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A-Level Biology AQA > 6. Organisms Respond to changes in their internal and external environments > Flashcards

6. Organisms Respond to changes in their internal and external environments Flashcards

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1
Q

how do organisms increase their chance of survival?

A

by responding to changes in their environment

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2
Q

what is a stimulus?

A

a change in the internal or external environment detected by receptors

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3
Q

what is a receptor?

A

a specialised cell or protein that detects stimuli, and is specific to one type of stimulus

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4
Q

what is an effector?

A

a cell that brings about a response (eg muscles and glands)

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5
Q

what is the simple reflex arc made up of?

A

3 neurones

sensory, relay and motor

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6
Q

what does the sensory neurone do? what does it look like?
what does the relay neurone do? what does it look like?
what does the motor neurone do? what does it look like?

A
  • sensory neurone transmits impulses from receptors to the CNS/relay neurone. its cell body is in the middle of the axon terminal
  • the relay neurone transmits impulses from the sensory neurone to the motor neurone. it is very branched, has and has no mylein sheath
  • the motor neurone transmits impulses from the CNS/relay neurone to the effectors
    it has a long axon terminal and the cell body is at the start, not the middle
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7
Q

where can the relay neurone be found? why does it not have a myelin sheath?

A
  • relay neurone is only found in the CNS (the grey matter)
  • it does not need a mylein sheath as it only needs to transport impulses short distances, so it doesnt need the extra speed provided by the insulation of the myelin sheath
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8
Q

how does the nervous system communicate?

A

using electrical impulses

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9
Q

what is a reflex?
what do reflexes do?

A

a rapid, automatic response that is involuntary and does not need to be learnt

  • reflexes are protected and prevent damage to the tissues
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10
Q

describe the process of the reflex arc if someone were to touch a hot plate

A
  • the STIMULUS is the hot object
  • the temperature and pain RECEPTORS IN THE SKIN would detect the stimulus
  • the SENSORY NEURONE would transmit this impulse to the spinal cord (as it is the closest component of the CNS) and into the relay neurone
  • the RELAY NEURONE would transmit this impulse to the motor neurone
  • the MOTOR NEURONE would then transmit this impulse to the effector
    the EFFECTOR would be the muscles in the arm which would contract to move the hand away
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11
Q

state 7 reasons why the reflex arc is important in organisms

A
  • its automatic and involuntary
  • it doesnt have to be learnt
  • it helps organisms escape predators
  • it prevents damage to body tissues
  • it helps maintain posture and balance
  • it helps animals find a mate
  • it regulates the control of homeostasis
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12
Q

-what pathway does the impulse from the sensory neurone take to reach the CNS?
-what is the bump in this pathway called, and why is it there?
-where is the relay neurone positioned in the CNS? why is this made up of? what surrounds this?
-what pathway does the impulse from the motor neurone take on its way to the effector?

A
  • dorsal root
  • dorsal ganglia, it is the cell body of the sensory neurone
  • in the grey matter/ due to a collection of cell bodies and nuclei/ white matter
  • ventral root
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13
Q

what are the three features of an electrical impulse?

A
  • localised
  • short lived
  • rapid
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14
Q

what are taxes and kinesis?

A

simple responses that can maintain a motile organism in a favourable environment

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15
Q

what is a taxes response?

A

when an organism moves its entire body towards a favourable stimulus (positive taxis) or away from an unfavourable stimulus (negative taxis)

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16
Q

what is a kinesis response?

A

when an organism changes the speed of its movement or the rate at which it changes direction in response to a non-directional stimulus.

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17
Q

explain kinesis in terms of beneficial stimuli and harmful stimuli

A

if an organism moves from an area with favourable conditions to an area with harmful stimuli, its kinesis response will be to increase the rate at which it changes direction, so that it can return to an area with favourable stimuli more quickly.

if an organism is completely surrounded by negative stimuli, the rate of turning decreases, and they move in a straight line to try and find a new location with favourable stimuli

if an organism moves into an area with favourable stimuli, rate of turning decreases as they would want to stay in this area for longer.

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18
Q

what are the advantages of taxes and kinesis behaviour?

A
  • move organisms away from other organisms to reduce competition
  • moves organisms away from predators/helps them avoid predators
  • prevent organisms from drying out
  • helps them find a mate
  • ensure they remain near a food source
  • increase dispersal
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19
Q

what is a trophism?

A

when a flowering plant grows towards (positive trophism) or away from (negative trophism) a directional stimulus.

20
Q

what is phototrophism?
what is geotrophism?

A
  • when a plant grows in response to a light source
  • when a plant grows in response to gravity (gravity pulls down, so positive geotrophism would mean the plant is growing downwards)
21
Q

what are plant responses regulated by?

A

growth factors

22
Q

what do growth factors do and where are they produced?

A
  • theyre chemicals t5hat speed up or slow down plant growth
  • theyre produced in shoot tips or roots
23
Q

what is the name of the specific growth factor you need to remember?

A

indoleacetic acid (iaa) / auxin

24
Q

describe how IAA causes plants to respond to phototropism

A
  • IAA produced in the shoot tip
  • IAA diffuses into the shaded part of the shoot, and the increased IAA concentration causes the cells in the shaded side to elongate, so the shoot bends towards the light
  • this increases the amount of light being absorbed for photosynthesis
  • in the root, increased IAA concentration inhibits growth, so root bends away from the light
  • this ensures the roots stay underground and can absorb the necessary nutrients for growth
25
Q

describe how IAA causes plants to respond to gravitrophism

A
  • IAA is produced in the shoot tip
  • IAA diffuses to the to the lower side (towards the pull of gravity), so IAA concentration on the lower side increases, causing cells to elongate and the shoot to grow upwards.
  • in the roots, IAA diffuses the lower side (towards the pull of gravity), causing the IAA concentration to increase and the growth to be inhibited, so the root grows downwards.
26
Q

explain how the uneven distribution of IAA causes a root to bend

A

at the bottom of the root, where IAA concentration is high, it inhibits the elongation of cells, so the root grows downwards

at the top of the root, where IAA concentration is low, there is less inhibition

27
Q

give one similarity and one difference between taxis and tropism

A
  • they both cause organisms to move in response to a directional stimulus
  • in taxis, the whole body of the organism moves towards the stimulus, whereas during tropism, the organism grows towards the stimulus
28
Q

define what is meant by myogenic and state which part of the heart is myogenic

A
  • it is able to contract and relax without receiving electrical signals
  • the cardiac muscle
29
Q

where is the sinoatrial node located in the heart?

A

the right atrium

30
Q

what is the function of the sinoatrial node (pacemaker)?

A

to initiate a heartbeat by sending a wave of electrical activity across the atrial walls, causing the atria to contract

31
Q

describe how the cardiac muscle controls the regular beating of the heart

A
  • SAN > AVN> bundle of his/purkyne fibres
  • sinoatrial node initiates a heartbeat by sending a wave of electrical activity over the atrial walls
  • this causes the atria to contract
  • a band of non-conducting collagen tissue prevents the wave of electrical activity from being passed directly from the atria to the ventricles
  • the wave of electrical activity is transferred to the atrioventricular node, which delays the impulse (allowing the atria to fully empty of blood) before the ventricles contract
  • the atrioventricular node then passes the impulse to the the bundle of His, which conducts the impulse to the bottom of the heart
  • the bundle of his branches into the purkyne tissue, which carries the impulse over both the ventricles at the same, causing them to contract simultaneously from the apex upwards.
32
Q

what is the purpose of the delay when electrical activity reaches the AVN?

A
  • to allow the atria to empty of blood before the ventricles contract
33
Q

when the heart beats, both ventricles contract at the same time. explain how this is coordinated in the heart after initiation of the heartbeat by the SAN

A
  • the electrical activity travels from the AVN to the bundle of His
  • bundle of His branches into purkyne fibres, which carry the impulse over both ventricles at the same time , causing them to contract simultaneously
34
Q

how do you calculate cardiac output?

A

stroke volume x heartrate

35
Q

what can heart rate be controlled and regulated by?

A

the autonomic nervous system

36
Q

which division of the nervous system is responsible for an increase in heart rate?

which division of the nervous system is responsible for a decrease in heart rate?

A

sympathetic

parasympathetic

37
Q

name the two receptors that are responsible for detecting changes in internal stimuli

A

baroreceptors and chemoreceptors

38
Q

where are baroreceptors located and what are their function?

A
  • located in the aorta and carotid arteries
  • detect changes in blood pressure
39
Q

where are chemoreceptors located and what are their function?

A
  • located in the aorta, carotid arteries and the medulla
  • detect changes in the concentration of oxygen and carbon dioxide in the blood, and the pH of the blood
40
Q

why does the pH of the blood decrease during exercise?

A

heart rate increases = breathe out more = more co2 produced = more carbonic acid in the bloodstream = blood more acidic = lower pH

41
Q

what does an increase in impulses to the SAN and sympathetic nervous system do to heart rate?

what does an increase in impulses to the SAN through the parasympathetic nervous system do to heart rate?

A

increase it

decrease it

42
Q

describe the role of receptors and the nervous system in the increase in heart rate during exercise

A
  • exercise causes an increase in the rate of respiration, which increases the amount of CO2 in the blood, causing blood pH to decrease
  • this change in pH is detected by the chemoreceptors in the carotid arteries, so chemoreceptors send an impulse to the medulla.
  • the medulla then sends this impulse to the SAN, which sends more frequent impulses to the sympathetic nervous system, causing the release of noradrenaline which increases heart rate and the frequency of impulses to the AVN
43
Q

how does increased intensity exercise lead to an increased heart rate?

A
  • leads to more co2 buildup in the blood, so blood pH decreases further
  • chemoreceptors send faster impulses to the medulla and SAN
  • more frequent impulses sent along the sympathetic nervous system, releasing more noradrenaline and sending more frequent impulses to the AVN
44
Q

describe the role of receptors and the nervous system in responding to high blood pressure

A
  • the baroreceptors in the carotid arteries would detect the increased blood pressure
  • they would send impulses to the medulla, which would send this impulse to the SAN
  • the SAN would then send the impulse down the parasympathetic nervous system, causing acetlycholine to be released, which decreases heart rate, so blood pressure returns to normal.
45
Q

which nervous system would the impulse go down if receptors were responding to low blood pressure?

A

sympathetic
to increase heart rate so blood pressure increases back to normal

A-Level Biology AQA (7 decks)

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