is a reflex?

A

An involuntary response that follows a specific pattern to a given stimulus

20
Q

What is a cholinergic synapse?

A

A synapse with the neurotransmitter acetylcholine

21
Q

What is acetylcholine composed of?

A

Acetyl and choline

22
Q

What are receptors?

A

Cells or proteins which detect stimuli (energy)
Can only detect a specific stimulus e.g. light

Can create generator potentials in sensory neurones
Can act as transducers that convert one form of energy to another

23
Q

What is the Pacinian corpuscle?

A

A receptor which can detect mechanical stimuli

The corpuscles wrap around the sensory nerve ending in layers of connective tissue called lamellae

24
Q

What does compression of the lamellae cause?

A

A sodium influx (due to stretch-mediated Na+ channels) which causes an action potential

25
Q

Where are Pacinian corpuscles found?

A

Abundant in the hands and feet

Also found in ligaments and tendons to determine which joints are changing direction

26
Q

What are the steps of the compression of the Pacinian corpuscle?

A

Shape of the corpuscle changed
Stretch-mediated Na+ channels open

Na+ diffuses into the neurone
The membrane is depolarised
A generator potential is produced
The greater the pressure, the greater the generator potential
The action potential develops if the threshold is reached

27
Q

What is the process of photoreceptors?

A

Light enters the eye through the pupil
The amount of light entering is controlled by the muscles in the iris

The lens focuses the light rays onto the retina
The retina contains the photoreceptor cells

28
Q

What is the forea?

A

An area of the retina with loads of receptors

29
Q

How do nerve impulses from the photoreceptor cells get to the brain?

A

They are carried from the retina to the brain via the optic nerve (a bundle of nerves)

30
Q

What is the blind spot caused by?

A

The spot where the optic nerve leaves the eye

31
Q

What is the process of information from the eyes reaching the brain?

A

Light sensitive optical pigments absorb light and chemically breakdown
Na+ permeability changes in the photoreceptor (Na+ channels close) and neurotransmitter release stops

A generator potential can be created in the bipolar neurone
A signal is transmitted to the brain

32
Q

What do rod and cone cells act as?

A

Transducers by conserving light energy into the electrical energy of a nerve impulse

33
Q

What are rod cells?

A

Lead to black and white imagery
More numerous than cone cells
Many connected to a single sensory neurone
Certain threshold has to be exceeded before a generator potential is created
Three connected to one bipolar cell which creates a greater chance of exceeding the threshold due to summation
Pigment must be broken down to create a generator potential
Give low visual acuity
Found in higher concentrations further away from the fovea

34
Q

What are cone cells?

A

Three types each responding to a different range of wavelength of light
The proportion of each causes images to be in full colour
One cone cell connects to one bipolar cell
Only respond to high light intensity due to no summation
Requires a higher light intensity to break down the pigment
High visual acuity
Found at the forea

35
Q

What are the differences between rods and cones in the eye?

A

Rods vs cones
Mainly located in the retina vs fovea

Black and white vs colour
Many rods connected to one bipolar neurone vs one cone
High sensitivity to light vs low sensitivity
Low visual acuity vs high

36
Q

Where is the sinatorial node found?

A

At the connection of the right atrium and the superior vena cava

37
Q

Where is the atrioventricular node found?

A

Between the walls of the two ventricles next to the semi lunar valves

38
Q

What can be increased or decreased in the heart?

A

The heart rate
The force of ventricular contractions
The stroke volume

39
Q

What does the sinatorial node do?

A

Causes the heart to speed up or slow down

Causes the atria to contract

40
Q

What does the atrioventricular node do?

A

Carries impulses from the sinatorial node down to the bottom of the heart
Ventricles contract from the base

41
Q

What determines the speed of the heart?

A

Receptors which detect activity

42
Q

What connects with the sinatorial node?

A

The brain

43
Q

What are the receptors involved in controlling the heart rate?

A

Chemoreceptors: detect changed in the pH due to increasing carbonic acid
Stretch receptors in the muscles

Stretch receptors which monitor blood pressure

44
Q

What are the two receptors connecting the heart and the brain?

A

Vagus and accelerans

45
Q

What is the process of controlling heart rate?

A

A wave of electrical excitation spreads out from the sinatorial node across both atria, causing them to contract
A layer of non conductive tissue between the atria prevents the wave from crossing to the ventricles
The wave of excitation enters the atrioventricular node which lies between the atria
The atrioventricular node, after a short delay, conveys a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which makes up a structure called the bundle of His
The bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres
The wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards

AQA A Level Biology (19 decks)

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