Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A-level Biology AQA > Organisms Respond to Changes in their Internal and External Environments > Flashcards

Organisms Respond to Changes in their Internal and External Environments Flashcards

1
Q

define stimulus

A

any change in the internal or external environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

define receptors

A

these are cells or proteins on cell membranes which detect stimuli.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define effectors

A

these are cells that bring about a response to a stimulus, to produce an effect. effectors include muscle cells and cells found in glands.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are the three main types of neurons?

A

sensory neurons
motor neurons
relay neurons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is the function of sensory neurons?

A

sensory neurons transmit electrical impulses from receptors to the central nervous system; the brain and spinal cord.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the function of motor neurons?

A

motor neurons transmit electrical impulses from the CNS to effectors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is the function of relay neurons?

A

relay neurons transmit electrical impulses between sensory neurons and motor neurons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how does the nervous system send information as electrical impulses?

A

a stimulus is detected by receptor cells and an electrical impulse is sent along a sensory neuron.
when an electrical impulse reaches the end of a neuron, chemicals called neurotransmitters take the information across to the next neuron, which then sends an electrical impulse.
the central nervous system processes the information and sends impulses along the motor neurons to an effector.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

define reflex.

A

a reflex is where the body responds to a stimulus without making a conscious decision to respond.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how do simple reflexes help organisms?

A

they help to protect the body because they’re rapid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

define reflex arc

A

the pathway of neurons linking receptors to effectors in a reflex.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

explain the hand-withdrawal response to heat as an example of a simple reflex arc.

A

thermoreceptors in the skin detect the heat stimulus.
the sensory neuron carries impulses to the relay neuron.
the relay neuron connects to the motor neuron.
the motor neuron sends impulses to the effector (your biceps muscle).
your muscle contracts to withdraw your hand and stop it from being damaged.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what happens if there is a relay neuron involved in the simple reflex?

A

its possible to override the reflex, e.g. like in the hand-withdrawal example where a relay neuron was involved, your brain could tell your hand to withstand the heat.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how is the nervous system communication localised, short-lived and rapid?

A

when an electrical impulse reaches the end of a neurone, neurotransmitters are secreted directly onto target cells; so the nervous response is localised.
neurotransmitters are quickly removed once they’ve done their job, so the response is short-lived.
electrical impulses are really fast, so the response is rapid; this allows animals to react quickly to stimuli.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how are flowering plants able to increase their chances of survival by responding to stimuli?

A

-they can sense the direction of light and grow towards it to maximise light absorption for photosynthesis.
-they can sense gravity, so their roots and shoots grow in the right direction.
-climbing plants have a sense of touch, so they can find things to climb up and reach the sunlight.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

define tropism

A

the response of a plant to a directional stimulus (a stimulus coming from a particular direction).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

how do plants respond to stimuli?

A

by regulating their growth.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

define positive tropism

A

growth towards the stimulus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

define negative tropism

A

growth away from the stimulus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

define phototropism

A

this is the growth of a plant in response to light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

how do shoots respond to phototropism?

A

shoots are positively phototropic and grow towards light.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how do roots respond to phototropism?

A

roots are negatively phototropic and grow away from light.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

define gravitropism

A

this is the growth of a plant in response to gravity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

how do shoots respond to gravitropism?

A

shoots are negatively gravitropic and grow upwards.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

how do roots respond to gravitropism?

A

roots are positively gravitropic and grow downwards.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

how are responses in plants brought about?

A

they are brought about using specific growth factors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what are growth factors?

A

these are hormone-like chemicals that speed up or slow down plant growth.
they are produced in the growing regions of the plant (shoot tips, leaves) and they move to where they’re needed in the other parts of the plant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what are auxins?

A

these are a growth factor which stimulates the growth of shoots by cell elongation; this is where cell walls become loose and stretchy, so the cells get longer.
high conc. of auxins inhibit growth in roots.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what is Indoleacetic Acid (IAA)?

A

it is an important auxin that’s produced in the tips of shoots in flowering plants.
IAA is moved around the plant to control tropisms; it moves by diffusion and active transport over short distances, and via the phloem over long distances.
this results in different parts of the plant having different concentrations of IAA. uneven distribution of IAA means there’s uneven growth.

30
Q

how does IAA act with phototropism in plants?

A

the IAA moves to the more shaded parts of the shoots and roots, so there’s uneven growth.

31
Q

how does IAA act in shoots in phototropism?

A

IAA concentration increase on the shaded side; cells elongate and the shoot bends towards the light.

32
Q

how does IAA act in roots in phototropism?

A

IAA concentration increases on the shaded side; growth is inhibited so the root bends away from the light.

33
Q

how does IAA act with gravitropism in plants?

A

IAA moves to the underside of shoots and roots, so there’s uneven growth.

34
Q

how does IAA act in shoots in gravitropism?

A

IAA concentration increases on the lower side; cells elongate so the shoot grows upwards.

35
Q

how does IAA act in roots in gravitropism?

A

IAA concentration increases on the lower side; growth is inhibited so the root grows downwards.

36
Q

what are the two simple responses that keep simple organisms in a favourable environment?

A

tactic responses (taxes)
kinetic responses (kineses)

37
Q

define taxes

A

the organisms move towards or away from a directional stimulus e.g light.

38
Q

explain an example of taxes using woodlice

A

woodlice show a tactic response to light (phototaxis). they move away from a light source. this helps them survive as it keeps them concealed under stones during the day (safe from predators) and keeps them in damp conditions (which reduces water loss).

39
Q

define kineses

A

the organisms’ movement is affected by a non-directional stimulus, e.g humidity.

40
Q

explain an example of kineses using woodlice

A

woodlice show a kinetic response to humidity. in high humidity they move slowly and turn less often, so that they stay where they are. as the air gets drier, they move faster and turn more often, so that they move into a new area.
(may need editing with another example).

41
Q

why are receptors described as specific?

A

they only detect one particular stimulus.

42
Q

what are the different types of receptors?

A

cells and proteins on cell surface membranes

43
Q

how do receptor cells that communicate information via the nervous system, work?

A
44
Q

what are pacinian corpuscles?

A

they are mechanoreceptors; they detect mechanical stimuli, e.g pressure and vibrations.
they are found in your skin.

45
Q

what do pacinian corpuscles contain?

A

they contain the end of a sensory neurone, imaginatively called a sensory nerve eneding. the sensory nerve ending is wrapped in lots of layers of connective tissue called lamallae.

46
Q

what happens when a pacinian corpuscle is stimulated?

A
  • the lamellae are deformed and this presses on the sensory nerve ending.
  • this causes the sensory neurone’s membrane to stretch, deforming the stretch-mediated sodium ion channels. the channels open and sodium ions diffuse into the cell, creating a generator potential.
  • if the generator potential reaches the threshold, it triggers an action potential.
47
Q

how do photoreceptors detect light?

A
  • light enters the eye through the pupil. the amount of light that enters is controlled by the muscles of the iris.
  • light rays are focused by the lens onto the retina, which lines the inside of the eye. the fovea is an area of the retina where there are lots of photoreceptors. the retina therefore contains photoreceptor cells — these detect light.
48
Q

what is a blind spot?

A
  • nerve impulses from the photoreceptor cells are carried from the retina to the brain by the optic nerve, which is a bundle of neurones.
  • where the optic nerve leaves the eye is called the blind spot. there are no photoreceptor cells and so it’s not sensitive to light.
49
Q

how do photoreceptors convert light into an electrical impulse?

A
  • light enters the eye, hits the photoreceptors and is absorbed by light-sensitive optical pigments.
  • light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium ions.
  • a generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone.
  • bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain.
50
Q

what are the two types of photoreceptors?

A

rods
cones

51
Q

where are rods found in the eye?

A

mainly found in the peripheral parts of the retina

52
Q

where are cones found in the eye?

A

they are found packed together in the fovea.

53
Q

what is the differences of optical pigments between rods and cones?

A

rods only give information in black and white (monochromatic vision), but cones give information in colour (trichromatic vision).

54
Q

what are the three different optical pigment cones?

A

red-sensitive
green-sensitive
blue-sensitive

55
Q

explain sensitivity of light in rods.

A

rods are very sensitive to light (they work well in dim light). this is because many rods join one neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential.

56
Q

explain sensitivity of light in cones.

A

cones are less sensitive than rods (they work best in bright light). this is because one cone joins one neurone, so it takes more light to reach the threshold and trigger an action potential.

57
Q

define visual acuity

A

the ability to tell apart points that are close together.

58
Q

explain the visual acuity of rods.

A

rods give low visual acuity because many rods join the same neurone, which means light from two points together can’t be told apart.

59
Q

explain the visual acuity of cones.

A

cones give high visual acuity because cones are close together and one cone joins one neurone.
when light from two points hits two cones, two action potentials (one from each cone) go to the brain — so we can distinguish two points that are close together as two separate points.

60
Q

explain the cardiac heart muscle as ‘myogenic’

A

it can contract and relax without receiving signals from nerves. this pattern of contractions controls the regular heartbeat.

61
Q

explain the process of the cardiac muscle controlling the regular beating of the heart.

A
62
Q
A
63
Q

What type of muscle is cardiac muscle?

A

Cardiac muscle is ‘myogenic’ — it can contract and relax without receiving signals from nerves.

64
Q

Where does the process of heartbeat initiation start?

A

The process starts in the sinoatrial node (SAN), which is in the wall of the right atrium.

65
Q

What is the function of the sinoatrial node (SAN)?

A

The SAN sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls.

66
Q

What happens when the SAN sends electrical activity to the atrial walls?

A

This causes the right and left atria to contract at the same time.

67
Q

What prevents the direct passage of electrical activity from the atria to the ventricles?

A

A band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles.

68
Q

Where are the waves of electrical activity transferred from the SAN?

A

These waves of electrical activity are transferred from the SAN to the atrioventricular node (AVN).

69
Q

What is the role of the AVN?

A

The AVN is responsible for passing the waves of electrical activity on to the bundle of His, with a slight delay to ensure the atria have emptied before the ventricles contract.

70
Q

What is the bundle of His?

A

The bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity between the ventricles to the apex of the heart.

71
Q

What are the Purkyne tissue?

A

The Purkyne tissue are finer muscle fibres in the right and left ventricle walls that carry the waves of electrical activity into the muscular walls of the ventricles.

72
Q

What is the result of the Purkyne tissue carrying electrical activity?

A

This causes the right and left ventricles to contract simultaneously, from the bottom up.

A-level Biology AQA (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions